- Email: [email protected]
Reduced-scale experimental investigation on ventilation performance of a local exhaust hood in an industrial plant
Building and Environment 85 (2015) 94e103
Contents lists available at ScienceDirect
Building and Environment journal homepage: www.elsevier.com/locate/buildenv
Reduced-scale experimental investigation on ventilation performance of a local exhaust hood in an industrial plant Yanqiu Huang a, Yi Wang a, *, Li Liu b, Peter V. Nielsen b, Rasmus L. Jensen b, Fanliao Yan a a b
School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, No. 13 Yanta RD., Xi'an, Shaanxi 710055, PR China Department of Civil Engineering, Aalborg University, DK 9000 Aalborg, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 September 2014 Received in revised form 13 November 2014 Accepted 18 November 2014 Available online 6 December 2014
Local ventilation systems are widely used in industrial production processes to capture heat release and/ or gaseous/particulate contaminants. The primary objective of this study was to determine important empirical factors on local pollutant capture efficiency and characteristics of thermal stratification in the working areas of industrial plants. Investigated factors were confined airflow boundaries, flow rates of the exhaust hoods, source strengths, airflow obstacles and distances between sources and exhaust hoods. Reduced-scale experiments were conducted with a geometric scale of 1:15 corresponding to a portion of the blast furnace workshop of a steel plant. The dependency of capture efficiency on Archimedes numbers was established. The results showed that confined airflow boundaries, flow rates of the exhaust hoods and source strengths were important empirical factors on pollutant capture efficiency. Hood performance was also evaluated by thermal stratification heights in the plants. This study could help improve the capture efficiency of local ventilation systems used in industrial plants. Safe operation heights are recommended in the upper space of industrial plants based on the thermal stratification in the plants. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Industrial ventilation Reduced-scale experiments Velocity fields Temperature fields Capture efficiency Thermal stratification heights
1. Introduction The intense heat and contaminants generated during some industrial production processes can cause harm to working environments, the outdoor atmospheric environment and workers' health. There were 26, 393 cases of occupational diseases in China in 2013. They consisted of 23,152 pneumoconiosis cases, 637 cases of acute occupational poisoning, 904 cases of chronic occupational poisoning, and 1700 cases of other occupational disease. The number of pneumoconiosis cases accounted for 87.72% of the total number of occupational disease cases in 2013 [1]. The dust resulted from the industrial production of mining, smelting, and machine manufacturing, etc. was the main cause of the pneumoconiosis. The factors causing occupational diseases in steel plants included dust, carbon monoxide, fluoride and manganese dioxide, etc., among which dust was the prevalent pollutant [2]. The dust concentration reached up to 13 mg/Nm3 in an existing steel plant, which was far more than the dust concentration limits, i.e. 8 mg/Nm3, in occupied zones [3]. It is therefore important to create a safe, healthy and
* Corresponding author. Tel./fax: þ86 29 82202729. E-mail address: [email protected] (Y. Wang). http://dx.doi.org/10.1016/j.buildenv.2014.11.038 0360-1323/© 2014 Elsevier Ltd. All rights reserved.
productive work environment inside industrial buildings. Local ventilation systems are widely used in industry to control contaminants from localized emissions. A system typically consists of an exhaust hood driven by a fan that removes localized contaminants more efficiently than a general ventilation system. Existing industrial exhaust hoods could collect and remove contaminants from local micro- and macro-environments [4,5]. When placed close to contaminant sources, exhaust hoods can minimize the spread of contaminants [6,7]. The hood size is generally larger than the contaminant source. In addition, an air curtain technique [8e11] can also be used to reduce contaminant leakage. However, the geometry and location of the exhaust hood established in this paper were based on a common type of exhaust hoods used in blast furnace workshops at existing steel plants, which neither had a larger size than the contaminant source, i.e., the oven, nor used an air curtain to contain particles generated during the process of pouring molten iron into an oven with a filling tank. The performance of an exhaust hood can be evaluated through its capture efficiency [12e14], which is the ratio between the flow rate of contaminants directly captured from the exhaust hood and the total flow rate of contaminants released from the contaminant source [12]. Related factors on capture efficiency according to actual
Y. Huang et al. / Building and Environment 85 (2015) 94e103
production processes include confined airflow boundaries, the flow rate of the exhaust hood [15], source strengths, the presence of a filling tank and the distance between the oven and the exhaust hood [16]. Few studies have been performed to reveal the relative importance of these factors on pollutant capture efficiency. This insufficient understanding has resulted in non-effective measures to protect workers from contaminants in plants. Optimization without the burden of major reconstruction is required to improve the performance of these local exhaust hoods. In addition to capture efficiency, the performance of a hood also can be evaluated through thermal stratification heights in the plants. Numerous studies have been conducted on the theory of thermal stratification [17e19] and have shown that particulate contaminants can be trapped in certain stratified layers. In this study, some high-temperature contaminants were leaked into the remaining area of the plant, and thermal stratification was developed under the influence of both general and local ventilation systems (see Fig. 1), thus allowing contaminants to accumulate above the thermal stratification height. To protect the health of crane workers who operate in the upper space of a plant, it is essential to develop a deep and solid understanding of these thermal stratification characteristics. To summarize, avoiding excessive flow rates into a hood can be efficient so long as the working environment under the thermal stratification heights is healthy and productive. It is important to improve existing exhaust hoods from the perspective of protecting workers from industrial contaminants. The primary objective of this study was to determine important empirical factors on both local pollutant capture efficiency and the characteristics of thermal stratification. During reduced-scale experiments, the contaminant source was assumed to be constant in terms of the flow rate and enthalpy. All measurements were conducted in a steady state. Flow field characteristics, capture efficiency and thermal stratification heights were compared and analyzed for different factors. These conclusions can help improve the capture efficiency of local ventilation systems currently used in industrial plants. Safe operation heights in the upper spaces of industrial plants can be recommended based on the thermal stratification in the plants.
95
2. Experimental protocol 2.1. Theory of reduced-scale experiment Some physical parameters, such as high temperatures or velocities, are difficult to test in practice because of safety issues. Therefore, a reduced-scale experiment is a useful and sometimes necessary tool for designing air distribution in large enclosures [20e22]. The similarity between the full scale and the model requires geometric similarity, kinematic similarity and dynamic similarity. Geometric similarity is usually achieved if the model is the same shape as the full scale; dimensions are equally scaled down by the appropriate factor. The 1:15 geometric scale used in this paper was easily achieved. The same velocity directions and velocity scale ratios between the points in the model and the corresponding points in the full scale could ensure kinematic similarity. To maintain dynamic similarity, the ratios of the dynamic parameters of the points in the model and the corresponding points in the full scale are constant. In practice, it is quite difficult to achieve strict similarity then some aspects are often neglected with the most important parameters focused on. In general, reducedscale experiments are made in a geometric similar model with identical Prandtl number, Reynolds number and Archimedes number. Thermal experiments have shown that the Prandtl number can be ignored in case of a high turbulent flow. Then the reduced-scale experiments are characterized by a Reynolds number and an Archimedes number [23]. It is found that flow is independent of the Reynolds number as long as the critical Reynolds number is exceeded. The value of the critical Reynolds number is difficult to determine due to varying conditions. But literature shows that with the usual piping installation, the flow will change from laminar to turbulent in the range of Reynolds number from 2000 to 4000. For the purpose of this treatment, it is assumed that the change occurs at the value of 2000, i.e., the critical Reynolds number for the pipe flow [24]. The velocity of the smoke flow was sufficiently high as to be turbulent in practice, so it was unnecessary for the Reynolds number to be identical in both the reducedand the full-scale versions [25,26]. Therefore, the Archimedes number became the crucial parameter for the description of the flow. The Archimedes number (Ar) can be defined as follows:
Ar ¼
gbhðT Tr Þ ghðT Tr Þ ¼ u2 u2 Tr
(1)
where g is the gravitational acceleration, in m/s2; b is the volume expansion coefficient, as 1/T; h is the characteristic length, in m; T is the absolute temperature of the airflow, in K; Tr is the reference absolute temperature, in K; and u is the airflow velocity, in m/s. In this paper, the Archimedes number of the exhaust duct (Arexh) in the local ventilation system is defined as
Arexh ¼
ghðTexh Tr Þ u2exh Tr
(2)
where g is the gravitational acceleration, in m/s2; h is the characteristic length, i.e., the height of the plant or the chamber, in m; Texh is the airflow absolute temperature of the exhaust duct at the Table 1 The dimensionless numbers of the exhaust duct at the sampling point between the full scale and the model.
Fig. 1. Schematic diagram of the development of thermal stratification in a cross section of the workshop; 1: fresh air inlet, 2: general ventilation outlet, 3: heat source, 4: exhaust hood.
