beelsebob wrote:Huh? No – heating air doesn't magically make some of it's mass disappear.
Yes, it makes it less dense, but the mass remains constant – the volume increases, which causes the velocity to increase, especially when pushed through a tiny exhaust hole. This is the same principal a jet engine works on.
Who said anything about decreasing the mass of the air? I said I believe the mass-flow rate will not increase as flow velocity won't increase (in my opinion). You clearly understand the topic involved so please don't belittle me or my opinion by dumbing it down and suggesting I said that heating the air will decrease its mass. At no point did I say that.
That being said I think I've not made myself clear enough in my previous post. The reason I think the mass-flow rate will not increase (
or at least not enough to provide enough velocity to blow the diffuser) is because I cannot see either of two things:
1.) A sufficiently small enough nozzle for these heated gases to be expelled through towards the diffuser at such speed. [Then again perhaps this has not yet been shown on the photos available]
2.) I don't believe that the exhaust pipes on the car will be able to heat the air sufficiently to expand the air enough to accelerate it through the nozzle (assuming there is one) which blows the diffuser.
The actual exhaust gases worked as they were being forced out by the engine at speeds far in excess of the free stream velocity (which clearly is what our starting point will be with this heat-exchanger idea).
Restricting air flow speeds it up, not slows it down...
While this is true, I would have thought that it isn't always quite so simple in terms of the overall design. An (admittedly rather extreme) example is a parachute. A parachute restricts flow, and there will be a point at which there is an accelerated flow through a small gap at the top of the chute...but the overall drag caused by this is great. Surely this "side-effect" would be undesirable on an F1 car.
As you say the theory works on Jet engines. But in the case of a Jet engine we are dealing with air that has already been compressed, mixed with fuel and combusted. The exhaust gases are being heated far more than this heat exchanger proposal will allow and are traveling at FAR greater speeds than they would in with the heat-exchanger idea. Which is why I believe the mass-flow rate won't be increased sufficiently for this proposal to have any determinable effect.
I hope I don't sound like I am "slagging off" the idea (tone of voice is very hard to convey over text) in fact I really do like the idea! It's just that I cannot see how it can work without some way of actually propelling this heated air over the diffuser as I just don't see the idea you are suggesting being capable of doing so.
But this is only my opinion.
Silence is golden when you don't know a good answer.