A dehumidifier is an appliance used for household purposes, where there is a reduction of humidity in air. Since humid air causes many health problems, dehumidifiers are used. The normal level of humidity in the air should be 30 – 50%. Dehumidifiers are used in industries to maintain a certain level of humidity.
The most common type of dehumidifier is the refrigerative or mechanical dehumidifier. In the 工業用抽濕機. former dehumidifier, the moist is removed by a refrigerated coil with a small fan in it. The mechanism of this dehumidifier is when temperature decreases, the vapour pressure also decreases which results in condensation of water in the air. The refrigerated coil is then used to reheat the air which is effective in higher temperature regions.
In regions where there is low temperature and low humidity level, a special type of dehumidifier is used namely “Desiccant Dehumidifier” where there is a desiccant material to reduce the humidity and it has got high affinity towards water vapour. This desiccant material is exposed to high humidity air stream to collect water vapour which in turn is exposed to low humidity air stream where the moisture retained is also collected. The stream used in the former is dehumidified and latter stream is used to regenerate the desiccant. These dehumidifiers consume heat energy to produce the effect of dehumidification. There are 2 kinds of desiccants namely absorbent and adsorbent. In the former, there is a chemical change when they retain water vapour. Adsorbent attract greater water molecules through the air pores present in it and there is no chemical change. The adsorbent material often used is the silica gel. This material can be reactivated by heat at a temperature of 160 – 170 oC and the heat required is 4800 KJ/Kg water removed.
The very small dehumidifier called “Electronic Dehumidifier” consists of low cost parts. There is a heat pump to produce a cold surrounding and there is no noise produced as there are no mechanical parts. Spray dehumidifier is used, when the temperature of water is lower than the dew point of the air flow. This spray dehumidifier resembles an air washer. When the moist in the air is saturated, the air is dehumidified when water is sprayed on the surface.
An example of a refrigerative dehumidifier is the “Air Conditioner”. They produce a cool surface. There is a refrigerated coil along with a fan which removes moisture. These thermally activated technologies employ heat energy to heat or cool the refrigerative dehumidifier. The energy from the thermal source can be in the form of heat. Thermally activated technology in dehumidifier is also used as a natural gas burner.
Dehumidifiers are used in a variety of applications. It is used in food & beverage industry as an absorption dehumidifier. This dehumidifier prevents the product from coagulating, corroding, breaking and also from bacterial growth. In baking industry, enrobing is done by these dehumidifiers to control humidity, product cooling is done for frost free cooling and when the product is stored, dehumidifier prevents from bacterial growth.
In cereals, when coating is done, it eliminates agglomeration. In candy industry, dehumidifier is used while panning is done to improve the quality of the product. While packing the candies, it is used to improve the sanitation facilities.
In biotechnological lab, dehumidifiers are used for sterile air inside the room. In water works, these are used to prevent condensation, wherein a pipe gallery is used. These pipe galleries are prevented from rusting, deterioration and also the life of painted pipes is extended. The advantages of using dehumidifier is to remove humidity, since humid air causes many health problems such as allergies, respiratory problems, damage of immune system, asthma. When excessive level of moisture is found, mold and dust mites will be formed. So, using a dehumidifier is very advantageous for the people who live in humid areas.