Relative Humidity vs. Dew Point in Compressed Air SystemsHave you learnt calculate dew level and relative humidity in your compressed air system? Understanding these measures and the way they’re associated will assist you preserve your compressed air system at optimum efficiency. To attenuate condensation issues in your system, it is very important know the way a lot moisture is within the air vs. how a lot moisture the air is able to holding. Measuring or calculating your dew level and relative humidity (RH) may help you keep away from issues along with your compressed air system and manufacturing purposes. Right here’s know in case your stress dew level is just too excessive—and what you are able to do to repair it.

What’s the Relationship Between Relative Humidity and Dew Level?

Dew level and relative humidity are associated, however they aren’t the identical factor. It helps to have an understanding of what every time period means and the way they’re interrelated.

What Is Dew Level?

The dew level is the temperature at which water vapor within the air begins to condense right into a liquid. The dew level is a measure of how a lot moisture is within the air. A better dew level means there’s extra moisture within the air.

The quantity of water that may be held in a quantity of air is immediately associated to its temperature. Hotter air can maintain extra water vapor than cooler air. As air is cooled at a continuing stress, it turns into an increasing number of saturated. Because the temperature continues to drop, extra water condenses as a liquid. The temperature at which this occurs is the dew level.

We see this in motion in nature at atmospheric stress. Heat daytime air holds extra moisture (or humidity). As temperatures cool in a single day, dew varieties on grass and different surfaces. The extra humidity within the air, the upper the temperature at which condensation begins to kind. In very low humidity, condensation could not kind till temperatures are beneath the freezing level of water. We name this the frost level.

Relative Humidity vs. Dew Point in Compressed Air Systems

What Is Relative Humidity?

Relative humidity (RH) is a measure of how saturated the air is—in different phrases, how a lot moisture is within the air relative to the entire capability of the air to carry moisture. Keep in mind, it is a relative measure. RH alone doesn’t let you know how a lot complete moisture is within the air. It merely tells you ways shut you’re to saturation for a given temperature and stress. At 100% RH, the air is totally saturated. Any extra moisture getting into the air at this level will trigger condensation to begin to kind. At 50% RH, the air can proceed to soak up extra moisture with out inflicting condensation.

Like dew level, relative humidity is immediately associated to temperature. A 40°F day with 100% humidity has a lot much less moisture within the air in absolute phrases than an 85°F day at 50% humidity. That’s why cooler days really feel drier, even when the reported RH is identical. As air cools, RH rises, despite the fact that no extra moisture has entered the air. After we attain the temperature the place RH is 100%, now we have hit the dew level.

Relative Humidity vs. Dew Point in Compressed Air Systems
Calculating Stress Dew level and Relative Humidity for Compressed Air

The quantity of moisture within the air of your compressed air system relies upon largely on the humidity of the air outdoors. The extra moisture current within the consumption air, the extra water vapor (and doubtlessly condensation) will find yourself in your compressed air system.

The dew level in a compressed air system is named the stress dew level (PDP), e.g., the dew level on the PSI at which the system is working. (That is contrasted to atmospheric dew level, or the dew level of air at atmospheric stress.) RH and dew level are particular to the stress the air is below. As air is pressurized, extra moisture is squeezed from the air like water from a sponge.

To visualise this, do not forget that the water holding capability of air will depend on its temperature. That implies that 1 m3 of consumption air and 1 m3 of compressed air on the similar temperature can maintain the identical quantity of water. However, throughout compression, we’re squeezing much more air (when it comes to precise air and water vapor molecules) into our 1 m3. If we elevate the stress from 1 bar (atmospheric stress) to eight bar (roughly 116 PSI), we’re squeezing that 1 m3 of consumption air into 1/8 m3 of area, so our 1 m3 of compressed air now accommodates eight instances the water vapor as 1 m3 below atmospheric stress. If the air was already saturated entering into (100% RH), all of that extra water will fall out as condensation.

It is necessary for producers to know the dew level and relative humidity for the pressures and working temperatures at which their system is operating. In different phrases, how a lot moisture is within the air within the system (absolute humidity) and the way shut they’re to the dew level of their system (relative humidity).

The right way to Measure Stress Dew Level for Compressed Air Programs

The best method to decide the stress dew level in your compressed air system is to measure it immediately. You may measure the PDP in your compressed air system utilizing a dew level sensor. The sensor measures temperature and hint moisture to find out the purpose at which condensation begins to happen.

Aire Tip: Most air dryers have built-in dew level sensors to repeatedly monitor the dew level of your system.

The right way to Calculate Dew Level and Relative Humidity for Compressed Air

It’s also attainable to calculate the dew level and relative humidity in your compressed air system. To do that, you need to know the way a lot moisture is within the air coming into the compressor. We’ll first have to calculate absolutely the humidity of consumption air—that’s, the entire quantity of water vapor current in a given quantity of air. We will work out absolute humidity in grams per cubic meter if we all know the relative humidity and temperature of the consumption air. To calculate absolute humidity in g/m3, you will have the consumption air temperature in Celsius and the RH (expressed as a %). Additionally, you will use the pure log (e). The method is:

Or, you should utilize one in all many useful on-line RH to AH calculators to do that for you.

