- Email: [email protected]
Comparative study on different additives with a jet array on cooling of a hot steel surface
Applied Thermal Engineering 137 (2018) 154–163
Contents lists available at ScienceDirect
Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng
Research Paper
Comparative study on different additives with a jet array on cooling of a hot steel surface
T
Ishita Sarkara, Samarshi Chakrabortya, Avinash Ashoka, Iman Senguptaa, Surjya K. Palb, ⁎ Sudipto Chakrabortya, a b
Department of Chemical Engineering, Indian Institute of Technology Kharagpur, India Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, India
H I GH L IG H T S
efficiency of jet array is studied over single free falling jet. • Cooling are conducted from an initial plate temperature of > 900 °C. • Experiments study done with surfactants, polymer and nanofluids. • Comparative cooling rate of 143 °C/s is achieved for PVP based coolant. • Highest • This enhanced cooling can be beneficial for the production of improved quality steel.
A R T I C LE I N FO
A B S T R A C T
Keywords: Jet array Run out table Cooling rate Heat flux Uniform cooling
The current work aims to investigate the efficiency of a jet array in cooling of a hot steel plate having surface temperature above 900 °C. The entire study has been divided into two phases. The first phase consists of experiments which are aimed to optimize the jet array impingement height and the water flow rate. It has been found that the cooling rate is enhanced by 60% in case of a jet array compared to a single jet at the same water flow rate and impingement height. In both the single jet and the jet array used in the present work, free falling flow occurs under gravity. In the second phase, the effect of seven different additives on heat transfer performance during cooling has been studied at the optimized values of water flow rate and impingement height. Sodium Dodecyl Sulphate (SDS), Cetyltrimethyl Ammonium Bromide (CTAB) and Tween 20 have been used as surfactant additives, Polyvinylpyrrolidone (PVP) as a polymer additive, Titanium dioxide (TiO2), Cu-Al layered double hydroxide (LDH) and PVP dispersed in TiO2 have been used as nanofluid additives. The results indicate that a maximum cooling rate of 143 °C/s has been achieved for PVP based coolant which is 28% more than that obtained for pure water. The results also prove that ultrafast cooling can be attained by using additive based jet array impingement.
1. Introduction Over the last decade, world crude steel production rate has increased by 41.20% reaching 1621 million tons (Mt) for the year 2015. Around 2500 different grades of steel are produced to cater the need of several industries ranging from structural to aero‐space. Increasing demand of steel has motivated researchers to develop new technologies that can produce high quality steels. Quality of steel can be enhanced by modifying the microstructure of steel [1]. Alloying with different elements and controlled cooling of steel during the hot rolling process of steel making are the two methods by which the microstructures can
⁎
be modified in order to meet the required hardness and strength specification [2,3]. Controlling the cooling rate of steel is preferred over alloying as the latter one is an expensive process. Hot rolling process is the final stage of steel making and consists of three steps. The temperature of steel strips is first increased to 900 °C followed by thickness reduction by passing through roughing and finishing mills. Finally the strips are cooled to 600 °C on the run out table (ROT) [4]. The microstructure of steel depends on the cooling rate at the ROT where the strips are cooled from 900 °C to 600 °C [5]. Transformation of austenite phase to various other phases occurs within the temperature range of 900–600 °C [6]. It has been observed that the hardness and strength of
Corresponding author. E-mail address: [email protected] (S. Chakraborty).
https://doi.org/10.1016/j.applthermaleng.2018.03.081 Received 11 October 2017; Received in revised form 23 March 2018; Accepted 24 March 2018 Available online 28 March 2018 1359-4311/ © 2018 Elsevier Ltd. All rights reserved.
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Nomenclature TC1 TC2 TC3 x y z T Tf
UFC AISI CHF HTC SDS CTAB PVP LDH TiO2
thermocouple 1 thermocouple 2 thermocouple 3 direction along the length of the plate (mm) direction along the thickness of the plate (mm) direction along the depth of the plate (mm) surface temperature (°C) coolant temperature (°C)
ultrafast cooling American Iron and Steel Institute Critical Heat Flux Heat Transfer Coefficient sodium dodecyl sulphate Cetyltrimethyl Ammonium Bromide polyvinylpyrrolidone layered double hydroxide titanium dioxide
Abbreviations ROT
run out table
to the interference of adjacent jets, the flow patterns were affected. Cooling rates can be enhanced by adding various additives such as surfactants, polymers, nanofluids, etc to coolant [20,21]. These additives alter the physical properties of coolant in order to have better contact with the solid surface leading to better heat transfer by [22,23]. Cooling rate increases significantly for surfactant added water as coolant. Addition of surfactant reduces surface tension of water thereby increasing the wetting diameter as compared to pure water resulting in better contact of coolant with solid surface and thus increasing the cooling rate [24]. It has been reported that certain polymers like polyvinylpyrrolidone (PVP) and hydroxyethyl cellulose (HEC) when used as additives significantly reduce surface tension of the coolant [25–27]. Molecular weight, polymer concentration and viscosity are the crucial parameters of polymer that determine the heat transfer rate. Nanofluids are also used as additives because they enhance heat transfer rate by increasing the thermal conductivity of the coolant. The reason for this increase is due to the Brownian motion of nanoparticles which increases the transport properties as well as the clustering of the nanoparticles which in turn enhances the thermal conductivity [28,29]. Elghanam et al. [30] conducted nucleate boiling heat transfer experiments with different types of additives and found out that additives also play a major role on increasing the number of active nucleation sites at the surface apart from altering the surface tension, viscosity and thermal conductivity of coolant leading to enhancement in heat transfer. Stability and uniformity of nanofluids are two main areas of concern while using them as additives. Various surfactants, polymers are added to nanofluids as dispersants in order to improve the stability of nanofluid [31]. The effect of surfactant dispersed Cu –water nanofluid on the cooling rate for free surface jet array cooling was studied by Tie et al. [32]. From open literature it is quite evident that very few works are available on free surface jet array cooling in nucleate and transition boiling regimes and hardly any work has been reported on the effect of different types of additive on jet array cooling at a high surface temperature of 1050 °C. All the previous works on cooling of high temperature surfaces are confined to a single jet or a single air-atomized spray nozzle. In the present work, experiments have been conducted to optimize impingement height and coolant flow rate using free surface jet array. Impingement height and flow rate are varied from 10 to 20 cm and 8 to 20 lpm, respectively. Seven different types of surfactant, polymer and nanofluid based additives have been added to water at their optimized concentrations to study their effects on cooling rate at optimized impingement height and cooling rate. In the earlier works, a pressurized jet flowing through a nozzle have been used for cooling purpose [20,22,33,34] but in the current work, free falling jet flowing through holes in the array under gravity have been employed. For all experiments, AISI 304 grade stainless steel plate has been used which is heated to a temperature around 1050 °C. Cooling rates have been calculated for a temperature range of 900–600 °C.
steel is the maximum for martensite phase which occurs during the rapid cooling of austenite phase during ROT operation [7,8]. Currently in the ROT operation, conventional laminar cooling technology is used that produces cooling rates around 30 °C/s to 80 °C/s due to low impingement pressure. The cooling rate achieved is very low and is insufficient for the desired phase transformation of austenite to martensite phase [9]. In order to overcome this problem of low cooling rate, a cooling technology has been developed known as Ultrafast cooling (UFC) which can achieve high cooling rates on the ROT [2,10]. Lucas et al. [11] have reported that if the product of plate thickness (mm) and cooling rate (°C/s) exceeds 800, the cooling process is termed as UFC. Spray and jet impingement cooling are the two main cooling techniques used to achieve UFC. Leidenfrost effect slows down the cooling rate for both spray and jet cooling. Leidenfrost effect occurs due to the formation of vapour layer when the coolant comes in contact with the superheated steel surface. This vapour layer acts as an insulator by preventing contact of coolant with the surface and affecting the heat transfer rates during cooling [12,13]. Air atomized spray cooling is used to overcome this problem, where the pressurized air drives away the insulating vapour layer [14]. The advantage of jet impingement cooling is that the jet impinges with high impact pressure resulting in removal of vapour layer and thus providing better heat transfer. A forced convention zone is generated around the stagnation point where the cooling rate is the maximum. At points away from the forced convection zone the cooling rate sharply decreases giving rise to non-uniform cooling throughout the surface and different heat transfer zones are produced as reported by Zumbrunnen et al. [15]. Due to this non uniformity in cooling, jet impingement cooling can be effectively used only for systems where the area of the jet is comparable with the surface area of the plate. Therefore, for systems having high surface to jet area ratio, jet array cooling technique is used which produces uniform cooling due to uniformly distributed multiple impingement points. Apart from common factors like coolant physical properties and flow rate, various jet array injection parameters like jet diameter, impingement height, jet spacing and array pattern also show significant influence on cooling rates during jet array cooling [16]. Impingement of jet on target surface causes an upward wall flow. During jet array cooling, adjacent developing wall flow collides to generate cross flows [17]. Metzger and Korstad [18] studied the influence of cross-flow on circular jets. They reported that due to the development of cross flow condition, the impingement flow pattern was disturbed and there was a significant reduction in heat transfer rates which concluded that cross flows are undesirable for jet array cooling. Uysal et al. [19] investigated the parameters that influence cross flow. They varied the free surface jet array nozzle diameters and conducted experiments for different flow rates and found out that the jet nozzle diameter and coolant flow rate influences cross flows. Yamane et al. [16] conducted oil flow visualization experiment on the target plate to study about the flow patterns produced by impinging jets on target plate and they observed that due 155
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
2. Experimental details of jet array cooling system
surface. The governing equation and the boundary conditions are as follows:
2.1. Experimental setup and procedure
∂ ⎛ ∂T ⎞ ∂ ⎛ ∂T ⎞ ∂T k + k = ρCp ∂x ⎝ ∂x ⎠ ∂y ⎝ ∂y ⎠ ∂t ⎜
Fig. 1 shows the schematic diagram of jet array system with the impingement plate. Perspex sheets were used to construct the jet array system of dimension 100 mm × 100 mm × 250 mm. The impingement plate was formed by 3 × 3 square array of circular holes of diameter 5 mm with 30 mm hole spacing. Meshes were provided for uniform distribution of liquid inside the jet array system. Experiments were carried out on an AISI 304 stainless steel plate of dimension 100 mm × 100 mm × 6 mm. Three K–type chromel–alumel thermocouples of 3 mm diameter each were used to measure the transient temperature data during the experiments. These thermocouples were inserted 3 mm beneath the plate surface through 3 mm diameter holes drilled up to 50 mm in the plate at different locations parallel to the plate surface. The thermocouple locations are 20 mm, 50 mm and 70 mm respectively, from one edge of the plate, as shown in Fig. 2. The jet array experimental set-up has been represented in Fig. 3. The steel plate was heated in a programmable electrical muffle furnace up to a temperature of 1050 °C. After the desired temperature was recorded by the thermocouples, the hot plate was taken out of the furnace and placed on the resting pad made of ceramic. The resting pad is grooved in order to maintain adiabatic boundary condition for all sides, except for the top surface where the jet array impinges. Flow rate of coolant was controlled by using a rotameter operating between 2 and 20 lpm. Initially a wooden plank was kept between the impingement plate and the hot steel plate in order to prevent irregular water flow on the heated plate. Once the water flow became steady the plank was removed and the plate was uniformly cooled from the top. The transient temperature data measured by the thermocouples were recorded in the computer through the data acquisition system (NIcDAQ-9174 and NI 9211 card) at a rate of 10 samples per second. The temperature data recorded during experiments were used to calculate the surface heat flux and surface temperature values via an inverse heat conduction solver (INTEMP).