Full scale Reduced-scale
Prandtl number
Reynolds number
Archimedes number
0.73 0.73
2179847 6282
0.25 0.23
96
Y. Huang et al. / Building and Environment 85 (2015) 94e103
Fig. 2. Photos from full scale and reduced scale: (a) Part of blast furnace workshops; (b) Reduced-scale model in laboratory; 1: Oven, 2: Exhaust hood, 3: Filling tank.
sampling point in the local ventilation system, in K; Tr is the reference absolute temperature, i.e., the temperature of fresh air inlet, in K; and uexh is the airflow velocity of the exhaust ducts in the local ventilation system, in m/s. In addition, the Archimedes number of the contaminant source (Arcs) is defined as
Arcs ¼
ghðTcs Tr Þ u2cs Tr
(3)
where g is the gravitational acceleration, in m/s2; h is the characteristic length, i.e., the height of the plant or the chamber, in m; Tcs is the absolute temperature of the contaminant source at the sampling point, in K; Tr is the reference absolute temperature, i.e., the temperature of fresh air inlet, in K; and ucs is the airflow velocity of the contaminant source, in m/s. The similarity was achieved between a portion of the blast furnace workshop of a steel plant and the reduced-scale chamber with the same Arexh and some aspects ignored in this paper. Table 1 presents the dimensionless numbers of the exhaust duct at the sampling point between the full scale and the model. As seen in Table 1, both of the Prandtl numbers of the full scale and the reduced-scale were the same. And both of the Reynolds numbers were far greater than the critical Reynolds number. Hence, the flow was independent of the Reynolds number. As for the Archimedes number, they were almost the same between the full scale and the reduced-scale. In addition, many measurements were also performed with various Arexh or Arcs because the development laws of capture efficiency and thermal stratification influenced by different empirical factors were the major concerns. The various practical parameters and conclusions could be determined corresponding to the measured results on the basis of similarity theory. All in all, the research conclusions based on the reduced-scale experiments could be guides for design or improvement in an industrial plant.
2.2. Experimental facilities All measurements were conducted in a reduced-scale chamber at Aalborg University, Denmark. The dimensions of the chamber
were 1.3 m (length) by 1.3 m (width) by 2.0 m (height), corresponding to a portion of the blast furnace workshop of a steel plant. Photos of the plant and the model are shown in Fig. 2. The practical situation in the plant is reproduced in the reducedscale experiments with some assumptions. All measurements were conducted with a geometric scale of 1:15. Fig. 3 shows a sketch of the experimental facility and the detailed sizes are included in the Supporting Information in the Appendix A. The shape and the location of the exhaust hood were established in accordance with the actual situation in the plant. The schematic drawing of the exhaust hood is depicted in Fig. 4 and the
Fig. 3. Sketch of the experimental facility: 1: Fresh air inlet, used in Case1-5, 2: General ventilation outlet, used in Case1-5, 3: Heat source, used in Case1-5, 4: Exhaust hood, used in Case1-5, 5: Horizontal baffle, used in Case1-5, 6: Vertical baffle, used in Case2-5, 7: Filling tank, used in Case3-4, 8: Exhaust duct, used in Case1-5.
Y. Huang et al. / Building and Environment 85 (2015) 94e103
97
A Srfex 2010 Fog Generator was used to enable smoke visualization. The mean diameter of the generated smoke particles was 1.545 mm. To observe the thermal stratification heights clearly and accurately, a laser beam was adopted with adequate lighting during smoke visualization experiments [30].
2.4. Layout of measuring points and test conditions
Fig. 4. Schematic drawing of the exhaust hood.
detailed sizes are included in the Supporting Information in the Appendix A.
2.3. Instrumentations A one-dimensional Laser Doppler Anemometer (LDA) was used to measure the velocity components. It could measure velocities with a range of 16~þ80 m/s and an accuracy of ±0.4% of the measured value. The LDA's probe emitted laser beams that could be precisely moved with a robot at an accuracy of ±1 mm. The temperature was measured by using K-type thermocouples with a range of 40~375 C and an accuracy of ±0.3 C [27]. The temperatures were logged with a Helios data logger connected to an ice point reference. The tracer gas technique was used in the field applications to estimate local ventilation direct-capture efficiency [13]. N2O was used to simulate CO2 (a common contaminant in industrial production processes) because it has the same molecular weight and is insensitive to human respiration during measurements. The constant release of the N2O concentration was regulated by a flow meter during the measurements [28,29]. The N2O concentration was measured with a multi-channel gas analyzer (Innova 1412 Photoacoustic Field Gas-Monitor) that was connected to a multipoint sampler monitor (Brüel & Kjaer 1303 Photoacoustic Gas-Monitor). The repeatability of the N2O measurement was ±1% of the measured value.
The velocity measurements were conducted near the exhaust opening with the LDA. The total number of the measuring points was 30. Fifteen were at the height of 0.63 m and fifteen were at the height of 0.50 m. All the intervals of the adjacent measuring points were 0.03 m, as shown in Fig. 5. The temperature measurements were carried out with 33 thermocouples. Three were respectively located at the entrance of the contaminant source, the exit of exhaust duct and the entrance of fresh air inlet. They were used for calculating the Archimedes number of the contaminant source (Arcs) or the exhaust duct (Arexh). The remaining 30 thermocouples were located between the contaminant source and the hood to illustrate the temperature variations (see Fig. 5). Five samplers were used to measure the N2O concentration at different locations. Two were used for taking air samples in the exhaust duct of the local ventilation system and in the duct of general ventilation system to calculate the capture efficiency. The other three were placed at heights of 0.40 m, 0.80 m and 1.20 m inside the center of the chamber to monitor the average concentrations. During the reduced-scale experiments, the contaminant source was assumed to be constant in each measurement in terms of the flow rate and enthalpy. All the measurements were conducted in a steady state. Table 2 shows the detailed measurement conditions.
3. Results and discussion The concentration distributions of the contaminants can be predicted based on the flow field characteristics. Furthermore, the impacts of factors on capture efficiency and thermal stratification heights can be subsequently predicted. The utilized factors were confined airflow boundaries, the flow rate of exhaust hood, source strengths, airflow obstacles and the distance between the source and the exhaust hood.
Fig. 5. Measuring points' layout between the contaminant source and exhaust hood: (a) AeA plane; (b) BeB plane; 1: Heat source, 2: Exhaust hood, 3: Horizontal baffle, 4: Plexiglass; ∙ Measuring points of both air temperature and velocity, + Measuring points of only air temperature, Measuring points of only air velocity.
▵
98
Y. Huang et al. / Building and Environment 85 (2015) 94e103
Table 2 Measurement conditions. Case no.
1 2 3 4 5
Vertical baffles
Without With With With With
Obstacle (filling tank)
Without Without With With Without
Contaminant source
Exhaust hood
Distance between source and hood d/m
Flow rate qcs/m3h1
Heat flow Q/W
0.40 0.40 0.44 0.44 0.44
35 35 35 20~140 35
200 200 200 200 200
3.1. The impacts of confined airflow boundaries The enclosure in a blast furnace plant varies during the production process, which can significantly impact the flow field characteristics and capture efficiency of an exhaust hood. Two scenarios were tested: one without vertical baffles and one with two vertical baffles on both sides of contaminant source (see Fig. 3). The capture efficiency was measured with a tracer gas technique. Detailed knowledge of the flow field near the exhaust openings can improve the accuracy [14]. The velocity vectors and the dimensionless temperature profiles can reveal the airflow movement.
3.1.1. Velocity vectors The total number of the sample points of velocity was 30. However, there were only 24 measured velocities within the range of the airflow. Thirteen were at the height of 0.63 m and eleven were at the height of 0.50 m. The measured velocity vectors of Case1 in the AeA plane, when qhood ¼ 80 m3/h, are shown in Fig. 6. The supplementary velocity component profiles are correspondingly included in the Supporting Information in the Appendix B. As seen in Fig. 6, the velocity vectors were almost symmetrically distributed and two maximums were on both sides at each height. This may have been due to the negative pressure on both sides being greater than in the middle of the exhaust hood because of the suction effect of the exhaust ducts on both sides (see Fig. 4). The velocity vectors at 0.63 m were almost accordingly greater than those at 0.50 m. Airflow confluence was the likely cause of this phenomenon. The length of the airflow coverage was 0.30 m at a height of 0.50 m and 0.36 m at a height of 0.63 m, i.e., the height of
Outlet
Size Length L/m
Width W/m
Height H/m
0.58 0.58 0.58 0.58 0.58
0.1 0.1 0.1 0.1 0.1
0.25 0.25 0.25 0.25 0.25
Flow rate qhood/m3h1
Flow rate qoutlet/m3h1
25~100 25~100 25~170 90 25~100
10 10 10 10 10
Range of Archimedes number
Arexh:0.15~12.38 Arexh:0.17~5.71 Arexh:0.04~5.61 Arcs:1.91~79.32 Arexh:0.14~5.93
the exhaust opening. Therefore, the measured velocity vector results inferred that the length of the existing hood (0.58 m) may have been too long. It is recommended that the length of the existing hood could be reduced to achieve higher capture velocity as long as it is longer than that of the airflow coverage at the exhaust opening in practice. 3.1.2. Temperature profiles The non-dimensional temperature decay ratio of the airflow (Dq/Dq0) is defined as:
Dq T Tr ¼ Dq0 Tcs Tr
(4)
where T is the absolute temperature of the airflow, in K; Tcs is the absolute temperature of the contaminant source at the sampling point, in K; and Tr is the reference absolute temperature, i.e., the temperature of fresh air inlet, in K. For example, substituting T ¼ 303.3 K, Tcs ¼ 316.1 K, and Tr ¼ 296.5 K into Eq. (4), the following equation could be obtained: Dq=Dq0 ¼ T Tr =Tcs Tr ¼ 303:3 296:5=316:1 296:5, which worked out toDq=Dq0 ¼ 0:35. The dimensionless temperature variations, when qhood ¼ 80 m3/ h, are shown in Fig. 7. As seen in Fig. 7, the dimensionless temperature variations all followed an approximate Gaussian distribution [31,32], as expected. In the AeA plane (the axisymmetric plane), the maximum of dimensionless temperatures all occurred in the middle of the thermocouple layout and varied from 0.35 to 0.20 within a height of 0.40 m to 0.60 m. In the BeB plane (the non-axisymmetric plane), the maximum of dimensionless temperatures all shifted to one side and varied from 0.48 to 0.35. The contaminant source close to the plexiglass on the right might have caused a Coanda effect, thus leading to the excursion of dimensionless temperatures. A significant large amount of entrained fresh air from the side inlet on the left may have also altered the excursion. Similar temperature variations occurred when the flow rate of the exhaust hood varied from 25 m3/h to 100 m3/h. In all, the obtained temperature profiles could indicate airflow movement and then predict the effects of different factors on contaminant control. 3.1.3. Capture efficiency profiles Capture efficiency has been widely used for evaluating different exhaust systems in the field of industrial ventilation. The definition formula of capture efficiency (a) can be written as follows [12]:
a¼
Fig. 6. Velocity vectors of Case1 in the AeA plane (qhood ¼ 80 m3/h): 1: Heat source, 2: Exhaust hood.
