An Integrated Chemical Reactor-heat Exchanger based on Ammonium Carbamate

In this work we present our recent effort in developing a novel heat exchanger based on endothermic chemical reaction (HEX reactor). The proposed HEX reactor is designed to provide additional heat sink capability for aircraft thermal management systems. Ammonium carbamate (AC) which has a decomposition enthalpy of 1.8 MJ/kg is suspended in propylene glycol and used as the heat exchanger working fluid. The decomposition temperature of AC is pressure dependent (60°C at 1 atmosphere; lower temperatures at lower pressures) and as the heat load on the HEX increases and the glycol temperature reaches AC decomposition temperature, AC decomposes and isothermally absorbs energy from the glycol. The reaction, and therefore the heat transfer rate, is controlled by regulating the pressure within the reactor side of the heat exchanger. The experiment is designed to demonstrate continuous replenishment of AC. This requires recovering the depleted glycol while expelling waste gases, dispersing and suspending fresh AC, and injecting the mixture into the heat exchanger. A gasketed plate heat exchanger is used as the reactor for this experiment, and heated water is used to provide the thermal load. The performance of the HEX reactor is characterized as a function of water flow rate and temperature, AC/glycol mixture flow rate, and AC concentration. Varying these parameters permits mapping the performance of the system under different conditions.