⎟
where k is the thermal conductivity of the steel plate (W/mK), ρ is the density of the steel plate (Kg/m3) and Cp is the specific heat capacity (J/ Kg K) The initial condition is as follows:
At t= 0 , T= Ti=1050 °C. The boundary conditions are as follows:
At x= 0 mm,
∂T = 0 for all y; ∂x
At x= 100 mm,
∂T = 0 for all y; ∂x
At y= 0 mm,
∂T = 0 for all x; ∂y
At y= 6 mm,
∂T = unknown for all x. ∂y
For the calculation of surface temperature and surface heat flux, INTEMP initially starts with a guess value of surface heat flux as a known boundary condition and thereafter calculates temperature at all the nodes by a standard conduction problem. Then INTEMP employs a nonlinear optimization technique to modify the surface heat fluxes so as to minimize the error between the temperature measured at a particular location and the nodal temperature predicted at the same location. When the error is found to be smaller than a formerly fixed tolerance value, INTEMP ends the iteration; else it restarts the calculation with a new guess of heat flux. Adiabatic boundary conditions are considered for all sides except for the top surface where the jet array impinges and heat transport due to radiation and free convection is assumed to be negligible when compared to forced convection during cooling. Moreover, precaution has been taken to minimize the heat loss from the three sides by placing ceramic heat resistant bricks during the cooling experiments. The entire computational domain is discretized into 4800 quadratic elements each having a directional step size of 0.50 mm and 0.25 mm in x and y direction respectively. The impinging surface has been divided into three constant heat flux zones namely (a) 0 to 35 mm, (b) 35 to 65 mm and (c) 65 to 100 mm. The node numbers corresponding to thermocouple locations are 2453 (TC1), 2513 (TC2) and 2553 (TC3). This procedure has been used by scientific community in earlier work [35]. The
2.2. Estimation of transient surface temperature and heat flux A 2D inverse heat conduction equation was formed by developing a 2D planar model with dimensions corresponding to the actual steel plate; 100 mm length and 6 mm thickness. An inverse heat conduction software (INTEMP) which applies finite element methodology to solve inverse heat conduction equation was used to estimate transient surface heat flux and overall temperature distribution across the impinging
Fig. 1. Schematic diagram of jet array system and impingement plate. 156
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Fig. 2. Schematic diagram of steel plate with thermocouple location.
Fig. 3. Schematic diagram of the jet array cooling system.
ionic surfactant) and Cetyltrimethyl Ammonium Bromide (Cationic surfactant) were the surfactant additives used. Polyvinylpyrrolidone, a water soluble polymer was used as polymer additive. Sodium Dodecyl Sulphate (SDS) and Tween 20 were brought from Merck, India. Cetyltrimethyl Ammonium Bromide (CTAB) and Polyvinylpyrrolidone (PVP) were procured from Sisco Research Laboratories Pvt. Ltd. (SRL), India. Two types of water based nanofluids were synthesised as additives. Titanium dioxide (TiO2) and Cu-Al layered double hydroxide (LDH) nanofluids were prepared via co-precipitation method as described in earlier studies carried out by researchers [36,37]. PVP
computational domain for the inverse heat conduction analysis has been shown in Fig. 4. The transient temperature data recorded by thermocouples were taken as the input to the nodes corresponding to the location of thermocouples. 2.3. Additives used Experiments were carried out by adding seven different additives to the base fluid. Normal tap water at room temperature was used as base fluid. Sodium Dodecyl Sulphate (Anionic surfactant), Tween 20 (Non157
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Fig. 4. Computational domain of inverse heat conduction analysis.
software. For a single jet it is found that the temperature drops significantly at the impingement (stagnation) zone due to forced convection whereas in the other places of the surface the temperature is higher resulting in non-uniformity of temperature throughout the surface. In the case of 3 × 3 jet array, nine forced convection zones are produced which results in almost uniform cooling along the surface except at x = 20, 50 and 80 mm, which correspond to impingement points of the jet array where the local temperature experiences a dip. The plot corresponding to the jet array relates to the temperature along the centerline of the plate (z = 50 mm) and at different x-locations.
dispersed TiO2 nanofluid was also used as an additive. Additives were used at the respective optimized concentrations, as described in Table 1. These optimised concentration values and the different thermo-physical values were obtained from earlier works [3,20,34,38]. 2.4. Design of experiments The entire jet array cooling system study was divided into two phases. First phase consisted of experiments which were aimed to optimise the jet array impingement height and the coolant flow rate using water as coolant and five sets of experiments were conducted. Experiment was also conducted with a single jet array at the optimized height and flow conditions so that the cooling results can be compared with that of a jet array. Each set consisted of four experiments in which the height was kept constant and the water flow rate was varied. Full set of experimental design for first phase is shown in Table 2. In the second phase, at the optimised value of water flow rate and impingement height the effect of different types of additive on heat transfer performance during cooling was studied. Seven experiments were conducted with seven different types of additive added to water at the respective optimised concentrations.
4.2. Effect of impingement height and water flow rate Jet impingement height and water flow rate have significant effects on heat transfer performance during cooling. Therefore it is necessary to optimize jet impingement height and water flow rate in order to maximize cooling rate and surface heat flux. During experiments, cooling rate within the temperature range of 900–600 °C was calculated for each set of water flow rate and impingement height. Fig. 6 shows the variation of cooling rate with impingement height for different water flow rates. It was found that on increasing impingement height from 10 cm to 15 cm, cooling rate increases and attains a maximum value for impingement height of 15 cm for all flow rates and thereafter it decreases. On increasing the impingement height, the potential energy increases which results in increase in impact energy upon impingement. On the other hand on increasing impingement height beyond 15 cm, heavy splashing of impinged water jet occurs which decreases contact time between water and hot steel surface resulting in adverse effect on cooling rates. This is in accordance with existing literature [33]. These findings are also in line with the study of Lienhard et al. [40], who have reported that heat transfer is affected by
3. Measurement uncertainty Each experiment has been repeated thrice and the average value obtained from the three experiments has been considered. The major sources of uncertainties arise from temperature and water flow rate measurement. The noise in the thermocouple leads to a bias error of 3.5% in the temperature measurement [39]. A calibrated rotameter has been used to measure water flow rate, the uncertainty in which is around 0.08%. The maximum error in the calculated cooling rate is found to be within 5%.
Table 1 Additives used and their optimized concentrations with thermo-physical properties.
4. Results and discussion 4.1. Uniform cooling As described earlier, jet array cooling produces multiple stagnation points on the hot steel surface which reduces non uniformity in heat transfer during cooling. Fig. 5 shows the variation of local surface temperature with position till 1.3 s after the temperature reaches 900 °C along with a schematic of the base plate of the jet array to indicate where the jet array hits the plate surface. The experiment has been conducted from an impingement height of 15 cm and a water flow rate of 16 lpm in case of a single jet and a jet array. Transient temperature values at all the surface nodes have been calculated by using INTEMP 158
Additives
Optimum concentration (ppm)
Surface tension (mN/m)
Thermal conductivity (W/ mK)
Viscosity (mPa-s)
SDS CTAB Tween 20 PVP Cu-Al LDH TiO2 TiO2 + PVP
600 240 56 110 120 56 40 (TiO2), 30 (PVP)
52.1 41.8 38.8 36 71 70.8 64.5
0.58 0.63 0.54 0.53 0.65 0.60 0.59
1.25 0.71 0.50 1.15 1.62 1.50 1.55
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Table 2 Experimental design to optimize water flow rate and impingement height (optimization based on maximum cooling rate). Sl. No
Impingement height (cm)
Water flow rate (lpm)
1 2 3 4 5
10 12 15 17 20
8, 12, 16, 20
splattering. To study the effect of water flow rate on heat transfer rates, transient surface temperature was calculated by using INTEMP software and plotted against time within the temperature range of 900–600 °C, as shown in Fig. 7. Experiments were conducted at an optimized impingement height of 15 cm. The average values of the surface temperature measured by the three thermocouples at each time step have been reported within the above mentioned temperature zone. It was found that surface temperature falls fastest for a water flow rate of 16 lpm as compared to other flow rates and reaches 600 °C at cooling time equal to 2.7 s. It was observed that on increasing water flow rate from 8 to 16 lpm, cooling rate increases and reaches a maximum value for water flow rate of 16 lpm irrespective of the impingement height and thereafter it decreases. An increase in water flow rate increases the impact pressure of water jet on steel plate due to the increase in jet velocities. Consequently, the spreadability of each jet on plate surface increases, thus enhancing the heat transfer rate. However further increase in water flow rate leads to splashing of water jet on impingement which decreases contact time between water and hot steel surface resulting in lower heat transfer rates. These findings conclude that both impingement height and water flow rate play a crucial role in enhancing heat transfer performance and highest cooling rate of 111.73 °C/s was obtained for an impingement height of 15 cm and water flow rate of 16 lpm.
