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.

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??

Let's assume R-134a is the refrigerant.

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.

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)

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.

Fantastic, thank you.