Abstract:
The two-phase evaporative heat transfer coefficient and pressure drop of HFC 134a are experimentally investigated. The test section is a 2.6 m long counter flow double tube heat exchanger. The inner tube is made from a copper tube of 7.9 mm inner diameter. Heat is supplied to the inner tube using hot water flowing through the annulus. Two experimental procedures are carried on. First, the inlet quality is set at a specific value with the evaporation temperature is kept at 13 centigrade degree and the rest of parameters are varied(mass flux; 340-850 kg/m2s, inlet quality; 14-30 percent). Second, the heat flux is set at a specific value and the rest of parameters are varied(mass flux; 430-860 kg/m2s, heat flux; 6.7-46.4 kwlm2, evaporationtemperature of 5, 10 and 15 centigrade degree), The experimental results are presented in the form of average heat transfer coefficient and frictional pressure gradient. The results show thataverage heat transfer coefficient and pressure drop increase with increasing mass flux, average quality and heat flux. Moreover, average heat transfer coefficient obtained is compared withthose predicted from Pierre and Wattelet correlations. The comparison reveals that the correlation of Chaddock-Noerager, Shah, Kandlikar and Gungor-Winterton give fair prediction while the correlation of Pierre and Wattelet shows over prediction. Similary, the presentmeasured data of pressure drop is compared with those predicted from Lockhart-Martinelli, Chisholm and Friedel correlations. It is found that the correlations of Lockhart-Martinelli and Chisholm give over prediction while the correlation of Friedel shows fair agreement.Thecorrelation for average heat transfer coefficient is proposed in the form of Reynolds number and Pierre number. Moreover, the correlation of pressure drop expressed in the function of Martinelli parameter is proposed.