quote Originally posted by Marvin McInnis: And why would you even want to do that? Not only is water immensely cheaper and immensely more plentiful than any synthetic refrigerant, but also the enthalpy (heat) of vaporization of water is more than 10 times that of R134a.

That sounds like a bad characteristic for a heat engine to me... It takes significantly more energy to change water to steam than it does to vaporize most refrigerants.

Will,

As, I think, Marvin was correctly trying to point out, the heat content of steam is MUCH more than freon vapor.

But the expansion ratio from liquid to vapor is what drives a turbine...

i think of it in terms of pressure difference from the inlet side to the exhaust side for example if there is 500 psi on thee inlet side and 100 psi on the exhaust then some work will be done but if both sides had 500 psi the turbine would just sit there doing nothing no matter how hot the steam is. what Will said is correct the more it tries to expand the higher the pressure

[This message has been edited by engine man (edited 05-21-2012).]

quote Originally posted by imacflier: Will, As, I think, Marvin was correctly trying to point out, the heat content of steam is MUCH more than freon vapor.

Consider why methanol in an engine makes more power than gasoline, despite having a fraction of the energy density...

quote Originally posted by Will: But the expansion ratio from liquid to vapor is what drives a turbine...

And it's the thermal energy in the working fluid that drives that expansion.

It's been many years since I've spent any time staggering my way through that labyrinth called steam tables, but the basic principle is that the output of an ideal (i.e. isentropic) turbine is proportional to the decrease in enthalpy (total thermal energy) of the working fluid as it passes through the turbine. Just do a simple energy balance through the turbine ... total energy out (thermal+mechanical) must equal total energy in (thermal). Specifically, though, I was thinking of the high-efficiency condensing steam turbines, where the heat of vaporization of water is indeed significant.

quote Consider why methanol in an engine makes more power than gasoline, despite having a fraction of the energy density...

Not relevant to the present discussion. In that case the methanol is being used as fuel, not as the working fluid. But we're getting way beyond the original topic, so I'll stop here.

[This message has been edited by Marvin McInnis (edited 05-22-2012).]

quote Originally posted by Marvin McInnis: Not relevant to the present discussion. In that case the methanol is being used as fuel, not as the working fluid. But we're getting way beyond the original topic, so I'll stop here.

The methanol definitely is the working fluid. The thermal energy from the combustion drives the change of state of the fuel from liquid to gas. The expansion ratio of the change of state creates the pressure that drives the engine. Because of this, a methanol engine only needs a tiny amount of coolant compared to a gasoline engine.

In a gasoline engine, the energy of combustion goes to heating the air rather than to a change of state.

Dam-it no sale on the car and work is talking about cutting my hours to about 35 i need to be just happy with the 3.4 DOHC for now

[This message has been edited by engine man (edited 05-22-2012).]