Fig. 6. Variation of cooling rate with impingement height at different water flow rates.
4.2.1. Boling curves Surface heat flux for each set of impingement height and water flow rate were calculated within a temperature range of 900–200 °C by using INTEMP and were plotted against transient surface temperature as shown in Fig. 8(a–e). It was observed that, irrespective of the impingement height and water flow rate, boiling curves followed a nonlinear variation of surface heat flux with change in surface temperature. During the initial stages of cooling, the temperature difference between
Fig. 7. Surface temperature variation with time.
the hot steel surface and impinged water jet was very high resulting in formation of an insulating vapour layer. As the cooling proceeded, surface temperature decreased and the surface heat flux rose to a maximum value known as critical heat flux (CHF) and thereafter it
Fig. 5. Variation of local surface temperature with position along with schematic of base plate of jet array. 159
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Fig. 8. (a–e) Effect of impingement height on boiling curve at different water flow rates.
10 cm to 15 cm, the CHF and average heat flux values were enhanced due to increase in impact pressure of water jet on the steel plate. On the other hand, further increase in impingement height from 15 cm resulted in lower CHF and average heat flux values due to heavy splashing of impinged water jet on the steel plate. Similar trend was noted on increasing the water flow rate, CHF and average heat flux values
decreased. Increase in surface heat flux was due to thinning of insulating vapour layer and this region to the right of the boiling curve is termed as transition boiling regime. On further cooling, due to the decrease in thermal energy of the steel plate, vaporization decreased and nucleate boiling dominated. It was observed that on increasing the impingement height from 160
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
nucleation sites are formed due to the deposition of nanoparticles on hot steel surface. These nucleation sites catalyses the rupture of insulating vapour film formed during cooling, thus increasing the solid–liquid contact. Nanofluids also exhibited appreciable rise in thermal conductivity compared to base fluid which led to improved heat transfer. In the current research, three types of surfactant additives (SDS, CTAB and Tween 20) and a polymer additive (PVP) were used to study the effect of reduction in surface tension of coolant on jet array cooling. Experiments were also conducted by using three types of water based nanofluids (Cu-Al LDH, TiO2 and PVP dispersed TiO2) as coolants. It was observed in earlier work that dispersion of PVP in TiO2 helps in stabilising the nanofluid [38]. All experiments were conducted at optimized impingement height and water flow rate of 15 cm and 16 lpm, respectively. Additives were used at the respective optimised concentrations. Fig. 12 shows the variation of surface temperature (900–600 °C) with time during cooling. It was found that decrease in surface temperature during cooling was slowest when water was used as coolant and was quickest for PVP added water as coolant reaching 600 °C at time equal to 2.6 s and 2.1 s respectively. Fig. 13 compares cooling rates achieved by using different coolants. It was found that the cooling rate enhanced by 60% in case of a jet array compared to a single jet (cooling rate 69 °C/s) under the same flow conditions and impingement height. It was observed that on adding additives, cooling rate increased significantly. Highest cooling rate of 143 °C/s was obtained for PVP based coolant an increase of 28% when compared to pure water. The remarkable decrease in surface tension due to addition of PVP in coolant is the main reason behind the improved cooling rate since low surface tension leads to better spreading of the coolant on the surface and better removal of heat [34]. The lowest cooling rate amongst the additives was obtained for SDS based coolant. This can be mainly attributed to the excessive foaming and high viscosity in case of SDS [35]. According to literature, UFC is said to be achieved when the product of cooling rate in °C/s and plate thickness in mm exceeds 800 units [11]. Since the thickness of the plate used in the current study is 6 mm, the minimum value of cooling rate required to attain UFC is 133.33 °C/s. Both PVP and PVP dispersed TiO2 coolant gave cooling rates in the UFC region since the cooling rates attained by them are 143 °C/s and 139 °C/s respectively. These findings conclude that additive based jet array can be used in steel manufacturing process to achieve UFC.
increased till 16 lpm due to increase in spreadability of jet on plate surface. However further increase in water flow rate resulted in reduction of CHF and average heat flux values due to the splashing of water jet on impingement. From the boiling curves it can be concluded that highest CHF and average heat flux values were obtained for a water flow rate of 16 lpm with an impingement height of 15 cm. Table 3 shows the variation of CHF and average heat flux with different water flow rates at an optimized impingement height of 15 cm. Maximum CHF and average heat flux values of 2.44 MW/m2 and 1.58 MW/m2 were obtained for a water flow rate of 16 lpm. It was also observed that on increasing water flow rate from 8 lpm to 16 lpm, both CHF and average heat flux increase by 14% and 31.66%, respectively, and thereafter both decrease. 4.2.2. Variation of surface heat flux with time Fig. 9 shows surface heat flux variation with time for different water flow rates for an optimized impingement height of 15 cm. These fluxes are the average of the three values measured at the three thermocouple locations at each time step. Initial part of curve belongs to transition boiling regime whereas the later part is in nucleate boiling regime. In order to achieve high cooling rate, it is desirable to reach CHF quickly as longer period of transition boiling lowers heat transfer performance. It was found out that the time required for reaching CHF decreased on increasing water flow rate from 8 to 16 lpm and thereafter it increased. Minimum time required to reach CHF was lowest for a water flow rate of 16 lpm, and is equal to 2.6 s starting from the time when the plate temperature reaches 900 °C while cooling. 4.2.3. Variation of heat transfer coefficient during cooling The heat transfer coefficient has been calculated as follows:
HTC = q/(T −Tf )
(1)
where HTC is the heat transfer coefficient (W/m2 °C), q is the surface heat flux (W/m2), T is the surface temperature (°C) of the steel plate and Tf is the coolant temperature (°C). The coolant has been used at room temperature. (T − Tf) is called the bulk temperature gradient. HTC values were calculated for each flow rate at an optimized impingement height of 15 cm. The average values obtained from the three thermocouple positions at each time step were plotted against surface temperature (900–600 °C), as shown in Fig. 10. It was observed that at high surface temperature HTC values were small which started increasing as the cooling started and surface temperature began to fall. The maximum HTC was obtained at a water flow rate of 16 lpm which resulted from high surface heat flux values at this flow rate. Almost linear trend is observed for the variation of HTC with surface temperature. This can be explained by Fig. 11 in which surface heat flux (q) has been plotted against bulk temperature gradient (T − Tf). Here also the plots are found to be almost linear and HTC being defined as a quotient of surface heat flux and bulk temperature gradient also exhibits a linear trend. Initially the temperature difference being very high, HTC values are low but as the bulk temperature gradient becomes small, the HTC starts increasing.
5. Conclusion The heat transfer performance of a jet array by using different coolants has been investigated in the current study. The experiments have been conducted on a stainless steel plate having surface temperature above 900 °C. The water flow rate and impingement height of the jet array have been optimized based on maximum cooling rate attained. The effect of different surfactant, polymer and nanofluid based additives on the cooling rate of the hot steel plate have been studied. The key findings of the study can be summarized as follows: (a) The rate of heat transfer was found to increase with water flow rate up to 16 lpm, and thereafter it decreased. (b) The cooling rate increased with impingement height up to 15 cm,
4.3. Effect of additives Physical properties of coolant such as thermal conductivity, viscosity, surface tension etc. strongly influence heat transfer rate during cooling. Based on the earlier work of researchers on jet cooling, it was observed that cooling rates increased significantly while using different types of surfactant added water as coolant [3,22]. Addition of surfactant reduces surface tension of water, thereby increasing the wetting diameter as compared to pure water. This results in better spreadability of coolant on the solid surface thus increasing the cooling rate. Water based nanofluids have also been used as coolants in previous works [20], and it has been found out that cooling rates were enhanced by using different types of nanofluid as coolant. During cooling, new
Table 3 Variation of critical heat flux and average heat flux with water flow rate.
161
Water flow rate (lpm)
Critical heat flux (MW/ m2 )
Average heat flux (MW/m2)
8 12 16 20
2.14 2.18 2.44 2.26
1.2 1.29 1.58 1.4
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Fig. 9. Variation of surface heat flux with time.
Fig. 12. Surface temperature variation with time for different coolants.
Fig. 10. Variation of heat transfer coefficient with surface temperature.
Fig. 13. Cooling rate comparison for different coolants.
