Why Does Identical h2 and h2' Not Indicate Best COP in Refrigeration Systems?

[skaboy607]

Hi,

I think I have confused myself over the COP of a refrigerator. I have refrigeration system and a certain set of values which enable me to plot a P-s diagram. The refrigerant is R-12. I also have another set of 4 results for varying evaporator pressures, and I have drawn all these cycles on thte P-s diagram. I have calculated the corresponding enthalpy values for all the sets of data and also h2' (based on ideal cycle) for each set. My question is...for one set of data, the h2 and h2' are almost identical which to me, made me think that this was the setup that maximised the net work output. however when calculating COP based on ideal cycle for all sets of data-this setup provide with the lowest value, the one with the worst performance?

I don't understand? Have I got my wires crossed?

Thanks

Will

 

[Achy47]

Hi Will,

First of all, it's great that you are investigating the performance of your refrigeration system and trying to understand the COP (Coefficient of Performance). It can be a bit confusing at first, but let me try to clarify things for you.

The COP of a refrigerator is defined as the ratio of the heat removed from the refrigerated space (Qc) to the work input (W) required to remove that heat. In mathematical terms, it is expressed as COP = Qc/W.

In your case, the h2 and h2' values being almost identical for one set of data does not necessarily mean that it maximizes the net work output. It only means that the actual cycle and the ideal cycle are very similar for that particular set of data. The ideal cycle is a theoretical cycle that assumes no losses and perfect efficiency, so it is not always achievable in real-world systems.

When calculating the COP based on the ideal cycle, it is important to use the same values for Qc and W as you did for the actual cycle. If you are using different values, then it is expected that the COP will be different. It is also important to note that the COP based on the ideal cycle is a theoretical value and may not reflect the actual performance of your system.

In conclusion, it is possible that the setup with the h2 and h2' values being almost identical may not have the highest COP. It is important to consider all the factors and use the correct values when calculating the COP. I hope this helps clarify things for you. Good luck with your research!