Study on Effects of Heat Loss and Channel Deformation on Thermal-Hydraulic Performance of Semicircular Straight Channel Printed Circuit Heat Exchangers

Effective and robust high-temperature heat transport systems are essential for the successful deployment of advanced high temperature reactors. The printed circuit heat exchanger (PCHE) is a strong potential candidate for the intermediate or secondary loop of high temperature gas-cooled reactors (HTGRs) due to their high power density and compactness. For high-temperature PCHE applications, the heat loss, which is difficult to be insulated completely, could lead to the degradation of heat exchanger performance. This paper describes an analytical methodology to evaluate the thermal-hydraulic performance of PCHEs from experimental data, accounting for extraneous heat losses. Experimental heat exchanger effectiveness results, evaluated without accounting for heat loss, exhibited significant data scatter while the data were in good agreement with the ε-NTU method once the heat loss was accounted for. The deformation of PCHEs would occur during the diffusion-bonding fabrication process or high temperature operations due to the thermal deformation. Computational assessment of the PCHE performance test data conducted at the Ohio State University showed that the deformation of flow channels caused increase of pressure loss of the heat exchanger. The computational fluid dynamics (CFD) simulation results based on the nominal design parameters underestimated the pressure loss of the heat exchanger compared to the experimental data. Image analysis for the flow channel inlet and outlet was conducted to examine the effect of channel deformation on the heat exchanger performance. The CFD analysis based on the equivalent channel diameter obtained from the image analysis resulted in a better prediction of PCHE pressure loss.