INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET)

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1 INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) International Journal of Mechanical Engineering and Technology (IJMET), ISSN (Print), ISSN (Online) Volume, Issue, July - August (213) IAEME ISSN (Print) ISSN (Online) Volume, Issue, July - August (213), pp IAEME: Journal Impact Factor (213): (Calculated by GISI) IJMET I A E M E HEAT TRANSFER CHARACTERISTICS AND EXERGY STUDY OF R7/R127 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 The use of carbon dioxide as alternative refrigerant in refrigeration plants and heat pumps has been focused recently. The experimental investigation of 5/5 blend of R7/R127 flow in a tube of 1.m length with an inner diameter of mm is carried out. This paper reports the results of heat transfer coefficient, inner wall temperature, Nusselt number and exergy analysis for inlet temperature between - o C and o C. Keywords: inlet temperature, exergy, heat transfer co efficient 1. INTRODUCTION In the field of vapour compression systems, the naturally occurring carbon dioxide (CO2) was brought back to the forefront as a working fluid because its Global Warming Potential (GWP) is negligible compared to synthetic refrigerants. Thus, CO2 is seen as a substitute, as it is neither toxic nor flammable (Lorentzen, 1995). Also HCs are excellent refrigerants, even if issues related to safety reasons are restricting the refrigerant charge depending on the application and, hence, their use is often limited to small size systems. Blends of CO2 and HCs could improve performances with respect to pure CO2 cycles, adopting small refrigerant charges of flammable fluids. Recently, research studies about blends of CO2 with HCs (Di Nicola et al., 25; Kimand Kim, 25; Niu and Zhang, 27; Kim et al., 27, 2) were published. In these works both thermodynamic properties and system performances were studied. One of the most interesting results is the behaviour of CO2 and propane blends with low mass concentration of propane. In fact, the energetic performance achieves a maximum at 25% of propane (see Kim et al. (2)), improving respect to pure CO2 cycles working between the same 166

2 International Journal of Mechanical Engineering and Technology (IJMET), ISSN (Print), ISSN (Online) Volume, Issue, July - August (213) IAEME temperatures; the critical temperature and the heat of vaporization increase; the discharge temperature from the compressor reduces. The problem associated with R7 is high operating pressure and low efficiency: to solve this issue an attempt is made by making a mix with R127. Theaim of this work is to discuss the heat transfer coefficient, inner wall temperature, Nusselt number and exergy degradation during flow boiling of CO2 and propylene blends in inlet temperature range o C to o C. 2. EXPERIMENTAL PROCEDURE The experimental system used to investigate the heat transfer of R7/R127 in a horizontal tube during evaporation is shown schematically in Fig. 1 and it is a similar set up and working as stated by Cho et al (1). 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. A direct-current heating is applied on the test section. The refrigerant enters the test section in two-phase state. The test section consists of 5 mm outer diameter with.25 mm thick copper tube having length of 1. m. The wall temperature is measured using type-t, thermocouples, positioned on the surface. Flow boiling tests were then performed at different inlet temperature to the test section. MF PREHEATER Test section CONDENSER P LIQUID RECEIVERR Fig.1. Schematic experimental set up The thermo physical properties are calculated based on the measured temperature and pressure. The local heat transfer coefficient 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.. 3. RESULTS AND DISCUSSIONS Following plots depicts the variations of inner wall surface temperature,heat transfer, Nusselt number and exergy destruction in the test section during the evaporation of R7/R127 blend at different inlet temperature conditions in fig

3 International Journal of Mechanical Engineering and Technology (IJMET), ISSN (Print), ISSN (Online) Volume, Issue, July - August (213) IAEME Inner wall temperature Fig.2. Variation of Inner wall temperature vs quality at different inlet temperature The inner wall temperature of the test section increases at a faster rate in the initial stage and then increases gradually, looks like stable in the test section. The inner wall temperature for this blend increases with increase of inlet temperature. The higher inner wall temperature is for inlet temperature of o C and minimum inner wall temperature is for inlet temperature of - o C.. Heat transfer coefficient Fig.3. Variation of heat transfer vs quality at different inlet temperature The heat transfer coefficient increases when the inlet temperature increases.the heat transfer co efficient is maximum for the inlet temperature of o C and is low for - o C. The heat transfer co efficient for the inlet of - o C follows different way as it lies far from the other inlet temperatures as is evident from the fig.3. The heat transfer co efficient decreases along the length of the tube. 16

4 International Journal of Mechanical Engineering and Technology (IJMET), ISSN (Print), ISSN (Online) Volume, Issue, July - August (213) IAEME Nu Fig.. Variation of Nusselt number vs quality at different inlet temperature The Nusselt number decreases up to middle then increases when the inlet temperature increases except for inlet temperature of o C.The Nusselt number is maximum for the inlet temperature of o C and is low for o C. The Nusselt number increases with increase of inlet temperature but for o C it decreases. The Nusselt number for the inlet of o C follows different way as it is decreases gradually with a slight increase at the end of section as in fig.3. Exergy Fig.5. Variation of exergy vs quality at different inlet temperature The exergy of the blend decreases as quality increases as in the figure 5. The decrease in exergy of the refrigerant blend is sharp till the middle of section and then it reaches stable condition. The exergy of the refrigerant blend is high for the inlet temperature - O C and minimum for the inlet temperature O C and lies in-between the maximum and minimum for the other values of inlet temperature. 169

5 International Journal of Mechanical Engineering and Technology (IJMET), ISSN (Print), ISSN (Online) Volume, Issue, July - August (213) IAEME 5. CONCLUSIONS The refrigerant blend behaves at different inlet temperature conditions in a similar pattern of the variations of inner wall surface temperature, heat transfer coefficient, Nusselt number and exergy destruction in the test section during the evaporation of blends R7/R127 (5/5) were presented. The inner wall temperature for this blend increases with increase of inlet temperature. The heat transfer co efficient for the inlet of - o C follows different way as it lies far from the other inlet temperatures. The Nusselt number increases with increase of inlet temperature for three inlet conditions but for o C it decreases. Thus paves way for making more research to confirm the results. 6. 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 5mm for an inclination angle 5,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 5 and 9.52 mm,ijr,3, Cooper, M.G., 199. 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. 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), Mao-Yu Wen a,*, Ching-Yen Ho(25)Evaporation heat transfer and pressure drop characteristics of R-29 (propane), R-6 (butane), and a mixture of R-29/R-6 in the threelines serpentine small-tube bank, Applied Thermal Engineering 25 (25) Xiaoyan Zhang, Changfa Ji, Xiuling Yuan (2)Prediction method for evaporation heat transfer of non-azeotropic refrigerant mixtures flowing inside internally grooved tubes, Applied Thermal Engineering 2 (2) Jin Min Cho, Min Soo Kim (27)Experimental studies on the evaporative heat transfer and pressure drop of CO2 in smooth and micro-fin tubes of the diameters of 5 and 9.52 mm International Journal of Refrigeration 3 (27) 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, Issue 2, 213, pp , ISSN Print: 976-6, 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: