Difference between the various COP formulae

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Homework Statement

Homework Equations

N/A

The Attempt at a Solution

My question is a simple one: how is the above equation for COPref different to the COPref equations I've already encountered (such as COPref = Qc/Win = (h1-h4)/(h2-h1). Is the above just a different form of these? Or is the above only used in specific situations?

Also, one other question. What does ''isostere'' mean exactly? I know isobar means equal pressure and isotherm means equal termperature but can't seem to put my finger on what ''isostere'' means. Wikipedia gives this: https://en.wikipedia.org/wiki/Isostere

But I think that is referring to isostere in a different context?

Thanks

 

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I edited the above post to include the isostere question but I have now found out that it means constant concentration. However, I can't seem to edit the above post to reflect this hence I decided to post this message.