Vacuum frying principle: The boiling point of water under normal pressure is 100 ° C, so the frying temperature under normal pressure must be much higher than 100 ° C, in order to smoothly remove the moisture inside the ingredients, and the oil temperature is traditionally heated, such as The fire and electric wire are heated, and the oil temperature is difficult to control, so the oil temperature is easy to overheat, making the outer surface of the fried food slices too hot and scorched. The internal center area is still in a sandwiched state due to insufficient temperature, which is caused by uneven heating. "Outer Coke Linen" reduces the nutritional value of the ingredients and also causes many harmful substances to accumulate on the outer surface.
According to the Clausius-Clapeyron equation, it can be concluded that the boiling point of water increases due to the increase of pressure, and the decrease of the pressure decreases. The vacuum system is in a negative pressure state relative to atmospheric pressure. When the vacuum degree is 700mmHg, the boiling point of water is 40 ° C. At this time, the oil temperature is controlled to not exceed 100 ° C using frying oil as a heat transfer medium. Water can evaporate smoothly when heated. On the other hand, the extremely thin air in the vacuum means that the oxygen content is extremely low. Under low oxygen conditions, the ingredients in the system greatly reduce the dangers of high temperature oxidation, such as fatty acid failure, enzymatic browning, and oxidative deterioration. Keep the original color and flavor of the food.
VF250 vacuum frying machine is the most popular model which can get 200pa vacuum condition during frying ,so the frying time is much shorter than the other brand vacuum fryer.
If you want to know more information about the TINDO vauum frying machine.
Vacuum freeze-drying principle: Vacuum freeze-drying is a drying technology that uses the principle of sublimation to dehydrate materials. After the material is quickly frozen, it is heated in a vacuum (below the triple point pressure of water).
As with other drying methods, in order to maintain the continuous sublimation drying, two basic conditions must be met, namely the constant supply of heat and the constant elimination of steam generation. At the beginning, if the material temperature is relatively high, the latent heat required for sublimation can be taken from the sensible heat of the material itself. However, as the sublimation progresses, the temperature of the material will soon drop to a temperature that is in equilibrium with the steam partial pressure in the drying chamber. At this time, if there is no external heating, the sublimation drying will stop. In the case of external heating, if the steam generated by sublimation is not removed in time, the partial pressure of steam will increase, and the temperature of the material will also increase. When the freezing point of the material is reached, the ice crystals in the material will melt. Freeze-drying is not possible.
The process of supplying heat is a process of heat transfer, and the process of removing steam is a process of mass transfer. Therefore, the sublimation drying process is essentially a simultaneous process of heat and mass transfer. There is a driving force for any process that occurs in nature. The driving force for heat transfer in sublimation drying is the temperature difference between the heat source and the sublimation interface, and the driving force for mass transfer is between the sublimation interface and the steam trap (or cold trap). Partial pressure difference of steam. The larger the temperature difference, the faster the heat transfer rate; the larger the steam partial pressure difference, the faster the mass transfer (ie, steam removal) rate.
When lyophilizing, it is necessary to maintain the good quality of the product and achieve a faster drying rate. The latent heat required for sublimation must be transferred from the heat source to the surface of the material to be dried through an external heat transfer process, and then to the actual place where the sublimation of ice in the material occurs through the internal heat transfer process. The generated water vapor must reach the surface of the material through the internal mass transfer process, and then be transferred to the steam trap (cold trap) through the external mass transfer process. Any one process or several processes together can become the "bottleneck" of the drying process, which depends on the design of the freeze-drying equipment, the operating conditions, and the characteristics of the material being dried. Only by increasing the heat and mass transfer efficiency and increasing the surface area of the lyophilized material per unit volume can a faster drying rate be achieved.
Water has three phases: solid, liquid, and gaseous. According to the theory of phase equilibrium in thermodynamics, as the pressure decreases, the freezing point of water does not change much, but the boiling point becomes lower and lower, approaching the freezing point. When the pressure drops to a certain degree of vacuum, the boiling point and the freezing point of water coincide, and ice can be directly vaporized into a gas without a liquid state. This process is called sublimation. Vacuum freeze-drying of food is below the triple point of water, that is, under low temperature and low pressure conditions, the frozen water in the food is sublimated and removed.
