Heat Transfer Enhancement in the Microscale: Optimization of Fluid Flow

Abstract

Microchannel heat sinks have emerged as a leading solution for high‐heat‐flux thermal management in electronics, aerospace, energy conversion and biomedical systems owing to their high surface‐to‐volume ratio and superior convective performance. As channel hydraulic diameters decrease to the microscale, however, fluid flow and heat transfer deviate markedly from classical continuum predictions. These deviations arise from pronounced scale effects, rarefaction, surface roughness, axial wall conduction and compressibility, together with the complex behavior of advanced working fluids such as nanofluids and phase‐change coolants. This review presents a systematic synthesis of microscale heat transfer and hydrodynamics from two complementary perspectives: (1) pure scale effects governing single‐phase convection, and (2) the coupled thermal–hydraulic phenomena that occur when microscale confinement interacts with advanced fluids. Key dimensionless parameters (Knudsen, Reynolds, Bond and Mach numbers) are examined in detail, and their influence on velocity slip, temperature jump, friction factor, Nusselt number, and two‐phase flow regimes is critically assessed. Emerging geometric strategies biomimetic fractal and leaf‐vein networks, shark‐skin and fish‐scale surfaces, honeycomb and raccoon‐type channels are evaluated with respect to heat‐transfer enhancement and pressure‐drop penalty. A comprehensive analysis of numerical methodologies is provided, spanning continuum Computational Fluid Dynamics, mesoscopic Lattice Boltzmann methods, molecular‐dynamics and direct‐simulation Monte Carlo techniques, as well as data‐driven optimization frameworks based on Genetic Algorithms, the Taguchi method, and Artificial Neural Networks (multi‐layer perceptrons, hybrid convolutional networks, and physics‐informed neural networks). Comparative performance metrics, unresolved modeling challenges, and practical selection criteria for each approach are identified. By integrating mechanistic insight with modern computational and optimization tools, this review establishes clear design guidelines and highlights priority research directions for the next generation of high‐performance microchannel heat sinks operating under extreme heat fluxes and compact spatial constraints.