Physical model development and optimal design of PCHE for intermediate heat exchangers in HTGRs

A printed circuit heat exchanger (PCHE) is considered for use as an intermediate heat exchanger (IHX) in high temperature gas-cooled Reactors (HTGRs), since PCHEs offer high effectiveness and a compact size. A PCHE consists of many micro-wavy channels, which increase heat transfer and pressure drop. The design parameters of PCHEs, such as angle, pitch, and hydraulic diameter, can significantly influence thermal-hydraulic performance. We investigated the thermal-hydraulic performance of a PCHE in a helium–helium test loop, both experimentally and numerically. In the tested PCHE, the channel has a 0.922 mm hydraulic diameter, 24.6 mm pitch, and 15° angle. The three-dimensional (3D) numerical model, which was based on the commercial fluid dynamics (CFD) code called FLUENT, was well validated against the experimental data. Then, we used the CFD code to develop physical models for the Fanning factor and the Nusselt number for various geometries, including angle, pitch, and diameter. The angle was varied from 5° to 45°, the pitch length was varied between 24.6 mm and 12.3 mm, and the diameter was varied from 1.51 mm to 2 mm. Dimensionless parameters, such as Reynolds number, Nusselt number, and Fanning factor, were averaged by a local-pitch using local information produced by the numerical results. Finally, we developed correlations for the Fanning factor and the Nusselt number for PCHEs with various geometries, and used those correlations to propose the optimal IHX through the cost analysis.