freeze vacuum drying characteristics and technology
Freeze vacuum drying technology is a high technical content, involving a wide range of technical knowledge in the field of drying technology, it is also a complex drying equipment, more energy consumption, higher cost drying method.
However, due to the particularity of vacuum dryer: freeze dried food has the advantages of good water performance, frozen and glossy frozen and dried food, good product maintenance, less nutrient loss, light weight, easy to carry, easy to long-term preservation, and its quality is far better than other dry food, making it become the forefront of drying technology research and development.
After studying the freeze-drying process of Chinese ham and West German fruit ridge, the eutectic point, melting point and collapse temperature, freeze-drying curve and heat and mass transfer characteristics were obtained. Then the precooling temperature and the high limit temperature of sublimation interface were obtained. The influence of system pressure on the freeze-drying rate was discussed, and the method of adjusting pressure by circulation was determined.
Freeze vacuum drying technology is very important for judging the end point of sublimation, sublimation is the main dehydration stage; if sublimation is not enough, there will be too much residual ice, heating will lead to co melting, leading to freeze-drying failure. On the other hand, if the sublimation is too much, heating will increase the temperature sublimation of materials, which will lead to the disintegration and degradation of biological activities of materials. In addition, more time spent in sublimation reduces productivity.
It is very important to find suitable parameters for the whole freeze vacuum drying process, especially for the sublimation stage. The important parameters are the temperature of vacuum dryer, vacuum and sublimation duration. In order to obtain good parameters, the freeze vacuum drying program was analyzed, and the control system was set up according to the process of the freeze vacuum dryer.
In the sketch of the experimental device used to perform the freeze vacuum drying process, the equipment includes a dryer, a cold trap, three compressors, a vacuum pump, a Roots pump, a circulating pump, a heater, a heat exchanger and a server valve for logic control.