Tn. Tran et al., SMALL CIRCULAR-CHANNEL AND RECTANGULAR-CHANNEL BOILING WITH 2 REFRIGERANTS, International journal of multiphase flow, 22(3), 1996, pp. 485-498
Boiling heat transfer experiments were performed in a small circular c
hannel (d = 2.46) and a small rectangular channel (d(h) = 2.40 mm) wit
h Refrigerant 12. The channel sizes are representative of flow passage
s in compact evaporators. An experimental technique minimized test sec
tion end effects which can be appreciable relative to the heat transfe
r in these small channels. Local heat transfer results were obtained o
ver a range of qualities up to 0.94, a mass flux range of 44-832 kg/m(
2)s, and a heat flux range of 3.6-129 kW/m(2). Saturation pressure was
nearly constant, averaging 0.82 MPa for most of the testing, with som
e tests performed at a lower pressure of 0.51 MPa. Local heat transfer
coefficients were determined experimentally as a function of quality
along the length of the test section. Heat transfer rates were compare
d with results of previous experiments in which Refrigerant 113 in a 2
.92-mm diameter small circular tube was used. The effects of channel g
eometry and fluid properties on heat transfer, as well as insights rel
ative to heat transfer mechanisms in small channels, are presented. Re
sults are presented for both nucleation- (wall superheat above 2.75 de
grees C) and convection-dominant boiling heat transfer regimes and com
pared with large-channel predictions. The heat transfer data for the t
wo fluids were successfully correlated in the nucleation-dominant regi
on. Copyright (C) 1996 Elsevier Science Ltd.