Low-flow critical heat flux in heated microchannels

Critical heat flux (CHF) associated with the flow of subcooled water in hea ted microchannels is experimentally investigated. Four different channels, all 16 cm in length, are used: two are! circular and uniformly heated and h ave 1.17- and 1.45-mm diameters, and the other two represent flow channels in a microrod bundle with a triangular array and 1.131-mm hydraulic diamete r with one uniformly heated over its entire surface and the other heated on ly over the surfaces of the surrounding rods. The test section parameter ra nges are as follows: 250 to 1000 kg/m(2) . s mass flux 344- to 1043-kPa exi t pressure, 407- to 1204-kPa inlet pressure, and 49 to 72.5 degrees C inlet temperature. The effect of noncondensables lair) on CHF is also examined b y repeating some of the experiments with degassed water and with water satu rated with air at test section inlet pressure and temperature. Critical heat flux occurs at very high flow qualities (0.36 and higher) in all the tests and indicates the occurrence of dryout. Furthermore, the CHF appears to monotonically increase with increasing mass flux or pressure. Th e CHF depends on channel cross-section geometry, and unlike high mass flux: data, it increases with increasing channel diameter The dissolved air slig htly increases the CHF for the smaller circular channel and reduces the CHF for the other test sections. The experimental data are compared with the p redictions of three widely used empirical correlations. The Bowring-1972 co rrelation could predict the data with reasonable accuracy.