Now, we have to decide the moisture carrying capability (often known as the saturation vapor density) of the compressed air. Once more, this will depend on its temperature. That is best to do utilizing a saturation curve or desk, like this one:

Relative Humidity vs. Dew Point in Compressed Air Systems

 

The dew level of your system is the purpose at which the RH of your compressed air is 100%, or when absolutely the humidity of air coming in equals the moisture carrying capability of the compressed air. RH is calculated as:

Relative Humidity vs. Dew Point in Compressed Air Systems

 

Or, you should utilize one in all many useful online RH to AH calculators to do that for you.

Now, we have to decide the moisture carrying capability (often known as the saturation vapor density) of the compressed air. Once more, this will depend on its temperature. That is best to do utilizing a saturation curve or desk, like this one: 

The dew level of your system is the purpose at which the RH of your compressed air is 100%, or when absolutely the humidity of air coming in equals the moisture carrying capability of the compressed air. RH is calculated as: 

RH = (precise vapor density/saturation vapor density) *100

If RH is larger than 100, you’ll have condensation. A quantity decrease than 100 provides you the RH of your system and tells you ways shut you’re to the dew level.

Let’s take a look at an instance:

  • Consumption air temperature is 20°C (68°F) with RH of 60%, for absolute humidity (precise vapor density) of 10.3 g/m3 (from NOAA calculator). 
  • Temperature of compressed air is 40°C (104°F). Saturation vapor density = 51 g/m3 (from chart). 
  •  Air is compressed from 1 bar to eight bar. New absolute humidity of the air is 10.3 g/m3 x 8 = 82.4 g/m3.
  • RH = (82.4/51) * 100 = 162%

Since 100% is the utmost RH, we all know that we’ll have condensation on this instance.

Now, let’s decrease the incoming RH to twenty%:

  • Precise vapor density = 3.4 g/m3 (from NOAA calculator)
  • With the identical compression, new absolute humidity = 3.4 g/m3 x 8 = 27.2 g/m3  
  • RH = (27.2/51) * 100 = 53%

On this case, RH is decrease than the saturation vapor density contained in the system, so condensation is not going to happen.

Compressed Air Temperature and Dew Level

Do not forget that the saturation vapor density for air inside your compressed air system relies on the temperature—and the temperature of that air is altering because it goes by way of the system. Air coming immediately out of the compressor can be extremely popular, so it is ready to maintain extra moisture than cooler air. That’s why condensation tends to fall out of compressed air because it sits in your air receiver or strikes by way of the air strains. Similar to dew varieties in a single day as air cools, condensation will begin to kind when air in your compressed air system cools to the dew level.

Aire Tip: Drain extra water each day from air receiver tanks and different locations water is prone to condense. Programmable or zero-loss drain valves will do that for you robotically.
Why Dew Level Issues for Compressed Air Programs

Why does dew level matter for compressed air?

In case your dew level is just too excessive—that’s, when you’ve got numerous moisture within the air in your system—you’ll have extra condensation and extra water vapor within the air popping out of the strains. In case you can decrease the dew level of your air, you’ll be able to keep away from issues related to extra liquid in your compressed air system.

Widespread Issues with Water in Compressed Air Strains

Water in compressed air techniques could cause plenty of issues. Essentially the most critical of those is corrosion within the compressor itself, air strains and different parts of the system. As well as, extra liquid within the air strains can result in:

  • Corrosion of instruments and gear powered by compressed air
  • Product high quality points (particularly for paint sales space purposes, prescription drugs, meals processing, and different purposes which can be delicate to moisture)
  • Threat of freezing within the management strains and injury to gear
  • False readings on air compressor devices 
  • Microbial development in management strains and air strains 

What Ought to the Dew Level Be for a Compressed Air System?

A steady dew level monitor will let you know the dew level at which your system is at present operating. Typical dew factors for compressed air techniques are between 50°F and 94°F.

Some purposes—corresponding to paint cubicles, printing, meals processing and prescription drugs—require super-dry air. For these purposes, it would be best to decrease the dew level of your system by eradicating moisture from the air.

Aire Tip: For many purposes, sustaining an RH of 75% or decrease relative to the dew level of your system can be satisfactory to maintain air strains liquid-free.

The right way to Decrease Dew Level in Compressed Air Programs

You may decrease the dew level of your compressed air system by eradicating extra moisture from the air. This may be performed by putting in a water separator filter, an air dryer, or each. There are two forms of dryers:

  • A refrigerated air dryer works by chilling air to 33-40°F, permitting extra water to condense, after which bringing air again as much as ambient temperatures earlier than including it to the system. This lowers the dew level to 33-40°F (the temperature to which the air was chilled). Refrigerated dryers decrease the dew level adequately for many purposes. 
  • Desiccant air dryers take away water from the air by way of a chemical course of. They will cut back the dew level to -40 to -100°F, creating ultra-dry air for delicate purposes. 

Learn extra: Getting Rid of Moisture in Your Compressed Air System.

Need assistance diagnosing moisture issues in your compressed air system? Fluid-Aire Dynamics may help you design an air drying system to scale back your dew level to the degrees wanted by your utility. Contact us for an analysis.

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