Boiling heat transfer of HFO-1234yf flowing in a smooth small-diameter horizontal tube

Transcription

1 Internationa Journa of Refrigeration 3 (11) Boiing heat transfer of HFO-13yf fowing in a smooth sma-diameter horizonta tube Shizuo Saitoha, Chaobin Dangb, Yoshitaka Nakamurab, Eiji Hiharab a Department of Mechanica Engineering, The University of Tokyo, 7-3-1, Bunkyo-ku, Tokyo 113-5, Japan b Institute of Environmenta Studies, Graduate Schoo of Frontier Sciences, The University of Tokyo, Kashiwanoha, Kashiwa-shi, Chiba, 77-53, Japan *Corresponding author. E-mai: [saitoh@hee.k.u-tokyo.ac.jp] Te./Fax: [ ] Abstract The fow boiing heat transfer coefficient of the ow-gwp (goba warming potentia) refrigerant HFO-13yf inside a smooth sma-diameter horizonta tube (inner diameter: mm) was experimentay investigated. The oca heat transfer coefficient was measured at heat fuxes of kw m-, mass fuxes of 1 kg m- s-1, evaporating temperature of.15 K, and inet vapor quaity of.5. The resuts show that the effect of heat fux on the heat transfer was arge at ow vapor quaity, whie the effect of mass fux was arge at high vapor quaity. The heat transfer coefficient of HFO-13yf was amost the same as that of R-13a. The heat transfer coefficients cacuated based on correations with Saitoh et a. agreed we with the measured vaues compared to other correations. The measured pressure drop agreed we with that predicted by the Lockhart-Martinei correation. Keyword: Boiing heat transfer, Pressure drop, HFO-13yf, Sma-Diameter tube 1. Introduction The reease of the MAC (mobie air conditioning) directive by the EU, which bans the use of refrigerants with goba warming potentia (GWP) above 15 in new types of mobie air conditioning from 11 in the EU market, has triggered the research and deveopment in a search for new refrigerants. Carbon dioxide is considered to be a promising candidate. Recenty, HFO-13yf, which is another promising candidate, was jointy deveoped by Honeywe and DuPont. Because the GWP of HFO-13yf is as ow as and its thermophysica properties are simiar to those of R-13a, it is expected to be a drop-in soution for current mobie air conditioners. Severa experimenta studies have been conducted on its thermophysica properties and cyce performance to estimate the feasibiity of using this new refrigerant in mobie air conditioners. Increasing concern due to environmenta predictions has ed to the reconsideration of refrigerants in other appications. -1-

2 One approach is to use a refrigerant mixture of HFO-13yf + HFC-3 to obtain a high system coefficient of performance (COP). The thermophysica properties of the refrigerant mixture are aso being evauated (i.e., Arakawa et a. 1). The system performance of an actua heat pump is ower than that of the theoretica cyce because of heat transfer oss inside the heat exchangers and pressure drop aong the duct. Therefore, the heat transfer performance must be anayzed to evauate the system performance of an actua heat pump system when a new refrigerant is considered as we as when designing heat exchangers. In this study, the boiing heat transfer of the refrigerant HFO-13yf fowing in a smooth sma-diameter horizonta tube (inner diameter (ID): mm) was experimentay investigated. The measured oca heat transfer coefficient of HFO-13yf was compared with that of R-13a, and a prediction method for the evaporation heat transfer coefficient of HFO-13yf is discussed.. Experimenta apparatus and procedure Figure 1 shows a schematic of the experimenta system used to measure the heat transfer coefficient and pressure drop and observe the fow patterns of HFO-13yf. The test oop incudes a Coriois-type fow meter, refrigerant temperature controer, fow contro vave, test tube (evaporator), and sight gass. The purity of the HFO-13yf used was over 99.7%. To reduce the heat oss from the test tube to the environment, the entire test tube was paced inside an air duct with the air temperature controed to be equa to the evaporating temperature. The fow rate and inet pressure of HFO-13yf were controed by adjusting the frequency of the magnetic gear pump and opening of the fow contro vave. The vapor quaity at the inet of the test evaporator was adjusted by the amount of heat suppied to the refrigerant in the pre-heater. A sub tank was used to adjust the amount of refrigerant in the test oop. When the performance of the condenser was poor, the evaporation pressure was controed by the amount of refrigerant. Figure shows the measurement points for outer surface temperature and pressure with the mm ID test tube, and thermocoupes attached to the tube. Tabe 1 ists the specification of the test tube and measurement interva of temperature and pressure. The test tube was heated by direct eectrification using a DC power suppy connected to two eectrodes sodered at the fanges of the two ends of the test tube. The pressures of the refrigerant in the test tube were measured using a precision aneroid manometer. The temperatures of the outer surface of the test tube were measured midway between the top and bottom of the tube aong the surface using T-type thermocoupes (outer diameter (OD):.1 mm), and the temperatures of the inner wa of the tube were cacuated from the measured temperatures of the outer wa of the tube using Fourier s aw. An m thick Tefon sheet was inserted between each thermocoupe and the test tube to prevent the current from affecting the thermocoupes. A the thermocoupes were caibrated by using a high-precision patinum resistance thermometer sensor (Chino, Mode CNA) with an accuracy of ±.3 K. The accuracy of the - -