(e) The cooling rate of a jet array is increased by 60% as compared to that of a single free falling jet at the same water flow rate and impingement height. (f) Maximum critical heat flux of 2.44 MW/m2 was achieved for a water flow rate of 16 lpm with impingement height of 15 cm. (g) Maximum cooling rate of 143 °C/s was obtained for PVP based coolant for an optimized impingement height and coolant flow rate, which is 28% more than that achieved for pure water. (h) The highest cooling rate attained indicates that ultrafast cooling can be obtained using additive based jet array impingement. References [1] N. Mebarki, D. Delagnes, P. Lamesle, F. Delmas, C. Levaillant, Relationship between microstructure and mechanical properties of a 5% Cr tempered martensitic tool steel, Mater. Sci. Eng., A 387–389 (2004) 171–175. [2] P. Bhattacharya, A.N. Samanta, S. Chakraborty, Spray evaporative cooling to achieve ultra fast cooling in runout table, Int. J. Therm. Sci. 48 (2009) 1741–1747. [3] S.V. Ravikumar, J.M. Jha, I. Sarkar, S.K. Pal, S. Chakraborty, Mixed-surfactant additives for enhancement of air-atomized spray cooling of a hot steel plate, Exp. Therm Fluid Sci. 55 (2014) 210–220. [4] S.D. Cox, S.J. Hardy, D.J. Parker, Influence of runout table operation setup on hot strip quality, subject to initial strip condition: heat transfer issues, Ironmaking Steelmaking 28 (2001) 363–371. [5] S.V. Ravikumar, J.M. Jha, I. Sarkar, S.K. Pal, S. Chakraborty, Enhancement of heat transfer rate in air-atomized spray cooling of a hot steel plate by using an aqueous solution of non-ionic surfactant and ethanol, Appl. Therm. Eng. 64 (2014) 64–75. [6] ASM Handbook, ASM International, 1991. [7] Z. Qiao, Y. Liu, L. Yu, Z. Gao, Effect of cooling rate on microstructural formation and hardness of 30 CrNi 3 Mo steel, Appl. Phys. A Mater. Sci. Process. 95 (2009) 917–922.
Fig. 11. Variation of surface heat flux with bulk temperature gradient.
after which it declined. (c) Almost uniform cooling can be achieved throughout the steel plate using jet array due to formation of several forced convection zones unlike a single jet where there is non-uniformity of temperature in the surface (See Fig. 5). (d) Maximum average cooling rate of 111.73 °C/s was achieved for a water flow rate of 16 lpm and impingement height of 15 cm. 162
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
water jet, J. Heat Transfer 135 (2013) 032101. [25] Z. Mingzheng, X. Guodong, L. Jian, L. Chai, Z. Lijun, Analysis of factors influencing thermal conductivity and viscosity in different kinds of surfactant solutions, Exp. Therm Fluid Sci. 36 (2012) 22–29. [26] J. Águila-Hernández, A. Trejo, B.E. García-Flores, Volumetric and surface tension behavior of aqueous solutions of polyvinylpyrrolidone in the range (288 to 303) K, J. Chem. Eng. Data 56 (2011) 2371–2378. [27] P. Kotchaphakdee, M.C. Williams, Enhancement of nucleate pool boiling with polymeric additives, Int. J. Heat Mass Transf. 13 (1970) 835–848. [28] S.K. Das, S.U.S. Choi, A Review of Heat Transfer in Nanofluids, in: F.I. Thomas, P.H. James (Eds.), Advances in Heat Transfer, vol. 41, Elsevier, 2009, pp. 81–197. [29] G. Puliti, S. Paolucci, M. Sen, Nanofluids and their properties, Appl. Mech. Rev. 64 (2012) 030803–030803. [30] R. Elghanam, M.E. Fawal, R.A. Aziz, M. Skr, A.H. Khalifa, Experimental study of nucleate boiling heat transfer enhancement by using surfactant, Ain Shams Eng. J. 2 (2011) 195–209. [31] X. Li, D. Zhu, G. Chen, X. Wang, Influence of SDBS on stability of copper nanoSuspensions, in: 2007 First International Conference on Integration and Commercialization of Micro and Nanosystems, American Society of Mechanical Engineers, 2007, pp. 971–975. [32] P. Tie, Q. Li, Y. Xuan, Heat transfer performance of Cu–water nanofluids in the jet arrays impingement cooling system, Int. J. Therm. Sci. 77 (2014) 199–205. [33] S.V. Ravikumar, J.M. Jha, S.S. Mohapatra, S.K. Pal, S. Chakraborty, Experimental investigation of effect of different types of surfactants and jet height on cooling of a hot steel plate, J. Heat Transfer 136 (2014) 072102-072102-072110. [34] I. Sarkar, D.K. Behera, J.M. Jha, S.K. Pal, S. Chakraborty, Effect of polymer additive on the cooling rate of a hot steel plate by using water jet, Exp. Therm Fluid Sci. 70 (2016) 105–114. [35] S.V. Ravikumar, J.M. Jha, S.S. Mohapatra, S.K. Pal, S. Chakraborty, Influence of ultrafast cooling on microstructure and mechanical properties of steel, Steel Res. Int. 84 (2013) 1157–1170. [36] S. Chakraborty, I. Sarkar, K. Haldar, S.K. Pal, S. Chakraborty, Synthesis of Cu–Al layered double hydroxide nanofluid and characterization of its thermal properties, Appl. Clay Sci. 107 (2015) 98–108. [37] R. Saleh, N. Putra, R.E. Wibowo, W.N. Septiadi, S.P. Prakoso, Titanium dioxide nanofluids for heat transfer applications, Exp. Therm Fluid Sci. 52 (2014) 19–29. [38] S. Chakraborty, I. Sarkar, D.K. Behera, S.K. Pal, S. Chakraborty, Experimental investigation on the effect of dispersant addition on thermal and rheological characteristics of TiO2 nanofluid, Powder Technol. 307 (2017) 10–24. [39] R.B. Abernethy, R.P. Benedict, R.B. Dowdell, ASME measurement uncertainty, J. Fluids Eng. 107 (1985) 161–164. [40] V.J.H. Lienhard, X. Liu, L.A. Gabour, Splattering and heat transfer during impingement of a turbulent liquid jet, J. Heat Transfer 114 (1992) 362–372.
[8] Z. Nishiyama, Martensitic Transformation, Elsevier, 2012. [9] R.M. Guo, Heat transfer of laminar flow cooling during strip acceleration on hot strip mill runout tables, Trans. ISS-AIME 8 (1993) 49–64. [10] M.J. Cho, B.G. Thomas, P.J. Lee, Three-dimensional numerical study of impinging water jets in runout table cooling processes, Metall. Mater. Trans. B 39 (2008) 593–602. [11] A. Lucas, P. Simon, G. Bourdon, J.C. Herman, P. Riche, J. Neutjens, P. Harlet, Metallurgical aspects of ultra fast cooling in front of the down-coiler, Steel Res. Int. 75 (2004) 139–146. [12] H.M. Al-Ahmadi, S.C. Yao, Spray cooling of high temperature metals using high mass flux industrial nozzles, Exp. Heat Transfer 21 (2008) 38–54. [13] S.V. Ravikumar, J.M. Jha, S.S. Mohapatra, A. Sinha, S.K. Pal, S. Chakraborty, Experimental study of the effect of spray inclination on ultrafast cooling of a hot steel plate, Heat Mass Transf. 49 (2013) 1509–1522. [14] B. Han, X. Liu, G. Wang, G. She, Development of cooling process control technique in hot strip mill, J. Iron. Steel Res. Int. 12 (2005) 12–16. [15] D.A. Zumbrunnen, R. Viskanta, F.P. Incropera, The effect of surface motion on forced convection, film boiling heat transfer, Trans. ASME J. Heat Transfer 111 (1989) 760–766. [16] Y. Yamane, Y. Ichikawa, M. Yamamoto, S. Honami, Effect of injection parameters on jet array impingement heat transfer, Int. J. Gas Turbine, Propulsion Power Syst. 4 (2012) 27–34. [17] Y. Pan, B. Webb, Heat transfer characteristics of arrays of free-surface liquid jets, Trans.-Am. Soc. Mech. Eng. J. Heat Transfer 117 (1995) 878–883. [18] D.E. Metzger, R.J. Korstad, Effects of crossflow on impingement heat transfer, ASME J. Eng. Power 94 (1) (1972) 35–41. [19] U. Uysal, P.-W. Li, M. Chyu, F. Cunha, Heat transfer on internal surfaces of a duct subjected to impingement of a jet array with varying jet hole-size and spacing, J. Turbomach. 128 (2006) 158–165. [20] I. Sarkar, S. Chakraborty, J.M. Jha, S.K. Pal, S. Chakraborty, Ultrafast cooling of a hot steel plate using Cu-Al layered double hydroxide nanofluid jet, Int. J. Therm. Sci. 116 (2017) 52–62. [21] A.M. Tiara, S. Chakraborty, I. Sarkar, S.K. Pal, S. Chakraborty, Effect of alumina nanofluid jet on the enhancement of heat transfer from a steel plate, Heat Mass Transf. (2016) 1–11. [22] S.S. Mohapatra, S.V. Ravikumar, A. Verma, S.K. Pal, S. Chakraborty, Experimental investigation of effect of a surfactant to increase cooling of hot steel plates by a water jet, J. Heat Transfer 135 (2013) 032101-032101-032107. [23] J.M. Jha, S.V. Ravikumar, A.M. Tiara, I. Sarkar, S.K. Pal, S. Chakraborty, Ultrafast cooling of a hot moving steel plate by using alumina nanofluid based air atomized spray impingement, Appl. Therm. Eng. 75 (2015) 738–747. [24] S.S. Mohapatra, S.V. Ravikumar, A. Verma, S.K. Pal, S. Chakraborty, Experimental investigation of effect of a surfactant to increase cooling of hot steel plates by a
163
Contents lists available at ScienceDirect
Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng
Research Paper
Comparative study on different additives with a jet array on cooling of a hot steel surface
T
Ishita Sarkara, Samarshi Chakrabortya, Avinash Ashoka, Iman Senguptaa, Surjya K. Palb, ⁎ Sudipto Chakrabortya, a b
Department of Chemical Engineering, Indian Institute of Technology Kharagpur, India Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, India
H I GH L IG H T S
efficiency of jet array is studied over single free falling jet. • Cooling are conducted from an initial plate temperature of > 900 °C. • Experiments study done with surfactants, polymer and nanofluids. • Comparative cooling rate of 143 °C/s is achieved for PVP based coolant. • Highest • This enhanced cooling can be beneficial for the production of improved quality steel.
