Yes one day it could be useful, and if they were able to convert even small heat differentials then when your device reaches heat saturation and you shut your device off the heat converter could continue to run cooling down your device.
Well, the thing is, regardless how efficient they are, they are only useful in situations where you would actually want added thermal resistance between surfaces.
A good example would be something like an oven, where you want to isolate the inside from the outside thermally to conserve energy, and the temperature difference is significant as well. You could recover some electrical power when using a material like that in/as the insulation between oven and ambient.
Another would be in buildings that need to be heated because it's cold outside. There you want the extra insulation too, though the temperature differences are much smaller and you'd probably not recover that much power.
In electronics you generally do NOT want any thermal isolation, as the goal generally is to keep things cold instead of hot on the inside. Some exceptions would be things like valves, but apart from microwave ovens we don't see many of those anymore in consumer electronics.
Can you not see that if they ever got the efficiency above 75% that the work done by the recovered heat would actually cool these electronic devices you say can't be isolated? My point all along has been IF the efficiency were high enough, these thermal conversion appliances would act to cool your hot electronic devices by the first law of thermodynamics. It is the conservation of energy.
We apply energy to a ceramic looking TEC pad to move heat, spend energy to move energy, we do the same with air conditioners, spend energy to move energy, we know how air conditioners work by compressing Freon and using a condenser and evaporator to move heat, but how is it done with a flame ?
What I'm talking about is off grid propane refrigeration, so how does a burning propane flame power a mover of heat from the inside of a insulated box to the outside ?
When studying refrigeration in thermodynamics class it was referred to as a heat pump. That is all anything that cools is doing. Pumping heat from a cold environment to a hotter one. That can be done by many different ways, but always uses power of some form to do work.
As you know at 32F where water freezes there's still a lot of energy, until absolute zero there is heat energy, but to harvest in real time down to room temp would be revolutionary.
The one key thing to remember is there has to be a differential in order for it to work, so in industry or collecting engine heat there is heat energy above the ambient air temperature.
One old engine that works on heat differential, or rather vacuum created by a heated cylinder cooling is the sterling engine, they are able to use the heat of a candle, but again there must be a differential so there is time involved, what amazes me is how fast metals impart heat into the air and create a vacuum that can do work.
All that coal and natural gas we burn is simply breaking down chemical bonds, the material is still here as ash and gases, and the electricity we generate from the heat ends up radiating out into the clouds and space after we make use lighting our homes and running motors and electronics it's converted back to light and heat and some RF, sound all the waves, but mostly heat, if we could recover that inexpensively from every device against room air that would be something.
Actually, we convert heat into electricity by heating water mostly. But, even nuclear or worse, coal power plants are only about 42% efficient. Most of the wasted heat goes into thermal water pollution. We end up dumping a lot of hot water into rivers and lakes. But, coal also dump$ the dirtiest crap into the air. Not just CO2, but all sorts of crap including heavy metals, sulfur, and particulates. Hydroelectric is the cleanest energy, but they have put up so many dams on rivers, like the Columbia, that spawning salmon can no longer get back up stream to replenish the stock, which is not only bad for us, but the forests that are nurtured by the dead salmon. There really is no free lunch.
I guess your teacher should use tungsten lights then, as they are less expensive and more efficient heaters
It all depends on where you live and what the local prices for things like electrical power or natural gas actually are. Here we mostly use gas for heating as this is cheaper than using eletrical power and heat pumps and such. But this is also in an area where air conditioners in private homes are not that common, so you don't already have the heatpump there that just need to be put in reverse.
In countries that have abundant electrical power at low cost available, like from hydropower, it could make more sense to go to the heat pump approach even for just heating.