SE S
(5)
where SE is the flow rate of the contaminant directly captured from the exhaust hood, in ppm; S is the total flow rate of the contaminant released from the contaminant source, in ppm.
Y. Huang et al. / Building and Environment 85 (2015) 94e103
99
Fig. 7. Dimensionless temperature variations of Case1 (qhood ¼ 80 m3/h): (a) AeA plane of Case1; (b) BeB plane of Case1.
Fig. 8. Comparison of capture efficiency variations under different confined airflow boundaries.
The capture efficiency variations influenced by the absence or presence of two vertical baffles on both sides of the contaminant source are shown in Fig. 8. Fig. 8 shows that the capture efficiency of Case2 was correspondingly greater than Case1. Significant deviations of capture efficiency occurred when Arexh was less than 1, i.e., qhood50 m3/h. In addition, the capture efficiency of Case1 approximately followed an exponential decay, with Arexh varying from 0.1 to 10.0, if the lggrid was used on the horizontal axis while that of Case2 changed linearly. As for Case2, the two vertical baffles on both sides of the contaminant source caused more contaminants to be sucked into the hood, thus achieving greater capture efficiency than Case1. The confined airflow boundaries could significantly influence the capture efficiency, and it could be beneficial from the perspective of contaminant control to construct as many confined boundaries as practically possible to form an enclosed space.
once all safety requirements are satisfied. Based on Eq. (2), it is obvious that the Archimedes number of the exhaust duct in the local ventilation system decreased with an increasing flow rate of the hood. During the measurements of Case3, only the flow rate of exhaust hood varied while the other parameters remained constant. The relationship of the capture efficiency and the Archimedes number of the exhaust duct (Arexh) is depicted in Fig. 9.
3.2. The impacts of flow rate of the exhaust hood The flow rate of an exhaust hood can have a significant impact on pollutant capture efficiency in certain circumstances. It is important to determine the most economical flow rate of a hood
Fig. 9. Capture efficiency variations with different flow rate of exhaust hood.
100
Y. Huang et al. / Building and Environment 85 (2015) 94e103
As seen in Fig. 9, the capture efficiency curve was found to follow an approximate Gaussian equation when Arexh was between 0.0 and 10.0 if the lg-grid was used on the horizontal axis, and the increasing percentage of capture efficiency gradually increased with the Arexh. The increasing percentage of capture efficiency was almost 10% (qhood80 m3/h) and 1%~2% (80 m3/h＜qhood＜150 m3/ h) and less than 1% (qhood150 m3/h). Therefore, the capture efficiency variations were divided into three regions in this study: a stable region, a slowly increasing region and a sharply increasing region. The experimental results indicated that it would be better to improve capture efficiency in the latter two regions to avoid an excessive flow rate of the hood.
varies. Therefore, different flow rates of the contaminant source that represent various source strengths should be tested to evaluate the performance of the exhaust hood. During the measurements of Case4, the airflow was assumed to be in a steady state, with only the flow rate of the contaminant source varying while the other parameters remained constant. Based on Eq. (3), it is obvious that the Archimedes number of the contaminant source decreased with the increasing flow rate of the source. Fig. 10 indicates the relationship of the capture efficiency and the Archimedes number of the contaminant source (Arcs). The results in Fig. 10 show that the capture efficiency was greater than 0.90 if Arcs was no less than 4.0, i.e., qcs100 m3/h when qexh ¼ 90 m3/h and qoutlet ¼ 10 m3/h. Otherwise, it reduced to approximately 0.45 if Arcs was less than 4.0, i.e., qcs＞100 m3/h when qexh ¼ 90 m3/h and qoutlet ¼ 10 m3/h. The sudden fall in capture efficiency reached 49.4% (as shown in Fig. 10). The curve of the capture efficiency resembled a step function, with Arcs varying from 1.0 to 100.0 if the lg-grid was used on the horizontal axis. Therefore, there was a risk of a sharp decline in capture efficiency after a critical amount of contaminant source that was equal to the total flow rate of the local exhaust ventilation and general ventilation. The significant amount of generated contaminants, which was greater than the critical amount, forced the airflow movement to intensify in the horizontal direction, causing most of the contaminants escaped from the hood. These results indicate that satisfying contaminant control might be achieved if the total flow rate of the local exhaust ventilation and general ventilation was no less than that of the amount of contaminants generated in practice.
3.3. The impacts of source strengths
3.4. The impacts of airflow obstacles
During the five-minute pouring process, molten iron is slowly poured into the oven. The amount of generated contaminants
The oven is in a closed enclosure in blast furnace workshops. The gate of the closed enclosure is opened when the filling tank
Fig. 10. Capture efficiency variations with varying source strengths (Arcs).
Fig. 11. Comparison of capture efficiency variations affected by an obstacle.
Fig. 12. Comparison of capture efficiency variations with different distance between contaminant source and exhaust hood (d is the distance between source and hood, d1 ¼ 0.44 m, d2 ¼ 0.40 m).
Y. Huang et al. / Building and Environment 85 (2015) 94e103
101
begins to pour molten iron into the oven. The filling tank is initially positioned at an angle of 0 in a vertical direction. The contaminants intensively escape once the angle reaches 30 during the pouring process. The final angle of the filling tank is 115 . The impact of airflow obstacles on pollutant capture efficiency was investigated under the worst-case condition of a filling tank positioned at an angle of 30 . However, the simulated filling tank only played the role of an obstacle; it did not pour liquid during the experiment. Fig. 11 illustrates the effect of an obstacle on the capture efficiency. Fig. 11 shows that small deviations of capture efficiency occurred between the two cases. Both curves exhibited a nearly linear function when Arexh was between 0.1 and 10.0 if the lg-grid was used on the horizontal axis. In short, there was little influence on the flow field from the obstacle if no liquid was poured. This was also verified through smoke visualization. Molten iron pouring from the filling tank might alter the flow of contaminants in practice. However, it was difficult to simulate this effect in the reduced-scale experiment. 3.5. The impacts of distance between source and exhaust hood
Fig. 13. Verification of thermal stratification heights using laser beams (Red line: laser beams). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
In practice, the distance between the oven and the exhaust hood typically varies because of the various pouring angles used during different pouring processes. Therefore, the minimum and maximum distance between the contaminant source and the hood were tested corresponding to distance ranges during different pouring processes. The capture efficiency variations caused by two distances are shown in Fig. 12. Fig. 12 indicates small deviations of capture efficiency between Case2 and Case5. In addition, there were nearly identical slopes and intercepts for both of these straight lines if the lg-grid was used on the horizontal axis (0.1＜Arexh＜10.0). This infers that the slight distance difference between the source and the hood did not
Fig. 14. Variations of dimensionless thermal stratification heights and corresponding capture efficiency versus Arexh among different cases: (a) Case1; (b) Case2; (c) Case3; (d) Case5.
102
Y. Huang et al. / Building and Environment 85 (2015) 94e103
significantly affect capture efficiency. Perhaps this is because 0.04 m was too short a distance to cause significant influence on the capture efficiency in this experiment. In short, the distance between the oven and the exhaust hood does not matter so long as it is within the permitted distance range during different pouring processes. 3.6. Thermal stratification profiles affected by different factors Smoke simulations were used to supplement the measurements and visualize the formation of thermal stratification [33,34]. The thermal stratification heights were verified by laser beams; a photo is shown in Fig. 13. The non-dimensional thermal stratification height (y*st) is defined as:
y*st ¼ yst =h
(6)
where yst is the measured thermal stratification height, in m, and h is the characteristic length, i.e., the height of the chamber, in m. Fig. 14 shows a comparison of dimensionless thermal stratification heights and corresponding capture efficiencies versus Arexh among different cases. Based on Fig. 14, we concluded that the variation trend of thermal stratification heights was consistent with the corresponding capture efficiency versus Arexh for these four cases. In other words, the thermal stratification heights could also indicate the performance of the local exhaust hood. In addition, the dimensionless thermal stratification height (y*st) range was summarized to fall between 0.20 and 0.36, with Arexh varying from 0.1 to 6.3, i.e., 25 m3/h＜qhood＜120 m3/h. To ensure the health of workers who operate in the upper space of a plant, safe operation heights should be lower than the corresponding thermal stratification heights in industrial plants.
(0.0 < Arexh<10.0). Based on the increasing percentage, the capture efficiency variations were divided into a stable region, a slowly increasing region and a sharply increasing region. As for varying source strengths, the capture efficiency curve mimicked a step function if the lg-grid was used on the horizontal axis (1.0 < Arcs<100.0). This means that there was a risk of a sharp decline in the capture efficiency after the critical amount of contaminant source that was equal to the total flow rate of the local exhaust ventilation and general ventilation. All of the capture efficiency variations were approximately linear with the horizontal lg-grid axis (0.1 < Arexh<10.0) when affected by airflow obstacles and changing distances between the source and the hood. There were nearly identical slope and intercept lines influenced by airflow obstacles or small distance deviations. In all, confined airflow boundaries, the flow rate of the exhaust hood and source strengths were important empirical factors on pollutant capture efficiency, based on the different function types between the capture efficiency and the Archimedes number. From the perspective of contaminant control, it could be beneficial to construct as many confined boundaries as possible to form an enclosed space and operate the exhaust hood at an economical flow rate in practice. The experimental results also indicated that satisfying contaminant control might be achieved if the total flow rate of the local exhaust ventilation and the general ventilation was no less than that of the amount of contaminants generated in practice. Based on the measurement data of thermal stratification heights and corresponding capture efficiency in four cases, the variation trend of the thermal stratification heights was consistent with capture efficiency. Moreover, the dimensionless thermal stratification height (y*st) range fell between 0.20 and 0.36, with Arexh varying from 0.1 to 6.3, i.e., 25 m3/h＜qhood＜120 m3/h. To ensure the health of workers who operate in the upper space of a plant, safe operation heights should be lower than the corresponding thermal stratification heights in industrial plants.
