Does a perfect concave mirror act as a radiation heatpump

[philrainey]

if one was able to make a perfect concave mirror with half a cube shape perfect mirror in front of it ( so thermally isolated from outside with a perfect vacuum inside it) And a black body almost covering the front of the Concave mirror that is red hot and another much smaller black body in the focal point of the perfect concave mirror ( perhaps white hot) could one take the higher temperature heat from the white hot body and put it through a heat engine with the red hot black body been used as the cold sink (heat needs to be added at the red body temperature) So the heat rejected by the heat engine is not lost but recycled by been concentrated by the concave mirror and reused. Could a system of higher than cannot efficiency be created?

 

[sophiecentaur]

I think the flaw in this is that the temperature of the receiver (absorber) can never get to be more than that of the source (radiator) - or the heat will flow the other way. You will get thermal equilibrium, eventually. You cannot "re-cycle" energy back from the cold to the hot; that would violate a lot of principles. The idea of focusing doesn't actually solve the problem.
The heat engine that you put in between, can only operate on a temperature difference so it depends upon a source at a higher temperature than a sink.

 

[philrainey]

I was just looking at some diagrams of concave mirrors and yes the light leaves the focal point and hits the mirror returning to the heat source. Can't win.

 

[sophiecentaur]

If you have an ellipsoid reflector, it has two foci and all the energy from a radiator at one focus will be reflected onto the other focus. But things will stabilise with the receiver at the same temperature as the source. This shape has no 'gaps' around it so more or less all the energy gets where it's wanted - it's all inside the container.

 

[philrainey]

With a ellipsoid reflector can you have a sharp focus and a fuzzy focus so you can have a large area black body at a temperature (because it has a larger surface area)emitting more radiation than a smaller black body in the sharp focus at the same temperature?

 

[sophiecentaur]

The focus is at a point and any object of finite size will not be exactly at the focus.
I am not sure where your question is going but, whatever size the transmitter and receiving objects are, the equilibrium situation will be that they both achieve the same temperature if no energy escapes from the system. The surface area is not relevant here.
Along the same lines, the reason that the Earth is not at the same temperature as the Sun is that the Earth is radiating energy over a whole sphere but receiving energy from the hot Sun over a very small angle. All things being equal (greenhouse effect etc. is not relevant to the surface temperature of the 'outside' of the Earth system), any other sized planet in our situation would reach the same steady temperature.

 

[philrainey]

the Stefan-Bolttzmann law states that the power emitted per unit of area is directly proportional to the fourth power of its absolute temperature. I was thinking along the lines that if a black body is let's say ten times larger than another black body at the same temperature it will emit as out going radiation 10 times more heat power. If a perfect ellipsoid reflector could be made that focuses all the heat output from a larger black body onto a smaller black body even if all the heat emitted by the smaller black body was focuses back onto the larger black body there would be a 9 times the heat emitted by the small black body gain by the small black body. It would get hotter till the radiation flows balanced.
I know I'm a bit mad and this would break said thermodynamic laws bit I don't know why but I kind of feel these laws are general rules and one day will prove not to be laws at all. there is just something in my crazy mind that makes me believe this.

 

[Dale]

If a perfect ellipsoid reflector could be made that focuses all the heat output from a larger black body onto a smaller black body even if all the heat emitted by the smaller black body was focuses back onto the larger black body there would be a 9 times the heat emitted by the small black body gain by the small black body

Can you show the geometry that supports this? I have seen this claim made several times but nobody has ever demonstrated that it is correct. Because the objects are not points you cannot simply claim that all of the energy leaving one object will reach the other object. Their centers may be at the focus, but their surfaces are not.

 

[sophiecentaur]

In this model there is nowhere for the radiation to go but onto one or other object. Does that not imply that they must reach equibrium at the same temperature even if your objection about focussing were valid.

 

[philrainey]

I have not made one in fact I have no concave or ellipsoid mirrors at my hand, perhaps a concave mirror could potentially do it just as well . I'm not saying that it is so it is more of a question that I don't have the ability to work out. It just comes from my mad disbelieve in carrnots law been the best possible that maybe there is better than a Isothermal engine with no fiction I just think that was the best they knew about so they made it the standard. I guess if I has a good concave mirror that reflected more than just light we can see if I could put it in a vaced vessel at a constant temperature and put a black body at its' focal point and see if it gets any warmer. But I have no money or resources to use to do this so I just float a idea and see if I can get anyone to think about it from first principles and not just write it off because of the laws. I'm 99 % sure it dose not work but I believe one day some one will find some thing that does.

