I have modelled a refrigeration system using finned and tube heat exchanger and adopted the tube by tube method. I chose the R134a as a baseline refrigerant and developed the model according to it, however now I need to conduct a comparative study using refrigerants like R1234yf, R450A, etc but they have different saturation temperature and pressure at the same inlet condition for baseline refrigerant r134a. So whenever I change the refrigerant the model does not work at these inlets showing error with saturations points.
Can you please tell me how to conduct this comparative study as I saw a lot of research paper have already been there?
Thank you
If you could show me the model or error, then possibly I can assist.
Matthew Schouw
The error is giving unrealistic values, and my question is how do we compare different refrigerants with the same model in heat pumps, if you could answer this I will be thankful
regards
Well your initial model is based on R134a thermodynamic properties and possibly it's equations/models
. Remember each refrigerant has different thermodynamic properties (which you can compare from the saturation pressure and temperature tables of R134a to R404a for instance )
So maybe you have to adjust/amend your model to include the new low GWP properties.
I hope I am clear.
Matthew Schouw
if we need to amend the model as per the new refrigerants then how can we we compare them since the entire system will be changed, so my concern is on which ground we can compare them.
As the operating conditions will change and the model will get amended ?
Well assuming you are using the same system, without changing any components - you are comparing them based on performance (COP) or looking at the VCC characteristics (such as comparing evaporating or condensing temperatures and pressures /suction and discharge pressures ). Possibly also the cooling or heating capacities.
Here's a link to an article (not published by me)-where they compare mixtures.
https://journals.sagepub.com/doi/epub/10.1177/1687814016676945
And remember when you amend your model - you are only changing the properties of the refrigerant not the VCC.
As an example, if we were looking to see how long different liquids would take to boil in a kettle, we would have to change the specific heat capacity(property change) in the model if we are using a different liquid.
Matthew Schouw
Thank you for sharing the research but it discusses very basic VCC system that is mostly used for thermodynamic analysis but for drop-in methods we modeled the components and realistic base calculations were taken so in such case if we change the refrigerant then the whole system behaves very differently, maybe I need to make changes that will then compromise the quality of performance assessment since we are optimizing the system with changing refrigerant, that does not really happen in real cycle
Yes - modifications is necessary. I am not sure exactly what you trying to achieve but it also depends on what refrigerants you are using.
All the best
Matthew Schouw
The goal is to compare the performance of the different refrigerants, that is what I want to achieve, and if we make changes in the system then its difficult to compare them
Maybe you need to reconfigure the system to handle your refrigerants. You base refrigerant is R134a and what are you exactly comparing to? Which other refrigerants?
I would recommend the document below for retrofitting of refrigerants - this will address the reconfiguring I was referring to. Changing compressor oil, expansion valve /super heat refrigerant charge adjustment
Also check the danfoss website (they got cool tools and videos explaining).
All the best.
Matthew Schouw Thank you Matthew, you are being helpful however I was asking for a drop in text as this retrofitting is an experimental work mine is simulation.
After reading the website, I think I got the answer that is choose similar properties refrigerants while comparing this would not impact the model
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