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Re: Humidifier question

Posted by snowman on March 11, 2002 at 22:23:51:

In Reply to: Humidifier question posted by saxgirl on March 11, 2002 at 09:34:25:

The main purpose of the heater is to replace lost due to the latent heat of vaporization, which is a whole bunch of heat.

As each gram of water evaporates it takes over 550 calories of heat with it (it only takes one calorie to heat, (or cool) one gram of water one degree).

Water evaporates better at higher temperatures than lower ones. In fact only a few degrees slows down evaporation to the point it is meaningless. If your water is below say 80 degrees F, it dosen't evaporate very well. The higher temp it gets the better it evaporates.

The only other parameter tthat corresponsds to evaporation is the surface area of the water, the more surface area the more the evaporation.

It turns out that the main factor for cpap is temperature. The surface area is relatively minor in comparason to heat.

As the cpap starts out the water is relatively warm and evaporation takes place. As the precess preceeds ( one or two hours max) the water getts cooler and nothing happens anymore, unless heat is added.

How much heat? Well a typical 80 watt heater, going full tilt, can just about keep up with a cpap set at 12 cm of H2O. That means the water will remain at room temp even though the heater is going full tilt!!!

If you do not beleive this just check the temp of the water after a couple of hours at 12 cm of H2O, It will feel cool to the touch, I.E. anything lower than 98.6 will tend to feel cool to the touch.

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