4. Conclusions Acknowledgments Based on a reduced-scale experiment with a geometric scale of 1:15 corresponding to a portion of a blast furnace workshop in a steel plant, the primary conclusions inferred from the results can be summarized as follows: Certain velocity vectors and dimensionless temperatures were obtained without vertical baffles on both sides of the contaminant source. The measured velocity vector results inferred that the length of the existing hood may have been too long. It is recommended that the length of the existing hood could be reduced to achieve higher capture velocity as long as it is longer than that of the airflow coverage at the exhaust opening in practice. The dimensionless temperature profiles indicated that the maximum dimensionless temperatures all occurred in the middle of the thermocouple layout in the axisymmetric plane while those all shifted to one side in the non-axisymmetric plane probably caused by the Coanda effect. The capture efficiency variations were investigated in terms of empirical factors that included confined airflow boundaries, the flow rate of the exhaust hood, source strengths, airflow obstacles and the distance between the source and the exhaust hood. In the absence of vertical baffles on both sides of the contaminant source, the capture efficiency mirrored an exponential decay if the lg-grid was used on the horizontal axis (0.1 < Arexh<10.0); it changed linearly if there were two vertical baffles on both sides. As for a varying flow rate of the exhaust hood, the capture efficiency was found to follow an approximate Gaussian equation if the lg-grid was used on the horizontal axis
This research was financially sponsored by the National Natural Science Foundation of China (Project No. 51238010). We also wish to thank the Division of Architectural Engineering, Civil Engineering Department, Aalborg University for their kind help and support in successfully conducting this experiment. Nomenclature Ar Arcs Arexh d d1 d2 g h H L qcs qexh qoutlet Q S
Archimedes number Archimedes number of the contaminant source Archimedes number of the exhaust duct distance between the contaminant source and the exhaust hood, m original distance between the source and the hood, m new distance between the source and the hood, m gravity acceleration, m/s2 characteristic length, namely the height of the chamber, m height of the exhaust hood, m length of the exhaust hood, m flow rate of the contaminant source, m3/h flow rate of exhaust duct in the local ventilation system, m3/h flow rate of outlet in the general ventilation system, m3/h heat flow supplied to the contaminant source, W total flow rate of the contaminant released from the contaminant source, ppm
Y. Huang et al. / Building and Environment 85 (2015) 94e103
SE T Tcs Texh Tr u ucs uexh W yst y*st Z
flow rate of the contaminant directly captured from the exhaust hood, ppm absolute temperature of the airflow, K absolute temperature of the contaminant source at the sampling point, K absolute temperature of the exhaust duct at the sampling point, K reference absolute temperature, namely the temperature of fresh air inlet, K airflow velocity, m/s airflow velocity of the contaminant source, m/s airflow velocity of exhaust ducts, m/s width of the exhaust hood, m measured thermal stratification height, m non-dimensional thermal stratification height height from the chamber's ground, m
Greek symbols capture efficiency volume expansion coefficient, 1/T non-dimensional temperature decay ratio of the airflow
a b Dq/Dq0
Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.buildenv.2014.11.038. References [1] Notification of occupational disease prevention. In: Disease Prevention and control Bureau of national health and Family Planning Commission of the People's Republic of China; 2013. [2] GBZ/T 231-2010, Technical code on occupational hygiene prevention and protection in the ferrous metal smelting and rolling processing industry. [3] GBZ 2.1-2007. Occupational exposure limits for hazardous agents in the workplace. [4] Alden JL, Kane JM. Design of industrial ventilation systems. New York: Industrial Press; 1982. p. 20e7. [5] ASHRAE handbook. Industrial exhaust systems: HVAC applications. Atlanta, GA, USA: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.; 1987. [6] Devienne R, Fontaine JR, Kicka J, Bonthoux F. Experimental characterization of a plume of passive contaminant above a thermal source: capture efficiency of a fume extraction hood. Ann Occup Hyg 2009;53(7):739e48. [7] Awbi HB. Ventilation of buildings. London: Taylor and Francis; 2003. [8] Navaz HK, Amin M, Dabiri D, Faramarzi R. Past, present, and future research toward air curtain performance optimization. ASHRAE Trans 2005;111: 1083e8. [9] Ciocanea A, Dragomirescu A. Modular ventilation with twin air curtains for reducing dispersed pollution. Tunn Undergr Sp Tech 2013;37:180e98. s JC, Pavageau M. Turbulent heat and mass transfer [10] Rivera J, Elicer-Corte through air curtains devices for the confinement of heat inside tunnels. Int Commun Heat Mass 2011;38:688e95.
103
[11] Traboulsi SR, Hammoud A, Khalil MF. Effects of jet inclination angle and geometrical parameters on air curtain performance. ASHRAE Trans 2009;115: 617e29. [12] Nielsen PV, Madsen U, Tveit DJ. Experiments on an exhaust hood for the paint industry. In: Proceedings of roomvent 1991, Cincinnati; 1991. [13] Madsen U, Breum NO, Nielsen PV. Local exhaust ventilation: a numerical and experimental study of capture efficiency. Build Environ 1994;29(3):319e23. [14] Ilpo K. Numerical simulation of the capture efficiency of an unflanged rectangular exhaust opening in a coaxial air flow. Ann Occup Hyg 1995;39(1): 21e33. [15] Rim D, Wallace L, Nabinger S, Persily A. Reduction of exposure to ultrafine particles by kitchen exhaust hoods: the effects of exhaust flow rates, particle size, and burner position. Sci Total Environ 2012;432:350e6. [16] Li YG, Delsante A, Symon J. Residential kitchen range hoods-Buoyancy capture principle and capture efficiency revisited. Indoor Air 1997;7(3):151e7. [17] Yang D, Huo R, Zhang XL, Zhu S, Zhao XY. Comparative study on carbon monoxide stratification and thermal stratification in a horizontal channel fire. Build Environ 2012;49:1e8. [18] Lin YJP, Lin CL. A study on flow stratification in a space using displacement ventilation. Int J Heat Mass Tran 2014;73:67e75. [19] Bouzinaoui A, Vallette P, Lemoine F, Fontaine JR, Devienne R. Experimental study of thermal stratification in ventilated confined spaces. Int J Heat Mass Tran 2005;48(19e20):4121e31. [20] Yang D, Huo R, Zhang XL, Zhao XY. Comparison of the distribution of carbon monoxide concentration and temperature rise in channel fires: reduced-scale experiments. Appl Therm Eng 2011;31:528e36. [21] Roux NL, Faure X, Inard C, Soares S, Ricciardi L. Reduced-scale study of wind influence on mean airflows inside buildings equipped with ventilation systems. Build Environ 2012;58:231e44. [22] Liu PC, Lin HT, Chou JH. Evaluation of buoyancy-driven ventilation in atrium buildings using computational fluid dynamics and reduced-scale air model. Build Environ 2009;44:1970e9. [23] Taehti E, Goodfellow H. Handbook of industrial ventilation. San Diego: Academic Press; 2001. [24] Streeter VL, Wylie EB, Bedford KW. Fluid mechanics. 9th ed. New York: McGraw-Hill Press; 1998. [25] Tilleya N, Rauwoensb P, Fauconniera D, Mercia B. On the extrapolation of CFD results for smoke and heat control in reduced-scale set-ups to full scale: atrium configuration. Fire Saf J 2013;59:160e5. [26] Nielsen PV. Model experiments for the determination of airflow in large spaces. In: Proceedings of indoor air 1993: the 6th international conference on indoor air quality and climate; 1993. Helsinki, Finland. [27] Artmann N, Vonbank R, Jensen RL. Temperature measurements using type K thermocouples and the Fluke Helios Plus 2289 datalogger. DCE Technical Reports No. 52. Department of Civil Engineering, Aalborg University; 2008. [28] Gao NP, Niu JL, Perino M, Heiselberg P. The airborne transmission of infection between flats in high-rise residential buildings: tracer gas simulation. Build Environ 2008;43:1805e17. [29] Laporthe S, Virgone J, Castanet S. A comparative study of two tracer gases: SF6 and N2O. Build Environ 2001;36:313e20. [30] Nielsen PV, Brohus H, Petersen AJ, Thorsen KS. Smoke movement in an atrium with a fire with low rate of heat release. In: Proceedings of indoor air 2008: the 11th international conference on indoor air quality and climate; 17th to 22nd August 2008. Copenhagen, Denmark. [31] Rodi W. Turbulent buoyant jets and plumes. Britain: Pergamon Press; 1982. [32] Zukowska D, Popiolek Z, Melikov A. Determination of the integral characteristics of an asymmetrical thermal plume from air speed/velocity and temperature measurements. Exp Therm Fluid Sci 2010;34:1205e16. [33] Karaismail E, Celik I, Steven G. Flow dynamics and contaminant transport in industrial-type enclosing exhaust hoods. J Occup Environ Hyg 2013;10(7): 384. [34] Sun YG, Zhang YH. An overview of room air motion measurement: technology and application. HVAC&R Res 2007;13(6):929.
