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Experimental Investigation of Flow Condensation Heat Transfer in Rectangular Minichann

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Experimental Investigation of Flow Condensation Heat Transfer in Rectangular Minichann
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  Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   251   EXPERIMENTAL INVESTIGATION OF FLOW CONDENSATION HEAT TRANSFER IN RECTANGULAR MINICHANNEL DODDESHI B C 1 , VILAS WATVE 2 , MANU S 3 , Dr. SANJEEVAMURTHY 4   1 M.Tech 4 th sem, Mechanical Engineering, Adichunchanagiri Institute of Technology, Chickmagalur, India 2 Assistant Professor, Department of Mechanical Engineering, Adichunchanagiri Institute of Technology, Chickmagalur, India 3 Assistant Professor, Department of Mechanical Engineering, Sri Siddhartha Institute of Technology, Tumkur, India 4 Professor, Department of Mechanical Engineering, Sri Siddhartha Institute of Technology, Tumkur, Karnataka, India ABSTRACT Condensation heat transfer coefficients and pressure drops in horizontal rectangular minichannel was measured using the specially designed aluminium test section with hydraulic diameter of 2mm. The data are reported for steam is a refrigerant and water as a coolant. The experimental investigation was carried out mass flux range of 88.89 kg/m 2 s to 177.78 kg/m 2 s, vapour quality ranges from 20-80% and a saturation temperature of 100°C. The mass flux and vapour quality were determined to have significant effects on condensation process and also determined to effect of wall temperature along the channel length, effect of mass flux on pressure drop. The experimental data of condensation heat transfer coefficients are compared with existing correlation. Keywords: Condensation, Heat transfer coefficient, Minichannel, Rectangular channel. 1. INTRODUCTION Minichannel heat exchangers are extensively used in modern heat exchangers of automotive air conditioning systems as a condenser. The hydraulic diameter of the minichannel heat exchangers are within the range of 200µm to 3mm. Minichannel heat exchangers provide a higher heat transfer performance as compared to conventional heat exchangers. As a result of its performance, new applications such as those in the field of residential and electronic device cooling are a important growing issue. However, in spite of their potential usage and present interest, thermal and flow characteristic behaviours in these minichannel are not well understood, and limited studies have been performed. Hence, determination of the condensation heat transfer coefficient and the pressure drop across minichannel is of great attention. In this study, experimentally determine the condensation heat transfer coefficients and pressure drops in rectangular single minichannel with hydraulic diameter of 2mm. The test was carried out using steam is a refrigerant and water as a coolant in the horizontal rectangular channel and of saturation temperature 100°C.The effect of wall temperature along the channel length, effect of vapour quality and mass flux on flow condensation, effect of mass flux on pressure drop were calculated. There are a few previous studies on the condensation heat transfer of refrigerants and the effect of mass flux on pressure drop inside a rectangular minichannel was experimentally investigated. Jeong Seob Shin & Moo Hwan Kim [1]   experimentally studied flow condensation heat transfer inside circular and rectangular minichannel. The results showed the influence of mass flux and vapour quality for all the test sections. The condensation Nusselt numbers increased with increasing vapour quality and mass flux due to the increase of higher vapour shear force. Also, the Nusselt number became more sensitive to the mass flux as the average vapour quality increased. M.J. Wilsona et al., [2] experimentally   INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 5, Issue 9, September (2014), pp. 251-258 © IAEME: www.iaeme.com/IJMET.asp Journal Impact Factor (2014): 7.5377 (Calculated by GISI) www.jifactor.com   IJMET   © I A E M E    Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   252   investigated the condensation in horizontal smooth and micro finned copper tubes having a diameter of 9 mm, were successively flattened in order to determine changes in flow field characteristics as a round tube is altered into a flattened tube profile. Refrigerants R134a and R410A was investigated mass flux range of 75 to 400 kg m -2 s -1  and a quality ranges from 10–80%. The experimental results showed, increasing mass flux and vapour quality increases the heat transfer coefficients due to the flattened tube may alter the flow field in a manner that increases the heat transfer without changing the flow field configuration. J.R.Thome et al., [3 ] investigated condensation in horizontal tubes, the simulation was developed to predict the trend. The trend was based on heat transfer coefficient as a function of vapour quality and mass velocity. The results showed, at the lowest flow rate of 30 kg m -2 s -1  the flow was in the stratified regime from inlet to outlet and the heat transfer coefficient falls off slowly with decreasing vapor quality due to surface tension.   Zhongyu Guo & N. K. Anand, [4] experimentally studied condensation for R-410A in a Rectangular channel. A two-phase loop to measure the condensation heat transfer coefficient was designed, built, and calibrated. The test section was 3 m long horizontal rectangular brass (63% Cu, 37% Zn by mass) tube 12.7 mm wide and 25.4 mm high. The results showed that average condensation heat transfer coefficient decreases with a decrease in vapour quality due to the liquid phase increases with increasing condensation   M. M. Rahman, et al., [5] experimentally investigated condensation heat transfer enhancement through inner grooved copper tubes in a heat exchanger. Experiment was conducted at mass flux variations of 200 to 600 kg/m 2  and the vapor qualities ranged from 90% at the inlet to 20% at the outlet and R-22 was used as the working fluid. The result showed that, condensation heat transfer coefficient and pressure drop are found to be increased as the mass flux is increased due to increasing in flow mean velocity. S.N. Sapali and Pradeep A.Patil [6]   experimentally investigated two phase heat transfer coefficients and pressure drops of R-404A for different condensing temperatures in a smooth (8.56 mm ID) and micro-fin tube (8.96 mm ID). The experiment was performed at average saturated condensing temperatures ranging from 35°C to 60°C. The mass fluxes are at a range of 90 and 800 kg m -2 s -1 . The experimental results showed that, the average heat transfer coefficients and pressure drop increases with mass flux but decreases with increasing condensing temperature.   