Abstract
Condensing heat transfer characteristic of an ozone-friendly refrigerant HFC-R134a (Hydrofluorocarbon R134a) flowing inside a 12.7mm helicoidal tube was investigated experimentally to obtain heat transfer data and correlations. For this long helicoidal pipe at horizontal and vertical helicoidal positions, heat transfer measurements were performed for the refrigerant flow mass fluxes from 100 to 400 kg/m2/s, in the cooling water flow Reynolds number range of 1500 < Rew < 9000 at fixed system temperature (33°C) and cooling tube wall temperature (12°C and 22°C). Experimental results show that, with the increase of mass flux, the overall condensing heat transfer coefficients of R134a increase. However, with the increase of mass flux (or the cooling water flow Reynolds number), the refrigerant side heat transfer coefficients decrease. The effects of cooling wall temperature on heat transfer coefficients were considered. Predictive correlations valid over the above water flow Reynolds number ranges and refrigerant flow mass fluxes were proposed. Helicoidal pipe heat transfer characteristics were compared with data from literature reports for horizontal straight tube. Experimental results show that helicoidal pipe, especially at horizontal position, conducts a much better heat transfer characteristic than that of horizontal tube even it was grooved. The helicoidal pipe’s position plays a very great role on heat transfer characteristic with 100 percent higher results at a horizontal position than that of vertical position.
Numerical simulation study of the heat transfer characteristic in Ω-shape grooved heat pipes
