Thermal-hydraulic performance of printed circuit heat exchangers with zigzag flow channels

Abstract

Printed circuit heat exchanger (PCHE) is one of the leading candidates to be employed in advanced nuclear reactors and next generation concentrated solar power applications due to its compactness and capability for high-temperature, high-pressure applications with high effectiveness. In the current study, thermal-hydraulic performance of a zigzag-channel PCHE with high-pressure, high-temperature helium on both the hot and cold sides was simulated using a computational fluid dynamics (CFD) software package STAR-CCM + . Comparisons between the experimental data and CFD simulation results showed good agreement with some discrepancies in the pressure drop and heat transfer results. Local thermal-hydraulic performance analyses indicated that a fully-developed flow condition was not observed in the PCHE, mainly due to the nature of the zigzag channels, leading to periodic flow disturbance at each of the zigzag bends. It was also found that the local and global heat transfer coefficients were considerably different in the PCHE. Furthermore, thermal boundary conditions showed that the fluid temperatures and heat fluxes were not uniform along the azimuthal direction of a cross section of the flow channel and that the helium temperature distribution for each segment along the flow direction presented a wavy profile. However, the distribution of the helium bulk temperature along the flow direction was approximately linear. For the heat flux distributions, although they were significantly different at different segments, the trend of the heat flux for each segment along the fluid flow direction was similar. Finally, effects of several parameters on the thermal-hydraulic performance of the PCHE were investigated, including the fluid and solid thermophysical properties, radius of curvature at zigzag bends, channel configuration, channel length pitch in the flow direction, and zigzag pitch angle. No considerable enhancement in the Nusselt numbers was observed when the zigzag pitch angles were greater than 30°.