3 caibrated thermocoupes was within ±.1 K. The mass fow rate (and thus the mass fux G) was measured by using the Coriois-type fow meter (Ova, Mode E1S-IN-) with an accuracy of ±.1%. The pressure was measured using the precision aneroid manometer (Nagano Keiki, Mode NKS) with an accuracy of ±1.5 kpa. The eectrica input power was measured using a votmeter and ammeter to confirm that the heat generated by direct eectrification was transferred we to the fuid and that the heat gain from surroundings was within 3%. The experimenta conditions are summarized in Tabe. To compare accumuated data of boiing heat transfer for R-13a, the evaporation temperature is chosen to be.15k as used in previous research for R-13a. The oca heat transfer coefficient h exp in the test tube was determined using the foowing equation: q hexp (1) T T wa sat where T wa is the temperature of the inner wa and T sat is the saturation temperature at the oca refrigerant pressure cacuated by interpoation of the adjoined pressure gauges. A experimenta data were coected after the steady state was reached for temperature, pressure, and refrigerant fow. In this study, the saturated vapor pressure of HFO-13yf was correated using experimenta data from Tanaka and Higashi (1), Nicoa et a. (1) and Huse et a. (9); thermodynamic properties at the saturation state were cacuated using Akasaka et a. s method (Akasaka et a., 1). Therma conductivities of iquid and vapor were cacuated using Latini et a. and Chung et a. s methods, respectivey (Poing et a., 1). Liquid and vapor viscosities were determined using Huse s et a. correation (9) and the Chapman-Enskog equation (Poing et a., 1), respectivey. The properties of the refrigerant R-13a were cacuated using REFPROP version. (Lemmon et a., 7). 3. Resuts and discussion 3.1 Fow boiing heat transfer coefficient Effect of heat fux Figure 3 shows the variation in the heat transfer coefficient against the vapor quaity. The mass fux was kept at kg m - s -1 ; we compared the measured resuts for three different heat fuxes:, 1, and kw m -. At the owest heat fux of kw m -, the measured heat transfer coefficient increased with the vapor quaity, showing that the convective heat transfer intensifies with increasing quaity. The dryout quaity was about. and did not change with heat fux. Increasing the heat fux from kw m - to 1 and kw m - showed that the heat transfer coefficient increases with heat fux at ow vapor quaity; thus, nuceate boiing is the dominant heat transfer coefficient mechanism at ow vapor quaity Effect of mass fux Figure shows the effect of mass fux on the boiing heat transfer at heat fux of 1 kw m -. The dryout occurs at vapor quaity of. for a the conditions. In the high-quaity region - 3 -

