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Experimental Study on R245fa Condensation Heat Transfer in Horizontal Smooth Tube and Enhanced Tube
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Energy Procedia 142 Energy Procedia 00(2017) (2017)4169–4175 000–000 www.elsevier.com/locate/procedia
9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK
Experimental Study on R245fa Condensation Heat Transfer in The 15th International Symposium on District Heating and Cooling Horizontal Smooth Tube and Enhanced Tube a a Assessing the feasibility ofDai using the heat demand-outdoor Shengchun Liua,*, Ming Songa, Baomin ,Yuan Tian , Mengjie Songb, Ning Maoc temperature a long-term heat 300134,China demand forecast a.Tianjinfunction key laboratory of for refrigeration technology, Tianjin district University of Commerce, b. Energy Research Institute at NTU (ERI@N), Nanyang Technological University, Singapore 637553, Singapore
a,b,c a a b c I.c. Andrić *, A. Pina , P. Ferrão , J. Fournier ., (East B. Lacarrière O. Le China Correc College of Pipeline and Civil Engineering, China University of Petroleum China), Qingdao,,Shandong, a
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract
Considerable attention has recently been given to R245fa for applications such as high temperature heat pump. In this paper, the condensation heat transfer characteristics of R245fa in a smooth tube and an internally enhanced tube are experimentally studied. Abstract The ranges of condensation temperature, mass flux and cooling water flux are 30~45oC, 84~197kg/m2·s and 732~1228kg/m2·s, respectively. The two tubes with a 4.58 mm inner diameter, 5mm outer diameter and 2000 mm length are used. The heat transfer District heating commonly addressed in the literature as onethat of condensation the most effective solutions for decreasing the coefficient in eachnetworks case was are analyzed carefully. The case study results show heat transfer coefficients increase greenhouse gas emissions frombut thedecrease buildingwith sector. systemstemperature. require highAnd investments whichofare returned through theheat heat with the increase of mass flux, the These condensation the influence cooling water flux on sales. Due to the ischanged climate conditions and building renovation heat tube demand in the future enhanced could decrease, transfer coefficient small. Compared the heat transfer coefficient betweenpolicies, the smooth and the internally tube, prolonging the investment return period. Enhanced rates is 1.8 to 2.5. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand districtPublished of Alvalade, locatedLtd. in Lisbon (Portugal), was used as a case study. The district is consisted of 665 ©forecast. 2017 TheThe Authors. by Elsevier buildings that vary in both construction periodcommittee and typology. weather scenarios (low,onmedium, and three district Peer-review under responsibility of the scientific of theThree 9th International Conference Appliedhigh) Energy. renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were comparedcondensation with resultsheat from a dynamic heat demand model,coefficient, previously developed validated Keywords: transfer characteristics, heat transfer enhanced tube,and smooth tube by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). 1.scenarios, Introduction The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease the number of heating hours of 22-139h during the heating season (depending on because the combination of weather and While theinrapid expansion of current economic, countries are facing grave problem of the environment renovation On the other function intercept increased 7.8-12.7% per decade (depending on the damage andscenarios shortageconsidered). of energy resources [1].hand, In this case the research focusfor is finding green alternative refrigerant, coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and tapping new sources, improving energy efficiency, and enhancing the efficiency of heat exchanger [2,3]. The improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +86-022-26684065; fax: +86-022-26667502. Cooling. E-mail address: [email protected]
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy . 10.1016/j.egypro.2017.12.342
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Shengchun Liu et al. / Energy Procedia 142 (2017) 4169–4175 Shengchun Liu et al./ Energy Procedia 00 (2017) 000–000
development history of refrigeration technology actually is the development history of refrigerant in miniature. The development process of refrigerant can be divided into several stages: CFC, HCFCs, HFCs, HCs and natural refrigerant. The long term using in CFCs, HCFCs lead to the damage of atmosphere and global warming [4,5]. R245fa was produced by Honeywell in American. The new green alternative refrigerant which the Environmental Protection Agency has approved have non chlorine atom that can damaging the Ozone Layer and lower GWP, and the ODP of refrigerant is zero, it live short in atmosphere [3,6]. In addition, R245fa is a non VOC (volatile organic compounds) compounds, and it has good safety performance, also have been proposed as substitutes for medium and high temperature refrigerant, such as R11, R114 and R141b, R245fa has a great prospect in application for low pressure water chillers, foaming agent [7], ORC cycle [8,9], high temperature heat pump [10] and polyurethane foam industry. Dobson etc. studied the relationship between the heat transfer coefficient and the flow pattern condensing on horizontal tubes with different inner diameters and different refrigerants [11]. The results showed that the lamellar condensation at the top of horizontal pipe is dominant. Bertsch etc. experimental studied on condensation heat transfer of R245fa and R134a in the horizontal micro tube [12]. The experimental results showed that the heat transfer performance of R245fa was higher than that of R134a in a same flux. Brazilian analyzed condensation flow pattern in a horizontal pipe, finding that the majority of flow pattern currently is obtained by observing adiabatic boiling phenomenon, so it had some deviation applied to condensation [13]. Liu had summarized the experimental study on condensation flow and heat transfer in the horizontal pipe [14,15]. Ouyang experimentally analyzed the condensation heat transfer of R410A outside a tube and the results showed that heat transfer coefficient increase with the increase of the super cooling [16]. Eckels and Pate experimental studied on condensation heat transfer of R134a and R12, resulting that the condensation heat transfer coefficient of R134a 10% higher than that of R12, and enhanced tube is as 2.5 times as the horizontal smooth tube [17]. Gu established the film condensation heat transfer coefficient model of a cluster low threaded tube [18]. Hong