Flow boiling pressure drop of R134a in the counter flow multiport minichannel heat exchangers

In the present study, the pressure drop characteristics during the boiling of R134a as it flows through the multiport minichannel heat exchangers are presented. The heat exchangers are counter flow tube-in-tubes. The refrigerant flow runs through the inner tube, while the hot water flows through the 25.4 mm round tube at outer edge of the heat exchanger. Two inner test sections are made from aluminium tubing with hydraulic diameters of 1.1 mm for 14 channels and 1.2 mm for eight channels. The experiments were carried out at mass fluxes ranging from 350 to 980 kg/(m2 s), heat fluxes ranging from 18 to 80 kW/m2, and saturation pressures of 4, 5 and 6 bar, at constant inlet quality of 0.05. The effect of relevant parameters on the frictional pressure drop, such as the saturation pressure, mass flux, heat flux, and aspect ratio, are examined and discussed in detail. Finally, the nine existing correlations that are based on both conventional tubes and small tubes are selected for comparison with the experimental results.

► The pressure drop characteristics during the boiling of R134a in two multiport minichannel heat exchangers are presented. ► The most of the experimental data are located within simi-annular and annular flow patterns. ► The mass flux has a more significant influence on the frictional pressure drop over the others. ► The Friedel correlation provided the best predictions among the nine selected correlations.