Investigation of the effect of the degree of vacuum on the convective heat transfer coefficient

Experiments were conducted to determine the effect of the vacuum level of a rarefied gas on the coefficient of convective heat transfer from a cylinder and a sphere to the gas and also the effect of the blackness level of the surfaces of these bodies on the coefficient. The sphere and cylinder were both electrocalorimeters fed with dc voltage; pressure in the gas was maintained at 0.1-6 x 10 to the -3rd mm; and the blackness levels were 0.22 for the cylinder and 0.8 for the sphere. It was found that the convective component has a negligible effect on the total heat transfer coefficient at a pressure of 6 x 10 to the -3rd mm for bodies with a blackness level of 0.22 and at a pressure of not greater than 0.1 mm for bodies with a blackness level of 0.8 and higher. This information is useful for the thermal design of radio equipment operating in rarefied-gas conditions.