Experimental proof-of-concept of bubble column evaporative cooling for PEMFC heavy-duty vehicle thermal management

Challenging heat rejection caused by small temperature differences between ambient air and low-temperature proton exchange membrane fuel cells (PEMFC) lead to significantly increased radiator dimension and fan power requirements, increasing the need for alternative cooling solutions. To overcome these limitations, the high latent heat of water that is produced in the hydrogen PEMFC can be utilized to enhance the overall system heat rejection. A novel bubble column evaporator concept for fuel cell (FC) thermal management has been developed. High heat and mass transfer rates make bubble columns a promising alternative to evaporate the product water. It consists of a semi-closed loop in which heat is transferred from the FC coolant to a secondary water circuit that is evaporatively cooled by injecting the FC exhaust air into a bubble column. This solution utilizes only air and water for cooling, provides additional heat storage, improves with increasing altitude and does not increase the vehicle’s drag. We present the novel counterflow bubble column evaporator concept together with proof-of-concept measurements to demonstrate its viability by validating theoretically predicted heat rejection rates. Higher superficial gas velocities than previously reported have been investigated to reduce system size, reaching up to 1.22 m/s. Based on the presented measurements and a verified heavy-duty PEMFC truck model, this approach could complement the conventional truck cooling system with 153 kW additional heat rejection for 23 minutes with 50 kg of water storage. At 20°C, this corresponds to an increase of over 40% compared to the conventional cooling system alone.