The Flow And Heat Transfer Of Nanofluids In The Microchannels

In recently years, the explorations and sustainable utilization of energy resources have being paid more and more attentions. Especially, with the great advancement of micro fabrication and microfabrication technology, micro-electro-mechanical systems (MEMS) have also put forward higher requirements in heat transfer for heat exchange equipments. The nanofluids meet this development of the tide. Their enhanced thermal conductivity significantly improves the heat transfer efficiency of the systems. Furthermore, since the nanofluids themselves are not easy to generate particle precipitation, abrasion and blockage in microchannels, therefore, they have been greatly applied in the industrial field.The microfluidic system itself has many special effects such as micro scale, capillary effect, slip effect, fast heat conduction effect and so on. Based on these effects, there are many ways to realize the movement of fluid in microchannels, for example, by utilizing of pressure, surface tension, electric field force, magnetic force, high frequency sound waves, etc. Especially, in the current rapid progress of electrophoresis system, electroosmotic flow is one of the dominant driving techniques. Because the electroosmotic driving is in possession of high efficiency, easy-controllability, and will not cause damage to mechanical components, it is widely applied in biology, chemistry, medicine and other fields currently.The streaming potential can also generate the electroosmotic flow in micro system, while the streaming potential itself is a kind of special phenomenon of electroosmosis. Distinguishing from the ordinary electroosmotic flow induced mechanism, this electroosmotic flow can be produced without the presence of external electric field. The study of streaming potential is relatively mature, and has achieved a great of results in both theoretical analysis and experimental verification. However, we also find that the researches on the nanofluid in term of streaming potential are still very scarce.Meanwhile, the magnetic force, i.e. the Lorenz force as an effective driving mechanism is broadly used in a variety of researches for microfluid, particularly in the issue of flow and heat transfer of the nanofluid. In the analysis of Lorenz force, the electric fields were considered as the synthesis effect of the motion of the fluid and the applied magnetic field in a lot of research work, and the external electric fields were ignored. However, those applied electric fields can also have significant impacts on the microsystem.Following the analysis mentioned above, this dissertation focuses on the flow and heat transfer of the nanofluid in the parallel plate and circular microchannels under the influences of streaming potential. Furthermore, we investigate the motion and heat transfer in the microchannel in the presence of coupling multi-field effect. In addition, we introduce the external electric field, and probe the EMHD flow and heat transport of nanofluids.For this analysis, we established the equations of electric double layer (EDL) and electric potential governed by Poisson-Boltzman distribution. By solving the electric field potential distribution, we further obtained the charge density distribution which was employed to describe the electric field force of whole system. Substituting the expressions of streaming potential and electric field force into modified momentum and energy equation of the nanofluid, we got the velocity and temperature distribution of the nanofluid under different boundary conditions. Meanwhile, the analytical expression of Nusselt number was induced, which was a significant parameter to describe the heat transfer of nanofluids.