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Micro fin tubes are widely being used in condensers and evaporators of commercial air conditioners. These tubes enhance the heat transfer without causing the similar increase in refrigerant charge and pressure drop. The condensation heat transfer characteristics are strongly dependent on prevailing flow regimes. The flow regimes, further, depend on the mass flux, vapour quality and fluid properties. Conventionally, two phase heat transfer correlations are used for the design of condenser [1-2] etc. These correlations can pose serious errors, if these are inconsistent with the prevailing flow regime [3]. The present study deals with the experimental investigations on local condensation heat transfer coefficient and local flow regimes at saturation temperatures of 35°C and 40°C respectively, in mass flux range of 200-400 kg/m2-s & vapour quality range of 0.1-0.9 for R134a and R410A respectively using two horizontal micro fin tubes having helix angles of 15° and 18°respectively. Various flow regimes encountered during the condensation of refrigerants R134a have been captured with high speed digital CMOS camera. Analysis of these flow regimes has been carried out to understand the relationship between the heat transfer coefficient and the prevailing flow regimes. Most of the flow regimes are observed to lie in Annular, Semi annular and Stratified zone. Three existing flow regime maps, namely that of Berbera et al. [4], Tandon et al. [5] and Thome et al. [6] have been used to predict the flow regimes corresponding to different experimental conditions. The observed flow regimes are then compared with the predicted flow regimes to check the applicability of existing flow regime maps. It has been observed that the prediction capability of Tandon et al. [5] flow regime map is very good as compared to Breber et al. [4] and Thome et al. [6] flow regime maps, for both pure refrigerant (R134a) and mixture refrigerant R410A. The local heat transfer coefficients for R134a & R410A ranged from 1095-8797W/m2-K & 1390-7255W/m2-K respectively. The uncertainties in the measurement of refrigerant mass flow rate, test condenser water flow rate, refrigerant saturation temperature, wall temperature and water temperatures are ±0.002 kg/s, ±0.05 lpm, ±0.15°C, ±0.5°C & ±0.1°C respectively. The overall uncertainty in the measurement of local heat transfer coefficient was in the range of ±6-40%
micro fin tubes, flow regimes, condensation heat transfer, pressure drop, helix angle
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