Todd M. Bandhauer and Akhil Agarwal Srinivas Garimella [7] developed a model for predicting heat transfer during condensation of refrigerant R134a in horizontal micro channel was presented. The result showed that, the heat transfer coefficient increases with increasing vapour quality and mass flux due to increase of shear stress and thin liquid film that reduces the thermal resistance. Melanie Derby et al., [8] experimentally investigated condensation heat transfer of R134a in 1mm square, triangular, and semi-circular mini-channels. The results showed, for all three test sections heat transfer coefficients increased with increasing mass flux and vapour quality due to experimental uncertainties or an effect of the relative magnitude of surface tension, shear, and gravity forces. A.S. Dalkilic, S. Wongwises [9 ] conducted an experiment to investigate the condensation on zeotropic refrigerants over the wide range of mass flux in horizontal tubes. The results showed that, heat transfer coefficient increases with increasing in the mass flux and quality in annular flow due to increased shear stress and thinner liquid film than in other flow regimes.   Al-Hajeri et al., [10 ]  investigated the heat transfer performance during condensation of R-134a inside helicoidal tubes. The refrigerant side heat transfer coefficient and overall heat transfer coefficient decrease as the saturation temperature increases due to surface tension effect. Gil Goss júnior et al., [11] performed experiments on heat transfer coefficient and pressure drop during condensation of R-134a inside parallel micro channels. The heat transfer coefficient is independent of the mass velocity. The dependence of heat transfer coefficient on the vapor quality is not clear for vapor quality greater than 0.6. It is important to note that, the fluid pressure is directly proportional to the mass velocity and the heat transfer coefficient increases with the rise in pressure, and the opposite occurs due to the effect of mass flow rate.   Somchai wongwises, Maitree polsongkram [12] the two phase heat transfer coefficient and pressure drop of pure HFC-134a condensing inside a smooth helically coiled concentric tube in tube heat exchanger are experimentally investigated. The experimental result showed that, pressure drop is increased with increasing vapour quality and mass flux due to increase of mass flux will increase the vapour velocity. Hence, the shear stress at the interface of the vapour and liquid film increases as a result pressure drop increases. 2. FABRICATION OF MINICHANNEL CONDENSER A aluminum bar of cross section (150mm X 50mm) is fabricated for single rectangular minichannel of hydraulic diameter 2mm and length of 96mm was cut on top and bottom sides of the rectangular block as shown in Fig.1(a), (b). The top and bottom of the rectangular block was covered with the help of cover plates. Two cover plates are provided with two drilled holes for the inlet and outlet of the working fluid and coolant. The channel plate and cover plate is tightened by using bolt and nuts. The entire shape of the test specimen was machined by C.N.C milling machine.    Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   253   Fig.1:  (a), (b): Fabrications of rectangular channel test section Table 1:  Specification of the test specimen Rectangular channel geometry Width Depth Hydraulic diameter Length 3mm 1.5mm 2mm 96mm 3. EXPERIMENTAL SETUP Fig.2:  Experimental Setup The experimentation involves two cycles they are refrigerant cycle and coolant cycle. The refrigerant cycle consists of pump, digital pressure gauge and thermocouple. In this refrigerant cycle, two major components are arranged in series as shown in Fig.2 and they are preheater and minichannel condenser. The experimentation was carried out using steam is a refrigerant and water as a coolant in the condenser. The preheater is completely insulated with the glass wool. Fig.2 shows the test line assembled for the experimental investigation of flow condensation in single rectangular minichannel. The booster pumps are used to circulate the refrigerant and coolant through the test line. The generated vapour is condensed in the test section. The five thermocouples are inserted between the refrigerant and the coolant side in the test section as shown in Fig.2. The properties like temperature, pressure and flow rate are measured at various points during testing. Finally the condensate from the condenser was measured using the chemical burette. (a) Rectangular channel for refrigerant side (b) Rectangular channel for coolant side    Proceedings of the 2 nd  International Conference on Current Trends in Engineering and Management ICCTEM -2014 17 – 19, July 2014, Mysore, Karnataka, India   254   4. OPERATING PARAMETERS Table 2:  Operating Conditions Sl.No Saturation temperature (°C) Saturation pressure (bar) Mass flow rate of water Mass flow rate of coolant Inlet Vapour quality g/s 1 100 1.01325 0.8 1 0.2/0.4/ 0.6/0.8 2 0.6 0.2/0.4/ 0.6/0.8 3 0.4 0.2/0.4/ 0.6/0.8 5. DATA REDUCTION The total heat input to the preheater is given by.                          (1) Where, m- Mass flow rate of the water (kg/sec) h fg  - latent heat of vaporization (kJ/kg) Cp - Specific heat of water (kJ/kg °C) T sat  - Saturated temperature of water (°C) T inlet  - Inlet cold water temperature (°C)   - Dryness fraction Heat absorbed by cooling water (Q c )   is given by;                     (2) Where, m c  - Mass flow rate of coolant (kg/s) C p  - Specific heat of cooling water (kJ/kg °C) T co  - Outlet coolant temperature (°C) T ci  - Inlet coolant temperature (°C) Heat transfer coefficient is given by; h=   󰀯          (3) Where, Q c - Heat absorbed by coolant (W) T s  - Saturated temperature of water (°C) Tw avg  - Average wall temperature (°C) A - Surface area of the channel (m 2 ) = (w + 2 a) × L w - Width of the channel (m) a - Depth of the channel (m) L - Length of the channel (m)
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