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Is one or two vapor condensers (cold trap) better in a freeze dryer?

1, Is one or two vapor condensers (cold trap) better in a freeze dryer?

The larger the vapor condenser, the larger the condensing capacity. The bigger the cooling capacity, the bigger the condensing capacity. That is to say, the bigger vapor condenser plus bigger cooling capacity, then the condensing capacity would be the biggest. If any one of them is small, the condensing capacity will also be small. Then, one vapor condenser is better, or two? The answer is anyone would be good, as long as the total condensing capacity is big. If two vapor condensers are very small, the total condensing capacity is not as good as one bigger vapor condenser, then the two vapor condensers are not good.

2. What are the disadvantages if the vapor condenser is too big?

Would it be better to increase both the size of vapor condenser and cooling capacity by 2 times, 3 times, even 5 times? Obviously not. The larger the vapor condenser, the more the power consumption, and the bigger the cooling capacity, the more the power consumption.

3. Is it better to have a vapor condenser at lower part of the chamber or at the back?

The lower position vapor condenser can make good use of space and make the machine more compact to save production costs, therefore, it is usually used in small and medium freeze dryers. The vapor condenser at the back of the chamber, there is a bigger distance from hot area to cold area, which separated the heat and cold well, so as to make condensing more efficiently. Due to the high cost, back position vapor condenser is usually used in large freeze dryers.

4. How about a vapor condenser that defrosts while freeze-drying production is on?

It will save 1 hour if defrosting is started at the same time when freeze-drying production is on. But, is it the best solution? Obviously not. Such a system has the following disadvantages:

1) Provide a system that freeze-drying production and defrosting happening at the same time. It requires the user to have a steam supply on site. However, there is usually no steam system supplied at the user site. If it requires to buy a steam system, the user's cost must be increased.

2) To provide such a system. The cheapest solution is to place vapor condenser under the same chamber. However, only two small vapor condensers with a long channel can be supplied in this solution, which is likely to result in ice accumulated at the front of the small vapor condenser and block the vapor passing through this area to the back of the condenser. It will reduce the working efficiency. If the back position vapor condenser is adopted, it is equivalent to providing two vapor condensers of the same size, which are used in independent chamber at the same time. This will greatly increase production costs.

3) In such a system, one vapor condenser is open and the other is sealed. After sealing, steam is injected for defrosting. It has very high requirements for sealing. If there is a leak, it will directly destroy the vacuum in the vacuum chamber, consequently freeze-drying production would be unable to continue, and the freeze-drying machine has to be stopped and wait for repairing. If it is a high-value product, this batch of products will become waste. It would increase risk to use the machine.

4) In such a system, the pressure of the open vapor condenser is -0.1Mpa, and the pressure of the sealed vapor condenser is 0.7Mpa. The difference between the two condensers is 0.8Mpa (8 bars). The freeze dryer was originally a non-pressure vessel (or negative pressure vessel). If such a system is adopted, it immediately becomes a high-pressure vessel. A simple structure immediately becomes a complex structure. A reliable device immediately becomes unreliable.

5) Which is better for defrosting? steam or hot water? Steam is a gaseous state, and hot water is a liquid state. As for solid ice, to remove the ice, it is very slow by spraying steam directly. On the contrary, using hot water produced by steam, first spray the ice with hot water like a shower, the sprayed water still has residual heat, and then use the spray water to soak the ice to make full use of residual heat. This method of defrosting is more efficient and safer than direct spraying steam.

6) In such a system, the vapor condenser is cold during running, but it would become hot during defrosting. During the defrosting process, steam is continuously consumed to maintain a higher temperature for defrosting. After defrosting, it needs to be cooled again. In this way, it would be switched continuously between the hot and cold which would waste a lot of energy.

A complex and expensive double vapor condensers system can save 1 hour of defrosting time, but it cannot improve the condensing capacity and efficiency. On the contrary, it wasted energy, reduced equipment reliability, increased the production cost, and brought risk in production. KEMOLO does not recommend such kind of unreliable parts to users, but KEMOLO can produce it if the customer insists on and likes it.  

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