4 (>.), the heat transfer coefficients at both mass fuxes ( and kg m - s -1 ) increased with increasing vapor quaity, and the heat transfer coefficient was higher at kg m - s -1 than at kg m - s -1. At a mass fux of 1 kg m - s -1, the effect of vapor quaity on the heat transfer coefficient was weak. The resuts suggest that in the high vapor quaity region, forced convective evaporation is dominant Comparison between HFO-13yf and R-13a Figure 5 shows a comparison between the boiing heat transfer performances of HFO-13yf and R-13a at a mass fux of 3 kg m - s -1 and heat fux of 1 kw m -. The figure shows that in the wide vapor quaity region, the difference between the heat transfer coefficients of HFO-13yf and R-13a is sma, which may be because the differences in their thermodynamic properties are sma. Saturation properties of HFO-13yf and R-13a at temperature of.15k are shown in tabe 3. The properties of HFO-13yf and R-13a are cacuated foowing Brown et a.(9) and using REFPROP ver., respectivey. The gas density, atent heat, iquid therma conductivity, and surface tension of HFO-13yf and R-13a at.15 K were.3 and 3.7 kg m -3, 15.5 and 1.59 kj kg -1,.7 and.5 W m -1 K -1, and.77 and.9 N m -1, respectivey. In the foowing, the heat transfer coefficient of HFO-13yf and that of R-13a is compared using the prediction mode by considering the contribution of nuceate boiing and convective heat transfer. The heat transfer coefficient due to nuceate boiing is evauated by Stephan-Abdesaam (19) correation, and that of forced convection for iquid aone in the tube mm ID is evauated by Dittus-Boeter equation. At a temperature of.15k, mass fux of 3 kg m - s -1 and heat fux of 1 kw m -, the heat transfer coefficients (HTCs) of nuceate boiing and forced convection for HFO-13yf are. kw m - K -1 and.9 kw m - K -1, respectivey, and that for R-13a are.3 kw m - K -1 and.9 kw m - K -1. The difference between the HTCs of HFO-13yf and that of R-13a is sma Boiing heat transfer coefficient vs. Lochart-Martinei parameter In genera, the fow boiing heat transfer in a tube is considered to be a combination of nuceate boiing heat transfer and forced convective evaporation. In forced convective evaporation, fow boiing data can be correated with the form h h X - -, where h L is exp L 1 n the heat transfer coefficient of the iquid aone and X is the Lockhart-Martinei parameter. When the superficia iquid Reynods number, Re, is smaer than 1, fow in the iquid phase is aminar, and h L.3. When the Re D is arger than 1, iquid fow is turbuent and the h L can be cacuated by Dittus-Boeter equation. The magnitude of forced convective evaporation can be expressed by the gradient n of a inear regression of the experimenta data. Figure shows the measured heat transfer coefficients in the pre-dryout region potted against 1/X. Most of the present data can be fitted to the regression ine

5 exp L.77 h / h 1 X. The scattering of the data is arger at ow 1/X (<7) than at high 1/X. At ow 1/X, i.e., ow vapor quaity, both nuceate boiing and forced convective evaporation occur, whereas at high 1/X (>7), the scattering of the data is sma because forced convective evaporation is dominant. When fow in the iquid phase is aminar, the heat transfer coefficient is barey infuenced by the Lockhart-Martinei parameter Pre-dryout heat transfer and predictions of some correations Saitoh et a. (5, 7) experimentay studied the boiing fow heat transfer mechanism of R-13a in tubes with ID of.51, 1.1, and 3.1 mm; the Chen-type correation was modified by considering the effect of the tube diameter characterized by the Weber number in the gas phase. For the pre-dryout heat transfer, the experimenta data and predictions of some correations were compared. These incuded Saitoh et a. s, Yoshida et a. s (199), Kandikar s (199), and Gungor-Winterton (Gungar and Winterton, 197) correations. Detais on these correations are shown in Tabe. The properties of the refrigerant HFO-13yf were cacuated using the resuts reported by Brown et a. (9). Figures 7(a d) show a comparison between the experimenta heat transfer coefficient h exp and cacuated heat transfer coefficient h ca based on our modified Chen-type correation (Saitoh et a., 7) with others for HFO-13yf in the mm ID smooth horizonta tubes. h ca based on the Saitoh et a. correation agreed we with h exp. However, h ca cacuated based on the Yoshida, Kandikar, and Gungor-Winterton correations did not agree we with h exp. Figure 7(e) and (f) show the comparison of four correations and measured heat transfer coefficient against vapor quaity. In the pre-dryout region, the predicted vaues by a the four correations increase with vapor quaity. In the ow quaity region (x<.5), the predicted vaues of Saitoh et a., Kandikar and Gugor-Winterton are cose to the measured vaues except for that of Yoshida. In the high quaity region (.5<x<.75), the difference of the predicted vaues of Kandikar correation and Gungor-Winterton correation with measured resuts are arge. The predicted vaue by the correation of Saitoh et a., which was proposed for fow boiing heat transfer of R-13a, approximatey coincides with the measured vaue of HTC for HFO-13yf. Tabe 5 ists the mean deviation and accuracy (defined as the fraction of data within ±% error) for each of the three correations. The Saitoh et a. correation showed an improved mean deviation and accuracy (9.% and 9.%, respectivey) compared to the Yoshida (.% and 51.9%), Kandikar (1.7% and 51.9%), and Gungor-Winterton (15.5% and.9%) correations. 3. Pressure drop The measured two-phase pressure drop ( p ) was compared with that predicted resuts using the Lockhart - Martinei correation, which defines the pressure drop as