A R T I C LE I N FO
A B S T R A C T
Keywords: Jet array Run out table Cooling rate Heat flux Uniform cooling
The current work aims to investigate the efficiency of a jet array in cooling of a hot steel plate having surface temperature above 900 °C. The entire study has been divided into two phases. The first phase consists of experiments which are aimed to optimize the jet array impingement height and the water flow rate. It has been found that the cooling rate is enhanced by 60% in case of a jet array compared to a single jet at the same water flow rate and impingement height. In both the single jet and the jet array used in the present work, free falling flow occurs under gravity. In the second phase, the effect of seven different additives on heat transfer performance during cooling has been studied at the optimized values of water flow rate and impingement height. Sodium Dodecyl Sulphate (SDS), Cetyltrimethyl Ammonium Bromide (CTAB) and Tween 20 have been used as surfactant additives, Polyvinylpyrrolidone (PVP) as a polymer additive, Titanium dioxide (TiO2), Cu-Al layered double hydroxide (LDH) and PVP dispersed in TiO2 have been used as nanofluid additives. The results indicate that a maximum cooling rate of 143 °C/s has been achieved for PVP based coolant which is 28% more than that obtained for pure water. The results also prove that ultrafast cooling can be attained by using additive based jet array impingement.
1. Introduction Over the last decade, world crude steel production rate has increased by 41.20% reaching 1621 million tons (Mt) for the year 2015. Around 2500 different grades of steel are produced to cater the need of several industries ranging from structural to aero‐space. Increasing demand of steel has motivated researchers to develop new technologies that can produce high quality steels. Quality of steel can be enhanced by modifying the microstructure of steel [1]. Alloying with different elements and controlled cooling of steel during the hot rolling process of steel making are the two methods by which the microstructures can
⁎
be modified in order to meet the required hardness and strength specification [2,3]. Controlling the cooling rate of steel is preferred over alloying as the latter one is an expensive process. Hot rolling process is the final stage of steel making and consists of three steps. The temperature of steel strips is first increased to 900 °C followed by thickness reduction by passing through roughing and finishing mills. Finally the strips are cooled to 600 °C on the run out table (ROT) [4]. The microstructure of steel depends on the cooling rate at the ROT where the strips are cooled from 900 °C to 600 °C [5]. Transformation of austenite phase to various other phases occurs within the temperature range of 900–600 °C [6]. It has been observed that the hardness and strength of
Corresponding author. E-mail address: [email protected] (S. Chakraborty).
https://doi.org/10.1016/j.applthermaleng.2018.03.081 Received 11 October 2017; Received in revised form 23 March 2018; Accepted 24 March 2018 Available online 28 March 2018 1359-4311/ © 2018 Elsevier Ltd. All rights reserved.
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Nomenclature TC1 TC2 TC3 x y z T Tf
UFC AISI CHF HTC SDS CTAB PVP LDH TiO2
thermocouple 1 thermocouple 2 thermocouple 3 direction along the length of the plate (mm) direction along the thickness of the plate (mm) direction along the depth of the plate (mm) surface temperature (°C) coolant temperature (°C)
ultrafast cooling American Iron and Steel Institute Critical Heat Flux Heat Transfer Coefficient sodium dodecyl sulphate Cetyltrimethyl Ammonium Bromide polyvinylpyrrolidone layered double hydroxide titanium dioxide
Abbreviations ROT
run out table
to the interference of adjacent jets, the flow patterns were affected. Cooling rates can be enhanced by adding various additives such as surfactants, polymers, nanofluids, etc to coolant [20,21]. These additives alter the physical properties of coolant in order to have better contact with the solid surface leading to better heat transfer by [22,23]. Cooling rate increases significantly for surfactant added water as coolant. Addition of surfactant reduces surface tension of water thereby increasing the wetting diameter as compared to pure water resulting in better contact of coolant with solid surface and thus increasing the cooling rate [24]. It has been reported that certain polymers like polyvinylpyrrolidone (PVP) and hydroxyethyl cellulose (HEC) when used as additives significantly reduce surface tension of the coolant [25–27]. Molecular weight, polymer concentration and viscosity are the crucial parameters of polymer that determine the heat transfer rate. Nanofluids are also used as additives because they enhance heat transfer rate by increasing the thermal conductivity of the coolant. The reason for this increase is due to the Brownian motion of nanoparticles which increases the transport properties as well as the clustering of the nanoparticles which in turn enhances the thermal conductivity [28,29]. Elghanam et al. [30] conducted nucleate boiling heat transfer experiments with different types of additives and found out that additives also play a major role on increasing the number of active nucleation sites at the surface apart from altering the surface tension, viscosity and thermal conductivity of coolant leading to enhancement in heat transfer. Stability and uniformity of nanofluids are two main areas of concern while using them as additives. Various surfactants, polymers are added to nanofluids as dispersants in order to improve the stability of nanofluid [31]. The effect of surfactant dispersed Cu –water nanofluid on the cooling rate for free surface jet array cooling was studied by Tie et al. [32]. From open literature it is quite evident that very few works are available on free surface jet array cooling in nucleate and transition boiling regimes and hardly any work has been reported on the effect of different types of additive on jet array cooling at a high surface temperature of 1050 °C. All the previous works on cooling of high temperature surfaces are confined to a single jet or a single air-atomized spray nozzle. In the present work, experiments have been conducted to optimize impingement height and coolant flow rate using free surface jet array. Impingement height and flow rate are varied from 10 to 20 cm and 8 to 20 lpm, respectively. Seven different types of surfactant, polymer and nanofluid based additives have been added to water at their optimized concentrations to study their effects on cooling rate at optimized impingement height and cooling rate. In the earlier works, a pressurized jet flowing through a nozzle have been used for cooling purpose [20,22,33,34] but in the current work, free falling jet flowing through holes in the array under gravity have been employed. For all experiments, AISI 304 grade stainless steel plate has been used which is heated to a temperature around 1050 °C. Cooling rates have been calculated for a temperature range of 900–600 °C.
steel is the maximum for martensite phase which occurs during the rapid cooling of austenite phase during ROT operation [7,8]. Currently in the ROT operation, conventional laminar cooling technology is used that produces cooling rates around 30 °C/s to 80 °C/s due to low impingement pressure. The cooling rate achieved is very low and is insufficient for the desired phase transformation of austenite to martensite phase [9]. In order to overcome this problem of low cooling rate, a cooling technology has been developed known as Ultrafast cooling (UFC) which can achieve high cooling rates on the ROT [2,10]. Lucas et al. [11] have reported that if the product of plate thickness (mm) and cooling rate (°C/s) exceeds 800, the cooling process is termed as UFC. Spray and jet impingement cooling are the two main cooling techniques used to achieve UFC. Leidenfrost effect slows down the cooling rate for both spray and jet cooling. Leidenfrost effect occurs due to the formation of vapour layer when the coolant comes in contact with the superheated steel surface. This vapour layer acts as an insulator by preventing contact of coolant with the surface and affecting the heat transfer rates during cooling [12,13]. Air atomized spray cooling is used to overcome this problem, where the pressurized air drives away the insulating vapour layer [14]. The advantage of jet impingement cooling is that the jet impinges with high impact pressure resulting in removal of vapour layer and thus providing better heat transfer. A forced convention zone is generated around the stagnation point where the cooling rate is the maximum. At points away from the forced convection zone the cooling rate sharply decreases giving rise to non-uniform cooling throughout the surface and different heat transfer zones are produced as reported by Zumbrunnen et al. [15]. Due to this non uniformity in cooling, jet impingement cooling can be effectively used only for systems where the area of the jet is comparable with the surface area of the plate. Therefore, for systems having high surface to jet area ratio, jet array cooling technique is used which produces uniform cooling due to uniformly distributed multiple impingement points. Apart from common factors like coolant physical properties and flow rate, various jet array injection parameters like jet diameter, impingement height, jet spacing and array pattern also show significant influence on cooling rates during jet array cooling [16]. Impingement of jet on target surface causes an upward wall flow. During jet array cooling, adjacent developing wall flow collides to generate cross flows [17]. Metzger and Korstad [18] studied the influence of cross-flow on circular jets. They reported that due to the development of cross flow condition, the impingement flow pattern was disturbed and there was a significant reduction in heat transfer rates which concluded that cross flows are undesirable for jet array cooling. Uysal et al. [19] investigated the parameters that influence cross flow. They varied the free surface jet array nozzle diameters and conducted experiments for different flow rates and found out that the jet nozzle diameter and coolant flow rate influences cross flows. Yamane et al. [16] conducted oil flow visualization experiment on the target plate to study about the flow patterns produced by impinging jets on target plate and they observed that due 155
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
2. Experimental details of jet array cooling system
surface. The governing equation and the boundary conditions are as follows:
2.1. Experimental setup and procedure
∂ ⎛ ∂T ⎞ ∂ ⎛ ∂T ⎞ ∂T k + k = ρCp ∂x ⎝ ∂x ⎠ ∂y ⎝ ∂y ⎠ ∂t ⎜
Fig. 1 shows the schematic diagram of jet array system with the impingement plate. Perspex sheets were used to construct the jet array system of dimension 100 mm × 100 mm × 250 mm. The impingement plate was formed by 3 × 3 square array of circular holes of diameter 5 mm with 30 mm hole spacing. Meshes were provided for uniform distribution of liquid inside the jet array system. Experiments were carried out on an AISI 304 stainless steel plate of dimension 100 mm × 100 mm × 6 mm. Three K–type chromel–alumel thermocouples of 3 mm diameter each were used to measure the transient temperature data during the experiments. These thermocouples were inserted 3 mm beneath the plate surface through 3 mm diameter holes drilled up to 50 mm in the plate at different locations parallel to the plate surface. The thermocouple locations are 20 mm, 50 mm and 70 mm respectively, from one edge of the plate, as shown in Fig. 2. The jet array experimental set-up has been represented in Fig. 3. The steel plate was heated in a programmable electrical muffle furnace up to a temperature of 1050 °C. After the desired temperature was recorded by the thermocouples, the hot plate was taken out of the furnace and placed on the resting pad made of ceramic. The resting pad is grooved in order to maintain adiabatic boundary condition for all sides, except for the top surface where the jet array impinges. Flow rate of coolant was controlled by using a rotameter operating between 2 and 20 lpm. Initially a wooden plank was kept between the impingement plate and the hot steel plate in order to prevent irregular water flow on the heated plate. Once the water flow became steady the plank was removed and the plate was uniformly cooled from the top. The transient temperature data measured by the thermocouples were recorded in the computer through the data acquisition system (NIcDAQ-9174 and NI 9211 card) at a rate of 10 samples per second. The temperature data recorded during experiments were used to calculate the surface heat flux and surface temperature values via an inverse heat conduction solver (INTEMP).
⎟
where k is the thermal conductivity of the steel plate (W/mK), ρ is the density of the steel plate (Kg/m3) and Cp is the specific heat capacity (J/ Kg K) The initial condition is as follows:
At t= 0 , T= Ti=1050 °C. The boundary conditions are as follows:
At x= 0 mm,
∂T = 0 for all y; ∂x
At x= 100 mm,
∂T = 0 for all y; ∂x
At y= 0 mm,
∂T = 0 for all x; ∂y
At y= 6 mm,
∂T = unknown for all x. ∂y
For the calculation of surface temperature and surface heat flux, INTEMP initially starts with a guess value of surface heat flux as a known boundary condition and thereafter calculates temperature at all the nodes by a standard conduction problem. Then INTEMP employs a nonlinear optimization technique to modify the surface heat fluxes so as to minimize the error between the temperature measured at a particular location and the nodal temperature predicted at the same location. When the error is found to be smaller than a formerly fixed tolerance value, INTEMP ends the iteration; else it restarts the calculation with a new guess of heat flux. Adiabatic boundary conditions are considered for all sides except for the top surface where the jet array impinges and heat transport due to radiation and free convection is assumed to be negligible when compared to forced convection during cooling. Moreover, precaution has been taken to minimize the heat loss from the three sides by placing ceramic heat resistant bricks during the cooling experiments. The entire computational domain is discretized into 4800 quadratic elements each having a directional step size of 0.50 mm and 0.25 mm in x and y direction respectively. The impinging surface has been divided into three constant heat flux zones namely (a) 0 to 35 mm, (b) 35 to 65 mm and (c) 65 to 100 mm. The node numbers corresponding to thermocouple locations are 2453 (TC1), 2513 (TC2) and 2553 (TC3). This procedure has been used by scientific community in earlier work [35]. The
2.2. Estimation of transient surface temperature and heat flux A 2D inverse heat conduction equation was formed by developing a 2D planar model with dimensions corresponding to the actual steel plate; 100 mm length and 6 mm thickness. An inverse heat conduction software (INTEMP) which applies finite element methodology to solve inverse heat conduction equation was used to estimate transient surface heat flux and overall temperature distribution across the impinging
Fig. 1. Schematic diagram of jet array system and impingement plate. 156
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Fig. 2. Schematic diagram of steel plate with thermocouple location.
Fig. 3. Schematic diagram of the jet array cooling system.
ionic surfactant) and Cetyltrimethyl Ammonium Bromide (Cationic surfactant) were the surfactant additives used. Polyvinylpyrrolidone, a water soluble polymer was used as polymer additive. Sodium Dodecyl Sulphate (SDS) and Tween 20 were brought from Merck, India. Cetyltrimethyl Ammonium Bromide (CTAB) and Polyvinylpyrrolidone (PVP) were procured from Sisco Research Laboratories Pvt. Ltd. (SRL), India. Two types of water based nanofluids were synthesised as additives. Titanium dioxide (TiO2) and Cu-Al layered double hydroxide (LDH) nanofluids were prepared via co-precipitation method as described in earlier studies carried out by researchers [36,37]. PVP
computational domain for the inverse heat conduction analysis has been shown in Fig. 4. The transient temperature data recorded by thermocouples were taken as the input to the nodes corresponding to the location of thermocouples. 2.3. Additives used Experiments were carried out by adding seven different additives to the base fluid. Normal tap water at room temperature was used as base fluid. Sodium Dodecyl Sulphate (Anionic surfactant), Tween 20 (Non157
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Fig. 4. Computational domain of inverse heat conduction analysis.
software. For a single jet it is found that the temperature drops significantly at the impingement (stagnation) zone due to forced convection whereas in the other places of the surface the temperature is higher resulting in non-uniformity of temperature throughout the surface. In the case of 3 × 3 jet array, nine forced convection zones are produced which results in almost uniform cooling along the surface except at x = 20, 50 and 80 mm, which correspond to impingement points of the jet array where the local temperature experiences a dip. The plot corresponding to the jet array relates to the temperature along the centerline of the plate (z = 50 mm) and at different x-locations.
dispersed TiO2 nanofluid was also used as an additive. Additives were used at the respective optimized concentrations, as described in Table 1. These optimised concentration values and the different thermo-physical values were obtained from earlier works [3,20,34,38]. 2.4. Design of experiments The entire jet array cooling system study was divided into two phases. First phase consisted of experiments which were aimed to optimise the jet array impingement height and the coolant flow rate using water as coolant and five sets of experiments were conducted. Experiment was also conducted with a single jet array at the optimized height and flow conditions so that the cooling results can be compared with that of a jet array. Each set consisted of four experiments in which the height was kept constant and the water flow rate was varied. Full set of experimental design for first phase is shown in Table 2. In the second phase, at the optimised value of water flow rate and impingement height the effect of different types of additive on heat transfer performance during cooling was studied. Seven experiments were conducted with seven different types of additive added to water at the respective optimised concentrations.
4.2. Effect of impingement height and water flow rate Jet impingement height and water flow rate have significant effects on heat transfer performance during cooling. Therefore it is necessary to optimize jet impingement height and water flow rate in order to maximize cooling rate and surface heat flux. During experiments, cooling rate within the temperature range of 900–600 °C was calculated for each set of water flow rate and impingement height. Fig. 6 shows the variation of cooling rate with impingement height for different water flow rates. It was found that on increasing impingement height from 10 cm to 15 cm, cooling rate increases and attains a maximum value for impingement height of 15 cm for all flow rates and thereafter it decreases. On increasing the impingement height, the potential energy increases which results in increase in impact energy upon impingement. On the other hand on increasing impingement height beyond 15 cm, heavy splashing of impinged water jet occurs which decreases contact time between water and hot steel surface resulting in adverse effect on cooling rates. This is in accordance with existing literature [33]. These findings are also in line with the study of Lienhard et al. [40], who have reported that heat transfer is affected by
3. Measurement uncertainty Each experiment has been repeated thrice and the average value obtained from the three experiments has been considered. The major sources of uncertainties arise from temperature and water flow rate measurement. The noise in the thermocouple leads to a bias error of 3.5% in the temperature measurement [39]. A calibrated rotameter has been used to measure water flow rate, the uncertainty in which is around 0.08%. The maximum error in the calculated cooling rate is found to be within 5%.
Table 1 Additives used and their optimized concentrations with thermo-physical properties.
4. Results and discussion 4.1. Uniform cooling As described earlier, jet array cooling produces multiple stagnation points on the hot steel surface which reduces non uniformity in heat transfer during cooling. Fig. 5 shows the variation of local surface temperature with position till 1.3 s after the temperature reaches 900 °C along with a schematic of the base plate of the jet array to indicate where the jet array hits the plate surface. The experiment has been conducted from an impingement height of 15 cm and a water flow rate of 16 lpm in case of a single jet and a jet array. Transient temperature values at all the surface nodes have been calculated by using INTEMP 158
Additives
Optimum concentration (ppm)
Surface tension (mN/m)
Thermal conductivity (W/ mK)
Viscosity (mPa-s)
SDS CTAB Tween 20 PVP Cu-Al LDH TiO2 TiO2 + PVP
600 240 56 110 120 56 40 (TiO2), 30 (PVP)
52.1 41.8 38.8 36 71 70.8 64.5
0.58 0.63 0.54 0.53 0.65 0.60 0.59
1.25 0.71 0.50 1.15 1.62 1.50 1.55
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Table 2 Experimental design to optimize water flow rate and impingement height (optimization based on maximum cooling rate). Sl. No
Impingement height (cm)
Water flow rate (lpm)
1 2 3 4 5
10 12 15 17 20
8, 12, 16, 20
splattering. To study the effect of water flow rate on heat transfer rates, transient surface temperature was calculated by using INTEMP software and plotted against time within the temperature range of 900–600 °C, as shown in Fig. 7. Experiments were conducted at an optimized impingement height of 15 cm. The average values of the surface temperature measured by the three thermocouples at each time step have been reported within the above mentioned temperature zone. It was found that surface temperature falls fastest for a water flow rate of 16 lpm as compared to other flow rates and reaches 600 °C at cooling time equal to 2.7 s. It was observed that on increasing water flow rate from 8 to 16 lpm, cooling rate increases and reaches a maximum value for water flow rate of 16 lpm irrespective of the impingement height and thereafter it decreases. An increase in water flow rate increases the impact pressure of water jet on steel plate due to the increase in jet velocities. Consequently, the spreadability of each jet on plate surface increases, thus enhancing the heat transfer rate. However further increase in water flow rate leads to splashing of water jet on impingement which decreases contact time between water and hot steel surface resulting in lower heat transfer rates. These findings conclude that both impingement height and water flow rate play a crucial role in enhancing heat transfer performance and highest cooling rate of 111.73 °C/s was obtained for an impingement height of 15 cm and water flow rate of 16 lpm.
