TED-AJ03-281 PREDICTION OF THE COOLING RATE FOR A FINITE-SIZE VERTICAL CYLINDER IN THE FILM BOILING REGION

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Film boiling heat transfer around three-dimensional bodies occurs often in such as metal quenching, manufacturing processes, emergency core cooling of nuclear reactor and so on. In order to control the heat transfer of these high temperature objects properly, it is quite important to predict their cooling rate in the film boiling region. The objective of the present study is to establish the prediction method with sufficient accuracy for the cooling rate of the finite-size vertical cylinder. In the present simulation, the convective heat transfer coefficient from the surface was estimated using the following methods (Fig. A-I). (1) Shigechi et al.'s semi-empirical correlation for the downward facing surface with the consideration for the effect of the vertical surface, (2) Bromley's correlation modified by Shigechi et al.'s with the effect of the vapor flow from the bottom surface for the vertical surface around the lower corner, and the Nishio-Ohtake correlation based on the vapor-film-unit model for the rest of the vertical surface, and (3) Berenson's correlation for the top surface. The calculation of the temperature distribution inside the cylinder was treated as an unsteady two-dimensional heat conduction problem and the simple explicit finite difference method was employed. The quenching experiments of the film boiling heat transfer to the saturated water from the vertical test cylinder was performed under the atmospheric pressure condition. The diameter and the length of each cylinder are 45mm and 45mm, respectively. The six kind of metals, silver (99.99% purity), copper, aluminum, carbon steels (S35C and S45C), and stainless steel, were used as the materials of the test cylinders in order to investigate the effect of the thermal diffusivity on the cooling rate. In order to evaluate the prediction method for the heat transfer from the surface, the experiment with the silver cylinders with aspect ratio (length/diameter) 0.08 to 20.0 was also carried out. The cooling rate was measured by the type-K sheath thermocouple with 1mm diameter which was inserted through the hole drilled into the center of the cylinder from its upper surface. The prediction method proposed in this study agreed in enough accuracy with the measured cooling rate at the center of the cylinder in terms of the cooling curve. The example of the comparison was shown in Fig. A-II.[figure]
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TED-AJ03-281 PREDICTION OF THE COOLING RATE FOR A FINITE-SIZE VERTICAL CYLINDER IN THE FILM BOILING REGION

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