A high-fidelity sharkskin inspired placoid-scales structured microchannel (SPMC) for advancement of heat transfer performance

Abstract

Bionic inspired configurations in microchannel heat sinks were supposed to improve the heat dissipation performance by manipulating flow modes, enlarging heat transfer area and reshaping the thermal boundary layers during the process of flow heat transfer. On account of which, in this work, a high-fidelity sharkskin inspired placoid-scales structured microchannel (SPMC) was proposed and manufactured to investigate the thermohydraulic characteristics compared to a conventional open rectangular microchannel (RMC) with comparable heat transfer area and hydraulic diameter by conducting several groups of flow boiling experiments with the working fluid of DI water. The inlet temperatures were set to be 25, 45 and 65 °C, and the mass fluxes were arranged as 365 and 535 kg/m2·s. The visualization results showed all nucleated bubbles were generated underneath the tail of placoid-scales and would annihilate in the subcooled mainflow after the process of growing and condensing. At certain working conditions, the wall superheats of SPMC were generally lower than RMC especially in single-phase region and early stage of two-phase flow, but were higher at low subcooling and high heat flux (Tinlet = 65 °C, qeff ≥ 1349.8 kW/m2). The convective (hcon) and two-phase (htp) heat transfer coefficients of SPMC were both improved compared to RMC (hcon was maximumly enhanced by 184 % at Tinlet = 25 °C) except at low subcooling and high heat flux likewise, which was ascribe to the placoid-scales provided a great number of nucleation sites and strengthened the turbulivity of the liquid to promote the heat dissipation efficiency. SPMC obtained mild growth in pressure drop during single-phase flow compared to RMC, and the total pressure drop of two microchannels were comparable in two-phase region at all inlet temperatures. Moreover, the critical heat fluxes (CHFs) of SPMC were superior than the ones of RMC for all working conditions. In summary, SPMC is expected to be a novel type of microchannel cooling device with excellent thermohydraulic performance during single-phase region and early stage of flow boiling.