Condensing heat transfer and pressure drop characteristics of an ozone-friendly refrigerant HFC-134a (hydrofluorocarbon 134a) flowing inside a 12.7 mm helicoidal tube were investigated experimentally to obtain heat transfer data and correlations. For long helicoidal pipe, heat transfer measurements were performed for the refrigerant flow mass fluxes from 100 to 400 kg/m(2)/s, in the cooling water flow Reynolds number range of 1500 < Re-w < 9000 at fixed system temperature (33 degrees C) and cooling tube wall temperature (12 degrees C and 22 degrees C). With the increase of mass flux, the overall condensing heat transfer coefficients of R134a increased, and slowly the pressure drops also increased. However, with the increase of mass flux (or the cooling water flow Reynolds number), the refrigerant side heat transfer coefficients decreased. The effects of cooling wall temperature on heat transfer coefficients and system pressure drops were considered. Predictive correlations valid over the above water flow Reynolds number ranges and refrigerant flow mass flux were proposed. Helicoidal pipe heat transfer characteristics were compared with data for horizontal straight pipe from literature reports.