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New Thermocell Could Turn 'Waste Heat' Into Electricity
dryriver sends this quote from Phys.org:
"Harvesting waste heat from power stations and even vehicle exhaust pipes could soon provide a valuable supply of electricity. A small team of Monash University researchers ... has developed an ionic liquid-based thermocell (abstract). Thermocell technology is based on harnessing the thermal energy from the difference in temperature between two surfaces and converting that energy into electricity. The new thermocell could be used to generate electricity from low grade steam in coal fired power stations at temperatures around 130C. This would be implemented by having the steam pass over the outer surface of the hot electrode to keep it hot while the other electrode is air or water cooled."
How do you keep the other side of the item cool? The waste heat goes somewhere?
Have you compiled your kernel today??
Greatest source of hot air in the country. Expected to solve the energy crisis.
We already suffer a glut of energy, but I suppose this might serve as a nice little accessory for your backyard distillery...
“He’s not deformed, he’s just drunk!”
Did Congress repeal the Laws of Thermodynamics?
The electricity issue is not a generation issue. We have enough technology to produce more electricity that we need. The problems we have are transmission , storage, and reliability. While we can produce much more energy than we need the challenge is to store it for when we need it, transmit it to where we need it and to be sure that it will not fail. For example, solar farms in the Sahara desert could power all of Europe. The issue is transmitting that power to Northern Europe and storing enough power to last the night. While Some HVDC line are being installed it is not enough to get that power to Germany and north.
Thermoelectric power has been around for a long time. There is, literally, nothing new about this. The efficiency is still not high enough to make it worthwhile for any sense of scale. They are better off using waste heat the way they currently do, to heat up the incoming cold fluids that get turned to steam through heat exchangers.
On cars, you do not get enough power out of the current materials to make it worthwhile.
Peltiers manage around 5% conversion efficiency.
Net energy loss is what you already have today.
Drive your car down the road, and your exhaust is always hotter than the ambient.
Run your exhaust thru this device, and you can recapture some of that existing loss to power your car's Air Conditioning.
This isn't the only research looking for such technology:
http://phys.org/news/2011-05-high-performance-bulk-thermoelectrics.html
Sig Battery depleted. Reverting to safe mode.
For efficient conversion of heat to you MUST have high temps. Modern pressurized water nuclear reactors run at about 150 atmospheres -- corresponding temperature of 315 C / 600 F. There is no way to avoid this with liquid water as the working fluid. Contain 150 atmosphere of pressure at all times dominates the design of the reactor. Some newer designs use different working fluid. E.g. a LFTR reactors (drawing board only) using a Brayton cycle based on helium or nitrogen gas and a 700 C temperature source -- no high pressure used in the the nuclear vessel.
Also look at the design of the power generation cycle in a power plant. There is a relatively small high-temperature turbine that generate 2/3 of the electricity and a much larger secondary turbine that generates 1/3 of the electricity. The lower-temp output of the first turbine is the input for the 2nd turbine.
Without going too deep into a lesson on thermodynamics, there is not going to be much chance that this works in a modern power station.
Let me put it this way. Current power stations are already engineered to be as efficient as possible. This generally means they are keeping the phase translations of the working liquid using the minimum temperature differentials possible to avoid entropy loss over the ideal Carnot cycle. Any thermally driven power producing device put in series with the heat exchangers is not likely to capture any more power than will be lost by the increased temperature differential required by the device. If this wasn't true, why don't we just attach a boat load of sterling heat engines (http://en.wikipedia.org/wiki/Stirling_engine) to do the same thing? Reason: It wreaks the efficiency of the power plant by making the temperature differentials higher.. Chances are this new idea has the same problem.
Now, on your car, or other internal combustion engines, there *might* be some application, but I don't think there will be enough power output to make up for the weight increase. There is a HUGE amount of waste heat from your car engine but the question is how efficiently can we capture that and make useful energy out of it? Answer: Not very... Worth looking at because of the amount of heat being just dumped and the high differential temperatures but not likely to be much gain overall.
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101
The most efficient nuclear power stations in operation today are the Advanced Gas-cooled Reactors (AGRs) in the UK. They use CO2 as a coolant circulating through the carbon-moderator core at over 600 deg C with a generating efficiency of about 41% conversion of thermal energy to electricity compared to steam-moderated PWRs at about 34%. The low cost of uranium fuel per kWh generated means the extra efficiency doesn't help that much in terms of price of electricity generated or operating costs.
