Very interesting thread.
FI, you have loads more experience with turbochargers than I do and I'm chiming in with the utmost respect for said experience but I have to throw in with dozer here.
The expansion valve analogy isn't appropriate because the refrigeration in that case comes primarily from the phase change.
And, to say all turbines work from the flow of gasses across the work surfaces is definitely incorrect. Steam turbines extract a massive amount of heat energy from the steam, otherwise we could just use air pressure.
Turbos are similar. If the exhaust gas is cooler at the turbo outlet than the inlet, where did the energy go? This is a reason exhaust driven superchargers are more efficient than engine driven superchargers. You are using leftover heat energy from the combustion process to compress the inlet charge instead of new mechanical energy (requiring more fuel consumption) from the crank. If it was purely a gas pressure-driven scenario, the pumping losses through the exhaust side of the turbo would not offset the gain from the increased inlet airflow.
Keep the dialogue going. I'm learning from everyone here.
