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View Full Version : Refrigerant efficiency based on Latent heat of vapourization values etc.







Z2TT
26-12-2015, 09:52 AM
Hi Guys.

I'm comparing R12 and R134a, most tradies or refrigeration mechanics who work on Automotive say that R134a is less efficient, is a worse conductor of heat and that R12 was a great refrigerant.

However I am trying to find out what technical data supports that. Most technical documents from compressor manufacturers mention that R134a is actually a more efficient refrigerant as it has a greater refrigerating affect so I'm trying to understand how it is a worse refrigerant than R12.

I have been comparing values of latent heat of vaporization - R12 is about 166 kj/kg and r134a is 215kg/kg, which means for R134a that for any given liquid amount in the evaporator, it can absorb more energyfrom the incoming air from the blower until it evaporates compared to R12, which would mean it can cool more air for a longer time.

I am wondering what exactly is it that makes R134a less efficient than R12, is it something to do with the required amount of energy required at the condensing stage to condense it into liquid, as it appears in the evaporation stage it is able to do much more work. All I know is that it runs at slightly higher pressures at the high side but it appears the trade off is worth it.

Thanks.

xxargs
26-12-2015, 02:18 PM
You must look at whole cooling cycle, not part of them - for example compression effort is higher for R134a depend of pressure ratio between low and high temperature point is higher compare R12 - ie. more work for compressor...

You need also calculate temperature heat capacity on liquid, gas, eventual heat exchange between them and how much of liquid vaporize in expansions valve to cool itself to evaporator temperature.

And for example HFO1234yf have very poor COP if not using heat exchange with cool suction gas from evaporator before expansions valve depend of low latent heat and high heat capacity in both gas and liquid and need lot higher mass-flow per time for same amount of cooling compare to R134a, but if using DME only using half amount of weight compare R134a if pipes on liquid side shrink down same scale and still using same compressor for same cooling capacity depend of high latent heat.

ie. ~170 -200 gram DME with smaller liquid pipes to replace 500 gram R134a load for same cooling capacity, but need 750-800 gram HFO1234yf and bigger pipes for same flow speed in pipes as R134a for same cooling capacity. ... and HFO1234yf still perform very badly in 50 degree C hot car and no using heat-exchange between liquid line and suction line as modern car (what i can see in north part of Europa) ...

you can simulate most (old) common refrigerant itself in program called coolpack and can download free from http://en.ipu.dk/Indhold/refrigeration-and-energy-technology/coolpack.aspx