Contents lists available at ScienceDirect
Building and Environment journal homepage: www.elsevier.com/locate/buildenv
Reduced-scale experimental investigation on ventilation performance of a local exhaust hood in an industrial plant Yanqiu Huang a, Yi Wang a, *, Li Liu b, Peter V. Nielsen b, Rasmus L. Jensen b, Fanliao Yan a a b
School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, No. 13 Yanta RD., Xi'an, Shaanxi 710055, PR China Department of Civil Engineering, Aalborg University, DK 9000 Aalborg, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 September 2014 Received in revised form 13 November 2014 Accepted 18 November 2014 Available online 6 December 2014
Local ventilation systems are widely used in industrial production processes to capture heat release and/ or gaseous/particulate contaminants. The primary objective of this study was to determine important empirical factors on local pollutant capture efficiency and characteristics of thermal stratification in the working areas of industrial plants. Investigated factors were confined airflow boundaries, flow rates of the exhaust hoods, source strengths, airflow obstacles and distances between sources and exhaust hoods. Reduced-scale experiments were conducted with a geometric scale of 1:15 corresponding to a portion of the blast furnace workshop of a steel plant. The dependency of capture efficiency on Archimedes numbers was established. The results showed that confined airflow boundaries, flow rates of the exhaust hoods and source strengths were important empirical factors on pollutant capture efficiency. Hood performance was also evaluated by thermal stratification heights in the plants. This study could help improve the capture efficiency of local ventilation systems used in industrial plants. Safe operation heights are recommended in the upper space of industrial plants based on the thermal stratification in the plants. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Industrial ventilation Reduced-scale experiments Velocity fields Temperature fields Capture efficiency Thermal stratification heights
1. Introduction The intense heat and contaminants generated during some industrial production processes can cause harm to working environments, the outdoor atmospheric environment and workers' health. There were 26, 393 cases of occupational diseases in China in 2013. They consisted of 23,152 pneumoconiosis cases, 637 cases of acute occupational poisoning, 904 cases of chronic occupational poisoning, and 1700 cases of other occupational disease. The number of pneumoconiosis cases accounted for 87.72% of the total number of occupational disease cases in 2013 [1]. The dust resulted from the industrial production of mining, smelting, and machine manufacturing, etc. was the main cause of the pneumoconiosis. The factors causing occupational diseases in steel plants included dust, carbon monoxide, fluoride and manganese dioxide, etc., among which dust was the prevalent pollutant [2]. The dust concentration reached up to 13 mg/Nm3 in an existing steel plant, which was far more than the dust concentration limits, i.e. 8 mg/Nm3, in occupied zones [3]. It is therefore important to create a safe, healthy and
* Corresponding author. Tel./fax: þ86 29 82202729. E-mail address: [email protected] (Y. Wang). http://dx.doi.org/10.1016/j.buildenv.2014.11.038 0360-1323/© 2014 Elsevier Ltd. All rights reserved.
productive work environment inside industrial buildings. Local ventilation systems are widely used in industry to control contaminants from localized emissions. A system typically consists of an exhaust hood driven by a fan that removes localized contaminants more efficiently than a general ventilation system. Existing industrial exhaust hoods could collect and remove contaminants from local micro- and macro-environments [4,5]. When placed close to contaminant sources, exhaust hoods can minimize the spread of contaminants [6,7]. The hood size is generally larger than the contaminant source. In addition, an air curtain technique [8e11] can also be used to reduce contaminant leakage. However, the geometry and location of the exhaust hood established in this paper were based on a common type of exhaust hoods used in blast furnace workshops at existing steel plants, which neither had a larger size than the contaminant source, i.e., the oven, nor used an air curtain to contain particles generated during the process of pouring molten iron into an oven with a filling tank. The performance of an exhaust hood can be evaluated through its capture efficiency [12e14], which is the ratio between the flow rate of contaminants directly captured from the exhaust hood and the total flow rate of contaminants released from the contaminant source [12]. Related factors on capture efficiency according to actual
Y. Huang et al. / Building and Environment 85 (2015) 94e103
production processes include confined airflow boundaries, the flow rate of the exhaust hood [15], source strengths, the presence of a filling tank and the distance between the oven and the exhaust hood [16]. Few studies have been performed to reveal the relative importance of these factors on pollutant capture efficiency. This insufficient understanding has resulted in non-effective measures to protect workers from contaminants in plants. Optimization without the burden of major reconstruction is required to improve the performance of these local exhaust hoods. In addition to capture efficiency, the performance of a hood also can be evaluated through thermal stratification heights in the plants. Numerous studies have been conducted on the theory of thermal stratification [17e19] and have shown that particulate contaminants can be trapped in certain stratified layers. In this study, some high-temperature contaminants were leaked into the remaining area of the plant, and thermal stratification was developed under the influence of both general and local ventilation systems (see Fig. 1), thus allowing contaminants to accumulate above the thermal stratification height. To protect the health of crane workers who operate in the upper space of a plant, it is essential to develop a deep and solid understanding of these thermal stratification characteristics. To summarize, avoiding excessive flow rates into a hood can be efficient so long as the working environment under the thermal stratification heights is healthy and productive. It is important to improve existing exhaust hoods from the perspective of protecting workers from industrial contaminants. The primary objective of this study was to determine important empirical factors on both local pollutant capture efficiency and the characteristics of thermal stratification. During reduced-scale experiments, the contaminant source was assumed to be constant in terms of the flow rate and enthalpy. All measurements were conducted in a steady state. Flow field characteristics, capture efficiency and thermal stratification heights were compared and analyzed for different factors. These conclusions can help improve the capture efficiency of local ventilation systems currently used in industrial plants. Safe operation heights in the upper spaces of industrial plants can be recommended based on the thermal stratification in the plants.
95
2. Experimental protocol 2.1. Theory of reduced-scale experiment Some physical parameters, such as high temperatures or velocities, are difficult to test in practice because of safety issues. Therefore, a reduced-scale experiment is a useful and sometimes necessary tool for designing air distribution in large enclosures [20e22]. The similarity between the full scale and the model requires geometric similarity, kinematic similarity and dynamic similarity. Geometric similarity is usually achieved if the model is the same shape as the full scale; dimensions are equally scaled down by the appropriate factor. The 1:15 geometric scale used in this paper was easily achieved. The same velocity directions and velocity scale ratios between the points in the model and the corresponding points in the full scale could ensure kinematic similarity. To maintain dynamic similarity, the ratios of the dynamic parameters of the points in the model and the corresponding points in the full scale are constant. In practice, it is quite difficult to achieve strict similarity then some aspects are often neglected with the most important parameters focused on. In general, reducedscale experiments are made in a geometric similar model with identical Prandtl number, Reynolds number and Archimedes number. Thermal experiments have shown that the Prandtl number can be ignored in case of a high turbulent flow. Then the reduced-scale experiments are characterized by a Reynolds number and an Archimedes number [23]. It is found that flow is independent of the Reynolds number as long as the critical Reynolds number is exceeded. The value of the critical Reynolds number is difficult to determine due to varying conditions. But literature shows that with the usual piping installation, the flow will change from laminar to turbulent in the range of Reynolds number from 2000 to 4000. For the purpose of this treatment, it is assumed that the change occurs at the value of 2000, i.e., the critical Reynolds number for the pipe flow [24]. The velocity of the smoke flow was sufficiently high as to be turbulent in practice, so it was unnecessary for the Reynolds number to be identical in both the reducedand the full-scale versions [25,26]. Therefore, the Archimedes number became the crucial parameter for the description of the flow. The Archimedes number (Ar) can be defined as follows:
Ar ¼
gbhðT Tr Þ ghðT Tr Þ ¼ u2 u2 Tr
(1)
where g is the gravitational acceleration, in m/s2; b is the volume expansion coefficient, as 1/T; h is the characteristic length, in m; T is the absolute temperature of the airflow, in K; Tr is the reference absolute temperature, in K; and u is the airflow velocity, in m/s. In this paper, the Archimedes number of the exhaust duct (Arexh) in the local ventilation system is defined as
Arexh ¼
ghðTexh Tr Þ u2exh Tr
(2)
where g is the gravitational acceleration, in m/s2; h is the characteristic length, i.e., the height of the plant or the chamber, in m; Texh is the airflow absolute temperature of the exhaust duct at the Table 1 The dimensionless numbers of the exhaust duct at the sampling point between the full scale and the model.
Fig. 1. Schematic diagram of the development of thermal stratification in a cross section of the workshop; 1: fresh air inlet, 2: general ventilation outlet, 3: heat source, 4: exhaust hood.
Full scale Reduced-scale
Prandtl number
Reynolds number
Archimedes number
0.73 0.73
2179847 6282
0.25 0.23
96
Y. Huang et al. / Building and Environment 85 (2015) 94e103
Fig. 2. Photos from full scale and reduced scale: (a) Part of blast furnace workshops; (b) Reduced-scale model in laboratory; 1: Oven, 2: Exhaust hood, 3: Filling tank.
sampling point in the local ventilation system, in K; Tr is the reference absolute temperature, i.e., the temperature of fresh air inlet, in K; and uexh is the airflow velocity of the exhaust ducts in the local ventilation system, in m/s. In addition, the Archimedes number of the contaminant source (Arcs) is defined as
Arcs ¼
ghðTcs Tr Þ u2cs Tr
(3)
where g is the gravitational acceleration, in m/s2; h is the characteristic length, i.e., the height of the plant or the chamber, in m; Tcs is the absolute temperature of the contaminant source at the sampling point, in K; Tr is the reference absolute temperature, i.e., the temperature of fresh air inlet, in K; and ucs is the airflow velocity of the contaminant source, in m/s. The similarity was achieved between a portion of the blast furnace workshop of a steel plant and the reduced-scale chamber with the same Arexh and some aspects ignored in this paper. Table 1 presents the dimensionless numbers of the exhaust duct at the sampling point between the full scale and the model. As seen in Table 1, both of the Prandtl numbers of the full scale and the reduced-scale were the same. And both of the Reynolds numbers were far greater than the critical Reynolds number. Hence, the flow was independent of the Reynolds number. As for the Archimedes number, they were almost the same between the full scale and the reduced-scale. In addition, many measurements were also performed with various Arexh or Arcs because the development laws of capture efficiency and thermal stratification influenced by different empirical factors were the major concerns. The various practical parameters and conclusions could be determined corresponding to the measured results on the basis of similarity theory. All in all, the research conclusions based on the reduced-scale experiments could be guides for design or improvement in an industrial plant.
