Study On Fabrication And Heat Transfer Performance Of Ultra-thin Heat Pipe With Copper Mesh Wick

The rapid increase of heat generation level has become a major technical challenge in the development and applications of contemporary advanced microelectronic chip system.As an efficient heat transfer device,micro heat pipes have been widely used for thermal management of electronic devices because of their excellent thermal performance and high reliability.However,with electronic devices having become highly integrated,lighter and thinner,the limited space significantly restricts the size of the thermal control components.This makes the conventional micro heat pipes,including cylindrical and flat-plate heat pipes,incapable of satisfying their usage requirements.To address the development requirements of mobile electronics,an ultra-thin micro heat pipe(UTHP)has been proposed and extensively investigated and applied.In view of this,this thesis has taken the UTHPs with copper mesh wick as research object.The preparation and capillary performance characterization of oxidized coppr mesh wick,and the design,manufacturing process and heat transfer performance of UTHPs were symmetrically studied.The main research works and conclusions are summarized as follows:To satisfy the heat dissipation requirements of different electronic devices,the manufacturing and forming process of UTHPs with different flattened thickness were symmetrically studied.The structural design and technical problems in the manufacturing process of UTHPs were resolved.An appropriate manufacturing process of sintered copper mesh wick was formulated by optimizing the sintering parameters.In addition,a forming scheme of UTHPs with copper mesh wick was made up by improving the manufacturing technique of conventional flattened heat pipes and stress analysis of heat pipes during the course of phase-change flattening.A novel sintered copper mesh wick fabricated by alkali assisted surface oxidation and sintering was proposed for improving the thermal performance of UTHPs.The micro-/nano-structures on the copper mesh surface were characterized by field emission scanning electron microscopy,and the capillary force of the novel mesh wicks was experimentally investigated by a capillary rate-of-rise test using two liquids,ethanol and acetone.The effects of corrosion time and sintering temperature on the capillary force were investigated.Results shows that the oxidized wicks can achieve optimum operating efficiency by choosing corrosion time of about 15 min and a sintering temperature of around 500 ?.Three UTHPs with the flattened thickness of 1.2 mm,1.0 mm and 0.8 mm were designed and fabricated on the basis of early research results.The thermal performance of these heat pipes were investigated under different inclination angles and heat inputs.Furthermore,the effects of oxidized copper mesh wicks on the thermal performance of UTHPs were examined,and the experimental results were compared with those obtained by an UTHP with sintered copper powder wick.At last,the influences of flattened thickness on the thermal performance of UTHPs were analyzed.The experimental results demonstrate that the heat transport capability of an UTHP can be significantly enhanced using oxidized copper mesh wick.To study the heat transfer characteristic of UTHPs with thicknesses below 0.5 mm,five UTHPs with the flattened thickness of 0.50 mm,0.47 mm,0.44 mm,0.41 mm and 0.38 mm were fabricated,and their startup performance and heat transfer performance under three different directions were investigated.The results show that the flattening thickness has a great influence on the thermal performance of UTHPs,the maximum heat transfer capability of UTHPs decreased with a decrease in the flattening thickness.In addition,the gravity has a minimal effect on the thermal performance of UTHPs with sintered copper mesh.