A mathematical study of silica aerogel as a solid greenhouse medium over a thermal absorber.

Energy-saving, energy alternatives and carbon-neutral energy conversion technologies are the most famous layman-used phrases in the present times. Energy catastrophes are not misconceptions and the aftermaths of endless exploitation of energy are horrific. It all comes to solutions like using clean energy technology, promising energy-saving methods and improving the efficiency of the available energy conversion technology sourced by renewable energy. Finding a factual way of saving and utilisation of energy should be our major concern. New generation thermal insulation is apt for energy conversion and energy saving. Silica aerogel is one of those exquisite insulating non-crystalline solid air-like nano porous materials. A transparent, nano porous, low thermal conductivity, convection obstructing ultra-light and infrared absorbing material can be analogous to the greenhouse effect of the earth. So, it can be used as a solid greenhouse medium. The solar radiation can come across through the earth's envelope and greenhouse gases can trap the heat by absorbing longer wavelength of thermal emission from the earth's surface likewise the solid greenhouse medium should be transparent to the incoming solar radiation and could absorb the thermal emission from higher temperature solid greenhouse covered body. By using the help of kinetic theory and Debye's phonon model the solid thermal conductivity and by using Knudsen diffusion model the gas thermal conductivity of silica aerogel are studied. Later in this paper, the attenuation cross-section of the extinction of the photons is investigated. The non-dimensional number greenhouse selectivity is being proposed. The condition for maximum stagnation temperature and the optimised thickness of the silica aerogel for maximum receiver efficiency is discussed. By using the Rosseland diffusion model the effective radiative conductivity and the Roseland radiative heat flux are generated. [ABSTRACT FROM AUTHOR]