Now we have a thermal gradient or difference, but we can't do anything with it because we don't have a way to get at it. The stack is just sitting there, with one end hot and one end cold, but nothing else is going on. In order to get useful work happening, we need to add heat exchangers at each end of the stack. Heat exchangers allow us to get heat energy in and out of our thermoacoustic engine. Usually they are built out of a network of fine tubes with liquid flowing through them, and fins on the tubes for better thermal contact with the air, like the radiator in your car's engine.
Figure 4. Heat exchangers at each end of the stack allow heat energy
to flow into the air at the cold end of the stack, and out of the air
at the hot end of the stack. The arrows show how the air parcel takes
in heat energy at the cold end and gives up heat energy at the hot
end.
This page maintained by Wil Howitt