Applying of mechanical failure criteria of brittle material to the design of high temperature heat exchanger

Previous studies have suggested using a ceramic high temperature heat exchanger as a sulfuric acid decomposer for hydrogen production within the sulfur iodine thermochemical cycle. The decomposer was manufactured using fused ceramic layers that allow the creation of channels with dimensions below one millimeter. The heat exchanger is expected to operate in the range of 950°C. Thermal stresses are however induced in the heat exchanger ceramic components. In this study, proper failure criteria are selected to evaluate the safety level of the ceramic components. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer, stresses and chemical reactions in the decomposer. Fluid, thermal and chemical reaction analyses are performed using FLUENT software. The temperature distribution in the solid is imported to ANSYS software and used together with pressure as the load for stress analysis. Results of this research can be used as a basis for the investigation of the optimal design of the decomposer that can provide a maximum chemical decomposition performance while maintaining stresses within design limits. The stress results are used to calculate the probability of failure based on Weibull failure criteria and the factor of safety based on Coulomb-Mohr failure criteria.; A parametric study of a straight channel sulfuric acid decomposer is made. Several different geometries of the decomposer channels which include straightforward, ribbed, hexagonal, and diamond forms are investigated. The influence of the mass flow rate and of the area of chemical reaction on the chemical decomposition performance for the decomposer are also explored. The analysis includes the steady state operating conditions and the transient operating conditions. The research considers stresses that are induced during transient scenarios, in particular, the cases of startup and shutdown. The analysis includes also the Bayonet design of heat exchanger as silicon carbide integrated decomposer (SID) which produces sulfuric acid decomposition product - sulfur dioxide. The product can be used within the sulfur iodine thermochemical cycle portion of the hydrogen production process. A two-dimensional axisymmetric geometry of the bayonet heat exchanger is created using GAMBIT software. A computational model is developed to investigate fluid flow, heat transfer and chemical reactions in the porous medium of the decomposer. Fluid, thermal and chemical reaction analyses are performed using FLUENT software. Temperature distribution in the solid is imported to ANSYS software and used together with pressure as the load for stress analysis.