Experimental Study On Heat Transfer Enhancement Performance Of Gravity Heat Pipe By Using Nanoparticles And Dispersant

Heat pipe is widely used in industry as an efficient heat transfer component. With its complex internal heat transfer mechanism, heat pipe is related to natural convection evaporation, nucleate boiling and laminar film condensation and other heat transfer modes. In the paper, based on summarizing and analyzing a large number of documents, nanofluid is proposed to be used in gravity heat pipe, and joint action of dispersant which is used during the preparation of making nanofluid and nanoparticles is studied in order to achieve enhancement of start performance and heat transfer for heat pipe. The main research contents are as follows:（1）Theoretically analyzed the force of nanoparticles in nanofluid. Combining DLVO theory, the causes of instability and impact of adding dispersant and base liquid physical properties on the nanoparticle suspension stability are discussed.（2） Prepared the Al₂O₃-water and SiO2-water nanofluid with 1% mass concentration by Two Steps Method, and adopted sodium dodecyl sulfate （SDS） and Arabic gum（AG） as the additives. The stability of the prepared nanoparticles is characterized by the turbidity method, and the influences of ultrasonic dispersing time, the type and concentration of the additive on the stability of nanofluid are analyzed, the surface tension of aqueous solution of AG and SDS is tested by the Ring Method, the critical micelle concentration of SDS aqueous solution is acquired under 25℃ And the best preparation method of two nanofluid with different dispersants is given under this experiment conditions.（3）Designed and built test-bed of gravity heat pipe performance to experiment and test start performance and heat transfer of heat pipe with various working fluids. By comparing the start-up time, temperature at evaporation and condensation sections, the wall temperature distribution under stable operation and total thermal resistance, the strengthening effect of different working fluids on heat pipe performance is investigated. It is showed that start-up time obviously decreases for heat pipe with nanofluid compared with and temperature difference at evaporation and condensation section is reduced, which means that isothermal performance is better. The effect of additives on the heat pipe performance cannot be ignored. Under low heat flux condition, the nanofluid heat pipe performance has little difference for various dispersant. But with the increase of heat flux,, the heat pipe performance using the SDS as dispersant is better than using AG as disperasant（4） Studied the experimental results combined with gravity heat pipe heat transfer mechanisms. Adding nanoparticles could increase the thermal conductivity of working fluid, thermal motion of nanoparticles could enhance the internal disturbances of working fluid and strengthen the convective heat transfer of gravity heat pipe. Addition of SDS could reduce the surface tension of working fluid, enhance the wettability, which make bubbles departure easier, and strengthens the nucleate boiling heat transfer of gravity heat pipe.