Heat transfer through a low-pressure gas enclosure as a thermal insulator: Design considerations

Abstract

SUMMARYHeat transfer through gases at low pressures, rarefied media, plays a very significant role in the design of solar receivers and low-temperature cooling equipment. It is shown here that low-pressure and transition regimes of heat transfer prevail in such applications. State-of-the-art procedures for estimating these heat-transfer rates are presented together with an improved expression for the thermal accommodation coefficient for monatomic gases on engineering surfaces. The latter are characterized with values of thermal accommodation and reflection coefficients. Numerical calculations relevant to design engineers interested in these industrial applications are presented and the same are discussed for the dependencies of the heat-transfer rates on different design and operating parameters. It is shown that the values of surface reflectivity coefficient have a pronounced contribution in low density heat-transfer calculations at low gas temperatures, and are negligibly small for the temperatures greater than 900 K.

Diffusive-to-ballistic transition of the modulated heat transport in a rarefied air chamber

“…This important transition has been investigated in semiconductor and dielectric thin films, 1 carbon nanotubes, 2,3 the Brownian motion of particles in a liquid, 4 the heat wave transport in strongly scattering thin samples, 5 the optical imaging of biological tissues, 5 and the heat transport in rarefied gases, [6][7][8][9][10][11] to cite some examples. Although heat propagation in rarefied air have been widely studied under steady-state conditions, [6][7][8][9][10][11] it has not yet been fully explored under a modulated thermal excitation, 22,23 which is addressed in the present work.…”