A comparison of heat transfer coefficient between a clean and fouled tube is made on the evaporation of HCFC22, HFC134a, CFC12 and CFC114 in a 6m long, 7.9mm ID smooth tube. The experiment is performed with a double pipe evaporator, where heating water flows in the outer annulus either countercurrently or parallel to the refrigerant flow direction. The heat transfer coefficient of a fouled tube is about 1.5∼2 times as large as that of a clean tube for the same pressure, mass velocity, heat flux and quality. However, at low heat flux and high quality region in the parallel flow, the heat transfer coefficient of a clean tube is slightly higher than that of a fouled tube.
