Effect of gravity on the distribution of CO2 in a parallel flow evaporator

Abstract

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.In this study, the distribution characteristics of C02, a promising natural refrigerant, were experimentally investigated for a parallel flow evaporator with 10 flat aluminum tubes. The tubes have the length of 1000 mm and each tube has six micro-channels with a diameter of 0.8 mm. To detect the flow distribution into the tubes, the wall temperatures were measured along the tubes which are heated by flexible electric resistance heating wires. If the mass flow rate in a tube is lower than others, the superheating of the refrigerant would occur earlier in that tube and the corresponding wall temperature become higher. To investigate the effect of the gravity, three installation positions of the evaporator were considered; vertical headers/ horizontal tubes (case I), horizontal headers/ horizontal tubes (case 2), and horizontal headers/ vertical tubes (case 3). Experimental results showed that case I was most greatly influenced by the gravity. The refrigerant vapor was supposed to be collected at the upper part of the inlet header because of the gravity. The refrigerant distribution becomes better with the increase of the evaporating temperature and mass flux.