6 dp dp dp g dz dz dz g where and g are the two-phase mutipiers in the iquid and gas phases, respectivey. They () are defined as 1 c/ X 1/ X and g 1cX X (Chishom, 197), where X is the Lockhart-Martinei parameter, which is the square root of the ratio between the pressure drop assuming iquid fow aone and assuming gas fow aone. When fows of iquid and gas phases are turbuent, c = ; when iquid phase is aminar and gas phase is turbuent, c = 1. In this study, the fow condition of the refrigerant was determined at the inet of the evaporator. Figures shows the measured pressure drops and those predicted using the Lockhart-Martinei correation. The measured pressure drops agreed we with that predicted using the Lockhart-Martinei correation.. Concusions The fow boiing heat transfer of the refrigerant HFO-13yf in a sma-diameter horizonta tube was experimentay investigated. The oca heat transfer coefficients were measured at mass fuxes of 1 kg m - s -1, heat fuxes of kw m -, and an evaporating temperature.15 K. The resuts are summarized as foows. 1. At ow vapor quaity, nuceate boiing heat transfer is the dominant heat transfer mechanism, and at high vapor quaity, forced convective evaporation is dominant.. The boiing heat transfer coefficient of HFO-13yf is amost the same as that of R-13a. 3. The heat transfer coefficient predicted by the Saitoh et a. correation in the pre-dryout region agrees with the measured data within a range of ±%, whie the measured pressure drops agreed we with that predicted using the Lockhart-Martinei correation. Nomencature Bo boiing number C g friction factor for gas, C g =. C friction factor for iquid, C = 1 c p specific heat at constant pressure in iquid phase, J kg -1 K -1 D inner diameter of a tube, m G mass fux, kg m - s -1 g acceeration of gravity, m s - h exp experimenta boiing heat transfer coefficient, W m - K -1 h L iquid phase heat transfer coefficient, W m - K -1. 1/3 GD c p hl D Re 1,.3.3 Re 1, hl D - -

7 p pressure, Pa q heat fux, W m - Re Reynods number Re G D, Re g Gg D g T wa T sat We x X inside-wa temperature, K saturation temperature, K Weber number vapor quaity Lockhart-Martinei parameter Re 1,.9 1 x X x Re g g 1.5 g.1 Re 1, Re 1 g C. G g X Re g C g G g g z coordinate aong the tube direction, m Greek symbos therma conductivity, W m -1 K -1 viscosity, Pa s density, kg m -3 surface tension, N m -1 two-phase fow mutipier Subscripts g gas-phase, vapor-phase L, iquid-phase TP two-phase Acknowedgment This study was sponsored by the project "Deveopment of Non-fuorinated Energy-Saving Refrigeration and Air Conditioning Systems" of New Energy and Industria Technoogy Deveopment Organization, Japan. The authors thank Mr. T. Kamiaka of the University of Tokyo Graduate Schoo for cooperation with cacuating therma property vaues. References Akasaka, R., Tanaka, K., Higashi, Y., 1. Thermodynamic property modeing for - 7 -

