Investigation of Heat Recovery Methods from Molten Salts with Phase Change

In the present times there is a progressive surge in the energy requirements for industrial and domestic purposes, hence it is imperative to harvest energy from renewable sources. In addition to serving as a sustainable source of energy, these energy sources prove to be indispensable in the mitigation of the greenhouse effects. In the past several decades, various methods and processes for utilizing renewable energy sources have been developed and continue to be improved. Hydrogen holds the highest energy density compared to any common fuel. Along with its abundance and lightweight nature hydrogen is more eco-friendly during utilization and can be produced via sustainable methods that do not pollute our planet. Through extensive research, numerous methods for extracting hydrogen are identified. Among them, a promising one is the thermochemical copper-chlorine (Cu-Cl) cycle, which is a clean hydrogen production method. As the Cu-Cl cycle is a relatively novel concept, it has been found that it is not well-defined in thermophysical and material properties for its specific application and thus predisposing it to approximation and assumptions from published data. In the Cu-Cl cycle, heat can be recovered from molten cuprous chloride (CuCl) and it is then reacted with aqueous hydrochloric acid (HCl) in stoichiometric proportions to produce the anolyte for the H2 production step of the cycle. However, the lack of precise thermophysical properties on CuCl heavily hinders the detailed investigations of heat recovery from the molten salt as it cools from 450°C to 90°C. A new method is developed to determine the thermophysical property of CuCl and silver chloride (AgCl) as the molten salts are changing phases to solid. This is achieved by correlating electrochemistry data with thermal data. A model that predicts the specific heat capacity during phase change process is developed based on the existing electromotive force (EMF) and thermal data from literature. The developed model shows the EMF derived specific heat capacity values of AgCl and CuCl are similar with a slight offset since they have similar EMF’s at higher temperatures. A numerical method is adopted for estimating the amount of heat that could be recovered during quenching process by analyzing the interactions between CuCl droplets with the nitrogen (N2). These interactions are modeled numerically in COMSOL Multiphysics for various droplet sizes of CuCl and AgCl with the developed specific heat model. The heat recovery analysis shows that after quenching, the average internal temperature of the droplet does not change significantly with droplet diameter and quenching height