Condensation Heat Transfer of New Refrigerants: Advantages of High Pressure Fluids

Heat transfer condensation tests inside a 8 mm ID tube for R-134a, R-410A and R-125 are reported at an average saturation temperature of 40°C, at mass velocities ranging from 65 to 750 kg/(m s), over the entire vapour quality range. After comparing the experimental data against a model able to predict both shear force and gravity driven condensation, a comparison among these fluids has been carried out. Drop ill saturation temperature is chosen as the benchmark, with R-22 as the reference fluid, to show advantages of high pressure fluids regarding heat transfer performance. NOMENCLATURE D diameter [m] p density [kg/m] DT temperature difference (T sat T w) [K] Subscripts G mass velocity [kg/(m s)] CALC calculated h heat transfer coefficient [W/(m K)] DR driving 1LG latent heat [J/kg] EXP experimental p pressure [Pa] f friction q heat flow rate [W] G gas phase T temperature [K] L liquid phase X vapour quality sat saturation z axial coordinate [m] w tube wall