PRESSURE EFFECT ON FLOW BOILING HEAT TRANSFER OF WATER IN MINICHANNELS

摘要

The effect of pressure on the flow boiling of water in minichannels has been experimentally studied. The range of pressure was 2 to 16 bars in the experiment. The experimental apparatus consisted mainly of the 1.73 mm inner-diameter round tube test section, gear pump, pre-heater, pressurizer, pre-evaporator, and condenser. The pre-evaporator was used for varying the vapor quality entering the test section. The pressurizer controls the desired system pressure. The test tube is made of 316 stainless steel and the test tube and the pre-evaporator tube were heated by DC electric current through the tubes. The measured flow boiling heat transfer coefficients were in the range of 10000～40000 W/m~2K and showed the general convection dominant trend in terms of vapor quality. The data also indicates that the pressure does not alter the heat transfer coefficient significantly. Comparisons of the experimental data to the existing correlations showed large discrepancy, implying that these correlations are not correctly accounted for pressure.