Incipient boiling superheat for exponentially increasing heat inputs to a platinum wire supported horizontally in a pool of water was measured for exponential periods ranging from 5 ms to 10 s and for subcoolings ranging from 25 to 75K under atomospheric pressure. The heat transfer coefficient before the initiation of boiling was related to those by conduction and by natural convection. The heat flux at the incipient boiling point increased with the decrease in the period. The log-log plot of the heat flux against the superheat at the incipient boiling point had a single asymptotic line of slope 2 which was independent of subcoolings in the high heat flux region. On the other hand, as the heat flux decreased to zero, the superheat tended to approach to a constant value for each subcooling. This asymptotic superheat at zero heat flux was higher for higher subcooling. Transient incipient boiling superheat was reasonably explained by the combination of two kinds of incipient boiling models.

Natural convection heat transfer from a vertical cylinder in liquid sodium was experimentally studied. Two test cylinders of different dimensions were used. They were 7.62 and 17.51 mm in diameter, and 186 and 257 mm in heated length, respectively. The surface heat flux was ranged from 2×10 4 to 2×10 6 W/m 2 at the bulk liquid temperatures of 673, 773 and 873 K. The local heat transfer coefficients on the cylinders were obtained systematically at various heights, x, from the leading edge of the heated section. On the other hand, theoretical equations for laminar natural convection heat transfer from a vertical cylinder were numerically solved by using PHOENICS code for the same conditions as the experimental ones considering the temperature dependence of thermo-physical properties concerned. with the deviations less than 20 % for the range of R f tested here. The Nu x on the rod diameter of a heat exchanger for a power plant, D=31.8 mm, were numerically analyzed by using this code. A correlation, which can describe the effects of the cylinder diameter and the cylinder height, was given based on the experimental and theoretical values. This correlation can describe the experimental and theoretical values of Nu x for R f ranging from 1.5×10 2 to 4.7×10 6 within 20 % difference.

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The critical heat fluxes (CHFs) of subcooled water flow boiling for the test tube inner diameters (d = 3 and 6 mm) and the heated lengths (L = 67, 120 and 150 mm) are systematically measured for the flow velocities (u = 4.0 to 13.3 m/s), the inlet subcoolings (∆T sub,in = 48 to 148 K), the outlet subcoolings (∆T sub,out = 10.5 to 95.1 K), the inlet pressure (P in = 753 to 995 kPa) and the outlet pressure