Flow friction and thermal performance of dimple imprinted based solar air-heater: A numerical study

Abstract

The thermal and flow characteristics of dimple imprinted absorber plate solar air-heater (SAH) are investigated numerically in this study. A forced-convection heat transfer mechanism is adopted to speed up the heat transfer rate between the air and the heated surfaces of the SAH. The three-dimensional simulations were run with ANSYS FLUENT (V-15) CFD code and the SST k-ω turbulence model, which closes the turbulence equation. By altering design variables such as pitch ratio (transverse pitch to longitudinal pitch) and Reynolds number, the thermal performance of staggered and inline dimple imprinted absorber plate, in SAH has been evaluated. Five alternative pitch ratios and Reynolds numbers ranging from 2500 to 12500 are used for each staggered and inline dimple imprinted absorber plate arrangement. A constant input heat flux of 1000 W/m2 to the absorber plate is used in the numerical analysis. The impact of pitch ratios and Reynolds numbers on a dimensionless number such as Nusselt number (Nu), friction factor (f), Nusselt number ratio (Nu/Nu 0), friction factor ratio (f/f 0) and thermo-hydraulic performance parameter (THPP) is investigated and addressed. The dimpled surface's heat transfer rates are measured and compared to the smooth surface’s result. When compared to the smooth duct; the dimpled imprinted absorber plate SAH demonstrates a considerable improvement in heat transfer and friction characteristics. At dimple pitches of S T/D = 2.5 and S L/D = 2, the heat transfer enhancement ratio of dimpled surfaces is around 1.597 times higher than the smooth surface in the staggered arrangement. At dimple pitches of S T/D = 2 and S L/D = 2.25, the heat transfer enhancement ratio for dimple surface is roughly 1.660 times better than the smooth surface in an inline arrangement.