8 ,3,3,3-tetrafuoropene (HFO-13yf), Int. J. Refrigeration 33, 5. Arakawa Y., S. Kim, T. Kamiaka, C. Dang, E. Hihara, 1, Thermophysica property measurement of HFO-13yf +HFC-3 mixture. 1 Internationa Symposium on Next-generation Air Conditioning and Refrigeration Technoogy, Feb ,Tokyo,Japan. NS. Brown, J. S., Ziio, C., Cavaini, A., 9. Estimations of the thermodynamic and transport properties of R-13yf using a cubic equation of state and group contribution methods. 3 rd IIR Conference on Thermophysica Properties and Transfer Processes of Refrigerants, June 3-, Bouder, Coorado, USA. IIR-17. Chishom, D., 197. A theoretica basis for the Lockhart-Martinei correation for two-phase fow. Int. J. Heat Mass Transfer 1, Gungor, K.E., Winterton, R.H.S., 197. Simpified genera correation for saturated fow boiing and comparisons of correations. Chem. Eng. Research & Design 5, Huse, R., Singh, R., Pham, H., 9. Physica properties of HFO-13yf. 3 rd IIR Conference on Thermophysica Properties and Transfer Processes of Refrigerants, June 3-, Bouder, Coorado, USA. IIR-17. Kandikar, S.G., 199. A genera correation for saturated two-phase fow boiing heat transfer inside horizonta and vertica tubes. ASME J. Heat Transfer 11, 19. Lemmon, E.W., Huber, M.L., McLinden, M.O., 7. NIST Thermodynamic and Transport Properties of Refrigerants and Refrigerant Mixtures (REFPROP) Version.. NIST. Nicoa, G. D., Paanara, F., Santori, G., 1. Saturated pressure measurements of,3,3,3-tetrafuoroprop-1-ene (HFO-13yf). J. Chem. Eng. Data 55, 1. Poing, B.E., Prausnitz, J.M., O Conne, J.P., 1. The Properties of Gases and Liquids, 5th ed. McGraw-Hi, New York. Saitoh, S., Daiguji, H., Hihara, E., 5. Effect of tube diameter on boiing heat transfer of R-13a in horizonta sma-diameter tubes. Int. J. Heat Mass Transfer, Saitoh, S., Daiguji, H., Hihara, E., 7. Correation for boiing heat transfer of R-13a in horizonta tubes incuding effect of tube diameter. Int. J. Heat Mass Transfer 5, Tanaka, K., Higashi, Y., 1. Thermodynamic properties of HFO-13yf (,3,3,3-tetrafuoropropene). Int. J. Refrigeration 33, Stephan, K., Abdesaam M., 19. Heat-transfer correations for natura convection boiing, Int. J. Heat Mass Transfer 3, Yoshida, S., Mori, H., Hong, H., Matsunaga, T Prediction of heat transfer coefficient for refrigerants fowing in horizonta evaporator tubes. Trans. of the JAR 11(1),

9 Figure 1. Schematic of experimenta system used to measure fow boiing heat transfer

10 P T T T T P P: pressure tap a=5.75 mm T: thermo coupe b=1 mm P T T T T T T T T P T T T T P a b b b a a b b b a a b b b a a b b b a 17 Test section T-type thermocoupe Junction Tube (SUS3) Ename Tefon sheet Side view Thermocoupe attachment Figure. Schematic of mm ID test tube

11 1 G= kg m - s -1, q= kw m - G= kg m - s -1, q=1 kw m - G= kg m - s -1, q= kw m - h exp [kw m - K -1 ]... x.. 1. Figure 3. Effect of heat fux on oca heat transfer coefficient

12 1 G=1 kg m - s -1, q=1 kw m - G= kg m - s -1, q=1 kw m - G= kg m - s -1, q=1 kw m - h exp [kw m - K -1 ]... x.. 1. Figure. Effect of mass fux on oca heat transfer coefficient

13 1 R-13a, 3 kg m - s -1, 1 kw m - HFO-13yf, 3 kg m - s -1, 1 kw m - h exp [kw m - K -1 ]... x.. 1. Figure 5. Comparison of heat transfer coefficients between HFO-13yf and R-13a at mass fux of 3 kg m - s -1 and heat fux of 1 kw m

