Numerical Investigation of Thermal Performance Factor in Dimpled-Solar Air Heater (SAH)

AbstractA novel solar air heater design with dimples in a rectangular channel with a 7:1 aspect ratio was examined mathematically by ANSYS FLUENT 14.0. Four different cases of dimples configuration namely A(a spherical dimple), B(hemispherical symmetric protrusion is made in the center), C (secondary protrusion is present at an angle of 26.5o) and D (secondary protrusion is made tangent to the upstream) were simulated over the Reynolds number range of 10,000 to 30,000. CFD simultaions were performed for the inlet mass flow rate corresponding to the Reynolds number value of 10,000 and constant wall temperature of 320 K. After turbulnec model selction and grid independence study, the numerical results are validated with the experimental data for case A and 10,000 Reynolds numbers within the error band of ±15%. To determine the most efficient design, the Nusselt number, friction factor, and thermal performance factor were used to compare the cases of dimples with protrusions. Moreover, parametric study was performed to study the effect of Reynolds number on performance parameters. By adding a secondary protrusion inside the dimple, an improvement in heat transfer and reduced flow recirculation was observed. The maximum thermal performance factor for the B, C, and D cases was found at Reynolds numbers of 10,000, 15,000, and between 20,000 and 30,000, respectively. Over the spectrum of Reynolds numbers, case D exhibits the most promising design overall with an increase of 37.5% in thermal performance factor. Over a wide range of Reynolds numbers, these design scenarios demonstrate an encouraging improvement in thermal performance factor.Keywords: DimpleThermal Performance factorHeat transfer enhancementNumerical studyfriction factor ratioSolar Air HeaterAugmentation and ProtrusionDisclaimerAs a service to authors and researchers we are providing this version of an accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proofs will be undertaken on this manuscript before final publication of the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to these versions also. AcknowledgmentsWe are truly thankful to the Advanced Computational Research Engineering Lab (ACRE) at Department of Nuclear Engineering, PIEAS, Nilore, Islamabad.Nomenclature and AbbreviationsTableDisplay TableGreek SymbolsTableDisplay TableDimensionless NumbersTableDisplay TableSubscripts/ SuperscriptsTableDisplay Table