Boiling Heat Transfer with Freon R-21 in Vertical Downflow for Assembly of Minichannels with Inclined Texture

Abstract

The heat transfer during boiling of freon R-21 in vertical downflow for an element of a plate-fin heat exchanger with textured and perforated fins was studied experimentally. The experiments were carried out for mass velocities of 30 to 60 kg/m²s and heat fluxes of 900 to 1900 W/m² for a heat exchanger with 850 fins per meter. The heat exchanger fin texture at an angle of 45 degrees to the flow direction of the vapor-liquid mixture made it possible to intensify the heat transfer and suppress the deterioration of the heat transfer at a vapor quality exceeding 0.8 in comparison with perforated fins. It has been found that the heat transfer coefficient is practically independent of the heat flux density and mass velocity, which shows the decisive influence of evaporation on the liquid film surface on the heat transfer under these conditions.