An experimental study on heat transfer characteristics of shelf heat exchangers, which are used in small-scale freeze dryers, is presented in this paper. The proposed heat exchanger consists of the multiport mini-channel flow paths, and a comparison with a conventional serpentine is carried out based on uniformity of the product temperature achieved. The experimental results indicate that the mini-channel shelf has better temperature uniformity than the latter. Skimmed milk is used as the test fluid. In the freezing and drying process, the product temperature variation is minimal in the mini-channel heat exchanger, with a variation of 12.5 % and 25%, respectively, and the heat transfer coefficient is found to be from 140 to 267 Wm⁻² K⁻¹. The moisture content in the product reduces to 50 % in 2 hours, and the drying rate is higher at 0.032 kg hr⁻¹ after 1 hour of the drying process. The redesign of the heat exchanger will be an essential tool to improve the performance with uniform temperature distribution on the product and to improve the product quality.

本文对小型冷冻干燥机中使用的架式热交换器的传热特性进行了实验研究。拟议的换热器由多端口微型通道流路组成，并根据获得的产品温度均匀性与常规蛇形管进行了比较。实验结果表明，微通道搁板比后者具有更好的温度均匀性。脱脂牛奶用作测试液。在冷冻和干燥过程中，微通道换热器中的产品温度变化最小，变化分别为12.5％和25％，并且传热系数为140至267 Wm ^-2 K ^-1。产品中的水分含量在2小时内降至50％，并且在干燥过程1小时后，干燥速率更高，为0.032 kg hr ^-1。换热器的重新设计将是必不可少的工具，可提高产品温度分布均匀的性能并提高产品质量。