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natural convection, heat transfer, low pressure, Knudsen number
This study provides experimental results on natural convection heat transfer of air in a cube below atmospheric pressure. The aim of this study is to present the experimental data of heat transfer characteristics of natural convection at small Rayleigh number (Ra) by reducing pressure. The originality of this study is to change Ra by varying pressure. Though we have already presented the experimental data of this problem in a paper (Hirano et al., Int. J. Heat Mass Transfer, 46, 4483-4488 (2003).), the detailed data using the revised experimental cell is provided in this study. The small Ra was attained by lowering pressure of air. Pressure was varied from 1.67 kPa (12.5 mmHg) to 99.6 kPa (747 mmHg). The effective volume of an experimental cell (cube) is 503 mm3 = 125 cm3. The temperature difference of 30 K is imposed through the vertically opposing copper plates with circulating water of constant temperature.
The average temperature of these walls was kept at 298.15 K. The other four walls of a cube were
insulated and constructed of acrylic resin whose thickness is 25 mm. These conditions give Ra from 100 to 350000 in this experiment. From the viewpoint of rarefaction with the Knudsen number, these experimental conditions guarantee that air adopted is continuous enough. Consequently, the measured temperature can be assumed valid to be used in estimating Ra. Obtained results suggest that the heat transfer characteristics approach those of conduction state as Ra becomes small due to more minute measurements of temperature.
10th The Asian Paciffic Confederation of Chemical Engineering
Research papers (proceedings of international meetings)
