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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Heat Transferred from Cold to Hot in Near-Critical Fluid Under Low Gravity

Get access (open in a dialog) DOI: 10.1615/IHTC15.mlt.009635
pages 5011-5019

Abstract

Near the critical point, thermodynamic and transport properties of fluids exhibit striking behaviors, including diverging isothermal compressibility and vanishing thermal diffusivity. However, instead of critical slowing down due to the singular properties, a prominent critical speeding up and even a overheating were observed near the critical point in the microgravity experiments. In this paper, we aim to clarify the physical mechanisms based on the theoretical analyses and numerical simulations. For the temperature quench at the boundary, the heating process at constant volume generates a boundary layer with high temperature and pressure. The internal energy of the boundary layer transports downstream in a form of wave, which can be called ‘internal energy wave’, due to pressure difference and in the diffusive form due to temperature difference. Here, the internal energy has twofold natures: the mechanical energy transferred in the form of wave and thermal energy transferred in the diffusive form. The simplified Navier-Stokes equation combined with energy conservation equation is solved to show that for the normal condition the positive temperature quench induced pressure wave decays quickly due to thermal diffusion, while its propagation distance can be much longer because of small thermal diffusivity for a near-critical fluid. Thus, the efficient wave transport of internal energy is dominant in a near-critical fluid, which gives a good explanation of the critical speeding up. The local overheating of is due to the superposition of two internal energy waves. Besides, the internal energy wave offers a great potential in heat transfer enhancement since its equivalent thermal conductivity is much increased.