T-type gas-circulation systems are widely used in gas lasers to remove waste heat from the discharge process. The structure of the heat exchanger is a very important factor that affects the performance of a T-type gas-circulation system. To develop a high-performance heat exchanger for such a gas-circulation application, a computational fluid dynamics approach was adopted for this study. A three-dimensional numerical model was established. A detailed study focused on the influence of the shape of the channel and the location of the finned tubes on the performance of the heat exchanger. Based on the heat-transfer characteristics and the flow structure, a novel geometric structure was proposed to reduce the volume of the heat exchanger. Comprehensive simulations to determine the optimum locations for the finned tubes were also conducted. As a result of this optimization, the heat exchanger for a T-type gas-circulation system could be made more compact and its pressure loss penalty decreased by 11.5% even though its heat-transfer ability remained unchanged. In addition, the results of a theoretical analysis and numerical simulation were found to be in good agreement with the results of the experiment, indicating the validity of the results of the research. (C) 2015 Elsevier Ltd. All rights reserved.