Study On The Influence Of Nanofluids Heat Transfer In Microchannel With Applied Electric Field

Time has witnessed the sharp development of MEMS field,the integration of electronic devices is increasing and the package volume is getting smaller,so the heat dissipation effect of MEMS is dramatically significant.If the heat cannot be dissipated timely,the performance of it especially the chip will be limited.The conception of microchannel for heat dissipation was introduced.The size of hydraulic diameter of the microchannel is within the range of 10um~1000um.Nanofluids showded a better performance than conventional fluids in heat transfer,so it is vital to apply nanofluids to heat transfer in microchannel.Firstly,the researches of nanofluids and EHD is listed.It is still unclear that the mechanism of heat transfer of nanofluids.The EHD as an active heat transfer method can be applied to the heat transfer of dielectric fluid.The application of low voltage can meet the need of electric field to transfer heat when considering the size of the microchannel,it will have no damage in the electrical parts,which shows the feasibility of electric field applyment to heat transfer of microchannel by nanofluids.Secondly,the applicability of the continuous media hypothesis of nanofluids in microchannel is analyzed,and it is also introduced that the three conservation equations of fluids,the computational model,the common numerical methods and the possible force action of nanoparticles.Then,the influence of linear potential on nanofluids was studied.The ratio of dielectrophoretic force and electrophoretic force of nanoparticles and base water can not be ignored at the end of the potential or the center of the microchannel,the results indicate that the electrophoretic force play a dominant role in most areas of the electric field.Nanoparticles will accumulate in large quantities on the wall near the electric field area due to the effect of electric field force,which will causing a slight rise in the temperature of this part of the wall.Large accumulation of nanoparticles near the wall will have a worse effect on heat transfer.There is no obvious change in the fluid flow and heat transfer when applying the linear potential,because the effect of electric field force on one direction will "offset" the effects of another,it also analyzed the heat transfer effect of electric field forces in each direction,and results show that the heat transfer effect is better and wall temperature has no deterioration when the vertical electric field wsa applied,so the vertical direction electric field will be studied in the next.Finally,the effects of different electric fields on the heat transfer enhancement of nanofluids were studied,which were evaluated by the heat transfer enhancement effect and the wall temperature deterioration.The results show that the heat transfer effect is better when the electric field direction is upward,and the wall temperature does not deteriorate.When the unidirectional electric fields are separated,the heat transfer effect is better.The heat transfer effect is also better that the number of positive electric fields is dominant when the electric fields are combined in different forms,but the nanoparticles gathering near the wall.By applying the sine and square wave electric field to avoid mass gathering of nanoparticles,the calculation results show that there is an optimal frequency makes the best heat transfer effect,when the frequency around 6000 Hz,the effect of electric field enhancing heat transfer of nanofluids is equivalent to water without electric field,this is because the nanofluids flow of the electric field change lag,but the high frequency makes the distribution of nanoparticles on the wall is not obvious sedimentary.The effect of Zeta potential on electric field enhancement of nanofluid heat transfer was also studied to obtain the heat transfer effects of different nanofluids under electric field.