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Vending machines can be seen everywhere in daily life. They are widely used in various retail scenes such as drinks, food, and blind box gifts. Many people are using vending machines, but few people know the underlying structural knowledge. Today, in this article, let's take a look: Why should vending machines be equipped with steam barriers?

Because of the different temperatures on both sides of the vending machine enclosure structure, it is easy to move the wet airflow with the heat transfer. This movement of moisture is called water vapor infiltration. We know that it is difficult to block water vapor infiltration, even more difficult than blocking heat flow. Generally speaking, the temperature difference between the two sides of the envelope will cause the partial pressure difference of water vapor, thus forming the power of water vapor infiltration.

For example, if the outside of a vending machine is 30℃, the partial pressure of water vapor is 19.09mm Hg when the relative humidity is 60%, and the low temperature side is 0℃, even when the relative humidity is 100%, the partial pressure of water vapor is only 4.58mm pump column. In this way, the partial pressure of water vapor on both sides of the envelope is (19.09mm Hg -4.58mm Hg) 14.51mm Hg, which is a considerable driving force compared with an ordinary fan with a head of 30-60mm water column. This driving force can push water vapor into the vending machine through the cracks of tiny air holes in the enclosure structure, which is equivalent to pushing wet air into the enclosure structure and insulation layer, which has a serious impact on the insulation of the vending machine body.

Because the thermal conductivity of ice is 2.0W, which is about 100 times larger than that of polyurethane (0.02W), the thermal insulation layer will be destroyed in severe cases. Therefore, it is very important to set a moisture-proof and gas-proof layer on the surface of the thermal insulation layer in order to ensure that the thermal insulation material maintains good thermal insulation performance, prolong its service life and maintain the normal use of the vending machine.

This is even more important for modified atmosphere vending machines. Water vapor entering the envelope will change the heat preservation function, and it will also change the gas in the vending machine. Take the fresh vending machine as an example, this is not conducive to the storage of fruits and vegetables. Driven by the partial pressure difference of water vapor, the water vapor outside the vending machine will penetrate into the vending machine. When water vapor permeates into the gas barrier of the building envelope, it will condense into water droplets or ice crystals in the gaps and gaps of the thermal insulation material when cold air reaches dew point or freezing point temperature, which will damp the thermal insulation material and reduce its thermal insulation performance.