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20172
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Subject: Agricultural Engineering × Start date: 2010 × Type: Thesis × Thesis Type: M.Tech. ×
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    ThesisItemOpen Access
    Recovery of sensible heat from air leaving drying chamber of conventional forced circulation solar dryer
    (Punjab Agricultural University, Ludhiana, 2017) Simranjeet Singh; Sukhmeet Singh
    Air leaving drying chamber of conventional solar crop dryers is at higher temperature than ambient which leads to wastage of energy. Therefore it is proposed to use thermal storage at exit of the drying chamber of solar dryers to extract heat from leaving air, which can later on be utilised. In this research work, the proposed method is tested for conventional forced circulation solar dryer. The setup consists of multi-tray drying chamber, air heating unit, electric air blower and sensible heat storage unit. Crushed rocks were used for sensible heat storage. Electric heaters were used instead of solar air heaters to have control over drying air temperature. Heat recovery was tested for extending drying operation in two scenerios, namely, with thermal storage only and thermal storage along with auxiliary heating. Evaluation was done at constant inlet air temperatures of 55, 60, 65 and 70oC and fixed air mass flow rate of 0.025 kg/s. 5.850 kg fresh carrots were loaded in each experiment. It was found that thermal storage at exit of drying chamber is beneficial in both cases. During testing, 1.08-9.41% energy savings were achieved along with extended drying operation. Further, heat recovery supplemented by auxiliary heating proved to be more effective. For drying at 60oC, recovered energy was 1.53 MJ and 1.7 MJ with and without auxiliary heating. Computer model has also been developed to predict drying rate for the same setup using air from solar air heater.
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    Effect of angle of attack on heat transfer and friction characteristics of inclined rib roughened solar air heater duct
    (Punjab Agricultural University, Ludhiana, 2017) Gurpreet Singh; Hans, V.S.
    Thermal performance of solar air heaters is very low due to formation of laminar sublayer over the heat transferring surface. By use of artificial roughness in the form of wires, thermal performance of solar air heaters can be increased considerably. This study represents an experimental investigation carried out to examine the effect of angle of attack on heat transfer and friction characteristics of inclined rib roughened solar air heater duct. The various parameters related to roughness geometry and flow were Reynolds number in the range of 2000 to 16000, relative roughness height (e/D) in the range of 0.02 to 0.043, relative roughness pitch (P/e) in the range to 6 to 14 and angle of attack (α) in the range of 45o to 75o: The results obtained from this experimental investigation suggested that ribs inclined at 67o, having relative roughness pitch and relative roughness height value of 10 and 0.043 respectively outperformed the other rib configuration in terms of thermal and thermo-hydraulic performance. Correlations for Nusselt number and friction factor in terms of roughness geometry parameters and flow parameters have also been developed from experimental data.