Air Off Dry Bulb Temp

[hvac69]

Got a small problem guys I am trying to calcualte Air Off conditions from known Air On conditions and a known quantity of steam injected (this is for an in duct humidifier). The problem I am having is that I am not sure how to calculte the air off conditions, well, namely the Air off Dry Bulb Temperature. I cna calculte everything else, once I have this!! Any more learned fellow out there can help me??

 

[atlas06]

Too many "offs" in your question. Will take some time to sit down and figure this out, and people don't have the time. Read ASHRAE, look for psychrometrics and air washer design manuals, or the steam humidifier manufacturer that might send you some engineering literature.
Just googling out (air washer leaving air temperature), I came up with this site. Look on the inetrnet, lots of answers out there.

http://www.answers.com/topic/humidity

 

[hvac69]

Thanks atlas06 I ahve spent plenty of time sitting in fron of Ashrae, just need a little direction I suppose. I tried using a method to calculate the Dry Air Off Temperature that used heat transfer physics. I think I will have to spend some more time in front of Ashrae and, I was hoping some one had maybe come across this before. Anyway, I will keep you informed of my progress and any results I deduce. Thanks for sparing the time to reply to my question.

 

[quark]

hvac69,

You don't even need fingers to do the calculation, as far as DBT is concerned, for steam humidification is an isothermal process. However, if you use any other method for humidification, for ex. air atomization etc. then treat the process as isenthalpic.

If you want to get the quantity of steam required, mark the state point of air before humidification on the psychro chart, draw a straight line perpenducular to DBT line to the RH curve you require and read the difference in moisture content. I hope you know the further procedure.

Armstrong has an excellent technical catalogue. Check their website.

 

[KiwiMace]

Isothermal - if the steam is dry saturated at the DBT of the entering air. This would be a vertical line upwards on the Psych Chart.

In reality, this may not be the case. The answer is the Enthalpy-Moisture Ratio (q' = delta h/delta W) which is found on ASHRAE psych chart protractors. For steam, the q' is equal to the hg enthalpy of the steam. This is the same as slope of the line because the chart is plotted in these coordinates. This line can be taken from the point on the outer scale on the protractor and plotted on the chart. Typical hg values have this line sloping up to the right.

The start and finish points of this line are determined by the Enthalpy and/or Humidity Ratio points, which you probably have defined.