Is Carnot efficiency valid?
I've done nearly everything possible I can think of to block the "flow" of heat out of a Stirling engine, with the idea that if the "heat rejection" could be blocked, the engine would quickly overheat and stop running, or be unable to start running in the first place.
To that end, I recently sent away for a silica Aerogel blanket, which is supposed to be very good at blocking heat. I was able to apply a propane torch to one side and not feel heat through the blanket with my hand on the othe
I have no major disagreement with that ("the direction of heat flow is determined by force of numbers"). True enough, but incomplete. (Not force of numbers exclusively. Also energy level).
You are also neglecting to address the fact that heat, as a form of motion or kinetic energy, may also be converted to some other form of energy entirely. At that point any "flow" of "heat" (in the form of sensible/measurable heat) comes to an abrupt end. The heat is gone having been replaced by the wheel