Flow boiling heat transfer of R134a, R236fa and R245fa in a horizontal 1.030mm circular channel
This research focuses on acquiring accurate flow boiling heat transfer data and flow pattern visualization for three refrigerants, R134a, R236fa and R245fa in a 1.030 mm channel. We investigate trends in the data, and their possible mechanisms, for mass fluxes from 200 to 1600 kg/m(2)s, heat fluxes from 2.3 kW/m(2) to 250 kW/m(2) at T-sat = 31 degrees C and Delta T-sub from 2 to 9 K. The local saturated flow boiling heat transfer coefficients display a heat flux and a mass flux dependency but no residual subcooling influence. The changes in heat transfer trends correspond well with flow regime transitions. These were segregated into the isolated bubble (IB) regime, the coalescing bubble (CB) regime, and the annular (A) regime for the three fluids. The importance of nucleate boiling and forced convection in these small channels is still relatively unclear and requires further research. (C) 2009 Elsevier Inc. All rights reserved.
Keywords: Boiling heat transfer ; Microscale ; Two-phase flow patterns ; Small-Diameter Tubes ; Pressure-Drop ; Refrigerant ; Microchannels ; R-134A ; Evaporation ; Equations ; Pattern ; Water ; Model
Record created on 2010-03-19, modified on 2016-08-08