Month: December 2014

I enjoy the days in Fall when you have the cool mornings, and the sunny afternoons. Have you awakened in the morning, poured yourself a hot cup of java, and looked outside your window? You notice that the grass, the leaves on the trees, and the seat of your lawn tractor are wet. The reason for this is attributed to dew point. Dew point is the temperature at which water vapor will condense and form water droplets. That same term applies in compressed air. If the dew point temperature and the air temperature are equal, then the air is 100% saturated (water vapor can start condensing to form water droplets).

Another way to get water in your compressed air system is by pressurizing it. When you take ambient air and compress it, the amount of “elbow” room for water vapor decreases. This causes the water vapor to condense and create liquid water. It would be similar to a water-soaked sponge.   As you compress it with your hands, like your compressor, the sponge will not be able to hold onto the water, and it will release the excess. Under that same hand pressure, the sponge is still fully saturated (i.e. if you continue to squeeze the sponge and dip it back into the water, it will not be able to absorb any more water). The compressed air system is the same. As soon as the air is compressed, water will start to form and fall out of the compressed air. Now you have water in your compressed air lines.

     A customer asked me about our Cabinet Cooler® system. He said that if we reduce the temperature by 54 ⁰F (30 ⁰C) in an electrical panel, will water condense onto the circuitry? Electricity and water can be a disaster but in this case we can be confident of no condensation on the circuitry. I researched this phenomenon a little further, see the details and analogy below.

Most facilities have some type of compressed air dryer in their system. This will reduce the dew point of the compressed air system. As an example, a refrigerated dryer will reduce the pressure dew point to 40 ⁰F (4.5 ⁰C). This means that liquid water will not be present in your compressed air line until the temperature is below 40 ⁰F (4.5 ⁰C). I also know that when you expand the air from 100 psig (6.9 barg) to atmospheric pressure, the air will become dryer (or the dew point will become less). Just like the example of the sponge, if you loosen your grip (going from a pressurized system to a non-pressurized system), the sponge will become “dryer” and can now absorb more water. As we combine these two concepts, we can determine if water will condense from the compressed air and become “dew” on the electrical components. If we take a typical 70 ⁰F (21 ⁰C) plant, the Cabinet Cooler® will cool the air to 16 ⁰F (-9 ⁰C). (The specification of our Cabinet Cooler® at 100 psig (6.9 barg) and 54 ⁰F (30 ⁰C) temperature drop). Let’s calculate the dew point temperature of the air exiting the Cabinet Cooler®. In looking at an elevated pressure/atmospheric pressure dew point chart, the 40 ⁰F (4.5 ⁰C) dew point of your compressed air line will drop to -6 ⁰F (-21 ⁰C) when it expands to atmospheric pressure. Thus, the temperature of the air coming out of the Cabinet Cooler® is 20 ⁰F (-7 ⁰C), and the dew point is -6 ⁰F (-21 ⁰C). So, no water will condense from the compressed air. With proper filtration, the efficiency and effectiveness of your Cabinet Cooler® will last you a long time and keep your electrical components cool and dry.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Image courtesy of Windell Oskay. Creative Comment License