No abstract

The main objective of this research was to create two different configurations of a flat-plate solar air heater, namely, Conventional-Case A and Modified-Case B, and develop a three-dimensional computational fluid dynamics (CFD) model using ANSYS R15.0. The purpose of the CFD model was to simulate the heat transfer behavior of the proposed solar air heaters under unsteady conditions. The RNG k-ε turbulence model was employed for this CFD study. The experiments were conducted on sunny days, under the same conditions as the Egyptian climate. The results of the experiments show that the simulated CFD model and the measured outlet airflow temperatures, relative humidity, and velocities of the two tested solar air heaters were compared. The developed model made very satisfactory predictions. Moreover, the deviations between the average CFD outlet air temperatures and the experimental results were 7% and 7.8% for Case B and Case A, respectively. The CFD-simulated average relative humidity was reduced by 31.6% when using Case B compared with Case A, and it was reduced by 28.8% when comparing the experimental data to Case B. Additionally, the average CFD thermal efficiencies obtained for Case B and Case A were 28.7% and 21.6%, respectively, while the average experimental thermal efficiencies for the cases were 26.4% and 18.2%, respectively. The proposed model can be used to design and simulate other solar air heater designs.

The purpose of the present study was to evaluate the Nusselt and Sherwood numbers during the drying of different products in a new conical type natural convection solar dryer. A comparison with the box-type collector-mode solar dryers was done. So, three types of solar dryers were designed and fabricated at Faculty of Engineering-Shebin El-Kom, Minoufiya University, Egypt. The dryers were constructed from materials that are readily available in the local area. The conical solar dryers with cone height to dryer diameter ratios ranged from 0.5 to 2 were tested. The performance of solar dryers was evaluated at the month of July 2009. The range of climatic conditions during the test period varied from 23 °C to 37 °C for ambient air temperatures and from 30 % to 55 % for the relative humidity during this test period. The products used in these experiments (grapes, apricots, onions and potatoes) were obtained from the local markets and were cleaned well from dirties before the drying process. The Nusselt and Sherwood numbers were calculated with the aid of both moisture evaporation measurements and Chilton-Colburn analogy. The results indicated that the highest Nusselt and Sherwood numbers occur for the conical solar dryer with height to dryer diameter ratio of unity. It is also observed that, the values of Nusselt and Sherwood numbers depend upon the drying mode and the product to be dried. In additions, the highest values of the Nusselt and Sherwood numbers were obtained for potato slices compared with the other products. The analogy between heat and mass transfer coefficients was also investigated.