Extracting usable work energy from waste heat has always been possible. The problem isn't making the heat do work. The problem is doing so cost-effectively. For most applications, these heat capture devices have such low power densities that it's counterproductive to add them (e.g. adding a stirling engine to your ICE car's exhaust system would burn more fuel due to the extra weight than the fuel savings you'd get from putting the heat energy to work). At that point, it's not worth implementing compared to just dumping the heat straight into a heat sink.
The abstract says they're getting power densities of 0.5 Watts/m^2 in an unoptimized device. That's pretty deep in "not worth it" territory. This device would have to have an area of 1,5000 square meters exposed to the car's exhaust gases just to generate 1 extra hp. I suspect the additional back-pressure alone from all that piping (never mind the weight) would cost the engine a lot more than 1 hp of generation capacity.
Right. What we have here is another crap materials science article. Somebody did something vaguely interesting at lab scale, and then issued a bullshit press release.
Trying to get the last remnants of recoverable energy out of a heat engine is an old game, going back to the reciprocating engine era. Basic steam engines had one cylinder running off boiler pressure. Double-expansion steam engines had a second cylinder running off the output of the first. The second cylinder is bigger and runs at lower pressure. Triple expansion steam engines had a third, even bigger cylinder. Some quadruple expansion engines were built, but this is a diminishing-returns thing, and triple expansion is about as far as it's worth going economically. Marine engines were often triple-expansion.
Large steam turbines do the same thing, with a succession of rotors of increasing size. Three to twelve stages have been used. Again, this is a diminishing returns thing. At some point the steam condenses to water, which you don't want to happen inside the turbine. Existing turbines get close to that limit. Some turbine plants have a partial vacuum going into the condenser to keep the steam as a gas below 100C. 90C exit temperatures are not uncommon. Almost all of the usable energy has been extracted with an exit temperature like that.
If this new thermoelectric thing is a better way to convert heat to electricity than a steam turbine, it should replace steam turbines, not just be used on the cold end of the system. An efficient solid-state way of converting heat to electrical energy would be valuable. All the existing thermoelectric devices have low efficiency compared to heat engines. Back around 2011, there were several startups getting Federal grants for R&D into "heat harvesting". Commercial products were supposed to appear in 2012. Didn't happen.
Commercial fossil power stations already drive their stack gas temperature about as low as practical via various heat capture methods, reheat systems, etc. The limiting factor generally is not recovering more energy from stack gasses but the desire to never drive the stack gas temperature below the dew point in that exhaust gas, doing so causes all sorts of negative chemical consequences for the stack itself, pollution control equipment, etc., increasing maintenance cost and reducing equipment life due to aggressive corrosion of stack components and structure. Plants I operated were strictly kept from dropping below dewpoint on the exhaust for this reason, not to mention temperature input constraints for effective operation of some pollution control equipment, you CAN recover more energy from stack gasses, but doing so hits a cost negative and reliability wall. Always remember that waste heat/energy for a utility station equates to large $$$, if there's a practical way to extract more energy from a given amount of fuel, they are likely there as quickly as they can implement it. But the carnot cycle and other less heat cycle related limitation put up a pretty tough barrier to going further, Perhaps this is useful for more "pure" exhaust gas or waste heat streams, but I don't see it happening for commercial fossil power stations
However, the carbon moderator core at over 600 C scares me. What if oxygen gets in there? Burning core, reminscent of Chernobyl. Very scary.
Contrary to what you might think, carbon is actually safer at those temperatures. Under neutron bombardment at low temperatures, the Wigner energy can build up, and that is the source of the problems. However, at the operating temperatures of molten salt reactors, solid graphite is quite safe. (You can purchase graphite crucibles good to 2500C.) There is further discussion here.
When you put money above dumping waste heat to the atmosphere (and the problems that will eventually cause)
Again, the problem here is that using that waste heat may cost more in whatever you value, money, environmental dogoodness, or whatever, that it is not worth the effort. Waste heat is easy to dissipate. It is not so easy to use.
And it's a waste of your time to put a moral connotation on money. Money is just a unit of exchange for things we value. A process which loses money, means that someone loses some ability to trade for things they value. One doesn't have to be a "cheap greedy fuck" to be concerned about activities which just lose money without doing anything useful enough in return.