Analysis of standing-wave stack for direct cooling and ortho-parahydrogen conversion of cryogenic hydrogen

Direct cooling of cryogenic hydrogen can be achieved by flow through a stack or regenerator of a thermoacoustic refrigerator. In addition, using a catalytic stack, the ortho-parahydrogen transformation can be conveniently realized in the same device. Analysis of this system element is carried out by integrating one-dimensional thermoacoustic equations with addition of empirical ortho-parahydrogen conversion reaction. Calculations in a standing-wave catalyzed setup demonstrate a selection process for optimal acoustic impedance and stack pore dimensions, showing significant advantage over non-catalyzed hydrogen- and helium-based stacks of similar kind. Results are presented for hydrogen flow characteristics and distributed heat load due to ortho-parahydrogen conversion inside a stack. The stack performance is also quantified at variable flow rate of hydrogen, stack length, mean pressure, and supplied acoustic power.