A Semi-Simulation Method Integrating CFD and Thermal Resistance Networks for Tubular Heat Exchangers

Tubular heat exchangers are essential in various industrial applications and often require costly CFD analysis due to the use of thousands of thin-walled tubes. This study proposes an efficient semi-simulation method that combines a thermal resistance network with CFD via outer wall surfaces, thereby reducing computational amount. In the semi-simulation method, the flow outside the tubes is simulated firstly with given temperature at the outer surfaces of the tubes. The calculated wall heat flux is in turn employed as boundary condition for the thermal resistance network. The thermal resistance network models heat transfer within the circular tube walls and the tube-side flow. The importance of radial, axial and circumferential heat transfer within the tube wall varies depending on the tube material and the flow type (laminar or turbulent) and must be considered properly. An empirical relation for the Nusselt number of the tube-side flow and the Newton's cooling law are employed to capture the heat transfer rate between the inner wall surface and the fluid inside the tube. The semi-simulation method is validated against a full-simulation of a 16-tube cross-flow heat exchanger. Under high accuracy requirements (1% error in the fluid bulk temperature), our method saves 11% of CPU time compared to the full simulation.