Wet Bulb Temp.'s Specific volume on Physchrometric Chart

[Kohos]

Hi, I tried google and all my references but I don't understand this:

on the 13th edition of MERM, example 38.4 has: .....40F (A)dry bulb and 35F (B) wet bulb are mixed ........etc

The solution has a specific volume of A as 12.65 ft3/lbm which makes sense. Then it has specific volume of B as 13.68 and I don't know where it came from. I verified the value from this online calculator (http://www.sugartech.co.za/psychro/index.php), but I don't know how it can be read from the graph. Please help!

Thanks!

 

[MikeGlass1969]

Two air streams are mixed:

(A) is 5000 ft^3/min @ 40Fdb/35Fwb

(B) is 15000 ft^3/min @ 75Fdb/50% rh

Find the mixed dry bulb temperature.

The specific volume for stream B @ 75Fdb/50%rh = ~ 13.7 ft^3/lbm 

Try using the psych chart in the MERM 13  Appendix A-137 it has 0.1 graduations for specif volume.

 

[McEng PE]

I recommend using the psych chart from Coolerado and print it in 11x17. It is really helpful and easy to read, plus it's free.

 

[MikeGlass1969]

I would actually recommend using the ASHRAE Chart, as that is what you will see on the exam.

 

[treadlight]

I would actually recommend using the ASHRAE Chart, as that is what you will see on the exam.

Truth

 

[Audi Driver P.E.]

FWIW I had 4 different 11x 17 formatted charts in my binder. Two of them were the available ASHRAE charts but in different units. The other two were ones that helpful formulas on them from the HVAC world and/or were more readable due to how the axis were laid out and labeled.

Both ASHRAE charts are here:

http://www.handsdownsoftware.com/ashrae-chart.pdf

The other two I used are here:

http://eestinc.com/_images/line_cards/Hvac line.pdf

http://www.speedytemplate.com/sea-level-ip-and-si-psychrometric-chart.asp

 

[Kohos]

Thank you! I think I was staring at it for too long, now that I look at the problem again, I see how simple it is. I read it wrong, so grateful for everyone's responses and I hope to return the favor! And thank you for the links, will download the charts