Simulation of an active and bidirectional thermochemical temperature control unit utilizing metal hydrides

Abstract

Many common temperature control techniques have a lack of active controllability and bidirectionality. One common method is liquid cooling with the ambient as heat sink, which only cools or uses parasitic power for pumps and radiator fans for heating. In the present contribution we would like to present a novel bidirectional, active temperature control module (TCM) which is suitable for hydrogen applications e.g. fuel cells. It is based on the thermochemical reaction between metal hydrides and hydrogen depending on temperature and gas pressure. Therefore, it operates as reversible thermal energy buffer. The metal reacts exo- and endothermically with the hydrogen while ab-and desorbing, respectively. While the absorption releases heat, the desorption takes up heat. In the overall process of the TCM, the absorbed hydrogen will be released to the hydrogen system during desorption. Therefore, no energy is consumed. The driving temperature difference for the cooling or heating can be controlled using the gas pressure, so the system temperature can be actively controlled in both directions. In order to address required thermal powers, the reactor design needs to consider heat and mass transfer. The reaction and heat transfer are simulated in a 0D model. The results of the model connected to a controller will be presented for the outlet temperature, loading status, pressure and energy and compared to experimental data. The results demonstrate the pressure change in the reactor depending on the interfering temperature of the HTF resulting in a controlled outlet temperature within the demonstrated limits of the TCM.