Fig. 6. Variation of cooling rate with impingement height at different water flow rates.
4.2.1. Boling curves Surface heat flux for each set of impingement height and water flow rate were calculated within a temperature range of 900–200 °C by using INTEMP and were plotted against transient surface temperature as shown in Fig. 8(a–e). It was observed that, irrespective of the impingement height and water flow rate, boiling curves followed a nonlinear variation of surface heat flux with change in surface temperature. During the initial stages of cooling, the temperature difference between
Fig. 7. Surface temperature variation with time.
the hot steel surface and impinged water jet was very high resulting in formation of an insulating vapour layer. As the cooling proceeded, surface temperature decreased and the surface heat flux rose to a maximum value known as critical heat flux (CHF) and thereafter it
Fig. 5. Variation of local surface temperature with position along with schematic of base plate of jet array. 159
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Fig. 8. (a–e) Effect of impingement height on boiling curve at different water flow rates.
10 cm to 15 cm, the CHF and average heat flux values were enhanced due to increase in impact pressure of water jet on the steel plate. On the other hand, further increase in impingement height from 15 cm resulted in lower CHF and average heat flux values due to heavy splashing of impinged water jet on the steel plate. Similar trend was noted on increasing the water flow rate, CHF and average heat flux values
decreased. Increase in surface heat flux was due to thinning of insulating vapour layer and this region to the right of the boiling curve is termed as transition boiling regime. On further cooling, due to the decrease in thermal energy of the steel plate, vaporization decreased and nucleate boiling dominated. It was observed that on increasing the impingement height from 160
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
nucleation sites are formed due to the deposition of nanoparticles on hot steel surface. These nucleation sites catalyses the rupture of insulating vapour film formed during cooling, thus increasing the solid–liquid contact. Nanofluids also exhibited appreciable rise in thermal conductivity compared to base fluid which led to improved heat transfer. In the current research, three types of surfactant additives (SDS, CTAB and Tween 20) and a polymer additive (PVP) were used to study the effect of reduction in surface tension of coolant on jet array cooling. Experiments were also conducted by using three types of water based nanofluids (Cu-Al LDH, TiO2 and PVP dispersed TiO2) as coolants. It was observed in earlier work that dispersion of PVP in TiO2 helps in stabilising the nanofluid [38]. All experiments were conducted at optimized impingement height and water flow rate of 15 cm and 16 lpm, respectively. Additives were used at the respective optimised concentrations. Fig. 12 shows the variation of surface temperature (900–600 °C) with time during cooling. It was found that decrease in surface temperature during cooling was slowest when water was used as coolant and was quickest for PVP added water as coolant reaching 600 °C at time equal to 2.6 s and 2.1 s respectively. Fig. 13 compares cooling rates achieved by using different coolants. It was found that the cooling rate enhanced by 60% in case of a jet array compared to a single jet (cooling rate 69 °C/s) under the same flow conditions and impingement height. It was observed that on adding additives, cooling rate increased significantly. Highest cooling rate of 143 °C/s was obtained for PVP based coolant an increase of 28% when compared to pure water. The remarkable decrease in surface tension due to addition of PVP in coolant is the main reason behind the improved cooling rate since low surface tension leads to better spreading of the coolant on the surface and better removal of heat [34]. The lowest cooling rate amongst the additives was obtained for SDS based coolant. This can be mainly attributed to the excessive foaming and high viscosity in case of SDS [35]. According to literature, UFC is said to be achieved when the product of cooling rate in °C/s and plate thickness in mm exceeds 800 units [11]. Since the thickness of the plate used in the current study is 6 mm, the minimum value of cooling rate required to attain UFC is 133.33 °C/s. Both PVP and PVP dispersed TiO2 coolant gave cooling rates in the UFC region since the cooling rates attained by them are 143 °C/s and 139 °C/s respectively. These findings conclude that additive based jet array can be used in steel manufacturing process to achieve UFC.
increased till 16 lpm due to increase in spreadability of jet on plate surface. However further increase in water flow rate resulted in reduction of CHF and average heat flux values due to the splashing of water jet on impingement. From the boiling curves it can be concluded that highest CHF and average heat flux values were obtained for a water flow rate of 16 lpm with an impingement height of 15 cm. Table 3 shows the variation of CHF and average heat flux with different water flow rates at an optimized impingement height of 15 cm. Maximum CHF and average heat flux values of 2.44 MW/m2 and 1.58 MW/m2 were obtained for a water flow rate of 16 lpm. It was also observed that on increasing water flow rate from 8 lpm to 16 lpm, both CHF and average heat flux increase by 14% and 31.66%, respectively, and thereafter both decrease. 4.2.2. Variation of surface heat flux with time Fig. 9 shows surface heat flux variation with time for different water flow rates for an optimized impingement height of 15 cm. These fluxes are the average of the three values measured at the three thermocouple locations at each time step. Initial part of curve belongs to transition boiling regime whereas the later part is in nucleate boiling regime. In order to achieve high cooling rate, it is desirable to reach CHF quickly as longer period of transition boiling lowers heat transfer performance. It was found out that the time required for reaching CHF decreased on increasing water flow rate from 8 to 16 lpm and thereafter it increased. Minimum time required to reach CHF was lowest for a water flow rate of 16 lpm, and is equal to 2.6 s starting from the time when the plate temperature reaches 900 °C while cooling. 4.2.3. Variation of heat transfer coefficient during cooling The heat transfer coefficient has been calculated as follows:
HTC = q/(T −Tf )
(1)
where HTC is the heat transfer coefficient (W/m2 °C), q is the surface heat flux (W/m2), T is the surface temperature (°C) of the steel plate and Tf is the coolant temperature (°C). The coolant has been used at room temperature. (T − Tf) is called the bulk temperature gradient. HTC values were calculated for each flow rate at an optimized impingement height of 15 cm. The average values obtained from the three thermocouple positions at each time step were plotted against surface temperature (900–600 °C), as shown in Fig. 10. It was observed that at high surface temperature HTC values were small which started increasing as the cooling started and surface temperature began to fall. The maximum HTC was obtained at a water flow rate of 16 lpm which resulted from high surface heat flux values at this flow rate. Almost linear trend is observed for the variation of HTC with surface temperature. This can be explained by Fig. 11 in which surface heat flux (q) has been plotted against bulk temperature gradient (T − Tf). Here also the plots are found to be almost linear and HTC being defined as a quotient of surface heat flux and bulk temperature gradient also exhibits a linear trend. Initially the temperature difference being very high, HTC values are low but as the bulk temperature gradient becomes small, the HTC starts increasing.
5. Conclusion The heat transfer performance of a jet array by using different coolants has been investigated in the current study. The experiments have been conducted on a stainless steel plate having surface temperature above 900 °C. The water flow rate and impingement height of the jet array have been optimized based on maximum cooling rate attained. The effect of different surfactant, polymer and nanofluid based additives on the cooling rate of the hot steel plate have been studied. The key findings of the study can be summarized as follows: (a) The rate of heat transfer was found to increase with water flow rate up to 16 lpm, and thereafter it decreased. (b) The cooling rate increased with impingement height up to 15 cm,
4.3. Effect of additives Physical properties of coolant such as thermal conductivity, viscosity, surface tension etc. strongly influence heat transfer rate during cooling. Based on the earlier work of researchers on jet cooling, it was observed that cooling rates increased significantly while using different types of surfactant added water as coolant [3,22]. Addition of surfactant reduces surface tension of water, thereby increasing the wetting diameter as compared to pure water. This results in better spreadability of coolant on the solid surface thus increasing the cooling rate. Water based nanofluids have also been used as coolants in previous works [20], and it has been found out that cooling rates were enhanced by using different types of nanofluid as coolant. During cooling, new
Table 3 Variation of critical heat flux and average heat flux with water flow rate.
161
Water flow rate (lpm)
Critical heat flux (MW/ m2 )
Average heat flux (MW/m2)
8 12 16 20
2.14 2.18 2.44 2.26
1.2 1.29 1.58 1.4
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
Fig. 9. Variation of surface heat flux with time.
Fig. 12. Surface temperature variation with time for different coolants.
Fig. 10. Variation of heat transfer coefficient with surface temperature.
Fig. 13. Cooling rate comparison for different coolants.
