Investigation of the effect of the gas permeation induced by pressure gradient on transient heat transfer in silica aerogel

A fractal permeability model considering both the tortuous gas transport path and the gas slippage effect for nanoporous silica aerogel is developed. The fractal model is verified by experimental results and existing models. Then, a one-dimensional macro model, which combines the influence of heat conduction, thermal radiation and gas permeation, is developed to investigate the influence of gas permeation induced by pressure gradient on transient heat transfer within bulk silica aerogel with the acquired gas permeability by the present model. It is found that gas transport within silica aerogel exerts important effect on the temperature response performance of bulk silica aerogel, which is mainly reflected on changing the pressure distribution and inducing energy migration within the bulk material. For silica aerogel, energy migration has remarkable effect on unsteady heat transfer process when the gas permeability reaches the order of 10(-14) m(2). The dynamic temperature response of the cold wall will be strengthened when the directions of gas flow and heat transfer are the same, and vice versa. (C) 2016 Elsevier Ltd. All rights reserved.