# Having trouble using Psychometric chart...

1. Nov 13, 2015

### christyu

• Member warned to use the formatting template for homework posts.
Hey guys, I'm actually studying vapor compression refrigeration cycle and would like you guys' help in understanding Psychometric chart. There are no calculations involved but need reasoning and guide.

Given (temperatures)
dry bulb entering condenser: 69oF
dry bulb leaving condenser: 75oF
Wet bulb entering evaporator: 59oF
wet bulb leaving evaporator: 58oF
dry bulb leaving evaporator: 63oF
wet bulb leaving condenser: 61oF

I was asked to use psychometric chart to find All air enthalpies.

I know that in order to find enthalpy you just need to match up dry bulb and wet bulb on the chart and see which value of enthalpy it lines up to. I hope to understand how things work with these problems I got.

1. I asked someone online for help the other day and he used condenser and wet bulb entering evaporator for finding enthalpy of condenser(Entering), and for finding enthalpy of condenser (exiting), he used dry bulb leaving evaporator and wet bulb leaving evaporator.
why did he choose these 4 values and left the other ones? What about evaporator?(entering,exiting)?

2. When he used psychometric chart to find enthalpy of condenser (Entering), he got the value as 30 Btu/lbm. When I tried it myself I got like a little bit over 25 btu/lbm and even checked it out with online psychometric chart calculator which provided similar value. did he do it wrong?

link to psychrometric chart (I checked it with my chart just in case if there's any difference):
http://web.uconn.edu/poultry/NE-127/NewFiles/psychrometric_inset.html

link to online psychrometric calculator (change unit to IP since it's Fahrenheit): http://www.sugartech.co.za/psychro/

3. One thing I would like to know is that, does value of dry bulb matter? I mean in the end, wetbulb already lines up with enthalpy side so as long as I have the value of saturation temperature/wet bulb temperature, dry bulb temperature can be neglected? or am I misunderstanding something...

Last edited by a moderator: Nov 19, 2015
2. Nov 19, 2015