| Nowadays, with the rapid progress of food science technology, cryobiology and cryomedicine, the applications of freeze-drying technology are changing more popular. The freeze-drying technology has many advantages compared with the other drying technologies, but it has some disadvantages too. It consumes much time and energy. Not only these, but when it puts use to the technology of cryobiology and cryomedicine, it needs high requirements for precooling, control temperature, process controlling etc. In order to solve these difficult problems, this study has invented a cryofreeze-dryer. This study is supported by the Shuguang project of Shanghai education department and educational development funds.The main tasks of this cryofreeze-dryer are to solve three questions: the first is the character of modulation; the second is the veracity of controlling temperature; the last is a wide temperature range. Based on these requirements of the food refrigeration principles and equipments, cryobiology and cryomedicine, the best methods for long storage of biology materials is to realize glassy. Realize glassy has a tarnal vital link with the cooling rates and terminal temperature of freezing. The veracity of controlling temperature is a good method to cope with antiglassy, too. During the precooling stage of the freeze-drying, the biology materials injury will be decreased lowest if they are realized glassy. And during the sublimation course, if controling the temperature accurately, the glassy water sublimating will has little harm to the biology materials. But at present, most freeze-dryers in the market can't realize shift cooling rates and has a narrow range of temperature. In this study, the cryofreeze-dryer use liquid nitrogen which produced by G-M liquid nitrogen machine as cold medium. Seal up the dewar, then, heat the liquid nitrogen, the internal pressure of the dewar will rise and compress the liquid nitrogen (cool nitrogen gas) flowed out. The internal pressure of the dewar is controlled by the electrical contact pressure gauge and Mitsubishi programmable logic controller. The different pressure corresponds with different flux. Liquid nitrogen (cool nitrogen gas) flowed through the circle pipe that emerged into the silicone oil pool and exchange heat with silicone oil. The shape of the heater is similar to a disc. The Mitsubishi programmable logic controller controlled the heater in the silicone oil pool. Consequently, the temperature is controlled, too. The tailor-made shelf that has a board and eight hollow pillars joins to the board. The hollow pillar can accommodate an ampoule bottle suitably. All of these can emerge into the silicone oil pool. This model can reach a goal of uniform heat transfer. The cooling medium flows into the silicone oil pool, then, flows into the cold trap during the precooling stage. During the sublimation course, change the direction of the cooling medium, make it flow into the cold trap firstly, then, flow into the silicone oil pool. Do it like this can have a big effect on saving energy. The vacuum system uses the sliding-vane rotary vacuum pump to draw the air. The pressure of the freeze-drying room can decrease to 13 Pa.After a long time design, facture and debugging, the capability of the cryofreeze-dryer is improved. These can be seen as below:1,Controlled cooling rates. By controlling the flux of the liquid nitrogen (cold nitrogen gas) can get different cooling rates. At present, the cooling rates range mediated by the cryofreeze-dryer is between -3.30℃and 0℃.2,The temperature is controlled more accurately and evenly. The Mitsubishi programmable logic controller of Japan using PID algorithm can control the temperature accurately; Using"silicone oil bath", the heat transfer is more evenly.3,A wide range of temperature. The liquid nitrogen (cool nitrogen gas) as cold medium can offer a lot of quantity of cold. But the lowest freezing point of silicone oil in the market is only at -106℃, so the temperature of the pillars and the shelf can reach about -100℃only.4,The data of the temperature and pressure can acquire in real-time. Adopting the module of Yanhua, ADAM-4018,ADAM-4520 and ADAM-4012A/D collect the data of temperature and pressure. They can connect with the serial interface of the computer and display on the computer. The data can auto save too.5,The convenient manipulation. The operation of the program can monitor on the computer. It allows the experimenter to change the set value on a keyboard during the operation course. Basing on the change of the temperature can make sure how the job is progressing. There has a state light will turn on when the heater is heating. When there is a fault, the computer will show the fault code. Basing upon the code can discovery the cause of the trouble, then, eliminate the fault. When there is a need to inject liquid nitrogen, a sounder and light alarm will remind the experimenter. In order to test the ability of freeze-drying of the vegetables and fruits that conducted by the cryofreeze-dryer, here, select apple as an example to freeze dry. And compare with the apple drying by the Tofflon freeze-dryer. The conclusions as below: 1,More lower temperature of the cold trap is beneficial to dehydration. The dehydration rate of the apple freeze-dried by the cryofreeze-dryer is bigger than the apple freeze-dried by the Tofflon freeze-dryer. The dehydration rate of the apple freeze-dried by the Tofflon freeze-dryer is 86.92%. The dehydration rate of the apple freeze-dried by the cryofreeze-dryer is 89.23%. 