Compressed air dryers.
This has been prepared in an attempt to clarify some of the basics of compressed air drying. It does not purport to claim that one manufacturer is better than another, nor does it claim that one form of drying is better than another. They all have advantages and disadvantages.
Dryer or drier ?
Dryer: An item of equipment used to dry something, i.e. a hand dryer, a hair dryer or a paint dryer.
Drier: The comparison of two items. i.e. the shirt on the left hand side of the washing line is drier than the shirt on the right hand side.
A huge number of compressed air dryers are make in America, unfortunately the Americans do not distinguish between the two words, therefore many sales leaflets refer to 'compressed air driers'.
General Facts:
Air has the ability to hold water in exactly the same way that a sponge can hold water, also the air around us contains water - in the form of vapour.
When air is compressed, water drips out in the same way as squeezing (compressing) a wet sponge. If you listen to the weather forecasts, they talk about low pressure fronts. When saturated low pressure air moves towards a high pressure front, the low pressure air gets squeezed (compressed) a little bit - it's going to rain.
If you let go of the sponge it expands back to its original size and now has the ability to absorb some more water. Air does the same when you expand it, it becomes drier and will readily absorb water from its surroundings.
Air also has another feature which we all take for granted. If you heat air up, it readily absorbs even more water. This is why puddles evaporate in the sun and hot hair dryers will dry wet hair. Try drying your hair with a cold hair dryer and see how long it takes.
Conversely, if you cool air down it loses its capacity to hold quite as much water. An example is a window in a warm living room on a cold winter night. When the warm air inside the living room touches the cold glass, the temperature of the air in contact with the glass drops and water condenses out of the air on to the window. The bigger the temperature differential, the greater the condensation.
Everything described above also happens inside compressed air pipework. Changes in temperature and pressure will affect how much water vapour the compressed air can carry before it decides to rain inside your pipework. Air is air is air.
If you add these features together you end up with all of the principles which are used in compressed air dryers.
The compressed air dryer market is served by five main types, these have been classified below. Just click on one for further information.
Approximate Market Sector.
- Refrigerated air dryers.
These have approximately 65% of the market in terms of volume sales. The pressure dewpoints vary from +15 deg C which is on the high side, to an absolute best of +2 deg C. - Desiccant air dryers.
These have approximately 30% of the market in terms of volume sales. Pressure dewpoints will be available from -20 deg C to -100 deg C. - Deliquescent air dryers.
Only really useful in countries with a hot ambient climate, these have less than 2% of the market in terms of volume sales. A pressure dewpoint depression up to 11 deg C can be achieved. - Membrane dryers.
Fairly new, based upon very old technology. These account for just over 2% of the market. A pressure dewpoint of 0 deg C can be achieved. - Filter system dryers.
It amazes me that people buy them, but nevertheless they account for just less than 1% of the market. A pressure dewpoint depression in the order of 2 deg C is usually achieved.