Effect of stagger angle on capillary performance of microgroove structures with reentrant cavities

Aluminum-based microgroove surfaces with reentrant cavities (MSRCs) were fabricated by two staggered ploughing/extrusion processes to meet the requirements of lightweight phase change heat transfer devices.Five MSRCs with different stagger angles between cavities and microgrooves (MGs) were fabricated to study the effect of stagger angle on capillary performance.Capillary rise and permeability tests were performed on all MSRCs and the results were compared with MGs having the same processing parameters.It was found that MSRCs with smaller stagger angles have higher capillary height,and the maximum enhancement maintained by MSRC45 was about 54.84%.However,MSRCs with larger stagger angles were found to have higher permeability.Therefore,the capillary parameter K·ΔP_(cap)was used as a comprehensive index to evaluate these wicks.MSRC90 and MSRC75 obtained the largest K·ΔP_(cap)values without and with the effect of gravity considered,respectively.Although all MSRCs had a higher capillary rise height than MGs,smaller stagger angles (≤60°) seriously reduced the permeability of MSRCs and even resulted in smaller K·ΔP_(cap)value than that of MGs when calculated considering the effect of gravity.Therefore,MSRCs with larger stagger angles (≥75°) may be the optimum wicks due to the good balance between capillary pressure and permeability.

Fabrication and boiling heat transfer characterization of multiscale microgroove surfaces

Microstructural functional surfaces play an important role in energy conversion applications including power generation,air conditioning,and thermal management of electronics through the boiling process.In this study,multi-scale microgroove surfaces were fabricated by the combination of wire electrical discharge machining(WEDM)and electrical discharge shaped machining(EDSM)to achieve a better boiling performance.The WEDM,with the advantage of high efficiency,was used to fabricate the first microgroove array,and rougher surfaces were formed by intense discharge.A wavy electrode was used in EDSM to fabricate the second microgroove array.Reentrant cavities at the intersections of microgrooves and rougher micro fins with spacing distribution were formed after EDSM.The boiling performance of the multi-scale microgroove surface was studied with water as the working medium under atmospheric pressure.The results indicated that the boiling performance of the microgroove surface is significantly enhanced.The critical heat flux and maximum heat transfer coefficient of microgroove surface were higher than the surfaces fabricated only by WEDM or EDSM,which were 2.34 and 3.29 times that of smooth copper plate,respectively.This study demonstrated that the combination of WEDM and EDSM is a convenient and effective method to fabricate high-performance microgroove boiling surfaces.