Experimental Study on the Modeling of Condensation Heat Transfer Coefficients in High Mass Flux Region of Refrigerant HFC-134a Inside the Vertical Smooth Tube in Annular Flow Regime

Abstract

This article presents an experimental investigation on the co-current downward condensation of R134a in a vertical smooth copper tube having inner diameter of 8.1 mm and a length of 500 mm. Condensation experiments are done at mass fluxes varying between 260 and 515 kg/m(2)-s. The condensing temperatures are 40 degrees C and 50 degrees C; heat fluxes are between 10.16 and 66.61 kW/m(2). The quality of the refrigerant in the test section is calculated considering the temperature and pressure obtained from the experiment. The pressure drop across the test section is directly measured by a differential pressure transducer. The average experimental heat transfer coefficient of the refrigerant is calculated by applying an energy balance based on the energy transferred from the test section. The average predicted heat transfer coefficient of the refrigerant is determined by means of the model of Kosky and Staub, and Von Karman universal velocity distribution correlations using different interfacial shear stress equations valid for annular flow in horizontal and vertical tubes to investigate the Chen et al. annular flow theory. The effects of heat flux, mass flux, and condensation temperature on the pressure drop are also discussed. A new correlation using a large number of data points for the turbulent condensation heat transfer coefficient is proposed.