基于涡流管制冷效应的怀山药常压冷冻干燥机理及干燥行为控制机制

The results of the former research showed that about 1/3 energy consumption can be saved for AFD (atmospheric freeze drying) due to removing the vacuum chamber and other ancillary equipments, and the drying quality for AFD was similar to vacuum freeze drying. However, the material sublimation interface temperature and water vapor partial pressure were unstable under the atmospheric condition, then ice crystals melting easily occured. Chinese yam is a traditional plant for food and medication, and rich in many active nutrition components. However, such quality deteriorations of products as tissue collapse, discoloration and activity decrease etc. often take place in the traditional Chinese yam drying processing.The project will take Chinese yam as the test material, by using vortex tube refrigeration effect, establish the mathematical distribution model of air flow in vortex tube cooling field; study Chinese yam pore forming mechanism under the atmospheric pressure; and investigate the control mechanism of sublimation processing based on vapor partial pressure; elucidate the decline mechanism of the function factor in Chinese yam during the AFD processing. The aim of this research is to develop an AFD process as a new promising alternative cost-effective Chinese yam dehydration method, and explore the effective control mechanism and drying behavior of AFD procudure. On the other hand, this sudty would supply a new way for low energy consumption and high efficient green freeze drying technology.

前期研究表明，常压冷冻干燥(AFD)因其无需配备真空装置，可节约近1/3能耗，而干燥质量与真空冻干相似。不足之处是在常压状态下物料升华界面温度及水蒸汽分压不稳定，导致冰晶熔化严重。怀山药富含营养因子，是我国传统药食同源食物，但在其常规干燥过程中极易出现组织塌陷、变色及活性降低等质量问题。本项目拟以怀山药为试验材料，采用涡流管高效制冷法，建立涡流管冷端排气场气流分布模型；研究常压下怀山药孔道形成机理，阐明基于水蒸汽分压的升华过程控制机制；揭示怀山药在AFD处理过程中功能因子衰退机制。本研究旨在提出怀山药AFD脱水新方法，探索怀山药干燥行为及质热传递的有效控制机制，同时为低耗、高效、绿色冻干技术提供新的解决途径。

怀山药位居四大怀药之首，是重要的食药同源食物，也是河南省中药材重要资源。目前，用于怀山药处理的干燥方法较多，如热风干燥、微波干燥、热泵干燥、常规冷冻干燥等等。无论是单一干燥处理，还是组合干燥法，干燥后期均出现了不同程度的组织塌陷、变色及活性降低等质量问题，而且在干燥周期及成本方面也不经济。涡流管制冷技术自发明以来，得到了飞速的发展。因其没有运动部件，运行十分可靠，简单而廉价。基于涡流管制冷效应的怀山药AFD处理是一种将可靠高效的冷气流场应用于常压节能干燥过程。AFD过程和常规真空冻干具有极大区别，由于对流现象的存在，其干燥速率会更高，干燥过程大幅度缩短。项目经济成本得以提升。. 项目不仅完成了对试验物料怀山药的AFD试验及数值模拟研究，还进行了多孔介质物料AFD传质传热的理论分析、多孔介质物料AFD传质传热的数值模拟以及多孔介质物料AFD传质传热等方面的实验研究。同时试制了常压冷冻干燥设备，并进行了系统和结构的优化设计，并对怀山药粉的流变特性、抗氧化特性及其他理化性质进行了测定，并通过变异系数权重法计算怀山药全粉的物理化学指标权重，并客观评价怀山药粉的品质。此外，项目通过构建传热传质干燥控制模型，能够准确预测并控制怀山药等多孔介质物料的AFD干燥行为。项目研究以期对附加值较高的多孔介质物料的干燥处理提供理论依据和技术支撑。