Design And Performance Testing Of Small-scale Solar Dryer For Candied Prunes

In this paper, a small scale solar drying equipment was designed based on the study of drying characteristics of preserved fruits of"Study of Drying Characteristics of Preserved Fruit".The test and applied research of the solar drying equipment was studied and the application of the results of different preserved fruits in the development of the solar drying equipment were analyzed compared to the traditional natural sun drying, hot air drying. The optimum conditions for drying preserved fruits under the solar drying equipment was to be find out and the advantages of the drying equipment was also to be find out. The actual operation of the solar equipment for plants was investigated.(1) The characteristics of the small scale solar drying devices is the reform of the V-plate solar collectors, making it not only transported hot air, but also stored heat in water. The device was comprised of heat collector, drying room, small fan, water storage tank, blast pipe, pumps, temperature and humidity sensors, small heat exchangers, control valves and air filter. And it composed of a complete set of system to collect solar energy and hot air drying system.Drying process during the daytime, the hot air was blew into the drying chamber from the bottom of the collector. Hot air discharged from the chamber was sent back into the chamber by the blower. When the drying chamber temperature was too high than desire, the automatic control valve opens to stored heat to the water tank by the heating collectors.Drying process during the nighttime, when the temperature sensor sensed that the internal temperature of the drying room was too low, the control valve inlet of the collector was interrupted, hot air blew from the pipe in the water tank into the drying chamber. The drying process was similar to the daytime drying process.When the second day started, the control valve inlet of the collector opened, collector plates began daytime drying process. The process was recycled to achieve continuous drying operation.During poor weather conditions, the water in the water tank was heated by the electric, the control valve inlet of the collector was interrupted, hot air blew from the pipe in the water tank into the drying chamber. The drying process was similar to the daytime drying process.The advantage of the solar drying equipment was continuous heating, low cost, simple structure, high drying and thermal efficiency.(2) Air convection of the solar drying equipment included natural convection and forced convection. And the drying characteristics of the sample were studied in the solar drying equipment. Drying time of the process of natural convection required to 14h to attain the drying requirement, while the process of forced convection drying time required 12h, far below the traditional the process of sun drying which required 50h. During drying process of the sample, the Deff value was 1.39×10-6m2/s under the natural convection, while the Deff value was 1.26×10-6 m2/s under the forced convection for the drying process of the sample. The Deff value of two drying processes could improve that the capacity of the water of the sample spread evenly.(3) Chemical quality and sensory characteristics of the plum samples were investigated under two drying methods of the solar equipment. The experiment results showed that with lower moisture content of the samples, the sugar content, acid content and the salt content of the sample increased at different layers of the drying room.For the color of the sample, the value of L* and the value of a increased caused by non-enzymatic browning. The peel and the pulp of the sample had the opposite trend during the drying process for the value of b. The b value of peel decreased while the b value of pulp increased. All the experiment value was according to the factory product quality requirements.Chemical quality and sensory characteristics of the plum samples were investigated in different layers of the solar drying equipment. Results show that appropriate adjustments to the location of materials were recommended during natural convection to improve the quality of the products. For the quality of products were relatively stable during forced convection drying process, it had no needs for adjusting the position to improve the quality of the sample.(4) The research of solar drying equipment under different drying methods showed that solar drying device has obvious advantages compared to natural sun drying, greenhouse drying, oven drying. The drying time of solar drying device was shortened up to 76%, while the total efficiency of the solar drying equipment was up to 63.4%.The drying process under solar drying equipment was environmental protection and energy conservation. The drying environment was with high temperature and low humidity. The product quality and drying efficiency was some kind of increasing while the costs decreased in varying degrees. The equipment could meet the drying requirement of varieties of agricultural products.(5) Samples were dried to target water content under different drying methods, the natural sun drying took about 50h, while greenhouse drying and oven drying took about 30h and 12h respectively. Drying time of solar drying equipment under natural convection and forced convection needed 14h and 12h respectively. The moisture content within 12h under forced convection drying, oven drying, natural convection drying, natural sun drying and greenhouse drying were reduced to 58.08%, 57.08%, 60.21%, 64.32%, 69.22% respectively. The water activity of dried product which was dried to the same water content under five different drying methods reached the storage requirements and the product quality met the requirements of the factory. In all, the solar drying device obtained the best drying effect.Fully aware of the analysis could be known that greenhouse drying, natural convection and forced convection drying were investigated by using the self-made solar drying equipment. The difference among solar drying equipment, traditional hot air drying and natural sun drying were also investigated. The test results provided theoretical basis for practical application of the self-made solar drying equipment to the factory production.