Quote:
Originally Posted by ForcedInduction
Not true. What really does the job is the aerodynamic flow of the expanding gasses across the turbine, not the heat itself. The exhaust gets cooler as it exits the turbine in the same way that refrigerant gets cold as it exits the expansion orifice, rapid expansion. Thats what confuses people into thinking that the exhaust heat is doing the work.
Think of a wind farm, they don't work by heat but by the flow of air across the blades.
|
No, that's not correct, in two senses....
First, it's not like a wind-genny; which works solely from lift over a wing; and extracts pretty much the same energy >>regardless of the temp of the gases flowing through it<<.
(important point/difference there)
Secondly, I think you're looking at it backwards; because it is the heat that CAUSES the gases to expand. It is the HEAT energy at work here....not the minimal pressure-differential across the expander.
The exact same kind of turbo-expanders are also used as "energy-recovery" machines in all sorts of industrial processes that handle -hot- gases......like refineries, ammonia-manufacture, etc..
Obviously, there does have to be -some- delta-P, to get the gas through the turbine in the first place; but the majority of the rotational power comes from the heat-energy stored in HOT gas....rather than the minimal mechanical-energy in the typically small delta-pressure across the turbine.
As a thought-experiment, imagine putting the same paltry low psi/delta-P of -cold- gas (i.e. ambient temp) into your turbo-turbine...
Even if the in/out pressures and flow-rate were identical to your engine exhaust, you'd hardly get any shaft-power at all.....simply because there just isn't any energy to speak of in 70F gas vs. 1000F gas.
hope I was coherent with the above...it's 1am here...
