[Bolvan (OP)]

Due to formula we have significant delta T in some cylinder if to pull piston out.
We have small cylinder total volume 10 , piston inserted and isolates 1.
Please, look at image. Delta T is large. Heat capacity of 1 cubic cm of air is 0.000001 Joules per Kelvin, but if to use 100 cubic cm of air ( size of average compressor ) at frequency 60 Hz we get 0.006 K removal per second. Or inverse heat multiplication to warm up the home.
Where am I mistaken? Why we use "freons" or other natural or man-made substances, but not just air?

[Bolvan (OP)]

Picture with calculations

[Bolvan (OP)]

And one more question - does anyone actually built Kelvin's device "as is" to compare with modern heat pumps in both ways - heating or cooling?

[Bolvan (OP)]

By the way "Ideal heat engine" calculation of Kelvin are very similar to present days performances of heat pumps ( considering obvious losses )

[Bolvan (OP)]

Many site of sort banned my for this question. So if you have collaterals feel free.

[Bored chemist]

We use freons because the heat of evaporation is large.
In general, using a phase change absorbs or releases a lot of heat.

[syhprum]

would not the use of air instead of Freon require very pressures the alternative to Freon is CO2 but much higher pressures are needed than Freon

[alancalverd]

Simple Stirling engines use air as the working fluid to convert lowgrade heat into mechanical work, and the reverse Stirling is used to liquefy nitrogen from ambient air, but for operation around ambient temperatures you get a lot more heat transfer in a given volume of machinery by using a liquid that evaporates around ambient temperatures and pressures.   

Bad news this week seems to be that banning Freons from domestic refrigerators may or may not have  had some effect on the ozone hole, but its replacement with propane may have caused the Tower Block fire in west London.

[puppypower]

The main reason they use freon is freon is not chemically reactive or flammable. Freons are a  class of compounds that are chlorofluorocarbons. When you make these, you begin with a hydrocarbon, like propane, and replace all the  reactive hydrogen, with chlorine and fluorine atoms. This makes the freon compound very stable, nonreactive and not flammable.

A diesel engine pressurizes hydrocarbon fuel, until it explodes. Freons will not explode under such pressure. Refrigeration cycles have to constantly compress and expand, with freons safe under a wide range of operation including high speed. Lack of reactivity also makes them less corrosive on compressor parts.

 

[Bored chemist]

The freons went outr of fashion a long while ago, and their "replacements"
https://en.wikipedia.org/wiki/Hydrofluorocarbon
are now also on the way out.

It's not a simple issue.
https://en.wikipedia.org/wiki/Refrigerant#Environmental_issues
Most things that would do the job are toxic, flammable or both.

Water and CO2 are "promising" on those grounds, but not very practical.

[Bolvan (OP)]

Please, explain "impractical".