Thermal effects in a H2O and CO2 assisted tubular direct carbon solid oxide fuel cell (DC-SOFC) are numerically investigated. Parametric simulations are further conducted to study the effects of operating potential, the distance between carbon and anode, inlet gas temperature, and anode inlet gas flow rate on the thermal behaviors of the fuel cell. It is found that the fuel cell with H2O as gasification agent performs considerably better than the cell with CO2 as gasification agent in all cases. It is also found that the temperature field of the fuel cell is highly uneven. The breakdown of the heat sources in the fuel cell shows that the H2O assisted DC-SOFC has much higher heat generation and consumption than the CO2 assisted cell. Interestingly, a thermal neutral voltage is observed, at which no heating or cooling of the cell is needed. In addition, the distance between the anode and the carbon layer is required to be as small as possible, which improves the temperature uniformity of the fuel cell. The results of this study demonstrates the importance of thermal effects in DC-SOFCs and form a solid foundation for DC-SOFC thermal management. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.