CO₂ Cold Trap Microwave Vacuum Drying Equipment Design And Experimental Research

Vegetables play an important role in people's daily diet.It is an important agricultural product second only to grain,and it not only provides coarse fiber,but also provides vitamins,minerals,trace elements and other nutrients.Because fresh vegetables had higher moisture content(more than 90%),Among them,free water accounts for the majority,and fresh vegetables are large and brittle,which bring difficulties to storage and transportation,resulting in huge losses.Therefore,it is an inevitable trend for the development of vegetable raw materials to be processed by industrialization,and to maintain its nutrition and flavor,and to produce the deep processed vegetable products which are convenient for storage and transportation and long shelf life,so that the value added of cheap vegetables and the creation of high added value are the inevitable trend of development,Vegetable drying is a common and effective processing method.There are many kinds of drying methods for vegetables,such as normal pressure hot air drying,microwave vacuum drying,vacuum freeze drying,far infrared drying technology,osmotic drying technology,etc.Each drying way has its own characteristics and advantages,and plays a unique role in the drying of some special vegetables.The CO2 cold trap microwave vacuum drying equipment designed in this paper combines the advantages and characteristics of microwave vacuum drying and vacuum freeze-drying technology.the liquid CO2 refrigeration system is introduced to improve the drying efficiency and quality of the equipment further.This paper comes from the sub project of the 12th Five-Year National Science and technology plan for rural areas,"CO2 cold trap vegetable microwave vacuum drying equipment research and demonstration".The project number is:2015BAD19B02-02,The beginning and stop years of the subject are as follows:April 1,2015-March 31,2018.Based on the existing microwave vacuum drying equipment,the improved design is made in this paper,by adding the spray quick-freezing device,the time of material freezing is controlled within 0??5? within 30s to increase and refine the quantity and shape of the internal ice crystallization in the material cells,and change the defects of the traditional freeze-drying machine which can only be heated and dry,but can not be integrated with freezing and drying,so that the whole drying process is made.more conducive to operation;With the addition of the CO2 cold trap,the vacuum degree and the vacuum rate of the drying room are improved,and the condensation rate of water vapor is accelerated after the sublimation of the freeze-drying,which is beneficial to the discharge and the quality after drying.The whole equipment has realized the combined operation of microwave vacuum and freeze drying,which improves the drying efficiency and quality of the material,reduces the energy consumption in the drying process,and makes the drying equipment develop further in the direction of small volume,light quality and compact structure.In this paper,white radish and garlic as test samples,experiments were carried out through the design of the prototype drying,the influence of the cold well device on the vacuum pumping is mainly studied.The experiment of microwave vacuum drying and rehydration of CO2 cold trap under different spray flow rate and microwave power is carried out,and the comparison and analysis of the two drying methods are also carried out.The test shows that after the improvement,the color,flavor,texture and taste of the dried samples are better than those obtained by microwave vacuum drying,and the color and aroma of the raw materials are preserved to a greater extent.