Experimental heat transfer coefficients for R-134a and R-600a in horizontal tubes with vertically positioned perforated strip-type inserts are reported in this paper. Tests were conducted using a single-tube evaporator test facility. The test section used was 2000 mm long, 10.6 mm inside diameter, horizontal, smooth copper tube with perforated strip-type inserts made from the same material (copper). Test parameters were varied as follows: heat flux 9.1-31.2 kW/m(2); mass velocity 82.3-603.3 kg/m(2) s; quality 0-0.85, and a saturation temperature of 6 degreesC. The flow pattern were identified for different test tubes and flow conditions. The heat transfer coefficients for R-600a were higher than those for R-134a. The heat transfer performance and pressure drop can be improved up to 2.5 and 1.5, respectively for a 96 perforated holes enhanced tube. All comparisons were based on the same nominal mass flow rate. Finally, an empirical correlation was developed. (C) 2003 Elsevier Science Ltd. All rights reserved.