Hi, how do I attempt to answer this:
At the commencement of compression in the reciprocating compressor
of a refrigeration plant the refrigerant is dry saturated at 1 bar. The
compression process follows the law pV^1.1 = C, until the
pressure is 10 bar.
•Calculate the work done on the refrigerant during the process?
Is it W = m(h2 - h1) ?
I don't know if the pV^1.1 is relevant.
Thanks for any help.
Fantastic, thank you.
This is the polytropic work formula:
Work = mR(T2 - T1) / n-1
I can factor out 'm' to have specific work, then have you substituted something in for T2?
Sorry, I am struggling with this derivation., my apologies.
Hi, really grateful for the answer, but where has this come from:
W = (RT1)*n/(n-1) * [(P2/P1)^((n-1)/n) - 1]
Is it general? Especially the first term: (RT1)*n/(n-1)
In that case,
using R-134a property tables
T1 (from P1 = 1bar) = -26.37 C = 246.78 K
and R = 0.08149 kJ/Kg.K
n = 1.1
Using the following formula you can calculate the work done.
W = (RT1)*n/(n-1) * [(P2/P1)^((n-1)/n) - 1]
Another method,
Find out h1 from P1 at X=1 (Dry saturated state)
then
calculate T2 from the following equation
T2/T1 = (P2/P1)^((n-1)/n)
Then using this T2 and P2 value from the superheated R134-a property table calculate h2.
Work done should be equal to W = (h2-h1) as you mentioned in your question.
Both methods should give the same answer.
Let's assume R-134a is the refrigerant.
As the compression process is going to be in the superheated region you can use ideal gas equations.
W = (RT1)*n/(n-1) * [(P2/P1)^((n-1)/n) - 1]
But I am not sure about T1. Because the name of the refrigerant is not given??