Experimental study on evaporation heat transfer of CO2/DME mixture refrigerant in a horizontal smooth tube

In-tube evaporation heat transfer coefficient of pure dimethyl ether (DME) and CO2/DME mixtures have been measured with water heated double tube heat exchanger under the conditions of mass flux of 100, 200, 300 kg m−2 s−1 and inlet saturation temperature of 10 °C. Test section was horizontally installed smooth tube with inner diameter of 4.2 mm. The heat transfer coefficient of mixture decreases with mixing CO2 into DME in which the degradation was about 20% for 10%CO2 and 48% for 25%CO2. Existent correlations predict the heat transfer coefficients of pure DME within ±30% error. On the other hand, heat transfer coefficient of the mixture with higher concentration 25%CO2 could not be predicted well by existent correlations, though those of 10%CO2 could be correlated fairly well.