The quantity of desiccant is the most important point in the application of desiccant.If the desiccant used less, can not effectively moisture-proof effect, the product will be damaged by moisture;If the desiccant used too much, it will produce waste, not economic.

Target humidity setting in product packaging

Before calculating the amount of desiccant, we must set a target humidity, that is, the maximum humidity allowed in the package.Generally speaking, ordinary products can be safely stored in a humidity environment of less than 50%, while many products require lower humidity, such as 20%.The lower the target humidity, the more desiccant is needed to keep the package dry.

Block the Water vapor transmission rate of package.

Water vapor transmission rate  (g/m2 / day) refers to the gram weight of water vapor permeated through the test material after 24 hours (one day) of test time in a static environment with stable temperature and humidity.

Blocking packaging of water vapor transmittance have a big affect on desiccant dosage.  the same volume of  the packaging require save the same time, if you use a good barrier property materials such as aluminum foil, the desiccant can use less, if you use a very poor barrier property of thin materials such as PE bag, you will need to put a lot of desiccant to have the same effect.

Therefore, we suggest to use barrier materials with good barrier property (i.e. low water vapor transmittance) to package products when conditions permit.In addition, the sealing of the blocking package must be tight, and there must be no air holes, any small leakage air holes will make the desiccant effect greatly reduced.

The water vapor transmittance of the same barrier material is different under different temperature and humidity conditions.The higher the temperature and humidity, the higher the water vapor transmittance.But when we calculate it, we can only use an average value. DIN55474 suggest us use the value of water vapor transmittance at 23℃,85%RH.It will make the calculation more accurate if the value is combined with the actual situation.

Three sources of moisture in packaging

In a particular package, there are three sources of moisture, and the desiccant's mission is to absorb these three parts of moisture and control the humidity in the package below the target humidity.

(1) Initial moisture contained in the air inside the package during product packaging.For example, the volume of product packaging is 1 cubic meter, the initial temperature and humidity of packaging is 23℃,  85% relative humidity, the air contains 17.47 grams of water.

(2) The moisture contained in the packaging auxiliary materials in the packaging of products will gradually volatilize out in the process of storage and transportation.Wood, for example, usually has a moisture content of 15-30%.

(3) In the process of storage and transportation, water vapor penetrates into product packaging by blocking packaging.For example, the PE bag with water vapor permeability of 2 g/m2 / day has an area of 6 m2. After 90 days, 1080 g of water will permeate into the package


Equation and Parameter of Desiccant Quantity Calculation
n = 1/a * (V*b + m*c + A*e*WDD*t)

n: Amount of desiccant in UNITS

a: The amount of water in grams, that a UNIT of desiccant will absorb at target humidity.

V: Inner volume of package (m3)
b:  Water content of air in  initial packaging at humiture.

m:  The weight of moisture contained in the packaging auxiliary materials (kg)

c:  The Moisture content rate of packaging auxiliary materials

A:   surface area of barrier packaging

e:  Correction coefficient under the condition of target humidity

WDD: Water vapor transmission rate of barrier packaging

Time of storage and transportation in day.