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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/m2K 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.

In the present study, the jet breakup characteristics of molten material is experimentally investigated in nonboiling condition using Wood's metal to isolate the key features of jet breakup phenomenon from the conjugated nature of melt breakup and steam generation. The experimental apparatus consists mainly of melt generating furnace and melt crucible equipped with variable nozzle diameter, a rectangular water tank of 350×350×800 mm equipped with temperature controlling heater and thermocouples. The jet diameters were 10 and 20 mm and the jet velocity was varied by pressurizing the melt container. Wood's metal of 70 • C melting temperature was used. Visualization of jet breakup provided characteristics of jet breakup in water. The range of jet velocity was 2.2-5.5 m/s. The debris were collected and sieved and it was shown that the debris sizes of 1.0-2.8 mm had the largest mass fraction, up to 50%. In the present experimental conditions, the Kelvin-Helmholtz instability is considered the most probable cause of jet breakup.

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