Flow boiling heat transfer of refrigerant R21 in microchannel heat sink

Boiling heat transfer in a refrigerant R 21 flow in a microchannel heat sink is studied. A stainless steel heat sink with a length of 120 mm contains ten microchannels with a size of 640x2050 A mu m at cross-section with a wall roughness of 10 A mu m. The local heat-transfer coefficient distribution along the heat sink length is obtained. The ranges of parameters are: mass flow from 68 to 172 kg/m(2)s, heat fluxes from 16 to 152 kW/m(2), and vapor quality from 0 to 1. The maximum values of the heat transfer coefficient are observed at the inlet of microchannels. The heat transfer coefficients decrease substantially along the length of channels under high heat flux conditions and, on the contrary, change insignificantly under low heat flux condition. A comparison with the well-known models of flow boiling heat transfer is performed and the range of applicability is defined.