 

[sophiecentaur]

You seem to be confusing two topics together here. Carnot's Law considers heat engines and relates maximum efficiency to temperature difference. Your idea about system of reflectors relates to equilibrium temperatures.
When you say "write it off because of laws" you seem to be suggesting the 'laws' are just thought up by someone. The thermodynamic laws result from experimental and theoretical work and 'make sense'; you can't just dismiss them as something 'optional'. Unless you base your belief on these laws then you have to start from basics and derive an alternative set of reality. That would be tough, or impossible.

 

[Dale]

I have not made one in fact I have no concave or ellipsoid mirrors at my hand, perhaps a concave mirror could potentially do it just as well . I'm not saying that it is so it is more of a question that I don't have the ability to work out. It just comes from my mad disbelieve in carrnots law been the best possible that maybe there is better than a Isothermal engine with no fiction I just think that was the best they knew about so they made it the standard. I guess if I has a good concave mirror that reflected more than just light we can see if I could put it in a vaced vessel at a constant temperature and put a black body at its' focal point and see if it gets any warmer. But I have no money or resources to use to do this so I just float a idea and see if I can get anyone to think about it from first principles and not just write it off because of the laws. I'm 99 % sure it dose not work but I believe one day some one will find some thing that does.

Unfortunately, that is the same attitude that every single "optical heat pump" proponent has. None of you has yet been willing to put in the effort needed to analyze the idea and rigorously show that it has any merit.

Btw, the laws ARE the first principles.

 

[philrainey]

several hundred years ago they believed stuff that we now know is not true and it will be the same in another several hundred years time as it has been since science began. I'm in debt to buy this computer I'm typing this on . But I'm lucky at least I get enough to eat. I have not got the money to risk on a one in a 1000 experiment. Of course it won't work but one day the laws of thermodynamics will be broken by man, as they are in nature (otherwise we would not be here). Maybe they will find how to with their accelerator machine.

 

[sophiecentaur]

Archimedes, Galileo and Newton have never been shown to be Wrong. Their initial ideas have merely been modified to cover more cases. Not a bad track record.
If someone wants to 'have a go' at thermodynamics, then they must go to the basics in detail and see what is actually involved. Thermodynamics is not just a list of fanciful statements. It works. When one relies on gut feelings about such things, rather than rigour, there is always a risk of wasting ones time.

 

[philrainey]

Drinking and getting out of control is a waste of time , the more people thinking about solutions the better as even if 99.9% is a waste there is still the 0.1%

 

[philrainey]

These scientist are the few there were many others who believed the wrong ideas of the day. Many that many of us have never read about. Many people believed the world was flat they were all wrong but they really believed it.

 

[Dale]

I have not got the money to risk on a one in a 1000 experiment.

I'm not talking about an experiment. I am talking about sitting down with a pencil and paper and doing the geometry. If you are going to seriously propose a device that clearly violates the laws of thermodynamics then at a minimum you need to show that it satisfies the laws of optics.

 

[sophiecentaur]

These scientist are the few there were many others who believed the wrong ideas of the day. Many that many of us have never read about. Many people believed the world was flat they were all wrong but they really believed it.

Those involved in serious thermodynamics were not of the Flat Earth fraternity. You would know that if you were to read some basic textbooks and find out what they are actually saying. It's not like Yogic Flying and it isn't a matter of thinking and hoping. It's hard nosed Science.

 

[philrainey]

What is Yogic flying or is that a typo that is logic flying?

 

[philrainey]

I think you are right I'm inventing my own logic and then trying to make it fly. I have done calculations with the help of a mirror manufacturer designer and it is not geomettically possible . Back to dreamland again.

 

[sophiecentaur]

Google "Yogic Flying".
It involves people who have their own views on the natural world and they conduct 'experiments' on their own terms. These 'experiments' confirm their mind set.
But do we believe they are right? Have they any credibility?

I don't think that the geometry of mirrors is at the heart of the flaw in your proposal - I think it's more basic than that, even.

 

[philrainey]

everything seems absurd to me I'm not sure anything has any credibility .

 

[sophiecentaur]

everything seems absurd to me .

To me too, on occasions. But there is light at the end of the tunnel!