Experimental Investigations Of Heat Transfer Characteristics Of Flat Plate Heat Pipe For Electronic Cooling

Electronic technology is developing rapidly in recent years, higher frequency,speed and denseness has become the developmental direction of electroniccomponents, which puts forward a higher requirements on electronic cooling. Becauseof the miniature flat heat pipe has high thermal conductivity and perfect uniformity oftemperature distribution, it is considered to be one of promising potential technologiesto solve the cooling problem. In this study, experimental tests, theorectical analysisand numerical simulations were used to investigated the heat transport capability ofthe flat plate heat pipes. The main contents are as follows.A flat plate heat pipe (FPHP) with grooved evaporation surface is developedand manufactured. The temperature fields and overall thermal resistances of theheat pipes under different experimental conditions are studied. The effects of heatflux，filling amount and gravity on the performance of the spreader is studiedexperimentally. The best filling amount of the spreader is obtained. Because the topand bottom plates act as the condensation and the evaporation surface, and the topends of the pillars in the evaporation surface are directly contact with thecondensation surface after welding, the heat transfer from the evaporation to thecondensation surface is not only by phase change heat transfer but also through heatconduction of the rectangular copper micro-pillars. By use of this special design，boththe axial and radial heat transfer is enhanced and a very effective capillary loopbetween condensation and evaporation surfaces is established. The results confirmthat the FPHP has not only a good performance for temperature leveling but also anexcellent axial heat transfer ability which is very important for efficient cooling.Excellent thermal performance is also observed in unfavorable titled positionsincluding vertical and anti-gravity orientation. A three-dimensional model for heat andmass transfer inside the grooves of the grooved flat plat heat pipe is developed. Thetemperature and velocity field in vapor chamber are obtained.A flat plate heat pipe with interlaced channels is developed andmanufactured. The temperature fields and overall thermal resistances of the heatpipes under different experimental conditions are studied. This FPHP ismanufactured from an identical copper block which has the same size as theabove-mentioned FPHP with grooved evaporation surface. The capillary structure isinterlaced channels. The interlaced channels form the passageway for the workingfluid and the vapor. With this design, the evaporation surface and the condensationsurface of FPHP are jointed together and formed a whole. Experimental results showthat the FPHP possess both advantages of copper plate for heat conduction ability in axial direction and the FPHP for temperature leveling ability in radial direction.This isbecause that with the special structure of the FPHP, the heat transfer from theevaporation surface to the condensation surface inside it is not only byboiling-condensation process as in the conventional heat pipes, but also by the directheat conduction of solid copper. The special structure eliminates part of theevaporation and the condensation heat transfer resistances, and increases the directheat conduction effect through the highly-conductive copper between the evaporationand condensation surfaces, so the axial heat transfer is effectively enhanced. At thesame time, the phase changing heat transfer still takes place on both the surfaces，andso it also takes the temperature-leveling advantage of the conventional FPHP at thecooling surface.The comparative study disclose that the special design of FPHP withinterlaced channels can improve the heat conduction in axial direction and enhancethe capillary effect. Otherwise, the temperature leveling ability of both FPHPs oncooling surface is similar in radial direction.A novel new type of grooved FPHP is developed and manufactured. Theheat transfer characteristics of the heat pipe under different heat fluxes andworking fluid filling ratioes are studied. The capillary structure of this FPHP isintersected micro-grooves on both evaporation surface and condensation surface. Theheat pipe manufactured with copper and filled with de-ionized water, were testedagainst heat fluxes and working fluid filling ratios. The temperature fields and overallheat transfer resistances of the heat pipe under different experimental conditions areobtained. The measured temperature differences and the heat transfer resistancesbetween the evaporation and the condensation surface of the FPHP are small, whichproves that the micro-grooved structure greatly enhances the phase change heattransfer. The best performance of the FPHP is obtained at the FPHP working fluidfilling ratio of87%and the measured overall heat transfer resistance is0.0287K/Wunder the optimal conditions which is even smaller than the thermal resistance of thecopper plate of the same thickness.The effects of nano-fluid and surper-hydrophobic surface on the theramperformance of the novel grooved FPHP are studed. The performance of the flatplate heat pipe with different working fluids was measured for different heat fluxes.We invistagated the heat transfer characteristics of the FPHP with the CNT as theworking fluid, and compare it with the water. The experiments show that the CNT canactually improve the thermal performance and decrease the thermal resistance,however, the strengthening effect is not very obvious.