Regenerator and stack experiment

What is the difference between the stack and regenerator? Stack is loose and we use it in the standing wave thermoacoustic engine. Regenerator is dense and we use it in the traveling wave thermoacoustic engine. The air is heated and cooled in the stack with a delay because is it loose. Standing wave engine makes a 90 degrees phase shift difference the between pressure and heat exchange with a delay in the heat exchanger (brayton cycle). The air is fast heated and cooled in the regenerator because it is dense. Traveling wave engine makes a 90 degrees phase shift difference the between pressure and heat exchange with a air displacer piston (stirling cycle). In the lamina flow engine restrictor is same as stack. Restrictor can be replaced with stack and visa versa. https://3.bp.blogspot.com/-3LxAT3cNVcQ/VzypFL… The reducer separates the hot and cold side, and makes a turbulence . The heat exchange so happens on