2,The conservation rate of ascorbic acid of the apple freeze-dried by the cryofreeze-dryer is inspected . The results show that the value is in accordance with the rule comes from the study of the apple freeze-drying conducted by the Tofflon freeze-dryer. The rule is"with different temperature of the first drying, the conservation rate of ascorbic acid have an obviously difference". When the temperatures of second drying are all set to 30℃, the temperature of the first drying was set to 0℃, the conservation rate of ascorbic acid is 57.69%; the temperature of the first drying was set to 10℃, the conservation rate of ascorbic acid is 32.00%; the temperature of the first drying was set to between 0℃and 10℃conducted by cryofreeze-dryer, the conservation rate of ascorbic acid is 44.20%.In order to test the ability of freeze-drying of biologic cells that conducted by the cryofreeze-dryer, here, do the initial experimental Study on freeze-drying of the nucleated cells of the whole human cord blood. And compare with the nucleated cells of the whole human cord blood drying by the Tofflon freeze-dryer. The conclusions as below:1,The cooling rate is bigger than the Tofflon freeze-dryer during the precooling stage. The cooling rate of the Tofflon freeze-dryer is 0.4～0.5K/min. The cooling rate of the cryofreeze-dryer can mediate. In this experiment, the cooling rate of the cryofreeze-dryer is 2.1K/min.2,The temperature of the silicone oil can keep in cryo-conditions and can be controlled accurately during the sublimation course. But it must ignore the influence of the time of injecting liquid nitrogen.3,The concentration of the lyoprotective solution can be decrease.4,Compare with the Tofflon freeze-dryer, the cells recovery rate under lower concentration of the lyoprotective solution relatively has improved. But the cells livability has be down. The whole human cord blood cells and the lyoprotective solution that contained 40%(w/w) polyvinylpyrrolidone, 20%(w/w) trehalose and 10%(w/w) mannitol freeze-dried by the Tofflon freeze-dryer, the recovery rate of rehydrated nucleated cells reaches 68.39% and the highest livability rate is 89.08% after being kept in a drawer at room temperature for 3 weeks. When using the cryofreeze-dryer, the recovery rate of rehydrated nucleated cells reaches 71.10% and the highest livability rate is 77.96%. The cells livability has be down maybe caused by the phenomenon of the secondary nucleation during the course of injecting liquid nitrogen.During the course of debugging and the experiments, find that the cryofreeze-dryer has some shortcomings that should be ameliorated. It includes:1,It consumes much time and energy. It uses liquid nitrogen (nitrogen gas) as cold medium. But one dewar of liquid nitrogen (30L) only can use 8 hours. Freeze-fry the apple needs 60L and freeze-dry the human cord blood needs 120L. So it consumes too much energy. Though the cooling rate improved can reduce the time of the precooling stage, but the sublimation course needs more time than the other freeze-dryer because the temperature is very low during the sublimation course. So this cryofreeze-dryer can't reach the goal that saving time and energy.2,The homogeneity of heat transfer need to improve. Because the freezing point of silicone oil is only at -106℃, closed to the exchange heat pipe, the silicone oil will be frozen ,then it deteriorates the heat transfer. Although adds a blender, it can't avoid the phenomenon of the silicone oil freeze up.3,Change the flow direction of the cold medium makes the operation become too complex. Not only this, during the precooling stage, the cold trap doesn't need the quantity of cold. Acting on this manner, it makes waste. On the whole, the diversity of the food, biologic materials and thermo–sensitive medicine etc. in nature determines they need many different freeze-drying technics. Using the cryofreeze-dryer to study the freeze-drying technics and ensure the freeze-dry parameters has a great significance. The good ability of the experimental cryofreeze-dryer will have a good usage prospect in the future. |
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