Heat and fluid flow analysis in a molten CuCl heat exchanger

Abstract

The Cu-Cl thermochemical cycle is a promising method to generate hydrogen as a clean fuel for human use in the future. The cycle can be coupled to nuclear reactors to supply its heat requirements. The cycle generates hydrogen by splitting water molecules through a series of chemical reactions. Thermal management within the cycle is crucial for improving its thermal efficiency. The cycle has an average theoretical efficiency of around 46% without any heat recovery. The efficiency may increase up to 74%, if all heat associated with the products of the cycle’s steps is recycled internally. The products of the different processes that transfer heat are; oxygen, hydrogen, and molten CuCl. The heat carried by oxygen and hydrogen can be recovered by the use of conventional heat exchangers. However, recovering heat from molten CuCl is very challenging due to the phase transformations that molten CuCl undergoes, as it cools down from liquid to solid states. This thesis presents a new model that predicts the fluid flow and heat transfer in a direct contact heat exchanger, designed to recover the heat from molten CuCl, through the physical interaction between CuCl droplets and air. Numerical results for the variations of temperature, velocity, heat transfer rate, and so forth, are given for two cases of CuCl flow. The predicted dimensions of the heat exchanger were found to be a diameter of 0.13 m, and a height of 0.6 and 0.8 m for 1 and 0.5 mm droplet diameters, respectively. The results obtained provide valuable insights for the equipment design and scale-up of the Cu-Cl cycle.