JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (JMET)

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1 JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (JMET) Journal of Mechanical Engineering and Technology (JMET) ISSN (Print), ISSN (Online), Volume 1, Issue 1, July -December (213) ISSN (Print) ISSN (Online) Volume 1, Issue 1, July-December (213), pp IAEME: JMET I A E M E EXPERIMENTAL STUDY OF HEAT TRANSFER CHARACTERISTICS OF R744/R134a IN A SMOOTH HORIZONTAL TUBE A.Ramanan 1*, P.Senthilkumar 2 1 Research Scholar, Dept. of Mechanical Engineering, Sathyabama University, Chennai- 6119, TAMILNADU, INDIA 2 Professor, Dept. of Mechanical Engineering, KSR College of Engineering, Tiruchengode , TAMILNADU, INDIA ABSTRACT This paper presents the heat transfer characteristics of the refrigerant mixture of R744/R134a flowing through the horizontal smooth tube. The refrigerant mixture is studied in different mass, heat flux and inlet temperature conditions. Experimental results on the heat transfer, inner wall temperature and exergy of mass flux from 4 to 8 kg/ m 2 s in a horizontal smooth tube of 4 mm inner diameter are presented. It is found that the mixture combination of R744/R134a in at a mass flux of 8 kg/ m 2 s gives maximum heat transfer. Keywords: heat flux, mass flux, refrigerant mixture 1. INTRODUCTION Conventional refrigerants, such as the CFCs and their alternatives the HFCs, have potential environmental problems, so their use is being curtailed. CO2 is non-flammable and nontoxic with a zero ozone depletion potential (ODP), and a global warming potential (GWP) that is very small compared with other conventional refrigerants such as R134a; therefore, CO2 is a promising refrigerant for environmental, economical and safety reasons, and is being applied in automobile air-conditioning, heat pump or other low temperature refrigeration systems, as suggested by Lorentzen and Pettersen(1993) and Riffat et al. (1997). 8

2 ISSN (Online), Volume 1, Issue 1, July -December (213) 2. EXPERIMENTAL APPARATUS AND PROCEDURE 2.1. Experimental apparatus Fighure (1) represents the experimental system used to investigate the heat transfer of R744/R134a in a horizontal tube during evaporation and it was used similar to the set up and working as mentioned by Cho et al (1). The refrigerant loop consists of a pump, test section, a Coirolis-type mass flow meter, a pre-heater and a condenser. The liquid refrigerant is pumped via pump. Then the refrigerant passes through a Coirolis-type mass flow meter before entering the pre-heater. The pre-heater is used to control the vapor quality at the test section inlet. The refrigerant enters the test section in two-phase state. The test section consists of mm outer diameter with.2 mm thick copper tube having length of 1.44 m. The wall temperature is measured using type-t, thermocouples, positioned on the surface. The refrigerant leaves the test section in two-phase or superheated state. It enters then a counter-current condenser where it is sub-cooled before entering the pump. Pressure is measured at the test section inlet and outlets. Flow boiling tests were then performed at different mass fluxes, heat fluxes and inlet temperatures. MF PREHEATER Test section CONDENSER P LIQUID RECEIVER R Fig.1. Schematic experimental set up 2.2 Data reduction The thermo physical properties are calculated based on the measured temperature and pressure. The local heat transfer at each thermocouple is calculated based on the following equation h = q / (Tw -Tsat) Where, q- heat flux, Tw is the inner wall surface temperature and Tsat is the saturated temperature of the refrigerant deduced from the fluid pressure. The variations of the refrigerant thermo-physical properties in the test section were calculated with REFPROP RESULTS AND DISCUSSIONS s (HTCs) are found to depend on some or all of the following parameters: heat flux, reduced pressure, vapor quality and often mass velocity; furthermore they might depend on surface roughness and channel geometry. Miyata et al. (211) present a correlation to predict heat transfer s with vaporization which takes into account nucleate boiling, forced convection evaporation and evaporation heat transfer through thin liquid film around vapor plugs in slug flow. Several equations have been proposed, but none is widely accepted. 81

