Design And Performance Investigation Of The Straightthrough Vacuum Tube Solar Heat Pump Combined Drying Device

As a major industrial energy consumer,drying industry accounts for about 12%of the total energy consumption of China’s national economy.Under the current severe energy crisis and environmental pollution,it is an irresistible trend to vigorously develop green and energy-saving drying technology.In the drying industry,developing new drying technology and system with low energy consumption,high efficiency and simple structure is the main research target of all countries at present.Solar thermal utilization technology and heat pump technology are both new energy saving technologies,and their combined application has attracted extensive attention in recent years.The combined drying technology of solar energy and air source heat pump is one of the methods for the combined application of solar energy heat pump.At the same time,it also helps to improve the performance of the heat pump,reduce the power consumption of the system,improve the stability and reliability of the drying system,shorten the drying time of materials,and improve the drying quality of materials.However,the current solar and heat pump drying systems are complicated in structure and high in cost.Based on the development and utilization of new energy and the actual drying requirements of agricultural and sideline products,this paper proposes a direct-through vacuum tube solar heat pump joint drying device,describes the design method and working principle of this joint drying device,and carries out experimental research on the system performance of this device under different modes.The specific work content and conclusion are as follows(1)Based on the existing drying research and theory,designed and built an experimental platform of a small direct-through vacuum tube solar heat pump combined drying device with chamber volume of 0.792 m~3.Through reasonable assumption,the material load of the combined drying system is calculated to be 16 kg.The effective heat collection area and air flow of the solar drying subsystem are calculated by calculating the heat consumption of the material in the drying process.The compressor power,the heat transfer area of evaporator and condenser in the heat pump drying subsystem are calculated and selected.(2)White radish was selected as drying material,drying experiments were carried out on the system under different drying modes,and the performance of solar drying subsystem,heat pump drying subsystem and solar heat pump combined drying system was analyzed.The experimental results show that compared with the system running in the separate heat pump drying mode at 55℃,the drying time of the system in the combined drying mode is shortened by 4 h and saved by 33.33%.The average heating coefficient increased by 6.19%,saving 2.68k W·h.From the perspective of drying time and system energy consumption,the system running combined drying mode has more advantages than the single heat pump drying mode.(3)Under the combined drying mode,the system carried out drying experiments on white radish under different slice thickness and drying temperature conditions,analyzed the influence of both on drying rate,and adopted Page drying model to fit the drying process of white radish under conditions of 50℃,60℃and 70℃.The results show that the temperature has more influence on the drying rate than the slice thickness.The fitting correlation coefficient and the determination coefficient of Page model were 0.996～0.998 and0.992～0.997,respectively,both above 0.99,and the reliability of curve fitting was high.Finally,Page model was modified and Page model fitting equation was obtained based on drying temperature T.