2.2. Experimental facilities All measurements were conducted in a reduced-scale chamber at Aalborg University, Denmark. The dimensions of the chamber
were 1.3 m (length) by 1.3 m (width) by 2.0 m (height), corresponding to a portion of the blast furnace workshop of a steel plant. Photos of the plant and the model are shown in Fig. 2. The practical situation in the plant is reproduced in the reducedscale experiments with some assumptions. All measurements were conducted with a geometric scale of 1:15. Fig. 3 shows a sketch of the experimental facility and the detailed sizes are included in the Supporting Information in the Appendix A. The shape and the location of the exhaust hood were established in accordance with the actual situation in the plant. The schematic drawing of the exhaust hood is depicted in Fig. 4 and the
Fig. 3. Sketch of the experimental facility: 1: Fresh air inlet, used in Case1-5, 2: General ventilation outlet, used in Case1-5, 3: Heat source, used in Case1-5, 4: Exhaust hood, used in Case1-5, 5: Horizontal baffle, used in Case1-5, 6: Vertical baffle, used in Case2-5, 7: Filling tank, used in Case3-4, 8: Exhaust duct, used in Case1-5.
Y. Huang et al. / Building and Environment 85 (2015) 94e103
97
A Srfex 2010 Fog Generator was used to enable smoke visualization. The mean diameter of the generated smoke particles was 1.545 mm. To observe the thermal stratification heights clearly and accurately, a laser beam was adopted with adequate lighting during smoke visualization experiments [30].
2.4. Layout of measuring points and test conditions
Fig. 4. Schematic drawing of the exhaust hood.
detailed sizes are included in the Supporting Information in the Appendix A.
2.3. Instrumentations A one-dimensional Laser Doppler Anemometer (LDA) was used to measure the velocity components. It could measure velocities with a range of 16~þ80 m/s and an accuracy of ±0.4% of the measured value. The LDA's probe emitted laser beams that could be precisely moved with a robot at an accuracy of ±1 mm. The temperature was measured by using K-type thermocouples with a range of 40~375 C and an accuracy of ±0.3 C [27]. The temperatures were logged with a Helios data logger connected to an ice point reference. The tracer gas technique was used in the field applications to estimate local ventilation direct-capture efficiency [13]. N2O was used to simulate CO2 (a common contaminant in industrial production processes) because it has the same molecular weight and is insensitive to human respiration during measurements. The constant release of the N2O concentration was regulated by a flow meter during the measurements [28,29]. The N2O concentration was measured with a multi-channel gas analyzer (Innova 1412 Photoacoustic Field Gas-Monitor) that was connected to a multipoint sampler monitor (Brüel & Kjaer 1303 Photoacoustic Gas-Monitor). The repeatability of the N2O measurement was ±1% of the measured value.
The velocity measurements were conducted near the exhaust opening with the LDA. The total number of the measuring points was 30. Fifteen were at the height of 0.63 m and fifteen were at the height of 0.50 m. All the intervals of the adjacent measuring points were 0.03 m, as shown in Fig. 5. The temperature measurements were carried out with 33 thermocouples. Three were respectively located at the entrance of the contaminant source, the exit of exhaust duct and the entrance of fresh air inlet. They were used for calculating the Archimedes number of the contaminant source (Arcs) or the exhaust duct (Arexh). The remaining 30 thermocouples were located between the contaminant source and the hood to illustrate the temperature variations (see Fig. 5). Five samplers were used to measure the N2O concentration at different locations. Two were used for taking air samples in the exhaust duct of the local ventilation system and in the duct of general ventilation system to calculate the capture efficiency. The other three were placed at heights of 0.40 m, 0.80 m and 1.20 m inside the center of the chamber to monitor the average concentrations. During the reduced-scale experiments, the contaminant source was assumed to be constant in each measurement in terms of the flow rate and enthalpy. All the measurements were conducted in a steady state. Table 2 shows the detailed measurement conditions.
3. Results and discussion The concentration distributions of the contaminants can be predicted based on the flow field characteristics. Furthermore, the impacts of factors on capture efficiency and thermal stratification heights can be subsequently predicted. The utilized factors were confined airflow boundaries, the flow rate of exhaust hood, source strengths, airflow obstacles and the distance between the source and the exhaust hood.
Fig. 5. Measuring points' layout between the contaminant source and exhaust hood: (a) AeA plane; (b) BeB plane; 1: Heat source, 2: Exhaust hood, 3: Horizontal baffle, 4: Plexiglass; ∙ Measuring points of both air temperature and velocity, + Measuring points of only air temperature, Measuring points of only air velocity.
▵
98
Y. Huang et al. / Building and Environment 85 (2015) 94e103
Table 2 Measurement conditions. Case no.
1 2 3 4 5
Vertical baffles
Without With With With With
Obstacle (filling tank)
Without Without With With Without
Contaminant source
Exhaust hood
Distance between source and hood d/m
Flow rate qcs/m3h1
Heat flow Q/W
0.40 0.40 0.44 0.44 0.44
35 35 35 20~140 35
200 200 200 200 200
3.1. The impacts of confined airflow boundaries The enclosure in a blast furnace plant varies during the production process, which can significantly impact the flow field characteristics and capture efficiency of an exhaust hood. Two scenarios were tested: one without vertical baffles and one with two vertical baffles on both sides of contaminant source (see Fig. 3). The capture efficiency was measured with a tracer gas technique. Detailed knowledge of the flow field near the exhaust openings can improve the accuracy [14]. The velocity vectors and the dimensionless temperature profiles can reveal the airflow movement.
3.1.1. Velocity vectors The total number of the sample points of velocity was 30. However, there were only 24 measured velocities within the range of the airflow. Thirteen were at the height of 0.63 m and eleven were at the height of 0.50 m. The measured velocity vectors of Case1 in the AeA plane, when qhood ¼ 80 m3/h, are shown in Fig. 6. The supplementary velocity component profiles are correspondingly included in the Supporting Information in the Appendix B. As seen in Fig. 6, the velocity vectors were almost symmetrically distributed and two maximums were on both sides at each height. This may have been due to the negative pressure on both sides being greater than in the middle of the exhaust hood because of the suction effect of the exhaust ducts on both sides (see Fig. 4). The velocity vectors at 0.63 m were almost accordingly greater than those at 0.50 m. Airflow confluence was the likely cause of this phenomenon. The length of the airflow coverage was 0.30 m at a height of 0.50 m and 0.36 m at a height of 0.63 m, i.e., the height of
Outlet
Size Length L/m
Width W/m
Height H/m
0.58 0.58 0.58 0.58 0.58
0.1 0.1 0.1 0.1 0.1
0.25 0.25 0.25 0.25 0.25
Flow rate qhood/m3h1
Flow rate qoutlet/m3h1
25~100 25~100 25~170 90 25~100
10 10 10 10 10
Range of Archimedes number
Arexh:0.15~12.38 Arexh:0.17~5.71 Arexh:0.04~5.61 Arcs:1.91~79.32 Arexh:0.14~5.93
the exhaust opening. Therefore, the measured velocity vector results inferred that the length of the existing hood (0.58 m) may have been too long. It is recommended that the length of the existing hood could be reduced to achieve higher capture velocity as long as it is longer than that of the airflow coverage at the exhaust opening in practice. 3.1.2. Temperature profiles The non-dimensional temperature decay ratio of the airflow (Dq/Dq0) is defined as:
Dq T Tr ¼ Dq0 Tcs Tr
(4)
where T is the absolute temperature of the airflow, in K; Tcs is the absolute temperature of the contaminant source at the sampling point, in K; and Tr is the reference absolute temperature, i.e., the temperature of fresh air inlet, in K. For example, substituting T ¼ 303.3 K, Tcs ¼ 316.1 K, and Tr ¼ 296.5 K into Eq. (4), the following equation could be obtained: Dq=Dq0 ¼ T Tr =Tcs Tr ¼ 303:3 296:5=316:1 296:5, which worked out toDq=Dq0 ¼ 0:35. The dimensionless temperature variations, when qhood ¼ 80 m3/ h, are shown in Fig. 7. As seen in Fig. 7, the dimensionless temperature variations all followed an approximate Gaussian distribution [31,32], as expected. In the AeA plane (the axisymmetric plane), the maximum of dimensionless temperatures all occurred in the middle of the thermocouple layout and varied from 0.35 to 0.20 within a height of 0.40 m to 0.60 m. In the BeB plane (the non-axisymmetric plane), the maximum of dimensionless temperatures all shifted to one side and varied from 0.48 to 0.35. The contaminant source close to the plexiglass on the right might have caused a Coanda effect, thus leading to the excursion of dimensionless temperatures. A significant large amount of entrained fresh air from the side inlet on the left may have also altered the excursion. Similar temperature variations occurred when the flow rate of the exhaust hood varied from 25 m3/h to 100 m3/h. In all, the obtained temperature profiles could indicate airflow movement and then predict the effects of different factors on contaminant control. 3.1.3. Capture efficiency profiles Capture efficiency has been widely used for evaluating different exhaust systems in the field of industrial ventilation. The definition formula of capture efficiency (a) can be written as follows [12]:
a¼
Fig. 6. Velocity vectors of Case1 in the AeA plane (qhood ¼ 80 m3/h): 1: Heat source, 2: Exhaust hood.
