Study Of Suspension Stability Of Nanofluids Flowing In Pipe

Nanofluids is a heat transfer enhancement working fluid which has a unique heat transfer characteristics, not only increase the thermal conductivity of basic fluid significantly, but also enhance the heat transfer performance of heat exchange system. Many scholars obtained unexpected results such as the convective heat transfer of nanofluids demonstrated deterioration compared to basic fluid, and explained that the deterioration of convective heat transfer may be directly caused by the variation of suspending stability of nanofluids in flow, however, there was no further research and discussion.Therefore, under the existed experimental conditions, this study used the method of centrifugal-sedimentation-dry-weigh by taking TiO₂-water nanofluids as object to investigate the suspending stability of nanofluids which flow in straight pipe and pipe with bend(bend pipe).And the centrifugal sedimentation weight was used for characterize the stability of nanofluids.The main research and conclusions are summarized as follows:(1) TiO₂-water nanofluids at the mass fraction of 0.5% prepared by using"two step method"got the best dispersion stability with ultrasonic vibration for 2 hours. The morphology of nanofluids was observed by transmission electron microscope (TEM).It was found that nanofluids dispersed well without obvious agglomeration and nanoparticles was small,uniform and similar to strip shap.The average diameter of nanofluids tested by laser particle size analyzer was 0.32μm.(2) The dynamic stability of nanofluids was better than its static stability whether nanofluids flowed in straight pipe or bend pipe.(3) In the low Reynolds number range of laminar (Re∈0⁵00), the dynamic stability of nanofluids which flowed in straight pipe decreased rapidly firstly, latter drops slowly with time; In the high Reynolds number range of laminar (Re∈1000²300), the dynamic stability of nanofluids which flowed in straight pipe changed a little with time. The dynamic stability of nanofluids which flowed in bend pipe decreased with time in laminar (Re∈500²000).It showed that the dynamic stability of nanofluids was related to time.(4) The dynamic stability of nanofluids which flowed in straight pipe became better with Reynolds number increased in the range of 0 to 2300. However, nanofluids which flowed in bend pipe obtain the best dynamic stability when Reynolds number was 1500.It can be infered that Reynolds number influence the dynamic stability of nanofluids.(5) Because of the dynamic stability of nanofluids changed, in laminar (Re∈400²300), the heat transfer performance of nanofluids which flowed in straight pipe decreased by 0.4% to 7.5% in 8 hours; In laminar (Re∈500²000), the heat transfer performance of nanofluids which flowed in bend pipe decreased by 3.2% to 8.8% in 8 hours.This study mainly discussed the changing law of the dynamic stability of nanofluids flowed in straight pipe and bend pipe, demonstrated that time and Reynolds number were the two major influence factors on the dynamic stability of nanofluids and the dynamic stability of nanofluids was one of the influence factors on transfer performance. Thus, this study provide experimental basis for how to obtain nanofluids in flow with good stability. Meanwhile, this study may be helpful for nanofluids applying in further scientific research and engineering application and showing its excellence heat transfer characteristics.