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Small circular- and rectangular-channel boiling with two refrigerants. (English) Zbl 1135.76563
Summary: Boiling heat transfer experiments were performed in a small circular channel ($$d = 2.46$$) and a small rectangular channel $$(d_{h} = 2.40 mm)$$ with Refrigerant 12. The channel sizes are representative of flow passages in compact evaporators. An experimental technique minimized test section end effects which can be appreciable relative to the heat transfer in these small channels. Local heat transfer results were obtained over a range of qualities up to 0.94, a mass flux range of 44-832 kg/m’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 some 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 compared with results of previous experiments in which Refrigerant 113 in a 2.92-mm diameter small circular tube was used. The effects of channel geometry and fluid properties on heat transfer, as well as insights relative to heat transfer mechanisms in small channels, are presented. Results are presented for both nucleation- (wall superheat above $$2.75^{\circ} C$$) and convection-dominant boiling heat transfer regimes and compared with large-channel predictions. The heat transfer data for the two fluids were successfully correlated in the nucleation-dominant region.

##### MSC:
 76Txx Multiphase and multicomponent flows
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