SE S
(5)
where SE is the flow rate of the contaminant directly captured from the exhaust hood, in ppm; S is the total flow rate of the contaminant released from the contaminant source, in ppm.
Y. Huang et al. / Building and Environment 85 (2015) 94e103
99
Fig. 7. Dimensionless temperature variations of Case1 (qhood ¼ 80 m3/h): (a) AeA plane of Case1; (b) BeB plane of Case1.
Fig. 8. Comparison of capture efficiency variations under different confined airflow boundaries.
The capture efficiency variations influenced by the absence or presence of two vertical baffles on both sides of the contaminant source are shown in Fig. 8. Fig. 8 shows that the capture efficiency of Case2 was correspondingly greater than Case1. Significant deviations of capture efficiency occurred when Arexh was less than 1, i.e., qhood50 m3/h. In addition, the capture efficiency of Case1 approximately followed an exponential decay, with Arexh varying from 0.1 to 10.0, if the lggrid was used on the horizontal axis while that of Case2 changed linearly. As for Case2, the two vertical baffles on both sides of the contaminant source caused more contaminants to be sucked into the hood, thus achieving greater capture efficiency than Case1. The confined airflow boundaries could significantly influence the capture efficiency, and it could be beneficial from the perspective of contaminant control to construct as many confined boundaries as practically possible to form an enclosed space.
once all safety requirements are satisfied. Based on Eq. (2), it is obvious that the Archimedes number of the exhaust duct in the local ventilation system decreased with an increasing flow rate of the hood. During the measurements of Case3, only the flow rate of exhaust hood varied while the other parameters remained constant. The relationship of the capture efficiency and the Archimedes number of the exhaust duct (Arexh) is depicted in Fig. 9.
3.2. The impacts of flow rate of the exhaust hood The flow rate of an exhaust hood can have a significant impact on pollutant capture efficiency in certain circumstances. It is important to determine the most economical flow rate of a hood
Fig. 9. Capture efficiency variations with different flow rate of exhaust hood.
100
Y. Huang et al. / Building and Environment 85 (2015) 94e103
As seen in Fig. 9, the capture efficiency curve was found to follow an approximate Gaussian equation when Arexh was between 0.0 and 10.0 if the lg-grid was used on the horizontal axis, and the increasing percentage of capture efficiency gradually increased with the Arexh. The increasing percentage of capture efficiency was almost 10% (qhood80 m3/h) and 1%~2% (80 m3/h＜qhood＜150 m3/ h) and less than 1% (qhood150 m3/h). Therefore, the capture efficiency variations were divided into three regions in this study: a stable region, a slowly increasing region and a sharply increasing region. The experimental results indicated that it would be better to improve capture efficiency in the latter two regions to avoid an excessive flow rate of the hood.
varies. Therefore, different flow rates of the contaminant source that represent various source strengths should be tested to evaluate the performance of the exhaust hood. During the measurements of Case4, the airflow was assumed to be in a steady state, with only the flow rate of the contaminant source varying while the other parameters remained constant. Based on Eq. (3), it is obvious that the Archimedes number of the contaminant source decreased with the increasing flow rate of the source. Fig. 10 indicates the relationship of the capture efficiency and the Archimedes number of the contaminant source (Arcs). The results in Fig. 10 show that the capture efficiency was greater than 0.90 if Arcs was no less than 4.0, i.e., qcs100 m3/h when qexh ¼ 90 m3/h and qoutlet ¼ 10 m3/h. Otherwise, it reduced to approximately 0.45 if Arcs was less than 4.0, i.e., qcs＞100 m3/h when qexh ¼ 90 m3/h and qoutlet ¼ 10 m3/h. The sudden fall in capture efficiency reached 49.4% (as shown in Fig. 10). The curve of the capture efficiency resembled a step function, with Arcs varying from 1.0 to 100.0 if the lg-grid was used on the horizontal axis. Therefore, there was a risk of a sharp decline in capture efficiency after a critical amount of contaminant source that was equal to the total flow rate of the local exhaust ventilation and general ventilation. The significant amount of generated contaminants, which was greater than the critical amount, forced the airflow movement to intensify in the horizontal direction, causing most of the contaminants escaped from the hood. These results indicate that satisfying contaminant control might be achieved if the total flow rate of the local exhaust ventilation and general ventilation was no less than that of the amount of contaminants generated in practice.
3.3. The impacts of source strengths
3.4. The impacts of airflow obstacles
During the five-minute pouring process, molten iron is slowly poured into the oven. The amount of generated contaminants
The oven is in a closed enclosure in blast furnace workshops. The gate of the closed enclosure is opened when the filling tank
Fig. 10. Capture efficiency variations with varying source strengths (Arcs).
Fig. 11. Comparison of capture efficiency variations affected by an obstacle.
Fig. 12. Comparison of capture efficiency variations with different distance between contaminant source and exhaust hood (d is the distance between source and hood, d1 ¼ 0.44 m, d2 ¼ 0.40 m).
Y. Huang et al. / Building and Environment 85 (2015) 94e103
101
begins to pour molten iron into the oven. The filling tank is initially positioned at an angle of 0 in a vertical direction. The contaminants intensively escape once the angle reaches 30 during the pouring process. The final angle of the filling tank is 115 . The impact of airflow obstacles on pollutant capture efficiency was investigated under the worst-case condition of a filling tank positioned at an angle of 30 . However, the simulated filling tank only played the role of an obstacle; it did not pour liquid during the experiment. Fig. 11 illustrates the effect of an obstacle on the capture efficiency. Fig. 11 shows that small deviations of capture efficiency occurred between the two cases. Both curves exhibited a nearly linear function when Arexh was between 0.1 and 10.0 if the lg-grid was used on the horizontal axis. In short, there was little influence on the flow field from the obstacle if no liquid was poured. This was also verified through smoke visualization. Molten iron pouring from the filling tank might alter the flow of contaminants in practice. However, it was difficult to simulate this effect in the reduced-scale experiment. 3.5. The impacts of distance between source and exhaust hood
Fig. 13. Verification of thermal stratification heights using laser beams (Red line: laser beams). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
In practice, the distance between the oven and the exhaust hood typically varies because of the various pouring angles used during different pouring processes. Therefore, the minimum and maximum distance between the contaminant source and the hood were tested corresponding to distance ranges during different pouring processes. The capture efficiency variations caused by two distances are shown in Fig. 12. Fig. 12 indicates small deviations of capture efficiency between Case2 and Case5. In addition, there were nearly identical slopes and intercepts for both of these straight lines if the lg-grid was used on the horizontal axis (0.1＜Arexh＜10.0). This infers that the slight distance difference between the source and the hood did not
Fig. 14. Variations of dimensionless thermal stratification heights and corresponding capture efficiency versus Arexh among different cases: (a) Case1; (b) Case2; (c) Case3; (d) Case5.
102
Y. Huang et al. / Building and Environment 85 (2015) 94e103
significantly affect capture efficiency. Perhaps this is because 0.04 m was too short a distance to cause significant influence on the capture efficiency in this experiment. In short, the distance between the oven and the exhaust hood does not matter so long as it is within the permitted distance range during different pouring processes. 3.6. Thermal stratification profiles affected by different factors Smoke simulations were used to supplement the measurements and visualize the formation of thermal stratification [33,34]. The thermal stratification heights were verified by laser beams; a photo is shown in Fig. 13. The non-dimensional thermal stratification height (y*st) is defined as:
y*st ¼ yst =h
(6)
where yst is the measured thermal stratification height, in m, and h is the characteristic length, i.e., the height of the chamber, in m. Fig. 14 shows a comparison of dimensionless thermal stratification heights and corresponding capture efficiencies versus Arexh among different cases. Based on Fig. 14, we concluded that the variation trend of thermal stratification heights was consistent with the corresponding capture efficiency versus Arexh for these four cases. In other words, the thermal stratification heights could also indicate the performance of the local exhaust hood. In addition, the dimensionless thermal stratification height (y*st) range was summarized to fall between 0.20 and 0.36, with Arexh varying from 0.1 to 6.3, i.e., 25 m3/h＜qhood＜120 m3/h. To ensure the health of workers who operate in the upper space of a plant, safe operation heights should be lower than the corresponding thermal stratification heights in industrial plants.
(0.0 < Arexh<10.0). Based on the increasing percentage, the capture efficiency variations were divided into a stable region, a slowly increasing region and a sharply increasing region. As for varying source strengths, the capture efficiency curve mimicked a step function if the lg-grid was used on the horizontal axis (1.0 < Arcs<100.0). This means that there was a risk of a sharp decline in the capture efficiency after the critical amount of contaminant source that was equal to the total flow rate of the local exhaust ventilation and general ventilation. All of the capture efficiency variations were approximately linear with the horizontal lg-grid axis (0.1 < Arexh<10.0) when affected by airflow obstacles and changing distances between the source and the hood. There were nearly identical slope and intercept lines influenced by airflow obstacles or small distance deviations. In all, confined airflow boundaries, the flow rate of the exhaust hood and source strengths were important empirical factors on pollutant capture efficiency, based on the different function types between the capture efficiency and the Archimedes number. From the perspective of contaminant control, it could be beneficial to construct as many confined boundaries as possible to form an enclosed space and operate the exhaust hood at an economical flow rate in practice. The experimental results also indicated that satisfying contaminant control might be achieved if the total flow rate of the local exhaust ventilation and the general ventilation was no less than that of the amount of contaminants generated in practice. Based on the measurement data of thermal stratification heights and corresponding capture efficiency in four cases, the variation trend of the thermal stratification heights was consistent with capture efficiency. Moreover, the dimensionless thermal stratification height (y*st) range fell between 0.20 and 0.36, with Arexh varying from 0.1 to 6.3, i.e., 25 m3/h＜qhood＜120 m3/h. To ensure the health of workers who operate in the upper space of a plant, safe operation heights should be lower than the corresponding thermal stratification heights in industrial plants.
