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Email Jim

That was a word that I didn't have to deal with much until recently.  With summer in full force in Virginia and me running some cold processors, I became painfully aware of condensation's effects.  Water was condensing on the SEPP through gaps in the insulation and dripped down on to my AGP video card.  After a couple of drops, I started getting some interesting effects on the screen.  Luckily I didn't toast anything, but I came close enough that steps had to be taken.

First, I had to revisit some middle-school science to remember what it was that I was dealing with and why it formed.  For those of you who actually remember those classes, you can skip the next section, but I needed a refresher course.

First, I needed a definition of the terms.

Humidity is a measure of the amount of water vapor in the air. It can be defined as the ratio of water vapor "mixed with" each sample of air. It is usually expressed as the number of grams of water vapor in each kilogram of air. In the atmosphere, the ratio can vary from nearly zero (in deserts, polar regions, and at high altitudes) to as much as 30 grams per kilogram (in warm, moist, tropical regions). 

Relative Humidity
Relative humidity (RH) is a measure of how much water vapor is actually in the air relative to (a percentage of) the air's maximum capacity to hold water vapor. The relative humidity of a sample of air can be expressed as: 

                      amount of water vapor in the air 
 RH    =   -------------------------------------------------------       x 100
                     air's capacity to hold water vapor 

By this definition, RH can change in two ways. It can change if the actual amount of water vapor in the air changes; and/or if the maximum capacity of the air to hold water vapor changes. Since the capacity of air to hold water vapor changes when the temperature changes, it follows that relative humidity depends both on the amount of water vapor in the air and on the temperature of the air. 

Dew Point Temperature
The Dew Point Temperature is the temperature at which condensation first starts to form.  If air that was not saturated with moisture started to cool, its capacity to hold water vapor would decrease but the actual amount of water vapor in the air wouldn't change. If the cooling continued, the capacity of the air to hold water vapor would continue decreasing until it could hold no more moisture. At that point, the air would then (by definition) be saturated.  The temperature at which this occurs is called the dew point temperature. 

At a particular pressure, the dew point temperature (the temperature at which a parcel of air would become saturated if it were cooled) depends only on how much water vapor is actually in the air. The more water vapor there is in the air, the higher the dew point temperature is. If saturated air cools further (below its dew point) then the air cannot hold as much vapor as it actually contains, and the excess vapor must condense to become liquid water. 

If air at 70°F and 50% relative humidity is cooled to 52°F, the relative humidity will reach 100% and condensation will begin.

Condensation is the forming of water from water vapor. It takes place when warm, moisture-laden air comes in contact with a cold surface.  In fact, condensation can only take place on a cold surface.  Cold, of course, is a relative term.

Controlling Condensation
There are a few methods for stopping condensation on a cold surface.  Some are more useful for the overclocker than others.  Here are the four I've considered.

This method relies on raising the temperature of the cold surface so that it stays above the dew point temperature.  Electrical wraps, inferred heaters and warm air blowers are sometimes used for this purpose.  A good method, but not for my application.

This method relies on reducing the relative humidity of the air by absorbing the moisture out of it. As the relative humidity drops, the dew point temperature is lowered. Surfaces that were previously below the dew point temperature are now above it and condensation does not occur.  Desiccants are used for this and work well in a contained area.  Very useful for those of us considering installing their motherboard in a Frigidaire.  Less useful when using the typical computer case.

Air Circulation
This method relies on the continuous supply of air of the same or lower relative humidity than the air in the vicinity of the cold surface. This is a good method to use in conjunction with other methods.

Thermal Insulation
This method relies on placing sufficient thickness of insulation over a cold surface so that the exterior surface of the insulation exposed to the moist air stays above the Dew Point Temperature.  This method works on the principle that if the moist air can't get to the cold surface, condensation can't occur.  This seems to be the best method for extremely cooled processors.

Insulating the Celeron ==>