Abstract

Large amounts of Chinese medicinal materials (CMMs) should be quickly dried during the harvest period because improper drying leads to a browning reaction, which deteriorates the medicinal value of CMMs. In this study, a bidirectional alternating hot air drying system was designed for thick-layered CMMs. The drying capacity could be greatly improved by increasing the thickness of the material layer. The time-weighted average temperature (TWAT) was defined to determine the appropriate reverse time of the airflow direction. The two-stage air supply could reduce the moisture content of the sample to a certain degree at a low temperature, and then realizing the rapid drying of the sample at a high temperature. When the moisture content of honeysuckle reduces to 60%, the browning reaction would be effectively inhibited. Moreover, the drying efficiency of the thick layer could be improved by reducing the frequency of changes in the direction of hot air. An equal TWAT could be obtained in each layer by adjusting the ratio of the upward to downward airflow supply duration. When the TWAT of the upper layer was equal to that of the lower layer, the drying uniformity improved. The difference between the moisture content of the middle layer of the sample and that of its upper and lower layers could serve as the standard for drying uniformity; the smaller the difference is, the better the drying uniformity will be. The bidirectional alternating hot-air drying method was applied to thick layer drying of Chinese herbal medicine and grain. On the one hand, it reduces the drying energy consumption, on the other hand, it helps to improve the uniformity of drying for Chinese herbal medicine. Additionally, this drying method can be applied for grain drying.

摘要

大量中药材在采收期间应迅速干燥，干燥不当会导致褐变反应，降低中药材的药用价值。在本研究中，为厚层坐标测量机设计了双向交替热风干燥系统。增加料层厚度可以大大提高干燥能力。定义时间加权平均温度 (TWAT) 以确定适当的气流方向反向时间。两级送风可以在一定程度上降低样品在低温下的水分含量，进而实现样品在高温下的快速干燥。当金银花的含水量降低到60%时，褐变反应将得到有效抑制。而且，通过减少热风方向变化的频率，可以提高厚层的干燥效率。通过调整向上和向下气流供应持续时间的比率，可以在每一层中获得相等的 TWAT。当上层的 TWAT 与下层的 TWAT 相等时，干燥均匀性得到改善。样品中层水分含量与其上下层水分含量的差异可作为干燥均匀性的标准；差值越小，干燥均匀性越好。双向交替热风干燥法应用于中草药和粮食的厚层干燥。一方面降低了干燥能耗，另一方面，有助于提高中草药干燥的均匀性。此外，这种干燥方法可用于谷物干燥。