Introduction to the Process of Dehumidification-
Here are the answers to why that there is a need for dehumidification:
It also deals with questions like : Where does the moisture come from ?
Does it help if I throw a pack of silica gel in my drawers ?
Does Heating up a place reduces the moisture ?
Click the following for the answers to the questions:
How does a dehumidifier (DH) reduce moisture ?
What is Relative Humidity ( or RH ) ?
What is Absolute Humidity ?
How to calculate Humidity load in general cases ?
Dehumidification is an on-going process to reduce and
keep the air moisture low.at an enclosed space.
How does moisture come into the space ? Normally, there is a certain air getting into the space
via cracks or gaps ( Infiltration) , or even through the wall (Permeation). Human being gives
moisture through' breathing and evaporation from the skin too. If the place stores things that give
up water like plants, wet towers, exposed water containers, wet sink etc. In the basement of
buildings, usually there are more moisture problems than other floors. This is caused by moisture
in the earth below and surrounding the walls of the basement. Though concrete wall is supposed
to be able to keep water from flooding in, moisture permeation has a very high power draw to
penetrate even this thick walls. As long as there is a small opening, more humid air will flow into
the areas with lower humidity. This is a physical process calls Diffusion. The Rate of Diffusion
( or the speed of molecular movement ) is determined by the vapour pressure difference between
the two spaces. A high moisture concentration constitute higher vapour pressure.
|If the space is left
alone, the infiltration, permeation and other moisture contributing process
will take place until the space reaches an equilibrium "wetness" ( or
Humidity ) level that these process no longer take place. This level of
wetness may usually be too damp for the equipment which may cause damage or
human discomfort. ( see Dehumidifier Applications
To get rid of this moisture, some form of Dehumidification process is needed to remove the moisture. As the moisture infiltration is process is a continuous one, by putting in a pack of silica gel usually does not work for a long time. Silica gel is a well known moisture absorbing material. It sucks up moisture like a sponge !. However, it will stop working once it is SATURATED. It does not suck up moisture forever ! That's why some camera box silica gel has blue (when dry) / red (wet) colour indication feature. Silica Gel, however, is very useful and cost effective for tight sealed packed product which has water proof skin like plastic or aluminium foil.
Heating as a form of reducing relative humidity is found in simple devices like a piano heater, or instrument box /cabinet with built-in heaters. Heating raises the space temperature and thus at the same moisture content of a space lower the relative humidity. It has, however, never removed a single droplet of moisture from the air ! It is relatively workable in cool and dry countries. Its effectiveness in hot and humid countries not as good. The good news is, the moisture damaging effect on product is proportional to the Relative Humidity of the Space rather than the actual amount of moisture content
( Absolute Humidity ).
Some of the modern bridges with welded box construction on cold countries are protected against corrosion by the help
of dehumidifiers, saving a lot of maintenance. Another area will be in the marine application. Ships are very sensitive to
moisture. Partly due to the salty atmosphere and partly caused by the vast temperature fluctuations. The upper deck
which is exposed to the air may be tens of degrees different in temperature compared to the lower part which is touching
the sea water. This variation usually causes large humidity differences and resulted in condensation of water on the metal
surface. Dehumidifiers are usually used to keep the air dry.
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