Abstract
Two-dimensional numerical analysis is conducted to determine the influence of upstream surface modifications of a novel clerestory shaped rib turbulator on thermal performance augmentation. The upstream surface of the rib is divided into two parts where the upper rib surface is always normal to the incoming flow and the lower rib surface, which is inclined to the flow. The elevation of the vertical surface is varied using non-dimensional approach length (h/e=0, 0.25, 0.5 and 0.75), and the inclination of the lower surface is varied using the rib angle (θ=15°, 45° and 90°). The relative roughness height and pitch of rib is fixed as 0.0421 and 12.5, respectively. RNG k-ϵ turbulence model is used in the analysis, and Reynolds number is varied from 8000-20000. The results reveal that the combined effect of flow impingement and the suppression of formation of recirculation zone leads to increased heat transfer. Lower values of non-dimensional approach length and rib angle provides a higher thermal enhancement factor. The highest increase in Nusselt number is found to be about 1.82 times that of the smooth duct at Re=8000 for h/e=0.25 and rib angle of 15°. The maximum thermal enhancement factor is found to have a range of 1.6-1.45 for an approach length of 0.25 and a rib angle of 15°.
Highlights
Energy is so vital for humans in the 21st century that it has become the fundamental necessity of modern life
The results reveal that the combined effect of flow impingement and the suppression of formation of recirculation zone leads to increased heat transfer
The simplest way of harnessing direct solar thermal energy is through a solar air heater (SAH), which transfers the heat energy received from the solar radiation using an absorber plate to the continuous stream of air flowing through a duct
Summary
Energy is so vital for humans in the 21st century that it has become the fundamental necessity of modern life. Increasing energy demand, depleting fossil fuels, and global warming issues have made it imperative to utilise renewable energy to cater for the requirement of this fundamental necessity. Though solar radiation is the most abundant source of thermal energy on earth, harnessing it for useful purposes has been really inadequate due to large collector area requirements, low conversion efficiency, and limited thermal energy storage capabilities. The simplest way of harnessing direct solar thermal energy is through a solar air heater (SAH), which transfers the heat energy received from the solar radiation using an absorber plate to the continuous stream of air flowing through a duct. The inherent limitation of SAH is the poor heat transfer properties of air which limits its performance. The suppression of convective mode of heat transfer by the presence of a laminar sublayer over the smooth heated surface further inhibits its efficacy
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