obtained the heat transfer empirical correlations of R22 flowing outside tube by Wilson graphical method [19]. Man-Hoe and Joeng-Seob reported condensation heat transfer of different copper tube, and the errors of heat transfer coefficient between calculations in this paper and Shah in ±15.6% [20]. Cavallini is analyzed condensation heat transfer coefficient through a lot of experimental data to summarize condensation heat transfer coefficient and pressure drop correlations [21-25]. Shao experimental study on condensation heat transfer characteristics of R134a in a horizontal straight pipe and threaded pipe, and the results showed that the condensation heat transfer coefficient of threaded pipe is larger than the straight tube [26]. From the above analysis, condensation heat transfer performance of R245fa had advantage in ORC and refrigeration cycle. This article design condensation heat transfer experiment platform to study condensation heat transfer performance of smooth tube and internally ribbed tube. 2 Experiment system and method 2.1 Experimental apparatus Fig.1 shows the experimental setup used in this study. The setup consists of refrigerant loop, cooling water loop and data acquisition system. The refrigerant loop is a closed loop consisting of a reservoir tank behind a pump to ensure smooth flow. The magnetic gear pump has a 1.5ml/r certified capacity. Immediately after the pump is a Coriolis mass flow meter with 4MPa maximum working pressure and 40kg/h maximum flow rate. Then a preheated heat exchanger is heated by electric to ensure that getting to the test section is completely gaseous state. And a coil heated by water precedes the test section to control the inlet temperature of the flow. The two test sections are designed to be a parallel to switch the two tube types freely after the condition is stable. Next to this, there is a coil cooled by constant temperature tank. The fluid cools down, condenses, and returns to the reservoir tank, thus completing one loop. Pressure transducers and PT100 thermocouples with 0.1% precision were installed around the loop to monitor and
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control the pressure and temperature during the experiment. These measurement devices and the digital output of the flow meter were connected to a data acquisition system that was monitored by a customized MX100 program. Reservoir tank T
P
gear pump
w
sight glass
Coriolis mass flowmeter
Preheating section
T
Dry filter
P
test section1 (smooth tube)
Heated coil (water bath)
T
T
T
T
T
T P
T
T
T
T
T
P
Cooled coil
test section2 (enchanced tube)
T T
T
constant temperature tank
Fig.1 Schematic diagram of experimental system
2.2 Test section Fig.2 shows the test section. The test section for this experiment consists of two tubes, one is inner tube made of copper and another is outside tube made of stainless steel. The two tubes’ outer diameter D is 5mm, inner diameter d is 4.58mm and overall length is 2000mm. The outside tube is divided into five segments and each segment’ length L is 354mm, so effective length of test section is 1770mm. About the internally ribbed tube, its biting height is 0.14mm, addendum angle is 40°, helix angle is 18° and threads are 4. The two ends of the casing are sealed with Bite type fitting. The parameters are shown in Table1 and 2. The fluid flowed in inner tube is R245fa, and the fluid flowed in outer tube is cold water. The inner tube has 20 points to measure temperature, in other words, every segment has 4 measured points. Every segment of the outer tube has one point located in middle. T-thermocouples and PT100 thermocouples with 0.1% precision are used to measure the temperature of inner tube and outer tube, respectively. T
T
354mm
354mm
T
354mm
T
354mm
354mm
2000mm
Fig.2 Schematic diagram of test section Table 1 Horizontal smooth tube parameters Brand
Type
H62
Φ5×0.21
Diameter （mm） 5
Tensile strength
Elongation
≧315
≧30
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Table 2 Enhancement tube parameters Type
Diameter （mm)
Φ5×0.21×0.14
±0.03 5.00
wall thickness Tw
Tooth height Hf
Addendum angle ɑ（˚）
Helix angle Β（˚）
Number Thread n
Weight g/m
±0.02
±5
±2
40
±1.5
0.21
0.14
40
18
±0.02
34.5
2.3 Data reduction In this experiment, the condensation heat transfer characteristic of R245fa is tested. The test was conducted at condensation temperature varying from 30 to 45oC, and the mass flux of R245fa and cooling water flux ranging in 84-191kg/m2 and 732-1228 kg/m2. There are five segments in the teat section, so the results also are divided into five segments. The condensation heat transfer coefficient is obtained by the following equation: Qr ,i hi (1) A(Tsat Twin ,i ) where, the released energy of R245fa (Qr,i) is equal to the absorbed energy of cooling water (Qw,i): Q Q mw,i cw,i Tw,i r ,i w ,i
(2)
and Tsat is the saturated steam temperature, Twin,i is the inner wall temperature of the inner tube. Then the Twin,i is: Q D T Twout ,i r ,i ln (3) win ,i 2 L d where Twin,i is the average temperature of the four tube wall temperature, measured by the four T-thermocouples installed on the inner tube. The export dryness of each section is calculated by the energy balance:
xout xin,i ,i
Qw,i
mr (hv hl )
(4)
3 Results and analysis The condensation heat transfer coefficient is researched in different operating condition by changing the condensing temperature, mass flow of R245fa, cooling water flow rate. Compare and analysis results obtain the condensation characteristic to provide theoretical basis for design and optimization of condenser. Fig.3 shows the heat transfer coefficients at a mass flux of 84 kg/m2, 117 kg/m2, 164 kg/m2 and191kg/m2. From the figure, it can be seen that condensation heat transfer coefficients decreases with the decrease of mass flow rate. Started at the condensation, the condensed liquid on the wall is less resulting in the thermal resistance less, so the heat transfers coefficients is larger. At this moment, the flow pattern is laminar annular flow. As the condensation continues, the condensed liquid becomes more and more, increasing the thermal resistance, so the heat transfer coefficient reduces. The difference of heat transfer coefficient between 84 kg/m2 and 117 kg/m2 is not much, so the effect of velocity can be ignored when the mass flux is small. The influence of mass flux on heat transfer coefficient is almost negligible when x<0.5. Because this moment has larger volume fraction of liquid, smaller flow rate and larger thermal resistance, and thermal conductivity is dominant. The heat transfer coefficient of enhanced tube is higher than that of smooth tube, as a result of the thread on the wall. The thread can increase disturbance thought breaking formed fluid film, and the guidance effect on fluid flow, thus enhancing the heat transfer performance.