4. Conclusions Acknowledgments Based on a reduced-scale experiment with a geometric scale of 1:15 corresponding to a portion of a blast furnace workshop in a steel plant, the primary conclusions inferred from the results can be summarized as follows: Certain velocity vectors and dimensionless temperatures were obtained without vertical baffles on both sides of the contaminant source. The measured velocity vector results inferred that the length of the existing hood may have been too long. It is recommended that the length of the existing hood could be reduced to achieve higher capture velocity as long as it is longer than that of the airflow coverage at the exhaust opening in practice. The dimensionless temperature profiles indicated that the maximum dimensionless temperatures all occurred in the middle of the thermocouple layout in the axisymmetric plane while those all shifted to one side in the non-axisymmetric plane probably caused by the Coanda effect. The capture efficiency variations were investigated in terms of empirical factors that included confined airflow boundaries, the flow rate of the exhaust hood, source strengths, airflow obstacles and the distance between the source and the exhaust hood. In the absence of vertical baffles on both sides of the contaminant source, the capture efficiency mirrored an exponential decay if the lg-grid was used on the horizontal axis (0.1 < Arexh<10.0); it changed linearly if there were two vertical baffles on both sides. As for a varying flow rate of the exhaust hood, the capture efficiency was found to follow an approximate Gaussian equation if the lg-grid was used on the horizontal axis
This research was financially sponsored by the National Natural Science Foundation of China (Project No. 51238010). We also wish to thank the Division of Architectural Engineering, Civil Engineering Department, Aalborg University for their kind help and support in successfully conducting this experiment. Nomenclature Ar Arcs Arexh d d1 d2 g h H L qcs qexh qoutlet Q S
Archimedes number Archimedes number of the contaminant source Archimedes number of the exhaust duct distance between the contaminant source and the exhaust hood, m original distance between the source and the hood, m new distance between the source and the hood, m gravity acceleration, m/s2 characteristic length, namely the height of the chamber, m height of the exhaust hood, m length of the exhaust hood, m flow rate of the contaminant source, m3/h flow rate of exhaust duct in the local ventilation system, m3/h flow rate of outlet in the general ventilation system, m3/h heat flow supplied to the contaminant source, W total flow rate of the contaminant released from the contaminant source, ppm
Y. Huang et al. / Building and Environment 85 (2015) 94e103
SE T Tcs Texh Tr u ucs uexh W yst y*st Z
flow rate of the contaminant directly captured from the exhaust hood, ppm absolute temperature of the airflow, K absolute temperature of the contaminant source at the sampling point, K absolute temperature of the exhaust duct at the sampling point, K reference absolute temperature, namely the temperature of fresh air inlet, K airflow velocity, m/s airflow velocity of the contaminant source, m/s airflow velocity of exhaust ducts, m/s width of the exhaust hood, m measured thermal stratification height, m non-dimensional thermal stratification height height from the chamber's ground, m
Greek symbols capture efficiency volume expansion coefficient, 1/T non-dimensional temperature decay ratio of the airflow
a b Dq/Dq0
Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.buildenv.2014.11.038. References [1] Notification of occupational disease prevention. In: Disease Prevention and control Bureau of national health and Family Planning Commission of the People's Republic of China; 2013. [2] GBZ/T 231-2010, Technical code on occupational hygiene prevention and protection in the ferrous metal smelting and rolling processing industry. [3] GBZ 2.1-2007. Occupational exposure limits for hazardous agents in the workplace. [4] Alden JL, Kane JM. Design of industrial ventilation systems. New York: Industrial Press; 1982. p. 20e7. [5] ASHRAE handbook. Industrial exhaust systems: HVAC applications. Atlanta, GA, USA: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.; 1987. [6] Devienne R, Fontaine JR, Kicka J, Bonthoux F. Experimental characterization of a plume of passive contaminant above a thermal source: capture efficiency of a fume extraction hood. Ann Occup Hyg 2009;53(7):739e48. [7] Awbi HB. Ventilation of buildings. London: Taylor and Francis; 2003. [8] Navaz HK, Amin M, Dabiri D, Faramarzi R. Past, present, and future research toward air curtain performance optimization. ASHRAE Trans 2005;111: 1083e8. [9] Ciocanea A, Dragomirescu A. Modular ventilation with twin air curtains for reducing dispersed pollution. Tunn Undergr Sp Tech 2013;37:180e98. s JC, Pavageau M. Turbulent heat and mass transfer [10] Rivera J, Elicer-Corte through air curtains devices for the confinement of heat inside tunnels. Int Commun Heat Mass 2011;38:688e95.
103
[11] Traboulsi SR, Hammoud A, Khalil MF. Effects of jet inclination angle and geometrical parameters on air curtain performance. ASHRAE Trans 2009;115: 617e29. [12] Nielsen PV, Madsen U, Tveit DJ. Experiments on an exhaust hood for the paint industry. In: Proceedings of roomvent 1991, Cincinnati; 1991. [13] Madsen U, Breum NO, Nielsen PV. Local exhaust ventilation: a numerical and experimental study of capture efficiency. Build Environ 1994;29(3):319e23. [14] Ilpo K. Numerical simulation of the capture efficiency of an unflanged rectangular exhaust opening in a coaxial air flow. Ann Occup Hyg 1995;39(1): 21e33. [15] Rim D, Wallace L, Nabinger S, Persily A. Reduction of exposure to ultrafine particles by kitchen exhaust hoods: the effects of exhaust flow rates, particle size, and burner position. Sci Total Environ 2012;432:350e6. [16] Li YG, Delsante A, Symon J. Residential kitchen range hoods-Buoyancy capture principle and capture efficiency revisited. Indoor Air 1997;7(3):151e7. [17] Yang D, Huo R, Zhang XL, Zhu S, Zhao XY. Comparative study on carbon monoxide stratification and thermal stratification in a horizontal channel fire. Build Environ 2012;49:1e8. [18] Lin YJP, Lin CL. A study on flow stratification in a space using displacement ventilation. Int J Heat Mass Tran 2014;73:67e75. [19] Bouzinaoui A, Vallette P, Lemoine F, Fontaine JR, Devienne R. Experimental study of thermal stratification in ventilated confined spaces. Int J Heat Mass Tran 2005;48(19e20):4121e31. [20] Yang D, Huo R, Zhang XL, Zhao XY. Comparison of the distribution of carbon monoxide concentration and temperature rise in channel fires: reduced-scale experiments. Appl Therm Eng 2011;31:528e36. [21] Roux NL, Faure X, Inard C, Soares S, Ricciardi L. Reduced-scale study of wind influence on mean airflows inside buildings equipped with ventilation systems. Build Environ 2012;58:231e44. [22] Liu PC, Lin HT, Chou JH. Evaluation of buoyancy-driven ventilation in atrium buildings using computational fluid dynamics and reduced-scale air model. Build Environ 2009;44:1970e9. [23] Taehti E, Goodfellow H. Handbook of industrial ventilation. San Diego: Academic Press; 2001. [24] Streeter VL, Wylie EB, Bedford KW. Fluid mechanics. 9th ed. New York: McGraw-Hill Press; 1998. [25] Tilleya N, Rauwoensb P, Fauconniera D, Mercia B. On the extrapolation of CFD results for smoke and heat control in reduced-scale set-ups to full scale: atrium configuration. Fire Saf J 2013;59:160e5. [26] Nielsen PV. Model experiments for the determination of airflow in large spaces. In: Proceedings of indoor air 1993: the 6th international conference on indoor air quality and climate; 1993. Helsinki, Finland. [27] Artmann N, Vonbank R, Jensen RL. Temperature measurements using type K thermocouples and the Fluke Helios Plus 2289 datalogger. DCE Technical Reports No. 52. Department of Civil Engineering, Aalborg University; 2008. [28] Gao NP, Niu JL, Perino M, Heiselberg P. The airborne transmission of infection between flats in high-rise residential buildings: tracer gas simulation. Build Environ 2008;43:1805e17. [29] Laporthe S, Virgone J, Castanet S. A comparative study of two tracer gases: SF6 and N2O. Build Environ 2001;36:313e20. [30] Nielsen PV, Brohus H, Petersen AJ, Thorsen KS. Smoke movement in an atrium with a fire with low rate of heat release. In: Proceedings of indoor air 2008: the 11th international conference on indoor air quality and climate; 17th to 22nd August 2008. Copenhagen, Denmark. [31] Rodi W. Turbulent buoyant jets and plumes. Britain: Pergamon Press; 1982. [32] Zukowska D, Popiolek Z, Melikov A. Determination of the integral characteristics of an asymmetrical thermal plume from air speed/velocity and temperature measurements. Exp Therm Fluid Sci 2010;34:1205e16. [33] Karaismail E, Celik I, Steven G. Flow dynamics and contaminant transport in industrial-type enclosing exhaust hoods. J Occup Environ Hyg 2013;10(7): 384. [34] Sun YG, Zhang YH. An overview of room air motion measurement: technology and application. HVAC&R Res 2007;13(6):929.