3 ISSN (Online), Volume 1, Issue 1, July -December (213) 3.1 Behaviour of R744/R134a mixture at different mass flux conditions The variation of heat transfer co efficient, inner wall temperature and exergy on the quality of refrigerant mixture flowing through the horizontal tube at different mass flux conditions of the refrigerant mixture of R744/R134a in combinations of, and is shown in fig. 2-4(a-d). a. Mass flux-4 kg/ m 2 s b. Mass flux-6 kg/ m 2 s c. Mass flux-7 kg/ m 2 s d. Mass flux-8 kg/ m2 s Fig.2 Variation of heat transfer at different mass fluxes The heat transfer of refrigerant mixture in three combination at the mass fluxes of 4, 6,7and 8 kg/ m 2 s is shown in the above figure2 (a-d).in all the cases the heat transfer of mixture of is higher than the mixture of at the same time the highest value is for the mixture combination.the heat transfer at the mass flux 4,the mixture of and combination is almost same but for the mixture of is well above and reduces drastically. The heat transfer for the mass fluxes 6, 7 and 8 follows the similar pattern in the flow. In all the cases the heat transfer is maximum for the refrigerant mixture of. The inner wall temperature along the test section at different mass flux conditions of 4, 6, 7 and 8 are shown in the following figure 3(a-d). 82

4 ISSN (Online), Volume 1, Issue 1, July -December (213) a. Mass flux-4 kg/ m 2 s b. Mass flux-6 kg/ m 2 s Inner wall temperature Inner wall temperature c. Mass flux-7 kg/ m 2 s d. Mass flux-8 kg/ m 2 s / 7 / /7 Fig.3 Variation of inner wall temperature vs quality at different mass fluxes of the test section for three refrigerant mixtures namely, and is following same pattern for all the mass flux conditions. The inner wall temperature increases along the test setion, lower value for mixture followed by mixture with the maximum value is for mixture as evident from the above figure. The exergy of the refrigerant mixture flowing through the test section for three combinations at different mass fluxes is shown in thefig4( a-d). 83

5 ISSN (Online), Volume 1, Issue 1, July -December (213) a. Mass flux-4 kg/ m 2 s b. Mass flux-6 kg/ m 2 s c. Mass flux-7 kg/ m 2 s d. Mass flux-8 kg/ m 2 s Fig.4 Variation of exergy vs quality at different mass fluxes variation of mixtures in all the three combinations at four different mass fluxes 4, 6, 7 and 8 are following the same pattern in general. The exergy of fluid decreases towards the end of tube. The exergy value of mixture refrigerant lies in between the higher value of and lower value of mixtures. The exergy of the mixture approaches close value before end point of the tube for the mass fluxes 4,6and 7 kg/ m 2 s. 3.2 Behaviour of R744/R134amixture at different heat flux conditions The variation of heat transfer co efficient, inner wall temperature and exergy on the quality of refrigerant mixture flowing through the horizontal tube at different heat flux conditions is shown in fig

6 ISSN (Online), Volume 1, Issue 1, July -December (213) a. heat flux-1 Kw/m 2 s b. heat flux-18 Kw/m 2 s c. heat flux-24 Kw/m 2 s d. heat flux-24 Kw/m 2 s Fig. Variation of heat transfer vs quality at different heat flux The heat transfer co efficient of the mixture is high at the beginning and then starts decreasing sharply towards the length of the tube. The heat transfer is lowest for mixture and slightly higher value for mixture. The maximum value occurs for the mixture combimation of in the beginning of the section and it starts decreasing towards end of the tube but the value reaches low at the end section of the tube. But for 24 Kw/m 2 s heat flux condition, the heat transfer has the lower value for mixture followed by and is higher value is for ie at this mass flux blend behaves differently. of the test section increases steadily from the beginning for all the heat flux conditions and for all blends as depicted in figure6 (a-d)below. 8

7 ISSN (Online), Volume 1, Issue 1, July -December (213) a. heat flux-1 Kw/m 2 s b. heat flux-18 Kw/m 2 s c. heat flux-21 Kw/m 2 s d. heat flux-24 Kw/m 2 s Fig. 6 Variation of inner wall temperature vs quality at different heat flux Variation of inner wall temperature of the test section for all the heat flux conditions are behaves in different way. At 1Kw/m 2 s the inner wall temperature is maximum for mixture and lower value is for mixture between these two mixture lies as the temperature increases towards the end of the tube as in fig a above. At 18Kw/m 2 s the inner wall temperature is maximum for mixture and lower value is for mixture between these two mixture lies as the temperature increases towards the end of the tube as in fig b above. At 21Kw/m 2 s the inner wall temperature is maximum for mixture and lower value is for mixture between these two mixture lies after first quarter of the tube as the temperature increases towards the end of the tube as in fig c above. At 24Kw/m 2 s the inner wall temperature is maximum for mixture and lower value is for mixture between these two mixture lies as close as to as in fig d above. The variation of exergy of the mixture on the quality along the tube at different heat fluxes for three blends is shown in fig7(a-d). 86

8 ISSN (Online), Volume 1, Issue 1, July -December (213) a. heat flux-1 Kw/m 2 s b. heat flux-18 Kw/m 2 s c. heat flux-21 Kw/m 2 s d.heat flux-24 Kw/m 2 s Fig.7 Variation of exergy vs quality at different heat flux of blends at 1 and 24 Kw/m 2 s vary in similar way as it decreases from beginning to end of tube. The maximum value is for blend and approaches to close values for and blends, lower than equal refrigerant blend. At 18 and 21Kw/m 2 s the exergy is maximum for mixture and lower value is for mixture between these two lies mixture as above. 3.3 Behaviour of R744/R134amixture at different inlet temperature conditions The heat transfer at different inlet temperatures of the test section decreases from the beginning for all the blends as depicted in figure8 (a-d) below. 87

9 ISSN (Online), Volume 1, Issue 1, July -December (213) a. inlet temperature -4 o C b. inlet temperature o C c. inlet temperature4 o C d. inlet temperature 8 o C Fig.8 Variation of heat transfer vs quality at different inlet temperature conditions The heat transfer co efficient of the refrigerant mixture is initially high and start decreasing towards the end of the test section.the heat transfer is high for mixture and lower value is for for the inlet temperatures of -4 o C and o C. In case of 4 o C and 8 o C the higher heat transfer is for mixture and low for mixture. of the test section increases steadily from the beginning for all the inlet temperatures and for all blends as depicted in figure9 (a-d) below. 88

10 ISSN (Online), Volume 1, Issue 1, July -December (213) a. Inlet temperature -4 o C b. inlet temperature o C c. inlet temperature4 o C d.inlet temperature 8 o C Fig.9 Variation of inner wall temperature vs quality at different inlet temperature conditions The inner wall temperature of the tube increases steadily towards the end. The inner wall temperature is high for followed by and low for mixture at the inlet temperature of -4 o C.In case of o C, the inner wall temperature is lowest for mixture and maximum is for in the first half of the section and in remaining section is for blend.in case of 4 o C and 8 o C, the inner wall temperature is lowest for mixture and maximum is for in between these two lies the mixture. of the test section decreases from the beginning for all the inlet temperatures and for all blends as depicted in figure1 (a-d) below. 89

11 ISSN (Online), Volume 1, Issue 1, July -December (213) a. inlet temperature -4 o C b. inlet temperature o C c. inlet temperature4 o C d. inlet temperature 8 o C Fig.1 Variation of exergy vs quality at different inlet temperature conditions In all inlet temperatures the maximum exergy appears at blend. The lower exergy is for blend at the inlet temperatures -4 and o C. In case of 4 o C inlet temperature the low exergy is for in the first half of the section and in second half of section it is for mixture. In case of 8 o C inlet temperature the low exergy is for in the first half of the section and in second half of section it is for mixture but the values approaches very close. 4. CONCLUSIONS Experimental results for the flow boiling of R744/R134a as, and mixture combination in a horizontal tube under variations in the mass flux, heat flux and inlet temperature were presented. The behaviours of the local heat transfer, inner wall temperature and exergy of different blends were investigated and the following conclusions could be drawn from this study: The heat transfer initially high and starts decreases towards the end of the in all cases experiment in general. The blend variation influences the heat transfer as it is clearly evident from the plots.- In the low heat flux conditions, it was possible to observe a significant influence of heat flux on the heat transfer. In the high heat flux conditions, this influence tended to disappear. 9

