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Critical Heat Flux in Heated Horizontal Thin Annuli


 The objectives of the work reported here were to experimentally study the critical heat flux in a heated thin, horizontal, annular flow passage cooled by subcooled water and to examine the applicability and relevance of the current predictive methods for critical heat flux to such passages. Experiments were performed in the Georgia Tech Microchannel Test Facility (GTMTF). The test section was an annulus with 6.45 and 7.77 mm inner and outer diameters, respectively (0.66 mm gap width), and an 18.5-cm long heated section. The experimental parameters investigated covered the following ranges: test section exit pressure: 0.344–1.034 MPa; coolant (water) mass flux: 100–380 kg/m2s; wall heat flux: 0.231–1.068 MW/m2; water inlet temperature: 30–65°C.
 The results, in agreement with the existing CHF data for large horizontal channels, indicated that CHF values were considerably lower than the expected CHF values for vertical test section configuration. In all the tests CHF occurred at relatively high equilibrium qualities, and was preceded by flow stratification which caused dryout of the upper surface of the flow channel. The data were correlated by introducing empirical correction multipliers into three widely-used correlations for vertical channels, and based on the compensated distortions method.