| As an efficient heat exchange technology,heat pipe has the advantages of miniaturization,simple structure and high thermal conductivity.It has been widely used in the fields of heat dissipation of electronic device,waste heat recovery.In recent years,nanofluids have attracted extensive attention of domestic and foreign researchers because of their high thermal conductivity.In this thesis,the acetone-based Al2O3 nanofluid and water-based Al2O3 nanofluid were prepared and filled into the parallel flat heat pipe(PFHP)to investigate the changes of phase behavior,working medium distribution and heat transfer characteristics in heat pipes under the conditions of different nanofluid concentrations,liquid filling ratios,working inclinations and base liquids.The main contents are as follows:(1)In order to study the heat transfer performance of Al2O3 nanofluid heat pipe under different parameters,a nanofluid heat pipe performance test bench was built,and a nanofluid parallel flat heat pipe heat transfer performance prediction model was proposed,in order to better evaluate the nanofluid parallel flat heat pipe heat transfer performance under different thermal environment and nanofluid concentration.The experimental results showed that for the same concentration of nanofluid heat pipe,the heat transfer performance of the PFHP was better in the vertical state with an optimal filling ratio of 30%,and the minimum thermal resistance was 0.0822 K/W.But the resistance to dry burning was not as good as the heat pipe with 50%filling ratio under small angle.The PFHP with good thermal performance was improved by 31.3%when the concentration was 5 wt.%,further increase of nanofluid concentration would reduce the performance of heat pipe.Under the same working condition,acetone-based Al2O3 nanofluid heat pipe had better temperature uniformity performance than water based Al2O3 nanofluid heat pipe.The heat transfer performance of heat pipe was greatly affected by power when the Q’ and C’ were small.The concentration had great influence on heat transfer performance of heat pipe when the Q’ and C’ were large.(2)A parallel flat heat pipe visual experiment platform was designed and built to study the flow morphology and internal heat transfer mechanism of parallel flat heat pipe with nanofluid under different parameters.The results showed that the reciprocating oscillation of working fluid between pipes was more intense when the heat pipe was in vertical state.The heat pipe with liquid filling ratio of 30%showed better thermal performance.The viscosity resistance of working fluid increased and the amplitude of working fluid decreased when the mass fraction of nanoparticles was higher than 0.5 wt.%.Compared with water based nanofluid,acetone based nanofluid was more suitable for intensified heat transfer of the PFHP.(3)The influence of Al2O3 nanofluid on the flow characteristics of PFHP was studied numerically by using the technique combined with Fluent+UDF.It was found that the addition of nanoparticles enhanced the nucleation number of the working fluid.The optimal concentration of nanofluid was 0.5 wt.%,and the thermal resistance value was 0.132 K/W.With the increasing of the concentration,the stability of heat pipe decreased.When the heat pipe was installed vertically,the flow pattern in the PFHP was abundant.With the decrease of inclination angle,the evolution velocity of bubbles in the pipes slowed down,and the thermal performance was decreased gradually.The reciprocating oscillation of the working fluid in the heat pipe with 30%liquid filling ratio was stronger and the fluid was transported higher for the same heat flux.The heat pipe charged with acetone-Al2O3nanofluid showed well temperature uniformity and heat transfer performance. |
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