This article presents an experimental investigation on condensation heat transfer of R-134a in horizontal straight and helically coiled tube-in-tube heat exchangers. The experiments were carried out at three saturation temperatures(35℃, 40℃ and 45℃) with the refrigerant mass flux varying from 100kg/m-s to 400kg/m-s and the vapor quality ranging from 0.1 to 0.8. The effects of vapor quality and mass flux of R-134a on the condensation heat transfer coefficient were investigated. The results indicate that the condensation heat transfer coefficients of the helical section are 4%-13.8% higher than that of the straight section. The experimental results were compared with the data available in literature for helical and straight pipes.

This paper presents an experimental investigation of condensation heat transfer of alternative refrigerant R-134a flowing inside a helical pipe with cooling water through the concentric annular passage in a counter-flow direction. The experiments were conducted with the helix axis of the test section in horizontal, vertical, and inclined orientation directions, respectively. The mass flow flux for R-134a ranges from 100 to 400kg/m2s and the Reynolds number of cooling water ranges from 1500 to 10000. The results demonstrate the orientation of helical pipe has a significant effect on both refrigerant-side heat transfer and overall heat transfer coefficients.