The pressure on the freeze dryer, how much is appropriate

The pressure on the freeze dryer is one of the important parameters that dryer users need to understand to be able to monitor, check and identify problems related to the vacuum system during the drying process. In this content, the author will analyze carefully so that readers can easily understand.

The image above is drying cordyceps mushrooms on a Freeze dryer from a customer in Lam Dong, specializing in the production of cordyceps mushrooms. With drying cordyceps mushrooms, you can dry a full tray because this product is light and difficult to stack neatly on the tray like sliced fruit products, dried meat….so the drying time usually lasts 30-35 hours or longer if drying a larger weight. When performing the freeze drying process, we need to understand the changes in the parameters on the display screen to know how the machine is operating, how dry the product is, when it will end or the dryer will is operating correctly or not. One of the important parameters we need to pay attention is the pressure on the Freeze dryer (sublimation dryer).

The sublimation drying pressure or pressure in the drying chamber is shown on the display screen as shown below. The Ap value will decrease continuously from the vacuum process is started, the lower this value the better. When the machine is operating properly, the Ap value is usually as low as 50pa, towards the end of the drying process the amount of steam remaining in the product is less and the Ap will be smaller.

The basic understanding is as follows: the lower the pressure, the lower the Ap value, the faster the product drying because the sublimation of ice occurs effectively, conversely, the higher the pressure, the higher the Ap value, the freeze drying efficiency is very poor. Therefore, when the Ap value reaches < 50pa, the machine operates well and appropriately, but when the Ap value is regularly > 50pa, the sublimation process will be poor. If Ap > 100pa, you need to check the vacuum pump. The vacuum oil may need to be changed if it has been dried continuously for 4-6 times.

To better understand the freeze drying process, you need to understand the principle of how freeze drying works. From the vacuum pump starts operating, the pressure in the drying chamber will gradually decrease, from 100,000pa until the pressure reaches 50pa, then the dryer will begin to increase the heat for the product so that the ice sublimates effectively.  After about 30 minutes since the vacuum pump operates, the AP pressure can decrease to 50pa, which is good operation. Initially, the amount of water in the product is a lot, the sublimation process of steam takes place very strong, causing AP to constantly maintain at the sublimation pressure threshold. After a relatively long period of 10-15 hours, the amount of water left in the product is not much, then the AP drops further, the lowest the AP gets at the end. When the product is completely dry, you can see that the AP only reports 3 – 15pa.

During the operation of the dryer, you may also need to pay attention to the indicator lights in the control box as shown above to know which parts are operating, which one runs first and which one runs last. The Compressor 1 light is the operating indicator light of the level 1 refrigeration system, the compressor 2 light is the level 2 refrigeration system, the CK Pump light is the operating indicator for the vacuum pump, DD Valve is indicator light for the solvent heat transfer system of the drying chamber, Valve BN is the cold transfer valve indicator light for the condenser chamber, Power light is the power indicator light.

So with the above basic analytical information, Readers have a better understanding of how the pressure on the freeze dryer will change during the product drying process. Customers who need further advice should contact Mactech Vietnam to be provided with appropriate information. Thank you for understanding the shared content.