Study on continuous cooling process coupled with ortho-para hydrogen conversion in plate-fin heat exchanger filled with catalyst

A mathematical model of the plate-fin heat exchanger filled with catalyst (CFPFHX) is established to investigate the continuous cooling process coupled with ortho-para hydrogen conversion at 42–70 K. The flow and heat transfer performance and the efficiency of ortho-para hydrogen conversion in the CFPFHX are quantitatively evaluated, and the effects of the structural parameters on the flow and heat transfer coupled with ortho-para hydrogen conversion are analyzed. The results show that the Elovich model is the best existing kinetic models of ortho-para hydrogen conversion with an average relative deviation of 1.8%. The Colburn heat transfer factor (j factor) of the hot side of the CFPFHX is 4.3 times that of the plate-fin heat exchanger (PFHX), and the thermal enhancement factor (TEF) of the hot side is 37.7% of that of the PFHX. Meanwhile, for the CFPFHX, the j factor and the TEF of the hot side under different structural parameters are always about 8–10 times and 68%–93% of that of the cold side respectively. Therefore, the CFPFHX can ensure the flow and heat transfer performance and realize the ortho-para hydrogen continuous conversion. And a fin with the larger flow area (high fin height, wide fin spacing and small fin thickness) has a better flow and heat transfer performance and ortho-para hydrogen conversion. The outlet para-hydrogen ratio y^out_p-H2 and the mass space velocity v_m in the CFPFHX have an approximate linear trend. When mass space velocity v_m ≤ 0.6589 kg/(m³·s), the outlet para-hydrogen ratio y^out_p-H2 can meet the requirement at 42–70 K. Above all, the mechanism of flow and heat transfer coupled with ortho-para hydrogen conversion is revealed for the first time in this study, which can provide a theoretical guidance for the application of the integrated technology in large scale hydrogen liquefaction process.