| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 102 === In the present work a bench-scale indirect solar dryer was designed, fabricated and tested to study the transport phenomena in the drying of a porous medium initially soaked with water. In the first section, a resistive heater was used to provide a stable heating of the drying air. Natural and forced convection experiments were conducted on solar dryers of inlet tubes with different sizes (Case A: i.d./o.d. 6mm/8mm, Case B: i.d./o.d. 16mm/20mm) to investigate the effects of flow conditions and the drying air inlet design on the drying performance. Experiments showed that the drying air flow rate has significant effects to the drying rate in Case A, whereas the effects are small in Case B. Moreover, under same air flow rate, the drying rate in Case B is much faster than that in Case A even though the inlet air temperature is lower in the later case. In the second section, a solar lamp was utilized to provide a simulated solar light to heat the drying air to a remodeled solar dryer (Case C). In an attempt to improve the dryer, a circulation cannel was designed and fabricated to recirculate the hot air at the outlet of the dryer to its inlet (Case D). Nevertheless, experimental results showed that the drying rate is decreased with using the circulation channel (Case D) due to higher humidity of the inlet drying air. Finally, a finite element method code was used to analyze the simultaneous heat and mass transport phenomena in the solar dryer. A semi-empirical model was modified and elaborated to obtain the mass diffusivity (D) and the mass transfer coefficient (h_m) of moisture from experimental results. Results showed that the analysis developed in the present study can be applied for dryer design.
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