[Escorpiuser]

I think that there is a point to take into account: an ideal gas is not ideal anymore when it is compressed. Then begin to arise other atomic/molecular factors that change the general expression PV=nRT.

About if the today refrigerants are wrong, what I remember from the College is that some liquids were discarded because they were flammable/explosive. Others, because were chemically corrosive/agresive, especially for the pipes, but also for humans. The candidates had also to be chemically stable. All these limits drove to elect the known CFCs, that now are being replaced by others (¿fluorocarbons?) less harmful to the ozone layer. Maybe they are not the best in terms of efficiency, but there are other factors that make them the most suitable in the state of art.

[SeanB]

The best refrigerant is ammonia, at least for large cold stores and freezers. Cheap, non corrosive ( or at least not terribly corrosive provided you keep water out of it) and works at sane pressures. Newest is CO2, used at insane pressures in commercial fridges, and doing a good job at it, though leaks are a little problem, pressures being up there with high pressure hydraulics - AKA making artificial diamonds, and failures are loud and announce themselves.

[Bored chemist]

" Newest is CO2, used at insane pressures in commercial fridges, and doing a good job at it, though leaks are a little problem, pressures being up there with high pressure hydraulics - AKA making artificial diamonds, and failures are loud and announce themselves."
In a very real sense.
According to this
http://www.scribd.com/doc/36474478/CO2-Refrigerant-for-Industrial-Refrigeration-1
The typical pressures are more like 60 bar
Those in hydraulic systems are more like 200 to 400 bar
http://www.omega.com/Green/pdf/HFP_Series.pdf

 and those for making artificial diamonds are about 50,000 bar (I may have lost track of a zero or two converting units on that one).

[SeanB]

The pressures are high compared to older refrigerants, who top out at around 20 bar. you have to use special connectors and piping, most of which is both expensive to buy and expensive to get the tooling to use it. Hydraulics are able to cope with slow leaks, the CO2 systems do not tolerate any weakness at all. They have been known to burst piping and parts in fault conditions.

[gotoluc]

I was looking at this vapor pressure chart in Wikipedia.  Sorry it only has a few substances, but the idea is the same. 

newbielink:http://en.wikipedia.org/wiki/Vapor_pressure [nonactive]


Looking at, say the difference in vapor pressure between -10°C (below freezing), and +20°C (room temperature).

If you choose, something like Propane (BP is -42°C), one goes from a vapor pressure from about 2.5 ATM to about 8.5 ATM, or a difference of about 6 ATM.

However, if one chooses a refrigerant like Diethyl-Ether, one goes from about 0.15 ATM up to about 0.6 ATM. 

So...
Theoretically, running the diethyl-ether in a vacuum, rather that under pressure, one should be able to force the phase change with an absolute difference of only about 0.5 ATM.

It would seem as if one should be able to design the diethyl-ether refrigerant to use less energy.  Although, I know that a vacuum pump in air, seems to have to work quite a bit to achieve a low pressure.

Hi CliffordK,

I just joined this site because of the topic you started.
I was searching the net for a gas that would expand and contract at temperatures found in the environment (weather) and found that diethyl-ether seems to fit the bill and also found this topic.

Let me tell you what I have in mind. I'm building a self sustained houseboat to which I'm considering to propel with solar electric as I have enough surface area for 2kw of photovoltaic panels. However, I'm always thinking of alternatives as my boat build is far from complete and was considering a heat engine and also thinking of using a gas in it.
I have a great source of heat (sun) and a great heat sink (river) I'm sure there could easily be a 50 degree Celsius difference between the two temperatures.
You seem to be open minded and interested in new ideas, so what would you think of using this great free energy temperature differences to expand and contract a gas in a piston heat engine?

Thanks for your time

Luc