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7000 10000
enchanced tube: 2 G=84(kg/m s) 2 G=117(kg/m s) 2 G=164(kg/m s) 2 G=191(kg/m s)
6000
smooth tube: Tsat=30C
enchanced tube: Tsat=30C
Tsat=35C
Tsat=35C
5000
6000
2
h (W/m k)
2
h (W/m k)
8000
smooth tube: 2 G=84(kg/m s) 2 G=117(kg/m s) 2 G=164(kg/m s) 2 G=191(kg/m s)
4000
Tsat=40C
Tsat=40C
Tsat=45C
Tsat=45C
4000 3000 2000
2000
1000 0 0.1
0.2
0.3
0.4
0.5
x
0.6
0.7
0.8
0.9
Fig.3 heat transfer coefficients vary with dryness under different working medium mass flow
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
x
Fig.4 heat transfer coefficients vary with dryness under different condensation temperature
Fig.4 shows the heat transfer coefficients at condensation temperature of 30oC, 35oC, 40 oC, 45 oC. From the figure, it can be seen that condensation heat transfer coefficients decreases with the decrease of temperature. Heat transfer coefficient approximate linear growth, when the dry is among 0.2 to 0.7 in smooth tube, and 0.2 to 0.8 in ribbed tube. Dry among 0.8 to 1, condensation heat transfer coefficient of enhanced tube is more one time than that of smooth tube. The rise of condensation temperature can change R234fa property. The higher the condensation temperature, the greater is the corresponding entry enthalpy. If enthalpy at exit remains unchanged, the increase of entry enthalpy can reduce the latent heat release. The release of latent heat can generate bubbles from the liquid, which increase thermal resistance. The decrease of gas speed can reduce shearing force and raise the thickness of liquid film, leading to the condensation heat transfer deterioration, thus cause the fall of condensation heat transfer coefficient. As shown in Fig.5, the condensation heat transfer coefficient increased with the increase of quality of cooling water flow rate increases, but the range ability is not obvious. The increase of cooling water flow rate can increases the heat transfer intensity of cooling water side, reduce the rise of temperature of cool water, then increase the average condensation heat transfer temperature difference, and hence increase the condensation heat transfer coefficient. However, cooling water, just as the carrier of heat exchange, only affects the wall temperature of cooling water side, but little effects on the flow pattern of the side of R245fa, so it has a little influence on the flow and heat transfer characteristics. Fig.6 shows the heat transfer coefficient of enhanced tube compared with the heat transfer coefficient of smooth tube at different refrigerant mass flux and cooling water flux. The total heat transfer coefficient of the enhanced tube is about 1.8-2.5 times of that of the horizontal smooth tube. In the event of condensation heat transfer, thermal resistance of refrigerant side mainly from the thickness of liquid film at the inner wall, enhanced tube condensation heat transfer coefficient is higher than the level of the smooth tube. It is mainly because the pure refrigerant R245fa flows by the internal thread guide on the inner wall, in near the wall portion of the fluid with internal threads to rotate. When the rotating flow of mass flow more obvious, it is beneficial to thin refrigerant liquid film thickness, and internal thread tube bulge and a part of refrigerant axial flow in the tube when the occurrence of periodic disturbance in tube collision increased, so it is to enhance the heat transfer performance.
Shengchun al. / Energy Procedia 142 000–000 (2017) 4169–4175 Shengchun Liu etLiu al./etEnergy Procedia 00 (2017)
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10000
smooth tube: 2 Gw=732(kg/m s)
enchanced tube: 2 Gw=732(kg/m s) 2
2
Gw=983(kg/m s)
Gw=983(kg/m s)
8000
2
2
Gw=1017(kg/m s)
2
Gw=1228(kg/m s)
Gw=1017(kg/m s)
2
6000
2
h(W/m K)
Gw=1228(kg/m s)
4000
2000
0 0.0
0.2
0.4
x
0.6
0.8
1.0
Fig.5 heat transfer coefficients vary with dryness under different cooling water flux
Fig.6 Enhanced tube heat transfer coefficients compare with smooth tube at different mass flux and cooling water flux
4 Conclusions This study examines the condensation heat transfer of R245fa in a smooth tube and an internally ribbed tube. The effect of different parameters, such as the condensation temperature, mass flux and cooling water flux, are studied. In each case, the heat transfer coefficient was also calculated and compared with the other cases. The dryness has the greatest effect on the increase in heat transfer coefficient. When dry varies with 1 to 0.8, condensation heat transfer coefficient is best. The influence of mass flux on heat transfer coefficient is almost negligible when x<0.5.The heat transfer coefficient decreases with the increase of condensation temperature. However, the cooling water flow rate has a little influence on the flow and heat transfer characteristics. The internally ribbed tube can increase the heat exchange area and turbulence intensity, so the heat transfer coefficient of ribbed tube is as 1.8 to 2.5 times as that of smooth tube.
