Flow pattern analysis and multi-objective optimization of helically corrugated tubes used in the intermediate heat exchanger for nuclear hydrogen production

Using the heat of the very-high-temperature gas-cooled reactor (VHTR) for large-scale and carbon-free hydrogen production provide an excellent option for a new sustainable energy economy. The intermediate heat exchanger (IHX) is a crucial component to realize this new hydrogen production mode. To supply sufficient heat for hydrogen production, the heat transfer of IHX needs to be enhanced. In this study, helically corrugated tubes (HCTs) were used to enhance the heat transfer of IHX. The flow pattern of HCTs was analyzed and a multi-objective optimization was then performed. First, the numerical experiment design with two objectives and three factors was conducted by Box-Behnken design in the response surface methodology (RSM). Second, the significant regression models for Nusselt number, friction factor, and performance evaluation criteria were obtained by the analysis of variance. Combining the analysis of turbulence kinetic energy and flow dead zone, a more comprehensive mechanism for the effect of corrugation parameters on flow and heat transfer was proposed. Finally, the fast-elitist non-dominated sorting genetic algorithm (NSGA Ⅱ) was adopted to conduct the multi-objective optimization of HCTs. The technique for order of preference by similarity to ideal solution (TOPSIS) was adopted for multi-objective decision-making. The CFD validation and comparison with RSM experimental design confirmed that the obtained Pareto optimal set and Pareto front can provide a comprehensive and effective design strategy for the IHX used for nuclear hydrogen production.