How to calculate the amount of desiccant?

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How to calculate the amount of desiccant?

How to calculate the amount of desiccant?

1.Related Concepts

How to calculate the amount of desiccant?First of all, let’s understand the relative humidity in the air. Under the standard air pressure, extract the water vapor in one cubic meter of air and weigh its weight to obtain the absolute humidity. It is expressed as the water content of one cubic meter of air (g/m3).
There is no specific amount for the calculation of the amount of desiccant, only a more appropriate amount. Of course, the more the dosage, the better, but the cost and placement space should be considered. Usually we calculate the amount of desiccant to customers through several aspects, such as: volume, desiccant type, product moisture content, packaging sealing degree, storage time, air humidity, air temperature, etc.

2.Desiccant Moisture Absorption

Polymer desiccant 200%~300%

Calcium chloride desiccant 100%~200%

Montmorillonite, minerals, activated carbon, molecular sieves are about 10%~30%

Silica gel, fiber, calcium oxide, potassium carbonate, magnesium chloride, phosphorus pentoxide, silicic acid, etc. are all at 30%~50%

Then the humidity of the air and the water content of the temperature:

With the above two data, we can start to calculate the amount of desiccant, we take calcium chloride desiccant as an example

For example: the humidity is 100%, the temperature is 30 degrees Celsius, the space is one cubic meter, then we can see that the water content in the air is 30 grams, and the low value of calcium chloride’s moisture absorption rate is 100%, we need 30 grams of desiccant to absorb This 30 grams of water, of course, is a theoretical value, and the moisture in the air will not be completely dry. So we usually reduce the amount.

Temperature/℃ Water vapor content per cubic meter of air at relative humidity (RH)/g
100% 90% 80% 70% 60% 50% 40% 30% 20%
65 160.3 144.3 128.2 112.2 96.2 80.2 64.1 48.1 32.1
55 103.9 93.5 83.1 72.7 62.3 52 41.6 31.2 20.8
45 65.2 58.7 52.2 45.6 39.1 32.6 26.1 19.6 13
35 39.2 35.3 31.4 27.4 23.5 19.6 15.7 11.8 7.8
25 22.8 20.5  18.2 16 13.7 11.4 9.1 6.8 4.6
15 17.7 11.4 10.2 8.9 7.6 6.4 5.1 3.8 2.5
5 6.8 6.1 5.4 4.8 4.1 3.4 2.7 2.0 1.4
-5 3.2 2.9 2.6 2.2 1.9 1.6 1.3 1.0 0.6

3.Factors to consider

We also need to take into account the air tightness of the package. There is no fully airtight package in time, so the amount of desiccant should be increased accordingly according to the air tightness.

If the storage time is too long, we should also increase the amount, and the amount needs to be calculated in combination with the packaging and sealing.

The water content of the product, here can refer to the amount of water that the product can evaporate. Correspondingly, the dosage needs to be increased.

4.Take an example

The temperature is 27°C, the humidity is 80%, an electronic product (the product has low water content), the packaging material PE composite film (relatively sealed), the shelf life is two years, and the product volume is 1 cubic meter. Then our dosage should be: 30 grams of calcium chloride desiccant.

The general understanding is that if the initial measured temperature is 25 degrees and the relative humidity is 60%, that is, the water content of the air in the table is 13.7 g. If you want to reduce the relative humidity to 40%, then you need to reduce the temperature to 18 degrees first. , the water content in the air is about 9 g at this time, then after placing the desiccant, after a certain period of time, more than 13.7-9=4.7 g of water can be absorbed, that is, when the temperature is 18 degrees, it is saturated at this time state; then the temperature needs to be raised to 25 degrees, (the relative humidity of this initial measurement is 60%, and the water content is 13.7 g), because after the temperature is lowered, the moisture in the air is only 9 g, so only the temperature rises after the temperature is lowered. In this case, the relative humidity will be reduced to 40%.