Research On Manufacturing Process And Heat Transfer Characteristic Of Ultra-thin Flat Heat Pipe

With the development of electronic devices,miniaturization and high performance have become the core technology points.However,the problem of increased heat flux density causes a significant drop in performance or even failure of electronic devices,and therefore requires a more efficient heat dissipation method.As a phase change heat transfer element,heat pipe is increasingly used in high-performance electronic equipment due to its excellent performance.The ultra-thin flat heat pipe with small thickness and excellent performance can effectively solve the heat dissipation problem in a narrow space.In this paper,the research on heat dissipation of flat heat pipe was firstly discussed.The research progress of capillary wick structure,forming process and capillary wick process parameters were reviewed.An ultra-thin flat heat pipe adopting a grooved porous structure was designed and fabricated from the background and actual production process.And the production process was described in detail,and the heat transfer performance of the ultra-thin flat heat pipe under two different cooling forms were obtained through experiments.The main tasks include:(1)The capillary wick structure was introduced and copper powder was selected as the main material of the grooved porous structure.The porous structure of the grooved was applied to the heat pipe for feasibility design and fabrication.A copper-water ultra-thin flat heat pipe with a thickness of 2.5 mm was produced.A grooved porous structure was sintered on the bottom plate,which can separate the gaseous working medium and the liquid working medium from flowing along the length direction,thereby reducing the viscous shear forces,and the structure itself can also serve as a support structure to reduce the placement of the support columns.The porosity of capillary wick with different particle sizes was calculated by the immersion medium method,and the surface observation was carried out by scanning electron microscopy.The capillary force and permeability of the capillary wick were analyzed briefly.It has the characteristics of simple structure and convenient production.The production steps of the ultra-thin flat heat pipe were studied and optimized,and a detailed production process route was formulated according to the flat heat pipe proposed in this paper.(2)The effects of heat load,copper powder width and channel width ratio,copper powder particle size on heat pipe performance under water circulation cooling were studied.The experimental results show that the ultra-thin flat heat pipe proposed in this paper can reach the steady state again after about 10 minutes after the heat load is changed,indicating that the heat pipe has good response performance.If the ratio of copper powder width to channel width is too large or too small,the heat pipe performance will be affected.The former affects the steam discharge resistance,and the latter mainly affects the evaporation area and internal pressure.For the copper powder particle size,the thermal resistance and heat transfer limit of the large particle size heat pipe are greater than those of the small particle size heat pipe.The thermal resistance and heat transfer limit of the large particle size heat pipe are 0.079 °C/W and 80 W,respectively,while the thermal resistance and heat transfer limit of the small particle size heat pipe are 0.049 °C/W and 60 W,respectively.(3)The effects of heat load,tilt angle,surface characteristics on the performance of heat pipe under natural cooling were studied.The experimental results show that after the heating load is changed,the axial temperature distribution of the heat pipe does not decrease monotonically with the axial direction,and the temperature of the heat pipe condensation section will rise first and then fall.The influence of the tilt angle on the temperature of the heat pipe evaporation section is mainly due to the change of the natural convection heat transfer coefficient,and the axial temperature difference is mainly due to the different condensation section temperatures.Under natural cooling,the heat pipe performance can be improved by increasing the emissivity of the heat pipe surface.At a power of 9 W,the evaporation zone temperature can be lowered by 10.3°C.