turbine? LOL thats the funniest thing i have ever heard of. Also you can coat the inside of the pipe as well. Also the heat is exiting the turbine not reversing direction and going back in.
The idea is simple keep hot air moves faster than cold air.
The other idea behind coating the turbine or wrapping it or shielding it is so you don't transfer heat from the turbine housing to the compressor housing.
But anyways not sure if this clears anything up for you as I am sure you already knew this.