Examination and visualization of pressure fluctuation during flow boiling heat transfer on smooth and structured surfaces

In this study, flow boiling heat transfer in a minichannel heat sink on smooth and pin-fins surfaces with open channel configuration was investigated experimentally. This study focuses on examining the pressure drop characteristics associated with boiling heat transfer on smooth surfaces, as well as surfaces featuring mini pin-fins of square and circular geometries, heat transfer coefficient (HTC) and Nusselt number. The experiments were done over different ranges of liquid mass fluxes from 36 to 144 kg.m⁻²s⁻¹ and a constant heat flux of 49 kW.m⁻². The minichannel has a rectangular shape with a hydraulic diameter of 2.85 mm. The experimental testing is carried out on aluminum surface in a minichannel that has a length of 270 mm, width of 30 mm, and height of 1.5 mm. The experimental results show that circular pin–fin surfaces achieved the highest HTC (8.91 kW.m^-2K⁻¹) compared to square pin–fin (5.75 kW.m^-2K⁻¹) and smooth surfaces (4.11 kW.m^-2K⁻¹) at a mass flux of 144 kg/m²s. The circular pin–fin surface exhibited a higher pressure drop due to the dense fin arrangement under boiling conditions, but it significantly dampened backflow fluctuations. In contrast, the square pin-fins surface had the lowest pressure drop while smooth surface experienced the highest backflow fluctuations, reducing its stability under boiling conditions.