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dr1ce Mar14-12 09:04 PM

Generating power from heat
Hi fellow science fans!

Say I have this 55-gallon drum full of water kept at an approximate constant temperature of 120 that I want to create power from. The air temperature is about 60

I'm thinking a possible way to do this would be to submerge a closed vessel full of a solvent that will boil at say +/- 100 and using the vapor from this solvent to spin a turbine, like a traditional steam generator. I would then like to use the ambient air temperature to condense the solvent back to a liquid for recycling.

I imagine someone has tried something like this at some point in history.

Is there a name for this sort of generator?

Any idea what sort of solvent would have the characteristics I'm talking about at these temperatures?

Also, I should mention, the hot water is free and I'm not trying to create "extra" energy from heating water or anything. Basically, pretend i'm using a hot spring the size of a 55 gallon barrel.

NascentOxygen Mar14-12 10:15 PM

Re: Generating power from heat
Hi dr1ce!

You plan to use the vapour's pressure? In which case, your working fluid will not boil until at a higher temperature while under pressure.

As an aside: this idea of an intermediate stage is used in nuclear power stations, but for a different reason: to put a stage of isolation between the fluid that circulates through the reactor (and which in the event of a problem could become radioactive) and the "outside world" of the steam turbine generators, so any outside leaks are of a hopefully uncontaminated fluid.

Mech_Engineer Mar14-12 10:21 PM

Re: Generating power from heat
You are describing a Rankine Cycle system:

A very common working fluid in a Rankine engine is water (steam), but that is not a requirement.

dr1ce Mar14-12 11:05 PM

Re: Generating power from heat
Exactly the info I was looking for!

Much Thanks...

sophiecentaur Mar15-12 05:06 AM

Re: Generating power from heat
At this stage it may be worth while asking how much power you would be expecting. Is this a fun project 'to show it can be done' or a serious attempt to harvest some free energy? Your problem here is that the temperature difference is very small (on the thermodynamic scale) and that means very low efficiency.

What is the power source that keeps your drum at 120(F?)?. If you are paying for the energy to do the heating then it doesn't make sense to try to use this warm water as an energy source. Better to insulate it and use the electricity you saved. But this may be a misplaced voice of reason and NO FUN AT ALL :rolleyes:

I have seen a number of model Stirling Engines, working with pretty small temperature differences. There are construction kits available for making them. They do little more than manage to turn their own mechanism but the do prove a point.

NascentOxygen Mar15-12 07:06 AM

Re: Generating power from heat

Quote by dr1ce (Post 3815829)
Hi fellow science fans!

Nanotechnology to the rescue.

sophiecentaur Mar15-12 07:22 AM

Re: Generating power from heat

Quote by NascentOxygen (Post 3816413)

No mention of actual power output from this device, of course. Whilst there is clearly some waste heat from your body, you still need a cold sink. What form would this take? A large radiator strapped to your back? How about on a sunny day?
I could be eating my words in a few years' time, I admit but, as my favourite song goes - "it's the numbers that count".

Mech_Engineer Mar15-12 09:09 AM

Re: Generating power from heat
Based on the 120 degree hot-side temperature (I assume you mean fahrenheit), and the 60 degree cold-side temp, the maximum efficiency you can attain is 10.4%. That assumes you're able to maintain both teperatures fairly well.

watermotorman Apr28-12 08:29 PM

Re: Generating power from heat
Hi all! Just wondering what ever became of the idea. Did you ever build one?

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