14 1 7 5 iquid(turbuent fow) iquid(aminar fow) 3 h exp /h L h exp /h L (1/X) /X Figure. Boiing heat transfer coefficient as function of Lockhart-Martinei parameter - 1 -

15 1 1 +% +% h exp [kw m - K -1 ] -% h exp [kw m - K -1 ] -% Mass fux :1~ kg m - s -1 Heat fux : ~ kw m - h ca [kw m - K -1 ] (a) Correation of Saitoh et a. 1 Mass fux :1~ kg m - s -1 Heat fux : ~ kw m - h ca [kw m - K -1 ] (b) Correation of Yoshida % +% h exp [kw m - K -1 ] -% h exp [kw m - K -1 ] -% Mass fux :1~ kg m - s -1 Heat fux : ~ kw m - Mass fux :1~ kg m - s -1 Heat fux : ~ kw m h ca [kw m - K -1 ] h ca [kw m - K -1 ] (c) Correation of Kandikar G= kg m - s -1, q=1 kw m - (measured) Correation of Saitoh et a. Correation of Yoshida Correation of Kandikar Correation of Gungor-Winterton (d) Correation of Gungor-Winterton h [kw/m K] h [kw/m K] G=3 kg m - s -1, q=1 kw m - (mesured) Correation of Saitoh et a. Correation of Yoshida Correation of Kandikar Correation of Gungor-Winterton x (e) Predicted and measured vaues for (f) Predicted and measured x vaues for mass fux kg m - s -1 and heat fux 1kW m - fux 3kg m - s -1 and heat fux 1kW m - Figure 7. Experimenta fow boiing heat transfer coefficient h exp vs. cacuated h ca for HFO-13yf, and comparison of four predicted and measured data

16 Pressure drop [kpa] [kg m - s -1 ] [kw m - ] exp.-1- ca. -1- exp.-1-1 ca exp.-- ca. -- exp.--1 ca. --1 exp.-- ca. -- exp.--1 ca. --1 exp.-- ca Tube ength [m] Figure. Comparison of pressure drops between measured vaues and cacuated by Lockhart-Martinei correation

17 Tabe 1 Specification of test tube and measurement intervas Materia of test tube Stainess stee (SUS3) ID of tube(mm) OD of tube(mm) Length of tube(mm) T.C. OD of T.C.(mm) Interva of T.C.(mm) Interva of pressure(mm) 3 17 T-type Tabe Experimenta conditions Refrigerant Inet temperature Quaity Heat fux Mass fux [ C] [1] [kw m - ] [kg m - s -1 ] HFO-13yf Tabe 3 Saturation properties of HFO-13yf and R-13a at temperature of.15 K g i g g c P [kg m -3 ] [kg m -3 ] [kj kg -1 ] [W m -1 K -1 ] [μpa s] [μpa s] [kj kg -1 K -1 ] [N m -1 ] HFO-13yf R-13a Tabe Correations for fow boiing heat transfer Saitoh et a. ; h Fh Sh F X We S Re Re Re F TP poo, g, 1 1. TP 1, TP poo.. G x D c p h h D 1.3 Re 1,.3, Re 1, D h qd b g Pr db T Yoshida; poo, d.51 b g g qd b g Pr, db T.5 tp..5 htp Fh Shpoo, F 1 1 X, S Re 1 Bo 1 X, Bo q Gh.. G 1 x D c p.3 Re 1, h.3, Re 1, h D D h Kandikar ; b g g.5 d C C 5 C 1 x g TP 1 5 o 3 K, x h h CCo Fr C Bo F Co for Co.5 : C 1.13, C.9, C 7., C.7, C Co.5: C.3, C., C 15, C.7, C.3 C for vertica tubes, and for horizonta with Fr..5 v

18 Gungor and Winterton ;.1Fr Fr x x g htp Eh, E 13Bo If the tubeis horizontaand the Froude number Fr is ess than.5 then E shoud be mutipied by the factor E Tabe 5 Mean deviation and accuracy of three correations for fow boiing heat transfer coefficient Correation Mean deviation (%) Accuracy defined as fraction of data within ±% error(%) Saitoh et a Yoshida Kandikar Gungor Winterton Mean deviation n h h n exp ca 1%, the number of data is h exp - 1 -