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Acknowledgements The authors gratefully acknowledge the financial supports from Tianjin Application Foundation and Advanced Technology Research Project (15JCYBJC21600), Cultivation Project of Tianjin University of Commerce for Natural Science Foundation of China (160121), National Natural Science Foundation of China (51676139). References [1] Liu SC, Li HL, Song MJ, Dai BM, Sun ZL. Impacts on the solidification of water on plate surface for cold energy storage using ice slurry [J]. Applied Energy. 2017. Accepted. [2] Song MJ, Liu SC, Deng SM, Sun ZL, Yan HX. Experimental investigation on reverse cycle defrosting performance improvement for an ASHP unit by evenly adjusting its refrigerant distribution [J]. Applied Thermal Engineering. 2017, 114: 611-620. [3] Sun ZL, Liu SC, Liang YC, Song MJ, Guo JH. Experimental study on the optimal charge of carbon dioxide in water-water heat pump system [J]. HKIE Transactions. 2017, 24(2): 99-106. [4] Yitai Ma. Preparing to ban fluoride in Europe [J]. Journal of Thermal Science and Technology, 2008, 7(2): 184-187. [5] Jianyi Zhang, Ying Xu. Development on refrigerants used in large and medium-size refrigerated warehouses [J]. Journal of Refrigeration, 2009, 30(4): 51-57. [6] Wu Qingping, Ma Zhenjun, Zhu Ruiqi. A New Working Fluid HFC-245fa [J]. Fluid Machinery, 2003, 31 (s1) : 117-119. [7] Yunfeil Feng, Junb Xie, Yon Yang, et al. The progress and tendency of new generation blowing agent HFC-245fa [J]. New Chemical Materials, 2005, 33(8): 8-14. [8] Luján J M, Serrano J R, Dolz V, et al. Model of the expansion process for R245fa in an Organic Rankine Cycle (ORC)[J]. Applied Thermal Engineering, 2012, 40(6): 248-257. [9] Jialing Zhu, Huayu Bo, Tailu L, et al. A thermodynamics comparison of subcritical and transcritical organic Rankine cycle system for power generation [J]. Journal of Central South University, 2015, 22(9):3641-3649. [10] Zhang S, Wang H, Guo T. Experimental investigation of moderately high temperature water source heat pump with non-azeotropic refrigerant mixtures [J]. Applied Energy, 2010, 87(5):1554-1561. [11] Dobson M K, Chato J C. Condensation in Smooth Horizontal Tubes [J]. Journal of Heat Transfer, 1998, 120(1):193-213. [12] Stefan Bertsh. velocity boiling characteristics of R134a and R245fa mixtures in a vertical circular tube [J]. Experimental Thermal and Fluid Science, April 2016 (Volume 72). [13] Xiaoru Zhuang, Maoqiong Gong, Xin Zou, et al. A review on flow pattern maps of condensation in horizontal tubes [J]. Journal of Refrigeration, 2016, 37(2): 9-15. [14] Liu S, Huo Y, Liu Z, et al. Theoretical Research on R245fa Condensation Heat Transfer inside a Horizontal Tube[J]. Engineering, 2015, 07(5):261-271. [15] Huo Yan, Liu Shengchun, Ning Jinghong. Current situation and prospect on condensation of refrigerants inside horizontal tubes [J]. Cryogenics and Superconductivity, 2013, 41(1): 55-61. [16] Ouyang Xinping, Yuan Daoan, Zhang Tongrong. Condensing test of R404A outside horizontal enhanced tubes and method of data processing [J]. Journal of Refrigeration, 2014, 35(1):92-97. [17] Eckels S J. An experimental comparison of evaporation and condensation heat transfer coefficients for HFC-134a and CFC-12[J]. International Journal of Refrigeration, 1991, 14(2):70-77. [18] Gu Bo. AnaIysis on the heat transfer model for thread tube [J]. Journal of Refrigeration, 2001(4): 6-10. [19] Hong Siwen, Ouyang Xinping, Jia Chuanlin, et al. Experimental Study on Heat Transfer on an Enhanced Condensation Tube [J]. Journal of Refrigeration, 2009, 30(1):30-34. [20] Man-Hoe Kim, Joeng-Seob Shin,Condensation heat transfer of R22 and R410A in horizontal smooth and micro fin tubes[J]. International Journal of Refrigeration,28 (2005) 949–957. [21] Cavallini A, Censi G, Col D D, et al. Condensation inside and outside smooth and enhanced tubes -a review of recent research [J]. International Journal of Refrigeration, 2003, 26(4):373–392. [22] Cavallini A, Col D D, Doretti L, et al. Heat transfer and pressure drop during condensation of refrigerants inside horizontal enhanced tubes [J]. International Journal of Refrigeration, 2000, 23(1):4-25. [23] A.Cavallini, G.Censi, D.Del Col, L.Doretti. Analysis and prediction of condensation heat transfer of the zeotropic mixture R-125/236ea[C]. In: Proceedings of the ASME Heat Transfer Division, ASME, New York, 2000: 103–110. [24] A Cavallini, R A Zecchin. Dimensionless correlation for heat transfer in forced convection condensation[C]. In: Proceedings of the 5th International Heat Transfer Conference, 1974, 3: 309-313. [25] A Cavallini, D Del Col, M Matkovic, L Rossetto. Pressure Drop During Two-Phase velocity of R134a and R32 in a Single Mini channel[J]. International Journal of Heat Transfer, 2009, 131(3): 1071 - 1078. [26] Shao Li, Han Jitian, Pan Jihong. Condensation Heat Transfer of R-134a in Horizontal Straight and Helically Cooled Tubes [J]. Journal of Refrigeration, 2007, 28(2):23-26.
ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy Procedia 142 Energy Procedia 00(2017) (2017)4169–4175 000–000 www.elsevier.com/locate/procedia
9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK
Experimental Study on R245fa Condensation Heat Transfer in The 15th International Symposium on District Heating and Cooling Horizontal Smooth Tube and Enhanced Tube a a Assessing the feasibility ofDai using the heat demand-outdoor Shengchun Liua,*, Ming Songa, Baomin ,Yuan Tian , Mengjie Songb, Ning Maoc temperature a long-term heat 300134,China demand forecast a.Tianjinfunction key laboratory of for refrigeration technology, Tianjin district University of Commerce, b. Energy Research Institute at NTU (ERI@N), Nanyang Technological University, Singapore 637553, Singapore
a,b,c a a b c I.c. Andrić *, A. Pina , P. Ferrão , J. Fournier ., (East B. Lacarrière O. Le China Correc College of Pipeline and Civil Engineering, China University of Petroleum China), Qingdao,,Shandong, a
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract
Considerable attention has recently been given to R245fa for applications such as high temperature heat pump. In this paper, the condensation heat transfer characteristics of R245fa in a smooth tube and an internally enhanced tube are experimentally studied. Abstract The ranges of condensation temperature, mass flux and cooling water flux are 30~45oC, 84~197kg/m2·s and 732~1228kg/m2·s, respectively. The two tubes with a 4.58 mm inner diameter, 5mm outer diameter and 2000 mm length are used. The heat transfer District heating commonly addressed in the literature as onethat of condensation the most effective solutions for decreasing the coefficient in eachnetworks case was are analyzed carefully. The case study results show heat transfer coefficients increase greenhouse gas emissions frombut thedecrease buildingwith sector. systemstemperature. require highAnd investments whichofare returned through theheat heat with the increase of mass flux, the These condensation the influence cooling water flux on sales. Due to the ischanged climate conditions and building renovation heat tube demand in the future enhanced could decrease, transfer coefficient small. Compared the heat transfer coefficient betweenpolicies, the smooth and the internally tube, prolonging the investment return period. Enhanced rates is 1.8 to 2.5. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand districtPublished of Alvalade, locatedLtd. in Lisbon (Portugal), was used as a case study. The district is consisted of 665 ©forecast. 2017 TheThe Authors. by Elsevier buildings that vary in both construction periodcommittee and typology. weather scenarios (low,onmedium, and three district Peer-review under responsibility of the scientific of theThree 9th International Conference Appliedhigh) Energy. renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were comparedcondensation with resultsheat from a dynamic heat demand model,coefficient, previously developed validated Keywords: transfer characteristics, heat transfer enhanced tube,and smooth tube by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). 1.scenarios, Introduction The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease the number of heating hours of 22-139h during the heating season (depending on because the combination of weather and While theinrapid expansion of current economic, countries are facing grave problem of the environment renovation On the other function intercept increased 7.8-12.7% per decade (depending on the damage andscenarios shortageconsidered). of energy resources [1].hand, In this case the research focusfor is finding green alternative refrigerant, coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and tapping new sources, improving energy efficiency, and enhancing the efficiency of heat exchanger [2,3]. The improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +86-022-26684065; fax: +86-022-26667502. Cooling. E-mail address: [email protected]
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy . 10.1016/j.egypro.2017.12.342
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Shengchun Liu et al. / Energy Procedia 142 (2017) 4169–4175 Shengchun Liu et al./ Energy Procedia 00 (2017) 000–000
development history of refrigeration technology actually is the development history of refrigerant in miniature. The development process of refrigerant can be divided into several stages: CFC, HCFCs, HFCs, HCs and natural refrigerant. The long term using in CFCs, HCFCs lead to the damage of atmosphere and global warming [4,5]. R245fa was produced by Honeywell in American. The new green alternative refrigerant which the Environmental Protection Agency has approved have non chlorine atom that can damaging the Ozone Layer and lower GWP, and the ODP of refrigerant is zero, it live short in atmosphere [3,6]. In addition, R245fa is a non VOC (volatile organic compounds) compounds, and it has good safety performance, also have been proposed as substitutes for medium and high temperature refrigerant, such as R11, R114 and R141b, R245fa has a great prospect in application for low pressure water chillers, foaming agent [7], ORC cycle [8,9], high temperature heat pump [10] and polyurethane foam industry. Dobson etc. studied the relationship between the heat transfer coefficient and the flow pattern condensing on horizontal tubes with different inner diameters and different refrigerants [11]. The results showed that the lamellar condensation at the top of horizontal pipe is dominant. Bertsch etc. experimental studied on condensation heat transfer of R245fa and R134a in the horizontal micro tube [12]. The experimental results showed that the heat transfer performance of R245fa was higher than that of R134a in a same flux. Brazilian analyzed condensation flow pattern in a horizontal pipe, finding that the majority of flow pattern currently is obtained by observing adiabatic boiling phenomenon, so it had some deviation applied to condensation [13]. Liu had summarized the experimental study on condensation flow and heat transfer in the horizontal pipe [14,15]. Ouyang experimentally analyzed the condensation heat transfer of R410A outside a tube and the results showed that heat transfer coefficient increase with the increase of the super cooling [16]. Eckels and Pate experimental studied on condensation heat transfer of R134a and R12, resulting that the condensation heat transfer coefficient of R134a 10% higher than that of R12, and enhanced tube is as 2.5 times as the horizontal smooth tube [17]. Gu established the film condensation heat transfer coefficient model of a cluster low threaded tube [18]. Hong obtained the heat transfer empirical correlations of R22 flowing outside tube by