Two-Phase frictional pressure drop with pure refrigerant vertical mini/micro channels /

Abstract

Conventionally used synthetic refrigerants (Chlorofluorocarbons, Hydro chlorofluorocarbons etc.) are considered to have significant impact on environmental degradation owing due to their high ozone depletion potential and global warming potential. Global treaties (Kyoto protocol) are now coming into force and asks for ban on utilization of potential harmful fluids. Refrigeration and air conditioning industry is therefore in search of environmental benign alternatives. With growing quest on optimum utilization of energy sources devices used for exchange of thermal energy are now becoming more compact while required thermal duty is increasing day by day. Phase change heat transfer process in compact channels is now becoming increasing popular due to its capability to withstand high heating/cooling loads. Pressure drop is an important parameter and in case of phase change process this may affect system’s thermal performance. Accurate estimation of pressure drop and its proper consideration in the design process is crucial to assure functionality of any thermofluid system involving phase change heat transfer process. The current research is therefore emphasized on frictional pressure drop during flow boiling of environmental benign refrigerants (GWP<150), isobutane, HFC-152a, HFO-1234yf were tested against commonly deployed HFC-134a. The data presented here was collected under heat flux controlled conditions, the test piece was a round tube (Lheated=245 mm) while experimentation was performed at 27 and 32°C with mass velocity in 50-500 kg/m²s range. The effects of key parameters like heat flux, mass velocity, exit quality, operating medium were critically analyzed. It was observed that pressure drop increases as mass velocity increases in the test piece, increases with increase in exit vapor quality while the same was noticed to decrease with an increase in operating saturation temperature. Parametric effects and prediction assessment of correlations is reported.