Experimental Investigation On Condensation Heat Transfer Of R410A During Upward Flow In Vertical Tubes

This paper presents experimental investigation on condensation of R410A upward flow in vertical rectangular channel and cooper tubes. The effect of mass flux on liquid film flowing characteristics was discussed. The effects of mass flux, saturation temperatures, tubes length on condensation heat transfer coefficient in smooth tubes were discussed. This study compares the heat transfer and pressure drop characteristics of micro-fin tube and smooth tube at the same cooling water flow conditions. Some well known heat transfer correlations were compared with the experimental data obtained from various experimental conditions both in micro-fin tube and smooth tube. Based on the experimental data, two new correlations for condensation heat transfer coefficient of micro-fin tube and smooth tube and a new correlation for frictional pressure drop of micro-fin tube are proposed.The condensate liquid film flowing characteristics of R410A flowing upward in the vertical rectangular channel were observed by high speed camera. The saturation temperature of refrigerant R410A vapor was28℃. The hydraulic diameter of the rectangular channel is14.34mm and the length is160mm. The test runs at mass fluxes1.8-23kg/m2s. It is shown that tadpole flow and laminar wave flow occurred with the increase of mass flux. The thickness of the liquid film and the wave frequency were found to be increased and enhanced with mass flux. The average condensing heat transfer coefficient increased at first, and then decreased with mass fluxes. Also, the local heat transfer coefficients at the middle points of the different segments divided by the temperature measuring points along the axis of the channel were obtained.An experimental investigation on condensation of R410A upward flow in vertical smooth tubes with the same inner diameter of8.02mm and different lengths of300mm,400mm,500mm and600mm. Condensation experiments were performed at mass fluxes of103-490kg/m2s. The saturation temperatures were31℃,38℃and48℃, alternatively. The average vapor quality in the test section is between0.91and0.98. The effects of tube length, mass flux and condensation temperature on condensation were discussed. Four correlations which can be used for the upward flow condensation were compared with the experimental data obtained from various experimental conditions. A modified correlation for smooth tube was proposed within a±15%deviation band.This study compares the heat transfer and pressure drop characteristics of refrigerant R410A condensation in a smooth tube with an inner diameter of8.32mm and a micro-fin tube with a fin tip diameter of8.46mm during vapor flow upward. The outer diameters of these two tubes are9.52mm. This comparison was performed at the same cooling water flowing conditions. The test runs were performed at saturation temperatures40℃and48℃with mass fluxes between80and345kg/m2s. Four different cooling water flow conditions of the test section were set up to compare the heat transfer enhancement effect and pressure drop penalty factors of the smooth tube and micro-fin tube, also in this way four different heat fluxes were obtained. The total pressure drop across the test section was directly measured by a differential pressure transducer. Four well known heat transfer coefficient correlations for micro-fin tubes were compared with the experimental data obtained from various experimental conditions. Based on the experimental data, Cavallini et al.correlation for condensation heat transfer coefficients and Haraguchi et al.correlation for frictional pressure drops of the micro-fin tube were modified within a±15%and±25%deviation band, respectively.