Wilson graphical method [19]. Man-Hoe and Joeng-Seob reported condensation heat transfer of different copper tube, and the errors of heat transfer coefficient between calculations in this paper and Shah in ±15.6% [20]. Cavallini is analyzed condensation heat transfer coefficient through a lot of experimental data to summarize condensation heat transfer coefficient and pressure drop correlations [21-25]. Shao experimental study on condensation heat transfer characteristics of R134a in a horizontal straight pipe and threaded pipe, and the results showed that the condensation heat transfer coefficient of threaded pipe is larger than the straight tube [26]. From the above analysis, condensation heat transfer performance of R245fa had advantage in ORC and refrigeration cycle. This article design condensation heat transfer experiment platform to study condensation heat transfer performance of smooth tube and internally ribbed tube. 2 Experiment system and method 2.1 Experimental apparatus Fig.1 shows the experimental setup used in this study. The setup consists of refrigerant loop, cooling water loop and data acquisition system. The refrigerant loop is a closed loop consisting of a reservoir tank behind a pump to ensure smooth flow. The magnetic gear pump has a 1.5ml/r certified capacity. Immediately after the pump is a Coriolis mass flow meter with 4MPa maximum working pressure and 40kg/h maximum flow rate. Then a preheated heat exchanger is heated by electric to ensure that getting to the test section is completely gaseous state. And a coil heated by water precedes the test section to control the inlet temperature of the flow. The two test sections are designed to be a parallel to switch the two tube types freely after the condition is stable. Next to this, there is a coil cooled by constant temperature tank. The fluid cools down, condenses, and returns to the reservoir tank, thus completing one loop. Pressure transducers and PT100 thermocouples with 0.1% precision were installed around the loop to monitor and
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control the pressure and temperature during the experiment. These measurement devices and the digital output of the flow meter were connected to a data acquisition system that was monitored by a customized MX100 program. Reservoir tank T
P
gear pump
w
sight glass
Coriolis mass flowmeter
Preheating section
T
Dry filter
P
test section1 (smooth tube)
Heated coil (water bath)
T
T
T
T
T
T P
T
T
T
T
T
P
Cooled coil
test section2 (enchanced tube)
T T
T
constant temperature tank
Fig.1 Schematic diagram of experimental system
2.2 Test section Fig.2 shows the test section. The test section for this experiment consists of two tubes, one is inner tube made of copper and another is outside tube made of stainless steel. The two tubes’ outer diameter D is 5mm, inner diameter d is 4.58mm and overall length is 2000mm. The outside tube is divided into five segments and each segment’ length L is 354mm, so effective length of test section is 1770mm. About the internally ribbed tube, its biting height is 0.14mm, addendum angle is 40°, helix angle is 18° and threads are 4. The two ends of the casing are sealed with Bite type fitting. The parameters are shown in Table1 and 2. The fluid flowed in inner tube is R245fa, and the fluid flowed in outer tube is cold water. The inner tube has 20 points to measure temperature, in other words, every segment has 4 measured points. Every segment of the outer tube has one point located in middle. T-thermocouples and PT100 thermocouples with 0.1% precision are used to measure the temperature of inner tube and outer tube, respectively. T
T
354mm
354mm
T
354mm
T
354mm
354mm
2000mm
Fig.2 Schematic diagram of test section Table 1 Horizontal smooth tube parameters Brand
Type
H62
Φ5×0.21
Diameter （mm） 5
Tensile strength
Elongation
≧315
≧30
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Table 2 Enhancement tube parameters Type
Diameter （mm)
Φ5×0.21×0.14
±0.03 5.00
wall thickness Tw
Tooth height Hf
Addendum angle ɑ（˚）
Helix angle Β（˚）
Number Thread n
Weight g/m
±0.02
±5
±2
40
±1.5
0.21
0.14
40
18
±0.02
34.5
2.3 Data reduction In this experiment, the condensation heat transfer characteristic of R245fa is tested. The test was conducted at condensation temperature varying from 30 to 45oC, and the mass flux of R245fa and cooling water flux ranging in 84-191kg/m2 and 732-1228 kg/m2. There are five segments in the teat section, so the results also are divided into five segments. The condensation heat transfer coefficient is obtained by the following equation: Qr ,i hi (1) A(Tsat Twin ,i ) where, the released energy of R245fa (Qr,i) is equal to the absorbed energy of cooling water (Qw,i): Q Q mw,i cw,i Tw,i r ,i w ,i
(2)
and Tsat is the saturated steam temperature, Twin,i is the inner wall temperature of the inner tube. Then the Twin,i is: Q D T Twout ,i r ,i ln (3) win ,i 2 L d where Twin,i is the average temperature of the four tube wall temperature, measured by the four T-thermocouples installed on the inner tube. The export dryness of each section is calculated by the energy balance:
xout xin,i ,i
Qw,i
mr (hv hl )
(4)
3 Results and analysis The condensation heat transfer coefficient is researched in different operating condition by changing the condensing temperature, mass flow of R245fa, cooling water flow rate. Compare and analysis results obtain the condensation characteristic to provide theoretical basis for design and optimization of condenser. Fig.3 shows the heat transfer coefficients at a mass flux of 84 kg/m2, 117 kg/m2, 164 kg/m2 and191kg/m2. From the figure, it can be seen that condensation heat transfer coefficients decreases with the decrease of mass flow rate. Started at the condensation, the condensed liquid on the wall is less resulting in the thermal resistance less, so the heat transfers coefficients is larger. At this moment, the flow pattern is laminar annular flow. As the condensation continues, the condensed liquid becomes more and more, increasing the thermal resistance, so the heat transfer coefficient reduces. The difference of heat transfer coefficient between 84 kg/m2 and 117 kg/m2 is not much, so the effect of velocity can be ignored when the mass flux is small. The influence of mass flux on heat transfer coefficient is almost negligible when x<0.5. Because this moment has larger volume fraction of liquid, smaller flow rate and larger thermal resistance, and thermal conductivity is dominant. The heat transfer coefficient of enhanced tube is higher than that of smooth tube, as a result of the thread on the wall. The thread can increase disturbance thought breaking formed fluid film, and the guidance effect on fluid flow, thus enhancing the heat transfer performance.
