adiabatic compression
adiabatic compression
(OP)
Hi there
hope everybody is fine.
please i am facing to following problem
1 - I have air @ 86F and 43 PSI abs
this air is compressed adiabatically @ ambient pressure
I need to know the new temperature.
I was thinking to utilize
TP^((1-y)/y) = const
where y = cp/cv = 1.4
But with my surprise when utilizing this formula I get an outlet temperature lower than 86F.
I would expect the opposite.
Please, can anybody help me ?
Many thanks
hope everybody is fine.
please i am facing to following problem
1 - I have air @ 86F and 43 PSI abs
this air is compressed adiabatically @ ambient pressure
I need to know the new temperature.
I was thinking to utilize
TP^((1-y)/y) = const
where y = cp/cv = 1.4
But with my surprise when utilizing this formula I get an outlet temperature lower than 86F.
I would expect the opposite.
Please, can anybody help me ?
Many thanks





RE: adiabatic compression
RE: adiabatic compression
from
86F and atmospheric pressure to
43 PSI abs
sorry
RE: adiabatic compression
RE: adiabatic compression
may I understand my method is correct ?
One question: in case of humid air (air with 50% RH ?)
many thanks
RE: adiabatic compression
RE: adiabatic compression
Tdisch=Tsuct*Rc(γ-1)/γ
where Rc=Pdisch/Psuct
I'm not sure where you got that Tdisch was constant, but it is anything but constant. Also putting "P" into the equation is just confusing. If Psuct = Patm =14.7 psia, then the I get 742R or 282°F, which is ione's answer ± some wobble in conversion factors and picking an atmospheric pressure.
There are MANY transient and unstable factors in this calculation and trying to adjust it for changes in humidity is going way outside of its value (i.e., is the discharge temperature going to be 280°F, 290°F, or 300°F?). When I'm using this relationship I never look at the "ones" column. Humidity variation changes it in the "tenths" or "hundredths" column--simply outside the accuracy of the calculation.
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: adiabatic compression
I think that, even the formulation in the OP has not been as rigorous as yours, what was meant was the same thing
Tdisch = Tsuct*(Pdisch/Psuct)^[(γ-1)/ γ]
Tdisch/ Pdisch ^[(γ-1)/ γ] = Tsuct /Psuct)^[(γ-1)/ γ]
Tdisch* Pdisch ^[(1-γ)/ γ] = Tsuct *Psuct)[(1-γ)/ γ]
So what remains constant is not the temperature, but the product of the temperature T multiplied by the pressure P raised to the exponent [(1-γ)/ γ]
RE: adiabatic compression
Absolutely correct. Since that formulation is only useful in deriving the one that is (very) useful, I keep forgetting that step. Thanks for clarifying.
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat