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View Full Version : Calculating properties of refrigerant blends (R507/R410A)



DaBit
30-01-2004, 01:22 PM
I am just wondering how I can calculate the properties of an R507/R410A blend.

An AC/R engineer and I have had a discussion if it is possible to increase compressor capacity slightly by adding some R410A to the main R507 refrigerant charge. This originates from the low evaporating temperatures needed in a 2-stage cascade running ethylene (R1150) in the low stage. At low SST, capacity of a compressor drops quickly, and we prefer to maintain -35C/-31F ethylene SCT or lower. A higher vapour pressure at low evaporating temperatures might help the high stage. I am aware that TEV superheat changes also when adding R410A, and so does condensing pressure. And probably a glide is introduced as well.

Now, I can answer this only if I can calculate the properties of an R507/R410A mixture (in fact an R32/R125/R143a mixture). And then mainly bubble/dew points.

How would I calculate this? And if it cannot be done easily, is there anyone with access to the NIST RefProp program who can calculate this at various temperatures (-40C / -40F and 32C / 85F are the most important temperatures) and various mixtures? RefProp is too expensive for me to buy for the few times it might come in handy.

I am just irritated by the fact that I cannot calculate this. Pure R410A is another viable option since condensing temperatures stay low, and thus condensing pressures stay within the allowable range for the R404a compressor. R507 TEV superheat error is about 6K at -40C / -40F evaporating, which could work if TEV superheat setting is lowered.

chemi-cool
30-01-2004, 02:51 PM
hi dabit,

maybe you can get some help at: http://www.fchart.com/ees/eesrefprop.shtml
the programme costs "only" $1000!!!

anyway I'm sure you can find it on the web.

chemi

DaBit
30-01-2004, 03:04 PM
I cannot find RefProp on the Internet, which is needed anyway. Not even a trial-license. Hell, even refprop6.dll plus a description of the API would be sufficient.

Prof Sporlan
31-01-2004, 02:34 AM
The thermodynamic equations exist for most of the commonly used refrigerants. In the case of R-404A, you can find the DuPont formulations here: http://www.dupont.com/suva/emea/pdf/thermo_suvahp62.pdf

Knowing the thermodynamic equations (and a bit of calculus) is helpful. The Prof might suggest one of his better publications :): http://www.sporlan.com/5-162.htm

The Prof has done this programming some time ago in conjuction with the Sporlan product selection program. A zip file can be downloaded from here: http://www.sporlan.com/pgm/svc351.zip

DaBit
31-01-2004, 09:16 AM
OK prof, thanks again :)

I will look into the program next week since it is too large to download it over an 28k8. The other two PDFs are useful.