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7000 10000
enchanced tube: 2 G=84(kg/m s) 2 G=117(kg/m s) 2 G=164(kg/m s) 2 G=191(kg/m s)
6000
smooth tube: Tsat=30C
enchanced tube: Tsat=30C
Tsat=35C
Tsat=35C
5000
6000
2
h (W/m k)
2
h (W/m k)
8000
smooth tube: 2 G=84(kg/m s) 2 G=117(kg/m s) 2 G=164(kg/m s) 2 G=191(kg/m s)
4000
Tsat=40C
Tsat=40C
Tsat=45C
Tsat=45C
4000 3000 2000
2000
1000 0 0.1
0.2
0.3
0.4
0.5
x
0.6
0.7
0.8
0.9
Fig.3 heat transfer coefficients vary with dryness under different working medium mass flow
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
x
Fig.4 heat transfer coefficients vary with dryness under different condensation temperature
Fig.4 shows the heat transfer coefficients at condensation temperature of 30oC, 35oC, 40 oC, 45 oC. From the figure, it can be seen that condensation heat transfer coefficients decreases with the decrease of temperature. Heat transfer coefficient approximate linear growth, when the dry is among 0.2 to 0.7 in smooth tube, and 0.2 to 0.8 in ribbed tube. Dry among 0.8 to 1, condensation heat transfer coefficient of enhanced tube is more one time than that of smooth tube. The rise of condensation temperature can change R234fa property. The higher the condensation temperature, the greater is the corresponding entry enthalpy. If enthalpy at exit remains unchanged, the increase of entry enthalpy can reduce the latent heat release. The release of latent heat can generate bubbles from the liquid, which increase thermal resistance. The decrease of gas speed can reduce shearing force and raise the thickness of liquid film, leading to the condensation heat transfer deterioration, thus cause the fall of condensation heat transfer coefficient. As shown in Fig.5, the condensation heat transfer coefficient increased with the increase of quality of cooling water flow rate increases, but the range ability is not obvious. The increase of cooling water flow rate can increases the heat transfer intensity of cooling water side, reduce the rise of temperature of cool water, then increase the average condensation heat transfer temperature difference, and hence increase the condensation heat transfer coefficient. However, cooling water, just as the carrier of heat exchange, only affects the wall temperature of cooling water side, but little effects on the flow pattern of the side of R245fa, so it has a little influence on the flow and heat transfer characteristics. Fig.6 shows the heat transfer coefficient of enhanced tube compared with the heat transfer coefficient of smooth tube at different refrigerant mass flux and cooling water flux. The total heat transfer coefficient of the enhanced tube is about 1.8-2.5 times of that of the horizontal smooth tube. In the event of condensation heat transfer, thermal resistance of refrigerant side mainly from the thickness of liquid film at the inner wall, enhanced tube condensation heat transfer coefficient is higher than the level of the smooth tube. It is mainly because the pure refrigerant R245fa flows by the internal thread guide on the inner wall, in near the wall portion of the fluid with internal threads to rotate. When the rotating flow of mass flow more obvious, it is beneficial to thin refrigerant liquid film thickness, and internal thread tube bulge and a part of refrigerant axial flow in the tube when the occurrence of periodic disturbance in tube collision increased, so it is to enhance the heat transfer performance.
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smooth tube: 2 Gw=732(kg/m s)
enchanced tube: 2 Gw=732(kg/m s) 2
2
Gw=983(kg/m s)
Gw=983(kg/m s)
8000
2
2
Gw=1017(kg/m s)
2
Gw=1228(kg/m s)
Gw=1017(kg/m s)
2
6000
2
h(W/m K)
Gw=1228(kg/m s)
4000
2000
0 0.0
0.2
0.4
x
0.6
0.8
1.0
Fig.5 heat transfer coefficients vary with dryness under different cooling water flux
Fig.6 Enhanced tube heat transfer coefficients compare with smooth tube at different mass flux and cooling water flux
4 Conclusions This study examines the condensation heat transfer of R245fa in a smooth tube and an internally ribbed tube. The effect of different parameters, such as the condensation temperature, mass flux and cooling water flux, are studied. In each case, the heat transfer coefficient was also calculated and compared with the other cases. The dryness has the greatest effect on the increase in heat transfer coefficient. When dry varies with 1 to 0.8, condensation heat transfer coefficient is best. The influence of mass flux on heat transfer coefficient is almost negligible when x<0.5.The heat transfer coefficient decreases with the increase of condensation temperature. However, the cooling water flow rate has a little influence on the flow and heat transfer characteristics. The internally ribbed tube can increase the heat exchange area and turbulence intensity, so the heat transfer coefficient of ribbed tube is as 1.8 to 2.5 times as that of smooth tube.
