Experimental research on coupled heat transfer of a heat source encapsulated into a subatmospheric Hypobaric Chamber

In this work, an experimental setup was built to measure the coupled heat transfer mechanism of natural convection and radiation in a low-pressure enclosure with a heating cubic element, in which the pressure varied from 90 kPa to 0.1 kPa. The cubic element was heated by six att ached electrical heating plates. An infrared thermography was used to measure the wall emissivities, based on which the net heat radiation fl ux between the component and hypobaric chamber was calculated by the Monte Carlo method. Eventually, the relative magnitude of natural convection and surface radiation can be estimated in the form of heat fl ux ratio, which was useful for bett er understanding the heat exchanger process in the low pressure environment. Experimental results provided the temperature distribution on the surface of the element, and heat dissipation was demonstrated. Considering the variable density of air at a low pressure, the average Nusselt numbers in the above pressure range could be correlated well with the Rayleigh number into three correlations, providing valuable reference for the engineering design calculations and thermal analysis.