The Flow And Heat Transfer Characteristics Of Drag-Reducing Nanoparticle Suspension

The purpose of this study is to systematically investigate the flow drag and heat transfer of nanofluid, and to use the enhanced heat transfer of nanofluid to solve the bad heat transfer of drag-reducing fluid. This study has summarized the literatures about the nanoparticle properties and the preparation, the heat conductivity, the convective flow drag and heat transfer characteristics of nanofluids; has prepared copper oxide (CuO)-water and carbon nanotube (CNT)-water nanofluids with surfactant and without surfactant (the later is called nanoparticle suspension); has measured the physical properties of the prepared nanofluids, such as heat conductivity and viscosity; has experimentally researched the convective flow drag and heat transfer characteristics of the nanoparticle suspensions in a small tube with an inner diameter of 1.02mm, taking the effect of fluid temperature into main consideration. the Reynolds number range was 500~10000; has developed a new fluid: drag-reducing nanofluid; has experimentally researched the convective flow drag and heat transfer characteristics of the drag-reducing nanofluid at different fluid temperature in a tube with an inner diameter of 25.6mm, the Reynolds number range was 10000~50000; and finally has simulated the heat transfer of CuO-water suspension to find out how the physical properties, such as density and heat conductivity, affects the heat transfer individually. From all these work, the following results are obtained: Both the nanoparticle concentration and fluid temperature have significant positive effect on the thermal conductivity of nanoparticle suspensions. The traditional correlation, which was established to describe the thermal conductivity of solid-liquid mixture of millimeter and micron magnitude, can not precisely describe the thermal conductivity of nanoparticle suspensions. The reason should be: since the nanoparticles are very small, they could have thermal motion like molecule. The collision between the particles and base fluid enhanced the heat transfer in an extra way.The flow drag of CuO-water nanoparticle suspension is lower than that of water. The reason should be the enchasing of CuO nanoparticles in the tiny clearance on the inner wall, which decrease the roughness and then reducing the flow drag. The CuO nanofluid and CNT suspension present no drag-reducing phenomenon. Because the surfactant sticks the CuO particles on the wall into irregular agglomeration, and the CNT has great slenderness ratio, they both couldn't stuff the tiny clearance on the inner wall.The CuO nanoparticle suspension can be regard as conventional fluid at room temperature and low particle concentration (≤2wt%). While the heat transfer characteristic of 4wt% suspension is higher than that of water. Nanometer characteristics are presented. The fluid temperature has great effect on the heat transfer characteristics of CuO and CNT nanoparticle suspensions. At 58C, both these two suspensions present considerable nanometer characteristics. The reason should be that the relative movement between the particles and base fluid becomes more intense at high temperature and particle concentration, which makes the heat transfer between particles and base fluid more frequent and effective.The best CTAC (cetyltrimethyl ammonium chloride) concentration for drag-reducing nanofluid is 300ppm under present testing condition. The suspension presents best drag-reducing function at 22C and best heat transfer enhancing function at 48C. Fluid temperature has great effect on the flow drag and heat transfer. If this feature is used reasonably, the integrated enhancing ratio can reach 3.0 (4wt% CNT drag-reducing suspension for instance). The drag-reducing suspension shows great applying value.The heat transfer simulation of CuO-water nanofluid shows that the thermal conductivity has the most important positive effect on the heat transfer coefficient, then density. While the change of specific heat and viscosity lower the heat transfer coefficient. When considering the integrative effect of all the physical properties, the heat transfer coefficient is enhanced than that of water, in accord with the present experimental results. The conventional equations can't accurately describe the heat transfer characteristic of nanoparticle suspension at high temperatures (58C for instance).