Review of critical-heat-flux enhancement methods

The study of the enhancement of critical heat flux (CHF) has a long history, with extensive experiments devoted in the last several decades to searching for approaches to expand thermal margin. It continues to be a promising topic in heat-transfer research fields, such as nuclear energy engineering, where higher heat-removal efficiency can improve the ultimate heat utilization as well as delay or even avoid the occurrence of accidents or system failures. In this paper, we present a comprehensive overview of CHF enhancement experiments, focusing on four broad categories of approaches. The first approach considered is amelioration of fluid properties by adding nanoparticles into the base fluid, by which both flow boiling and pool boiling achieve significant improvements in CHF. The second prevailing method recently advanced to increase CHF is surface modification, where various nano/microstructures on the surface were fabricated by advanced techniques. Third, we review the effect of various modified channel structures on the boiling process. Finally, some creative and notable hybrid approaches are presented. Based on this review of the state-of-the-art in CHF enhancement, future research directions are also proposed. In addition, according to the conclusions and results of the comparisons of many experiments, we provide optimal design options for heat-transfer systems. Moreover, following the analysis of experimental data, a better understanding of the highly complex mechanism of enhanced CHF can be realized.