(e) The cooling rate of a jet array is increased by 60% as compared to that of a single free falling jet at the same water flow rate and impingement height. (f) Maximum critical heat flux of 2.44 MW/m2 was achieved for a water flow rate of 16 lpm with impingement height of 15 cm. (g) Maximum cooling rate of 143 °C/s was obtained for PVP based coolant for an optimized impingement height and coolant flow rate, which is 28% more than that achieved for pure water. (h) The highest cooling rate attained indicates that ultrafast cooling can be obtained using additive based jet array impingement. References [1] N. Mebarki, D. Delagnes, P. Lamesle, F. Delmas, C. Levaillant, Relationship between microstructure and mechanical properties of a 5% Cr tempered martensitic tool steel, Mater. Sci. Eng., A 387–389 (2004) 171–175. [2] P. Bhattacharya, A.N. Samanta, S. Chakraborty, Spray evaporative cooling to achieve ultra fast cooling in runout table, Int. J. Therm. Sci. 48 (2009) 1741–1747. [3] S.V. Ravikumar, J.M. Jha, I. Sarkar, S.K. Pal, S. Chakraborty, Mixed-surfactant additives for enhancement of air-atomized spray cooling of a hot steel plate, Exp. Therm Fluid Sci. 55 (2014) 210–220. [4] S.D. Cox, S.J. Hardy, D.J. Parker, Influence of runout table operation setup on hot strip quality, subject to initial strip condition: heat transfer issues, Ironmaking Steelmaking 28 (2001) 363–371. [5] S.V. Ravikumar, J.M. Jha, I. Sarkar, S.K. Pal, S. Chakraborty, Enhancement of heat transfer rate in air-atomized spray cooling of a hot steel plate by using an aqueous solution of non-ionic surfactant and ethanol, Appl. Therm. Eng. 64 (2014) 64–75. [6] ASM Handbook, ASM International, 1991. [7] Z. Qiao, Y. Liu, L. Yu, Z. Gao, Effect of cooling rate on microstructural formation and hardness of 30 CrNi 3 Mo steel, Appl. Phys. A Mater. Sci. Process. 95 (2009) 917–922.
Fig. 11. Variation of surface heat flux with bulk temperature gradient.
after which it declined. (c) Almost uniform cooling can be achieved throughout the steel plate using jet array due to formation of several forced convection zones unlike a single jet where there is non-uniformity of temperature in the surface (See Fig. 5). (d) Maximum average cooling rate of 111.73 °C/s was achieved for a water flow rate of 16 lpm and impingement height of 15 cm. 162
Applied Thermal Engineering 137 (2018) 154–163
I. Sarkar et al.
water jet, J. Heat Transfer 135 (2013) 032101. [25] Z. Mingzheng, X. Guodong, L. Jian, L. Chai, Z. Lijun, Analysis of factors influencing thermal conductivity and viscosity in different kinds of surfactant solutions, Exp. Therm Fluid Sci. 36 (2012) 22–29. [26] J. Águila-Hernández, A. Trejo, B.E. García-Flores, Volumetric and surface tension behavior of aqueous solutions of polyvinylpyrrolidone in the range (288 to 303) K, J. Chem. Eng. Data 56 (2011) 2371–2378. [27] P. Kotchaphakdee, M.C. Williams, Enhancement of nucleate pool boiling with polymeric additives, Int. J. Heat Mass Transf. 13 (1970) 835–848. [28] S.K. Das, S.U.S. Choi, A Review of Heat Transfer in Nanofluids, in: F.I. Thomas, P.H. James (Eds.), Advances in Heat Transfer, vol. 41, Elsevier, 2009, pp. 81–197. [29] G. Puliti, S. Paolucci, M. Sen, Nanofluids and their properties, Appl. Mech. Rev. 64 (2012) 030803–030803. [30] R. Elghanam, M.E. Fawal, R.A. Aziz, M. Skr, A.H. Khalifa, Experimental study of nucleate boiling heat transfer enhancement by using surfactant, Ain Shams Eng. J. 2 (2011) 195–209. [31] X. Li, D. Zhu, G. Chen, X. Wang, Influence of SDBS on stability of copper nanoSuspensions, in: 2007 First International Conference on Integration and Commercialization of Micro and Nanosystems, American Society of Mechanical Engineers, 2007, pp. 971–975. [32] P. Tie, Q. Li, Y. Xuan, Heat transfer performance of Cu–water nanofluids in the jet arrays impingement cooling system, Int. J. Therm. Sci. 77 (2014) 199–205. [33] S.V. Ravikumar, J.M. Jha, S.S. Mohapatra, S.K. Pal, S. Chakraborty, Experimental investigation of effect of different types of surfactants and jet height on cooling of a hot steel plate, J. Heat Transfer 136 (2014) 072102-072102-072110. [34] I. Sarkar, D.K. Behera, J.M. Jha, S.K. Pal, S. Chakraborty, Effect of polymer additive on the cooling rate of a hot steel plate by using water jet, Exp. Therm Fluid Sci. 70 (2016) 105–114. [35] S.V. Ravikumar, J.M. Jha, S.S. Mohapatra, S.K. Pal, S. Chakraborty, Influence of ultrafast cooling on microstructure and mechanical properties of steel, Steel Res. Int. 84 (2013) 1157–1170. [36] S. Chakraborty, I. Sarkar, K. Haldar, S.K. Pal, S. Chakraborty, Synthesis of Cu–Al layered double hydroxide nanofluid and characterization of its thermal properties, Appl. Clay Sci. 107 (2015) 98–108. [37] R. Saleh, N. Putra, R.E. Wibowo, W.N. Septiadi, S.P. Prakoso, Titanium dioxide nanofluids for heat transfer applications, Exp. Therm Fluid Sci. 52 (2014) 19–29. [38] S. Chakraborty, I. Sarkar, D.K. Behera, S.K. Pal, S. Chakraborty, Experimental investigation on the effect of dispersant addition on thermal and rheological characteristics of TiO2 nanofluid, Powder Technol. 307 (2017) 10–24. [39] R.B. Abernethy, R.P. Benedict, R.B. Dowdell, ASME measurement uncertainty, J. Fluids Eng. 107 (1985) 161–164. [40] V.J.H. Lienhard, X. Liu, L.A. Gabour, Splattering and heat transfer during impingement of a turbulent liquid jet, J. Heat Transfer 114 (1992) 362–372.
[8] Z. Nishiyama, Martensitic Transformation, Elsevier, 2012. [9] R.M. Guo, Heat transfer of laminar flow cooling during strip acceleration on hot strip mill runout tables, Trans. ISS-AIME 8 (1993) 49–64. [10] M.J. Cho, B.G. Thomas, P.J. Lee, Three-dimensional numerical study of impinging water jets in runout table cooling processes, Metall. Mater. Trans. B 39 (2008) 593–602. [11] A. Lucas, P. Simon, G. Bourdon, J.C. Herman, P. Riche, J. Neutjens, P. Harlet, Metallurgical aspects of ultra fast cooling in front of the down-coiler, Steel Res. Int. 75 (2004) 139–146. [12] H.M. Al-Ahmadi, S.C. Yao, Spray cooling of high temperature metals using high mass flux industrial nozzles, Exp. Heat Transfer 21 (2008) 38–54. [13] S.V. Ravikumar, J.M. Jha, S.S. Mohapatra, A. Sinha, S.K. Pal, S. Chakraborty, Experimental study of the effect of spray inclination on ultrafast cooling of a hot steel plate, Heat Mass Transf. 49 (2013) 1509–1522. [14] B. Han, X. Liu, G. Wang, G. She, Development of cooling process control technique in hot strip mill, J. Iron. Steel Res. Int. 12 (2005) 12–16. [15] D.A. Zumbrunnen, R. Viskanta, F.P. Incropera, The effect of surface motion on forced convection, film boiling heat transfer, Trans. ASME J. Heat Transfer 111 (1989) 760–766. [16] Y. Yamane, Y. Ichikawa, M. Yamamoto, S. Honami, Effect of injection parameters on jet array impingement heat transfer, Int. J. Gas Turbine, Propulsion Power Syst. 4 (2012) 27–34. [17] Y. Pan, B. Webb, Heat transfer characteristics of arrays of free-surface liquid jets, Trans.-Am. Soc. Mech. Eng. J. Heat Transfer 117 (1995) 878–883. [18] D.E. Metzger, R.J. Korstad, Effects of crossflow on impingement heat transfer, ASME J. Eng. Power 94 (1) (1972) 35–41. [19] U. Uysal, P.-W. Li, M. Chyu, F. Cunha, Heat transfer on internal surfaces of a duct subjected to impingement of a jet array with varying jet hole-size and spacing, J. Turbomach. 128 (2006) 158–165. [20] I. Sarkar, S. Chakraborty, J.M. Jha, S.K. Pal, S. Chakraborty, Ultrafast cooling of a hot steel plate using Cu-Al layered double hydroxide nanofluid jet, Int. J. Therm. Sci. 116 (2017) 52–62. [21] A.M. Tiara, S. Chakraborty, I. Sarkar, S.K. Pal, S. Chakraborty, Effect of alumina nanofluid jet on the enhancement of heat transfer from a steel plate, Heat Mass Transf. (2016) 1–11. [22] S.S. Mohapatra, S.V. Ravikumar, A. Verma, S.K. Pal, S. Chakraborty, Experimental investigation of effect of a surfactant to increase cooling of hot steel plates by a water jet, J. Heat Transfer 135 (2013) 032101-032101-032107. [23] J.M. Jha, S.V. Ravikumar, A.M. Tiara, I. Sarkar, S.K. Pal, S. Chakraborty, Ultrafast cooling of a hot moving steel plate by using alumina nanofluid based air atomized spray impingement, Appl. Therm. Eng. 75 (2015) 738–747. [24] S.S. Mohapatra, S.V. Ravikumar, A. Verma, S.K. Pal, S. Chakraborty, Experimental investigation of effect of a surfactant to increase cooling of hot steel plates by a
163