[01] Man Singh Azad, CSIR-Central Mechanical Engineering Research Institute, Durgapur, India. [02] Dipankar Chatterjee, CSIR-Central Mechanical Engineering Research Institute, Durgapur, India. [03] Apurba Layek, Department of Mechanical Engineering, National Institute of Technology, Durgapur, India. [04] Dilip Kumar Biswas, CSIR-Central Mechanical Engineering Research Institute, Durgapur, India.

In an objective to improve the thermo hydraulic performance of a solar air heater, a novel idea is proposed in this paper following a passive heat transfer enhancement technique. The technique uses the concept of providing artificial roughness on the absorber plate of the heater with diagonally cut cuboids. A numerical study using a computational fluid dynamics (CFD) method is performed to show the enhancement of the thermo hydraulic performance of the heater for the relative roughness pitch of 6 to 8 and cross section of cuboids from 8mm to 12mm with a constant relative roughness height of 0.0889. The Reynolds number is kept in the range of 5000 to 22500 with a constant heat flux of 1000 W/m² on the absorber plate. The standard k-ε turbulence model with enhanced wall treatment is used to handle the flow turbulence. The Nusselt number and the average friction factor are determined for different values of the relative roughness pitch and cross sectional areas of the roughness element. In order to determine the enhancement of heat transfer and increment in the friction factor, the Nusselt number and friction factor are compared with those of smooth duct under similar flow conditions. It is observed that the thermal performance of the heater is increased in presence of the chamfered square roughness elements.

Solar Air Heater, CFD, Artificial Roughness, Thermal Performance, Overall Enhancement Ratio

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