Experimental study on the evaporative heat transfer and pressure drop of CO2 flowing upward in vertical smooth and micro-fin tubes with the diameter of 5 mm

摘要: Abstract Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristic pressure drop carbon dioxide flowing upward in vertical smooth micro-fin tubes were investigated by experiment with regard to evaporating temperature, mass flux flux. The outer diameter (OD) 5 mm length 1.44 m selected as a test section measure evaporative coefficient. tests conducted at fluxes from 212 530 kg/(m2 s), saturation temperatures −5 20 °C 15 45 kW/m2, where was heated direct heating method. differences characteristics between analyzed respect enhancement factor (EF) penalty (PF). Average coefficients for tube approximately 111–207% higher than those same conditions, PF increased 106 123%.