Grain Drier Project Report for task 2 dated July 1990 edited 1991, 1992. Follow up report

摘要

One of the original projects undertaken under the cooperative agreement No. DE-FC04-87AL42558 between the Massachusetts Photovoltaic Program and the United States Department of Energy was to design, build, and test a grain drier which utilized solar energy effectively. Different grains have different drying requirements, and the grain drier team chose to design the drier for rice because of the worldwide economic importance of this staple food and also because of the challenges that drying rice presents. Rice loses much of its market value if it is exposed to large temperature changes while drying; therefore, a solar rice drier must be designed so as to try to level the temperature variations which naturally arise from the intermittency of the solar source. The design team committed itself early in the project to a hybrid concept, where solar energy is utilized in two ways: it is captured 'thermally' in a rock-bed which acts at the same time as thermal storage and buffer, and it is converted 'directly' in a small photovoltaic panel which generates electricity to power a small fan to circulate air through the rock-bed and the grain during daylight hours. At night, natural convection drives the air flow. The design of most of the system is flexible, in that the drier can be built with materials available at the intended site, with non-specialized labor. The team has purposely avoided any 'high tech' solution which would increase the drier cost for third-world users. Therefore, the drier design does not incorporate selective surfaces or a vacuum, two common methods of enhancing solar thermal performance. The design does incorporate a small but relatively high value element, the PV panel and fan package. A major part of the group effort was devoted to data acquisition, to analyze the effects of different modifications on the drier performance. The results of the effort are summarized in this report.