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Acknowledgements The authors gratefully acknowledge the financial supports from Tianjin Application Foundation and Advanced Technology Research Project (15JCYBJC21600), Cultivation Project of Tianjin University of Commerce for Natural Science Foundation of China (160121), National Natural Science Foundation of China (51676139). References [1] Liu SC, Li HL, Song MJ, Dai BM, Sun ZL. Impacts on the solidification of water on plate surface for cold energy storage using ice slurry [J]. Applied Energy. 2017. Accepted. [2] Song MJ, Liu SC, Deng SM, Sun ZL, Yan HX. Experimental investigation on reverse cycle defrosting performance improvement for an ASHP unit by evenly adjusting its refrigerant distribution [J]. Applied Thermal Engineering. 2017, 114: 611-620. [3] Sun ZL, Liu SC, Liang YC, Song MJ, Guo JH. Experimental study on the optimal charge of carbon dioxide in water-water heat pump system [J]. HKIE Transactions. 2017, 24(2): 99-106. [4] Yitai Ma. Preparing to ban fluoride in Europe [J]. Journal of Thermal Science and Technology, 2008, 7(2): 184-187. [5] Jianyi Zhang, Ying Xu. Development on refrigerants used in large and medium-size refrigerated warehouses [J]. Journal of Refrigeration, 2009, 30(4): 51-57. [6] Wu Qingping, Ma Zhenjun, Zhu Ruiqi. A New Working Fluid HFC-245fa [J]. Fluid Machinery, 2003, 31 (s1) : 117-119. [7] Yunfeil Feng, Junb Xie, Yon Yang, et al. The progress and tendency of new generation blowing agent HFC-245fa [J]. New Chemical Materials, 2005, 33(8): 8-14. [8] Luján J M, Serrano J R, Dolz V, et al. Model of the expansion process for R245fa in an Organic Rankine Cycle (ORC)[J]. Applied Thermal Engineering, 2012, 40(6): 248-257. [9] Jialing Zhu, Huayu Bo, Tailu L, et al. A thermodynamics comparison of subcritical and transcritical organic Rankine cycle system for power generation [J]. Journal of Central South University, 2015, 22(9):3641-3649. [10] Zhang S, Wang H, Guo T. Experimental investigation of moderately high temperature water source heat pump with non-azeotropic refrigerant mixtures [J]. Applied Energy, 2010, 87(5):1554-1561. [11] Dobson M K, Chato J C. Condensation in Smooth Horizontal Tubes [J]. Journal of Heat Transfer, 1998, 120(1):193-213. [12] Stefan Bertsh. velocity boiling characteristics of R134a and R245fa mixtures in a vertical circular tube [J]. Experimental Thermal and Fluid Science, April 2016 (Volume 72). [13] Xiaoru Zhuang, Maoqiong Gong, Xin Zou, et al. A review on flow pattern maps of condensation in horizontal tubes [J]. Journal of Refrigeration, 2016, 37(2): 9-15. [14] Liu S, Huo Y, Liu Z, et al. Theoretical Research on R245fa Condensation Heat Transfer inside a Horizontal Tube[J]. Engineering, 2015, 07(5):261-271. [15] Huo Yan, Liu Shengchun, Ning Jinghong. Current situation and prospect on condensation of refrigerants inside horizontal tubes [J]. Cryogenics and Superconductivity, 2013, 41(1): 55-61. [16] Ouyang Xinping, Yuan Daoan, Zhang Tongrong. Condensing test of R404A outside horizontal enhanced tubes and method of data processing [J]. Journal of Refrigeration, 2014, 35(1):92-97. [17] Eckels S J. An experimental comparison of evaporation and condensation heat transfer coefficients for HFC-134a and CFC-12[J]. International Journal of Refrigeration, 1991, 14(2):70-77. [18] Gu Bo. AnaIysis on the heat transfer model for thread tube [J]. Journal of Refrigeration, 2001(4): 6-10. [19] Hong Siwen, Ouyang Xinping, Jia Chuanlin, et al. Experimental Study on Heat Transfer on an Enhanced Condensation Tube [J]. Journal of Refrigeration, 2009, 30(1):30-34. [20] Man-Hoe Kim, Joeng-Seob Shin,Condensation heat transfer of R22 and R410A in horizontal smooth and micro fin tubes[J]. International Journal of Refrigeration,28 (2005) 949–957. [21] Cavallini A, Censi G, Col D D, et al. Condensation inside and outside smooth and enhanced tubes -a review of recent research [J]. International Journal of Refrigeration, 2003, 26(4):373–392. [22] Cavallini A, Col D D, Doretti L, et al. Heat transfer and pressure drop during condensation of refrigerants inside horizontal enhanced tubes [J]. International Journal of Refrigeration, 2000, 23(1):4-25. [23] A.Cavallini, G.Censi, D.Del Col, L.Doretti. Analysis and prediction of condensation heat transfer of the zeotropic mixture R-125/236ea[C]. In: Proceedings of the ASME Heat Transfer Division, ASME, New York, 2000: 103–110. [24] A Cavallini, R A Zecchin. Dimensionless correlation for heat transfer in forced convection condensation[C]. In: Proceedings of the 5th International Heat Transfer Conference, 1974, 3: 309-313. [25] A Cavallini, D Del Col, M Matkovic, L Rossetto. Pressure Drop During Two-Phase velocity of R134a and R32 in a Single Mini channel[J]. International Journal of Heat Transfer, 2009, 131(3): 1071 - 1078. [26] Shao Li, Han Jitian, Pan Jihong. Condensation Heat Transfer of R-134a in Horizontal Straight and Helically Cooled Tubes [J]. Journal of Refrigeration, 2007, 28(2):23-26.