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Subject: Renewable Energy Resources × End date: 2020 × Thesis Type: Ph.D ×
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    Optimization of roughness geometry parameters of roughened evacuated tube collector solar air heater
    (Punjab Agricultural University, Ludhiana, 2020) Singla, Mohit; Hans, Vishavjeet Singh
    A 3-Dimensional CFD analysis of an evacuated tube collector solar air heater roughened artificially with circular rib has been carried out to study the impact of operating and roughness parameters on Nusselt number and friction characteristics. The investigated roughness parameters include relative roughness pitch range of 6-12, relative roughness height range of 0.0429-0.0714 and Reynolds number range of 2500 to 8000. The turbulence model RNG k-ε with enhanced wall treatment for one periodic length was selected for carrying out the analysis. Maximum enhancement in Nusselt number and friction factor is found to be 1.88 and 2.89 times over smooth evacuated tube collector solar air heater, respectively. The maximum value of thermo-hydraulic performance factor is obtained to be 1.36 at relative roughness pitch of 10, relative roughness height of 0.0714 and Reynolds number value of 8000, which indicates the advantage of use of roughened evacuated tube collector over smooth evacuated tube collector in solar air heater. Using computational fluid analysis, statistical correlations for Nusselt number and friction factor have been developed as function of roughness geometry and operating parameters. Optimum values of roughness geometry parameters have been determined on the basis of thermal and effective efficiency. Under the similar operating conditions, results obtained for roughened evacuated tube collector solar air heater have been compared with smooth evacuated tube collector solar air heater experimentally. Experimental results shows good agreement with the results obtained from CFD analysis. The difference between CFD and experimental results vary from to 4.7 to 19.6% for roughened evacuated tube collector solar air heater.