| Summary: | 碩士 === 國立屏東科技大學 === 機械工程系 === 94 === This research studies the fluid and temperature fields in a close greenhouse under the influence of solar radiation mainly by the means of computational fluid dynamics (CFD). The influence of greenhouse effects due to solar radiation is further understood through simulation for the water wall in the greenhouse is either in operation or totally turned off. By using discrete ordinates (DO) radiation model, the ground temperature changes obtained through CFD approach was compared with the actual measurements. The three most critical input parameters for the DO radiation model including the blackbody emissivity, the absorption coefficient, and the diffusion fraction of material were individually adjusted so that the corresponding CFD results agreed with the measurements. To speed up the process to determine the sun blackbody emissivity, a photometer was used to provide a good initial guess. After that, a simulation was performed using these three parameters and its result was compared with the experimental data to confirm the accuracy of the simulation.
According to the simulation results, a water wall in operation in a greenhouse can effectively reduce the temperature in the greenhouse and therefore restrain the greenhouse effects from taking place in the greenhouse. However, the water wall in operation has very little influence on the airflow in the greenhouse. Regardless of the situations whether the water wall is in operation or not, there exists a flow circulation at the corner between the water wall and the greenhouse roof where heat accumulation takes place and leads to an increase in local temperature. For the case for which the water wall is not in operation, the maximum relative error between several ground temperature measurements in the greenhouse with their associated simulation results was 1.52 %. Furthermore, the minimum relative error was found to be 0.06 % at the velocity inlet on the water wall. Apparently, simulation results can predict the temperature distribution in the greenhouse and can be used as a guide to improve greenhouses without wasting a great deal of time and money.
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