Numerical investigation of the fluid flow and heat transfer characteristics of tree-shaped microchannel heat sink with variable cross-section

[Display omitted] •A tree-shape microchannel heat sink with a variable cross-section was firstly designed.•The coupling effects of bonic fractal and variable cross-section on heat transfer was studied.•Cavities in the TMHS can enhance branching effects, while ribs can suppress branching effects.•The TMHS-C exhibits a highest comprehensive performance.•Higher Reynolds number enhances heat transfer and the coupling effects. The bionic fractal microchannel heat sink (MHS), which is characterized by a uniform velocity distribution and higher heat transfer efficiency, is an ideal heat sink candidate, while the structure of the variable cross-section has a great impact on the fluid flow and heat transfer performance of the MHS. Considering the coupling effects of the bionic fractal and variable cross-section, a tree-shaped MHS (TMHS) with a variable cross-section is firstly proposed. The flow characteristics, heat transfer characteristics, pressure drop characteristics, and comprehensive performance of TMHSs with cavities and ribs were analyzed numerically using the commercial software Fluent, and compared with the traditional smooth TMHS. The results indicate that the structure of varibale cross-section can further enhance heat transfer performance of the TMHS. The TMHS with ribs (TMHS-R) exhibited the highest heat transfer performance, but also had the highest pressure drop. Finally, the heat transfer index was put forward to consider both heat transfer and pressure drop characteristics, and the results found that the TMHS with cavities (TMHS-C) had the highest comprehensive performance at the range of the calculating Reynolds number.