Natural convection induced by the absorption of solar radiation: A review

Natural convection primarily driven by the absorption of thermal energy known as penetrative or thermo-convection is a topic that generates attention due to its importance in various physical systems. A very common example of where this process can be found in geophysical systems such as lakes, where radiation induced natural convective transport have been seen to influence water temperature, biological activity and water quality. The present paper reviews previous analytical, experimental and numerical studies reported in literature concerning natural convection driven by absorption of thermal radiation. Many of the reviewed studies were motivated by the interest of investigators to understand the physical processes in volumetric absorption thermal radiation in a fluid layer process and its associated energy transport. In this class of problems, temperature fields are generally described as non-linear and the associated fluid flow is considered rather complex owing to coupling between the direct absorption of radiation and fluid flow. Parametric investigations for the effect of various parameters of interest such as the Rayleigh numbers, Prandtl numbers, spectral nature of incident radiative flux, optical depth, fluid absorptivity, aspect ratio, albedo and boundary emissivity on natural convection have been investigated. The overall aim of the current review is to present a comprehensive review of the previous and recent approaches applied in the investigations of radiation induced natural convection in reservoirs. The paper also aims to contribute to improving the understanding of the physical processes, heat transfer and fluid dynamics associated with the thermal energy deposition into a fluid layer. The paper is also highlight the potential application of this concept to help keep solar energy capture costs to a minimum and inform efficient designs of energy systems based on the concept of direct absorption of thermal energy inside a fluid layer.