CO_(2)冷阱微波真空干燥装置设计与试验

Design and Experiment of Microwave Vacuum Drying Equipment with CO_(2) Cold Trap

为优化微波真空冷冻干燥工艺,基于微波真空冷冻干燥原理研制了CO_(2)冷阱微波真空干燥装置,并介绍了该装置的主要结构、工作原理和工作流程。创新采用液态CO_(2)作为制冷媒,通过合理布局实现CO_(2)的循环利用。采用喷淋冷冻技术,从液态CO_(2)喷淋预冷冻原理出发,设计了喷淋装置结构,并匹配计算了转盘转速,旨在提高物料预冷冻效果。设计了翅片式冷阱管,根据翅片式冷阱管传热系数公式确定了冷阱管的具体规格尺寸;分析了冷阱内部有相变的对流换热过程,通过计算判断冷阱室内气体处于滑流区。由此得到冷阱室内对流换热强烈程度评价指标Nu≈4.3,换热效率较好。以白萝卜为例进行了喷淋流量与微波功率对干燥速率的影响试验,结果表明:在不对物料产生冻伤的情况下,喷淋流量越大,物料预冻结效果越好;在一定范围内,物料干燥速率与喷淋流量和微波功率呈正相关,且均呈现先快后慢的趋势。

In order to optimize the technology of microwave vacuum freeze drying,a microwave vacuum dryer with CO_(2)cold trap was developed based on the principle of microwave vacuum freeze-drying,and the main structure,working principle and working process of the device were introduced.It innovatively used liquid CO_(2)as a refrigerant,and achieved the recycling of CO_(2)through a reasonable layout.Based on the principle liquid CO_(2)spray pre-freezing,the structure of spray device was designed,and the rotating speed of rotary table was calculated to improve the effect of material pre-freezing.The finned cold trap tube was designed,and according to the formula of heat transfer coefficient of fin type cold well tube,the specific size of the cold well tube was determined.The convective heat transfer process with phase change in the cold well was analyzed,the gas in the cold well was located in the slipstream zone by calculation,and the evaluation index of convective heat transfer intensity in the cold well was Nu≈4.3,indicating that the heat transfer efficiency was good.Taking white radish as an example,the effect of spray flow and microwave power on drying rate was tested.The results showed that in case of no frostbite on materials,the larger the spray flow was,the better the material pre-freezing effect was;in a certain range,the material drying rate had a positive correlation with the spray flow and microwave power,and both show a trend of fast first and then slow.