The dew point of air has significant ramifications for compressed air users. Here’s what dew point is all about.
Let our minds wander to where we are sitting on the back deck, and the hot summer sun is beaming down. A bead of sweat trickles down our chest, and we are thirsty! We reach into the cooler for another, and poor a frosty bottle of our favorite barley and hop beverage into our glass.
Let us also imagine that we put this ice-cold mug of suds on the railing of the deck right beside us. Very quickly we’ll see beads of water forming on the outside of the cold glass.
Why? Because of the dew point!
The dew point is the temperature at which the water vapor in the air can no longer stay in a vapor form, and condenses from a vapor into a liquid on a surface.
The film of air around the mug in the picture cools rapidly due to the cold temperature of the surface of the glass. The air that is actually touching the glass quickly gives up the moisture it is carrying and deposits it onto the surface.
The temperature of the air that is touching the glass has quickly fallen below its dew point, reducing the ability of that air to hold vapor, and forcing that water vapor to condense out of that air.
That newly-condensed water then trickles down your mug and onto the front of your chest as you swallow the frosty beverage. Mmmm, delicious!
In order for the water in the air to remain in a vapor form, whether it is the air on your back deck touching the glass or the compressed air in your plant compressed air lines, or in the hose to your air tool, the air passing through the pipe or hose or tube must be warmer than the surface it is touching, otherwise, water will condense out.
Compressed Air Is Often Hot
Now think of your compressed air supply. Through the compressing process, the air in the compressor tank or receiver can get very warm. And as a result that warm air will contain a significantly greater amount of water in vapor form than the free air outside the compressor and the compressor tank.
As I’ve said, as air cools, it can hold less water vapor.
Result? Water Condenses In The Air Lines
What happens when the hot, vapor-laden air from your compressor tank reaches the plants air lines? The compressed air cools rapidly, the water vapor in the air condenses out, and you now have free water flowing through your air lines.
However, if the air entering your plant from your compressor had a dew-point that was below the temperature existing throughout your plant, then no water vapor should condense from the compressed air into free water in your air lines.
Air Dryers Lower The Dewpoint
That is why industrial compressed air users use air dryers.
Air dryers help to take water and water vapor out of the compressed air stream. They lower the dew point of the compressed air stream to try and make sure that water won’t condense from your compressed air as it traverses your air mains.
Cooling the air helps. Drying it helps too.