【摘要】 针对直接式太阳能干燥系统在实际应用过程中会存在干燥物料表面温度过高导致品质低下的问题,该文自行设计搭建一种直接式太阳能干燥系统,以红薯为干燥对象对该系统进行试验分析;同时在综合考虑室外气象参数、干燥物料热物性、搭建系统特性的基础上,基于能量平衡原理建立系统热性能动态数学模型,利用MATLAB2014a进行编程求解出干燥物料表面温度,将干燥物料表面温度的试验值与模拟值进行相关性分析,并对设计搭建的直接式太阳能干燥系统的应用进行分析。研究结果表明:物料表面温度的试验值与模拟值之间的决定系数为0.98,均方根误差为1,说明建立的系统动态热性能数学模型能够较准确的预测室内干燥物料表面温度,对防止物料表面温度过高导致物料干燥品质下降具有重要意义;直接式太阳能干燥系统的平均干燥速率比开放式太阳能干燥系统高7.7 g/h,干燥系统所获得的总热能量为3.92 k W?h,其平均太阳能热利用效率为21.23%。更多还原

【Abstract】 The direct solar drying system has the advantages of simple structure, cheapness, and protecting the dried materials from being damaged by dust, rain, dew, and so on; however, there are some disadvantages such as overheating of the dried materials surface, poor quality of the dried material and drying ability limited. In order to solve problems of drying product overheating and drying process uncontrollable in direct solar dryer, a direct solar drying system was designed and built to test system performance by using sweet potatoes as drying material. The system was mainly composed of air inlet, air outlet, dry material tray, transparent glass cover and stainless steel plate. The frame of drying chamber was made of aluminum alloy, and the black endothermic material was uniformly applied to the inner surface of the stainless steel plate of the drying chamber.The tilt angle of the roof glass of the drying chamber was 26.7°. The length, width and height of the drying chamber were1 000, 800 and 800 mm, respectively. The insulation material of the drying chamber was made of 20 mm thick polyurethane insulation cotton to prevent the heat loss, and the transparent surface of drying chamber adopted ordinary glass with transmittance of 90%. The dry material used in this experiment was fresh sweet potato, purchased in Jingdong Mall, with the origin of Yuxi, Yunnan. Before the experiment, the sweet potatoes were cut into pieces of uniform size and thickness, and divided into 2 parts with the same mass by the balance; one part was used for the experimental group of direct solar drying and the other part was used for the comparison group of open sun drying. The experimental test was conducted on May 7, 2017,from 8:30 to 17:00. The initial mass of dry materials in the experimental group and the control group was 240 g. In addition,dynamic mathematical models of thermal performance of system were built and calculated with the help of MATLAB 2014 a software, outdoor meteorological parameters, the characteristics of drying materials and building systems were given, and the correlations between experimental value and simulation value were analyzed. The results showed that the transmittance of drying chamber ranged from 51.7% to 89.6%. The highest air temperature in the drying chamber appeared half an hour later than the peak of outdoor solar radiation intensity. It indicated that the drying chamber had certain delay and resistance to the change of outdoor environment interference. The average drying rate of the direct solar drying system was 7.7 g/h higher than that of the open solar drying system. Time period with drying air temperature ranging from 50 to 70 ℃ accounted for 80% of the total drying time, which showed that the direct solar drying system can provide the most suitable drying temperature for most dry materials. The total thermal energy obtained by the drying system was 3.92 kW凮h, and the average solar heat utilization efficiency was 21.23%; the correlation coefficient of the experimental value and the simulated value was 0.98, and the root mean square error was 1, which proves that the dynamic model of dynamic thermal performance can accurately predict the surface temperature of the dry materials in the drying chamber.更多还原