Empirical Equation of Natural Convection Heat Transfer in Low-Pressure Field

The purpose of this study is to propose an experimental equation of natural convection heat transfer in low-pressure fields, where the pressure is given between the vacuum region and the atmospheric pressure. In this study, the thermal field under the cooled circular plate is analyzed by experiment using laser holographic interferometry. The test section is set in a vacuum chamber, and the pressure ratio between the test field and atmospheric pressure is set as 0.1-1.0. The field gas is chosen here as air, Argon and CO2 in order to expand the range of experimental conditions. The temperature difference between cooled plate and the surrounding gas is varied from 30 to 50 K. As a result, the mean Nusselt number of the cooled surface is expressed as a combined function of Rayleigh number and pressure ratio of the field in relation to atmospheric pressure for the range of 3×105