Anoop Kanjirakat, Sadr Reza
Micro Scale Thermo Fluids (MSTF) Laboratory, Mechanical Engineering Program, Texas A&M University at Qatar, P,O, Box 23874, Education City, Doha, Qatar.
Nanoscale Res Lett. 2012 May 31;7(1):284. doi: 10.1186/1556-276X-7-284.
Colloidal suspensions of nano-sized particles in a base fluid, nanofluids, have recently gained popularity as cooling fluids mainly due to their enhanced heat transfer capabilities. However, there is controversy in the literature on the reported properties of nanofluids and their applicability, especially since there is no fundamental understanding that explains these enhancements. A better understanding of these fluids and how they interact with a solid boundary may be achieved by a detailed near-wall fluid flow study at nanoscale. This work presents for the first time the near-wall velocity measurements for nanofluids using nanoparticle image velocimetry. This novel technique uses evanescent illumination in the solid-fluid interface to measure near-wall velocity field with an out-of-plane resolution on the order of O(100 nm). Nanofluids of different concentrations were prepared by dispersing silicon dioxide particles (10 to 20 nm) in water as the base fluid. Initially, viscosity measurements were conducted for the prepared nanofluids. The near-wall velocity data were then measured and compared with that of the base fluid at the same flow condition. It was observed that even though nanofluid viscosity had increased with particle loading, the near-wall velocity values were similar to that of the base fluid for a given flow rate. Together, these measurements vindicate the homogenous and Newtonian characteristics of the nanofluids in the near-wall region. Despite the low particle concentrations investigated, the present work also discusses the complexity involved in utilizing the methodology and possible errors arising during experimentation so as to implement this measurement tool more effectively in the future.
纳米流体是纳米尺寸颗粒在基液中的胶体悬浮液，最近作为冷却流体受到广泛关注，主要是因为其增强的传热能力。然而，关于纳米流体的报道性质及其适用性，文献中存在争议，特别是因为目前还没有能解释这些增强现象的基本认识。通过在纳米尺度上进行详细的近壁流体流动研究，可能会更好地理解这些流体以及它们与固体边界的相互作用。这项工作首次展示了使用纳米粒子图像测速技术对纳米流体进行近壁速度测量。这种新技术利用固液界面中的倏逝光照明，以平面外分辨率约为O(100 nm)来测量近壁速度场。通过将二氧化硅颗粒（10至20纳米）分散在水中作为基液，制备了不同浓度的纳米流体。首先，对制备的纳米流体进行了粘度测量。然后测量近壁速度数据，并与相同流动条件下的基液数据进行比较。结果发现，尽管纳米流体的粘度随着颗粒负载量的增加而增大，但在给定流速下，近壁速度值与基液相似。这些测量结果共同证明了纳米流体在近壁区域具有均匀和牛顿流体的特性。尽管研究的颗粒浓度较低，但本工作还讨论了使用该方法所涉及的复杂性以及实验过程中可能出现的误差，以便未来更有效地应用这种测量工具。
