Design And Performance Research Of Micro Loop Heat Pipe With Nanofluids

A micro loop heat pipe (LHP) cooling system was designed to solve the thermal controlproblem for the microelectronics chip with high level integration. A new functional fluid ofnanofluid was proposed to be used as heat transfer working fluid in the micro LHP coolingsystem. The performance of micro LHP was investigated by varying the Cu-Water nanofluidand capillary wick structure. The experimental result shows that nanofluid greatly improvedthe heat transfer performance of micro LHP. And the optimized capillary wick structure wasobtained. Main research results are as follows:(1) Design of micro LHP cooling systemThe designed micro LHP cooling system was composed of evaporator, condenser, vaporline, liquid line and working fluid. The vapor line and liquid line was connected by PU tube.To improve the efficiency of evaporation and condensation, the boiling surface microstructureand finned structure was used in the evaporator and condenser, respectively. Meanwhile, theporous metal materials were selected as the capillary wick structure. The whole system didnot require an outer driving part to supply external energy.(2) Preparation and characterization of nanofluidThe Cu-Water nanofluid was obtained using the dispersing method. The solid/liquidcontact angle of copper fiber sintered felt with80%porosity and red copper sheet was testedand analyzed. Compared with deionized water, the contact angle between the nanofluid andcopper fiber sintered felt as well as red copper sheet was decreased greatly. Especially, thefully wettability phenomenal was observed for the copper fiber sintered felt with80%porosity.(3) Performance testing and analysis of micro LHP cooling systemA test system platform of micro LHP system was constructed, the heat transferperformance of LHP system was then studied using the nanofluid as working fluid. Later,these experimental results are compared with the deionized water and pure ethanol in detail. Moreover, an optimized concentration of nanofluid was obtained after testing the heat transferperformance of LHP system with different mass concentrations of nanofluid. The restartoperation performance of LHP was also studied by using the1.5%quality concentration ofnanofluid under different heating power. In addition, the performance of LHP system withfour kinds of porous capillary wick structure was tested and analyzed. It is found that thecopper powder sintering plate presented the better heat transfer performance.(4) Investigation on the application mechanism of nanofluid as working fluid in LHPNanofluid and deionized water were boiled to evaporate, the electrical conductivity andvolume of condensing recovery liquid from vapor were comprised and analyzed. It is foundthat the nanoparticles would not enter into the condensing tube in the boiling evaporationprocess. This phenomenon indicated that the boiling heat transfer performance of evaporatorfor LHP was greatly affected by the nanofluid. Moreover, the volume of condensing recoveryliquid was30.4%higher than deionized water. This result shows that it can enhance theboiling heat transfer characteristics while add the nanoparticles to the deionized water.