what are the simplest means for converting heat energy to electricity, the only one i can think of is using the heat to generate steam from water and turn turbines… any others? does that work with other liquids with lower boiling points such as say alcohol, or in a closed system?
Yes the general concept will work with other liquids with varying efficiency depending on properties of the materials. Some of the heat that you put into the liquid will have to be dumped to the enviroment for the material go back to a liquid. Materials with high specific heats will be in general less effecient.
Depending on what you mean by a closed system it will work. If you mean a system that reuses the liquid by cooling it down after it flows through the turbine then yes you can do that. All you need is a way to cool down the liquid such as a refridgerator, AC unit or simple conduction/convection to the enviroment.
Thermocouples.
Heat applied to one junction of two dissimilar metals causes a voltage potential that causes current to flow. No moving parts, nothing to leak.
Electricity directly from heat. Not a bunch, mind you, but some.
In actual practice thermopiles haven’t proven to be all that practical or efficient. They’re best used in applications that simply cannot tolerate moving parts, e.g. deep space probes.
Oh sure, no doubt about it, they’re not very efficient. And outside of temperature probes or flame safety switches you don’t see a lot of applications. But they are very practical for those.
But the question wasn’t “What’s the most practical or efficient way to generate electricity from heat”, it asked about the simplest. You can’t get much simpler.
RJKUgly’srightCrafter_Man, you can’t get much simpler than a thermocouple.
I once saw a science fair exhibit with a bunch of thermocouples in series placed over a candle that ran a small transistor radio. It was cool. I would want that kid with me at the end of civilization, if in fact, he made the apparatus.
You can’t create electricty, or any other form of energy from heat itself, you can only get energy out of a movement of heat from ‘hot’ to ‘cold’, reverse this process and you have to input energy to make heat move from ‘cold’ to ‘hot’.
Peltier devices (also known as thermo-electric coolers, or TECs) are commonly used in computers to cool down the processor. I’ve also seen them in portable electric coolers (as in a picnic basket type cooler, for your beverages and such). A peltier device is made up of a bunch of P and N type silicon semiconductors. I found this pic. It’s not in english, but I think you should get the idea.
Here’s a picture of one that attaches to a CPU:
http://www.karbosguide.com/images/peltier.jpg
Anyway, when you run electricity through a peltier device, it works like a bunch of itty bitty heat pumps. One side gets hot, and the other side gets cold. They are reversible, so if you flip the polarity of the electricity around, the opposite side gets hot and cold.
They also work completely in reverse. If you apply a heat differential from one side to the other, they generate electricity.
Like thermocouples, they have no moving parts and aren’t terribly efficient.