Multi-objective optimization of the plate-fin heat exchanger coupled with ortho-para hydrogen conversion for hydrogen liquefaction

Catalyst-filled plate-fin heat exchangers (CFPFHE) are the preferred choice for converting ortho-hydrogen to para-hydrogen in hydrogen liquefaction systems. However, the effects of combining heat exchanger structural variations with changes in catalyst particle parameters on ortho-to-para hydrogen conversion are rarely discussed. This study first conducts the sensitivity analysis on the structural parameters of the heat exchanger and the geometric parameters of the catalyst particles. Then, based on the response surface methodology (RSM), the interaction effects of these parameters on the overall performance of CFPFHEs are explored. The results indicate that the fin spacing and porosity are the key factors affecting the comprehensive performance of CFPFHEs. The heat transfer enhancement factor TEF is defined to comprehensively assess the thermal performance (j factor) and hydraulic performance (f factor) of the CFPFHE. The ortho-para hydrogen conversion rate eta is introduced to evaluate the conversion efficiency of the CFPFHE. Finally, the multi-objective optimization targeting TEF and eta is conducted and the optimal parameters for the CFPFHE in the specific commercial hydrogen liquefaction process is obtained. Compared to the initial design scheme, it is found that the TEF of the optimized structure increases by 109.6%, and the eta increases by 63.8%. Additionally, the TEF and eta calculated through numerical simulation have the errors within 5% compared to the predicted results. Therefore, the multi-objective optimization method for the CFPFHE based on the RSM is relatively reliable. This method can provide guidance for the design and optimization of CFPFHEs in the hydrogen liquefaction process.