Problem :
Water at 100 degrees F enters a cooling tower at the rate of 250,000 lb/hr. water leaves at 80 degrees F
Atmospheric conditions:
85 F db
70 F Wb
29.92 in. Hg
Air leaves the cooling tower at :
95F db
70% relative humidity
It is asking to solve for the volume flow rate(cfm) of atmospheric air required to cool the water
The solution guide gets the following equation
250,000(68) +Mair*h1 = (250,000 – Mevap)(48) +Mair*h2
Could you please tell me where the 68 and 48(numbers in red) come from? I can get all the enthalpies and humidity ratios from the Psychometric charts but cannot figure out where these numbers come from. I would really appreciate your help
This is number 507 out of the 2001 mechanical PE NCEES sample problems.
Water at 100 degrees F enters a cooling tower at the rate of 250,000 lb/hr. water leaves at 80 degrees F
Atmospheric conditions:
85 F db
70 F Wb
29.92 in. Hg
Air leaves the cooling tower at :
95F db
70% relative humidity
It is asking to solve for the volume flow rate(cfm) of atmospheric air required to cool the water
The solution guide gets the following equation
250,000(68) +Mair*h1 = (250,000 – Mevap)(48) +Mair*h2
Could you please tell me where the 68 and 48(numbers in red) come from? I can get all the enthalpies and humidity ratios from the Psychometric charts but cannot figure out where these numbers come from. I would really appreciate your help
This is number 507 out of the 2001 mechanical PE NCEES sample problems.