12 ISSN (Online), Volume 1, Issue 1, July -December (213) The inner wall temperature increases in all conditions for all blends towards end of the tube at the same time variations in blend influences and similarly the exergy decreases from the beginning to towards end of tube with the influence of blend. To fully exploit the opportunity with natural refrigerants, it is necessary to rely on acceptable general predicting procedures are still far from satisfactory, and an increased research effort on this matter definitely desirable.. REFERENCES 1. Jin Min Cho,Yong Jin Kim and Min Soo Kim (21) Experimental studies on the characteristics of evaporative heat transfer and pressure drop of CO2 /PROPANE mixtures in horizontal and vertical smooth and microfin tubes,ijr,33, Jin Min Cho, Yong Jin Kim and Min Soo Kim(21) Experimental studies on the evaporative heat transfer and pressure drop of CO 2 and CO 2 /propane mixtures flowing upward in smooth and micro-fin tubes with outer diameter of mm for an inclination angle 4,IJR,33, Jin Min Cho and Min Soo Kim (27) Experimental studies on the evaporative heat transfer and pressure drop of CO2 smooth and microfin tubes of diameters and 9.2 mm,ijr,3, Cooper, M.G., Flow boiling-the apparently nucleate regime. Int. J. Heat Mass Transfer 32, Kandlikar, S.G., 199. A general correlation for saturated two phase flow boiling heat transfer inside horizontal and vertical tubes. J. Heat Transfer 112, Kandlikar, S.G., 22. Two-phase flow patterns, pressure drop and heat transfer during boiling in mini-channel flow passages of compact evaporators. Heat Transfer Eng. 23 (1), Alberto Cavallini, Davide Del Col, Luisa Rossetto(213) and pressure drop of natural refrigerants in minichannels (low charge equipment),ijr36, J.B. Copetti, M.H. Macagnan, F. Zina (213)Experimental study on R-6a boiling in 2.6 mm tube,ijr,36, Dongsoo Junga,*, Heungseok Leeb, Dongsoo Baeb, Jongchul Ha(2),Nucleate boiling heat transfer s of flammable refrigerants on various enhanced tubes, International Journal of Refrigeration 28, Ju Hyok Kima, Jin Min Chob, Il Hwan Leeb, Jae Seung Leeb, Min Soo Kimb(27),Circulation concentration of CO2/propane mixtures and the effect of their charge on the cooling performance in an air-conditioning system, International Journal of Refrigeration 3, Yong Jin Kim, Jin Min Cho, Min Soo Kim( 2 8 ) Experimental study on the evaporative heat transfer and pressure drop of CO2 flowing upward in vertical smooth and micro-fin tubes with the diameter of mm, i n t e r n a t i onal journal o f r e f r i g e ra t i o n 3 1, Ju Hyok Kim a, Jin Min Cho b and Min Soo KiM(28) Cooling performance of several CO 2 /propane mixtures and glide matching with secondary heat transfer fluid, International Journal of Refrigeration,Volume 31, Issue, Pages

13 ISSN (Online), Volume 1, Issue 1, July -December (213) 13. C.Y. Park, P.S. Hrnjak (27)CO2 and R41A flow boiling heat transfer, pressure drop, and flow pattern at low temperatures in a horizontal smooth tube, International Journal of Refrigeration 3, , 14. John R. Thome*, Jean El Hajal(24) Flow boiling heat transfer to carbon dioxide:general prediction method, International Journal of Refrigeration 27,(24) Rin Yun, Yongchan Kim *, Kookjeong Seo, Ho Young Kim(22) A generalized correlation for evaporation heat transfer of refrigerants in micro-fin tubes, International Journal of Heat and Mass Transfer John R. Thome*, Jean El Hajal(24)Flow boiling heat transfer to carbon dioxide:general prediction method, International Journal of Refrigeration 27, Mao-Yu Wen a,*, Ching-Yen Ho(2)Evaporation heat transfer and pressure drop characteristics of R-29 (propane), R-6 (butane), and a mixture of R-29/R-6 in the three-lines serpentine small-tube bank, Applied Thermal Engineering 2 (2) Xiaoyan Zhang, Changfa Ji, Xiuling Yuan (28)Prediction method for evaporation heat transfer of non-azeotropic refrigerant mixtures flowing inside internally grooved tubes,applied Thermal Engineering 28 (28) R. Mastrullo a, A.W. Mauro a, A. Rosato a,*, G.P. Vanoli(21)Carbon dioxide heat transfer s and pressure drops during flow boiling: Assessment of predictive methods,. i n t e r n a t i o n a l journa l o f r e f r i g e r a t i on( 2 1 ) Kwang-Il Choia, A.S. Pamitrana, Chun-Young Ohb, Jong-Taek Ohc(27) Boiling heat transfer of R-22, R-134a, and CO2 in horizontal smooth minichannels, International Journal of Refrigeration 3 (27) Abhishek G. Ramgadia, Arun K. Saha (213) Numerical study of fully developed flow and heat transfer in a wavy passage, International Journal of Thermal Sciences 67 (213) Er. Pardeep Kumar, Manoj Sain and Shweta Tripathi, Enhancement of Heat Transfer using Wire Coil Insert in Tubes, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 212, pp , ISSN Print: , ISSN Online: D. Tcheukam-Toko, B. Allahdjaba, A. Kuitche and R. Mouangue, Study of Turbulent Flow in a Heated Horizontal Tube, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 4, Issue 2, 213, pp , ISSN Print: , ISSN Online: Kavitha T, Rajendran A, Durairajan A and Shanmugam A, Heat Transfer Enhancement using Nano Fluids and Innovative Methods - An Overview, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 212, pp , ISSN Print: , ISSN Online: