应用化学专业英语两篇摘要.doc

Major problems of the arid region are transportation of agricultural products and losses due to spoilage of the products, especially in summer. This work presents the performance of a solar drying system consisting of an air heater and a dryer chamber connected to a greenhouse. The drying system is designed to dry a variety of agricultural products. The effect of air mass flow rate on the drying process is studied. Composite pebbles, which are constructed from cement and sand, are used to store energy for night operation. The pebbles, which are placed are placed at the bottom of the drying chamber and are charged during the drying process itself. A separate test is done using a simulator, a packed bed storage unit, to find the thermal characteristics of the pebbles during charging and discharging modes with time. Accordingly , the packed bed is analyzed using a heat transfer model with finite difference technique described before and during the charging and discharging processes. Graphs are presented that depict the thermal characteristics and performance of the pebble beds and the drying patterns of different agricultural products. The results show that the amount of energy stored in the pebbles depends on the air mass flow rate, the inlet air temperature, and the properties of the storage materials. The composite pebbles can be used efficiently as storing media.

The long-term performance of various systems was determined and the economic aspects of solar hot water production were investigated in this work. The effect of the collector inclination angle, collector area and storage volume was examined for all systems, and various climatic conditions and their payback period was calculated. It was found that the collector inclination angle does not have a significant effect on system performance. Large collector areas have a diminishing effect on the system’s overall efficiency. The increase in storage volume has a detrimental effect for small daily load volumes , but a beneficial one when there is a large daily consumption. Solar energy was found to be truly competitive when the conventional fuel being substituted is electricity, and it should not replace diesel oil on pure economic grounds. Large daily load volumes and large collector areas are in general associated with shorter payback periods. Overall , the systems are oversized and are economically suitable for large daily not water load volumes.