Curvature–bifurcation coupling effects on heat transfer enhancement and flow resistance in wavy microchannel heat sinks across laminar and transitional Reynolds regimes

• The performances of Hybrid Wavy Bifurcated MCHS are investigated numerically. • The introduction of a second bifurcation consistently intensifies heat transfer. • Peak PEC values depend on Re and the considered geometrical layout. • Curvature induced Dean vortices can destabilize the main flow. • Increasing the curvature angle and/or geometrical bifurcations leads to attenuation of spectral amplitudes. Recent studies have shown that microchannel heat sinks with wavy walls or internal bifurcations can substantially enhance convective heat transfer, often at the expense of increased pressure losses. In this work, a hybrid microchannel heat sink combining periodic wall waviness with one or two internal geometrical bifurcations is investigated by means of three dimensional numerical simulations. A systematic parametric analysis is carried out for 300 ≤ Re ≤ 1500 by varying the curvature angle of the sinusoidal walls ( ϕ = 30°, 37.5°, and 45°), together with the number and downstream position of the physical barriers that partition the main flow into subsidiary branches. The results show that the introduction of a second bifurcation consistently intensifies heat transfer, yielding the highest Nusselt numbers for all curvature angles. For ϕ = 30°, the configuration with two bifurcations, the second starting at 57% of the channel length, provides the maximum thermal enhancement but also produces the largest friction factor. In terms of performance evaluation criterion (PEC), however, the geometry with the second bifurcation located at 70% of the channel length emerges as the most favorable compromise with PEC values between 1.7 and 2.05. For larger ϕ , peak PEC values close to 2 can still be obtained, but the optimal layout depends on the Reynolds number. Flow visualizations indicate that these trends arise from the interaction between curvature induced Dean vortices and bifurcation driven disturbances. For relatively high values of the Reynolds number, these effects can even destabilize the main flow, leading to unsteady and transitional flow regimes that further enhance heat transfer. However, as shown by a dedicated Fast Fourier Transform analysis, increasing the curvature angle and/or introducing geometrical bifurcations can lead to a systematic attenuation of spectral amplitudes.