A Review of Boundary Layer and Turbulence Theory and Their Impacts on Heat Exchanger Performance

Abstract

Growing thermal loads in modern high-density electronics, data-center equipment and electrified vehicles have significantly increased the relevance of compact heat exchangers and liquid cooling channels for system efficiency. In forced convection, the dominant contribution to thermal resistance comes from the thermal boundary layer near the surface, therefore, the nature of the flow in this layer (laminar, transitional or turbulent) significantly affects heat transfer and hydraulic resistance. The goal of this review is to analyze the formation of boundary layers, the transition to turbulence, and the coupled thermal and hydraulic effects of turbulence based on literature review, theoretical synthesis and comparative analysis, with a focus on heat transfer enhancement and hydraulic resistance induced by the same boundary layer disturbances. The key issue is how the enhancement of heat transfer and the increase in hydraulic resistance, stemming from the same boundary layer disturbances, should be evaluated and optimized. The concepts of the j/f ratio, performance evaluation criteria (PEC), field synergy and entropy generation minimization will be compared, and passive and active enhancement techniques are classified according to their disturbance and regeneration of the boundary layer.