Numerical modeling of a cogeneration system based on a direct carbon solid oxide fuel cell and a thermophotovoltaic cell

A new combined system model is proposed to numerically assess the feasibility and effectiveness of using a thermophotovoltaic cell (TPVC) for waste heat recovery from a direct carbon solid oxide fuel cell (DC-SOFC). The system model mainly consists of an irreversible TPVC model and a 2D tubular DC-SOFC model considering the ionic/electronic charge transport, mass transport, momentum transport, and chemical/electrochemical reactions. Mathematical expressions of the power density and efficiency for the proposed system are derived and the performance characteristics of the combined system are revealed. The impacts of operation conditions and designing parameters including the operating temperature of the DC-SOFC, distance between the carbon layer and anode, and band-gap energy of the TPVC on the combined system performance are examined. It is found that the TPVC can efficiently harvest the waste heat from the DC-SOFC. The maximum power density of the combined system is approximately 56.2% larger than that of the stand-alone DC-SOFC. Moreover, a higher operating temperature of the DC-SOFC and a smaller distance between the carbon layer and the anode are beneficial to the performance enhancement of the combined system. The power density of the combined system can be further improved through designing the TPVC with an optimum band gap.