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How to reduce RH of air from evaporative cooler?

  1. Mar 12, 2015 #1
    Hi guys! I'm new here and this is my first post! I'm a fresh engineering graduate and I'm facing a dilemma. I'm currently in charge of a project. We intend to use an evaporative air cooler for a carbonated soft drink filling line.

    The flow of air intake is as follows:
    evaporative cooler --> blower --> filter box --> ductings --> diffusers --> room

    evaporative air cooler specifications:
    max airflow = 30,000 CMH
    air pressure = 280 Pa
    effective area = 200-250 sq m

    The resulting air however, would be humid. We still want to keep RH relatively low (below 50) to prevent mold growth in the area. We also want to protect the ducts from corrosion. We live in a tropical climate, so the ambient air is often hot and humid.

    I'm looking at using a mist eliminator/coalescer after the evaporative cooler but I'm not sure if it is effective enough given the air conditions. Or are there economical ways to lower the dew point temperature? Any thoughts on this? Thanks in advance. :)
     
  2. jcsd
  3. Mar 12, 2015 #2
    How much cooling does our psychometric chart say will be achieved by this method.?
    What is your initial incoming air temperature and RH to the evaporative cooler.? Air temperature and RH output? Will you be able to achive the air temperature drop you expect for the room?

    Evaporative coolers work best in arid locations, as you probably know, and since you mention tropical climate, with high humidity, some calculations beforehand would indicate if this is a feasable the route to follow.

    You could pass the cooled air with increase RH from the evaporator to a heat exchanger on one side, with the circulating room air on the other, to eliminate adding moisture to the air.

    A mist eliminator removes aerosols from the air, in your case droplets of water coming from the evaporator. Would you not want the droplets to evaporate? Isn't that the basis behind an evapotative cooler?
     
  4. Mar 13, 2015 #3

    russ_watters

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    Staff: Mentor

    This sounds like exactly the wrong application for an evaporative cooler. What is the reason behind the decision to use it?
     
  5. Mar 15, 2015 #4
    The reason for using the evaporative cooler because they do not want to use air conditioning per se, but cooling air would be necessary during the hot-dry season as the weather (at 32-35 deg C) is already uncomfortable for the operators. They intend to use it only when necessary. Currently, they do not have any ventilation at all. (There are two exhaust fans but both are not working)
     
  6. Mar 15, 2015 #5
    Hi, thanks for the reply. Sorry I forgot to mention this, the supply of air outside the room is indoor air from a large building, with average RH 60-70% and temperature 27-32 deg C. The temperature we are after is 25 degrees C or lower. We're still looking at whether the indirect evaporative cooling, with heat exchanger, as you mentioned, will be economical for this application.

    In the case of using a mist eliminator, we are looking also at the feasibility of using a filter coalescer before contact with the room (that is, after air cooling). It worked well before in the case of a highly humid air going inside an electrical control room.
     
  7. Mar 15, 2015 #6

    russ_watters

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    Staff: Mentor

    Picking something in the middle, 30C at 65% for the incoming air is a wet bulb temp of 23C. The wet bulb is what you can achieve for a new dry bulb with direct evaporative cooling. Indirectly, you might get 60% of that temperature drop, for an incoming air condition of 26C @ 83% RH.

    With indirect evaporative cooling, there isn't anything for a mist eliminator to do: there is no mist to eliminate in the airstream going into the building. It's just really, really humid. Reducing the humidity requires a dehumidifier -- either via air conditioning or perhaps a heated desiccant.

    The title says you want to decrease the RH, but nothing being described can do that. At best, the absolute humidity stays the same and the RH increases (with indirect evaporative cooling).
     
    Last edited: Mar 15, 2015
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