Tom Booth

OK, that makes sense, I think. So then, as far as using the formula, it doesn't matter that adding heat does not produce useful work in this situation. Rather, removing heat stores potential energy in the water, which if then allowed to freeze, can crystalize and lift a weight as heat is lost? Can the sign just be ignored and change the negative (heat rejected) to positive? Or is it necessary to measure the heat absorbed by the ice in melting and use that number. Or doesn't it matter? I feel like my brain is getting a whiplash trying to follow the logic of all this. Then would W/Qh be identical to W/Qc, one can't just be substituted for the other can it? I should have said, or my intended meaning was: " I don't think expansion volume is a determinant of the available energy" - all by itself. Of course. I guess. An engine is a vessel designed to easily "rupture" in such a way as to perform work by means of a moveable wall; the piston, attached to a crankshaft or whatever. The "ice bomb" engine would have to be similarly constructed. Something like a very strong hydraulic jack. The impracticality of the small distance traveled might be overcome by attaching the piston to some kind of long extended lever.

That assumes some cooling apparatus. As already stated, that is not the case. The process could, for example be taking place in winter, or at the north pole where below freezing temperature is the prevailing condition. To have a complete cycle, it can be assumed the engine must contact a higher temperature reservoir to re-melt the ice, but no energy is expended in freezing or thawing as far as calculating efficiency is concerned. The Carnot model of an ideal heat engine assumes the pre-existence of two "reservoirs" of different temperature, neither of which needs to be created. "Efficiency" depends "only" on the difference in temperature and does not address in what way that difference came into existence. I don't think expansion volume is a determinant of the available energy. For example, if I lift a ping pong ball ten feet and a ten ton block of concrete 0.5 inches, which one of the two has the greater potential energy?

The Joule–Thomson effect, used in refrigerators and heat pumps and in the liquefaction of gases. (Linde process) The air, held back in the mouth under increased pressure does result in higher temperature, higher kinetic energy, which quickly equalizes with the body temperature and is carried off by the blood stream, so when the air finally escapes, it can expand and reclaim the lost heat. That is to say, it is now colder due to having previously lost heat while under pressure. the air also does a bit of work while escaping, pushing the outside air aside. So a bit of the Claude system of refrigeration as well.

A cold reservoir. Not an energy source. An energy sink.

An "Ice bomb" is made by filling a very strong iron container with water and freezing it. As water freezes it expands in volume exerting a force of some 100,000 pounds per square inch. The "ice bomb", usually a grenade shaped cast iron container, when frozen, will explode with tremendous force. If contained within a wooden box when it explodes, it will destroy the box. A conventional hot air or heat engine similarly utilizes the property of a gas that expands and exerts a force with a change in temperature. A gas is heated in a cylinder and the expanding gas expands and drives a piston. Could a thermal engine be constructed that utilizes the property of water to expand when frozen, taking advantage of the same force that causes the "ice bomb" to explode? If not, why not? We know that the efficiency of a heat engine is represented by the formula: efficiency = W/Q hot or the work output of the engine divided by the heat input. In the case of the theoretical ice bomb engine, however, Q hot is negative as heat is taken away to cause the ice to expand and output useful work. Therefore, is the efficiency of the "Ice bomb" engine also negative? Can the efficiency of a thermal engine be less than zero, yet still operate? It seems clear to me that by containing water as it freezes and expands, useful work could be extracted.