# Heat Transfer Enhancement of Nanofluids with Non-Spherical Nanoparticles: A Review
## 4 Conclusions  
Research on heat transfer enhancement of nanofluids is a long-term global initiative, and the unified understanding of this issue continues. Herein, we reviewed the heat transfer enhancement of nanofluids containing non-spherical nanoparticles. Non-spherical nanoparticles suspended in nanofluids were divided into three categories based on the dimension of the geometric particle structure. We collected and analyzed data on thermal conductivity and convective heat transfer enhancement of nanofluids measured in experiments. Recent studies investigated the numerical predictions and related heat transfer mechanisms. The main conclusions for NSN nanofluids are as follows:  
Due to large aspect ratios, thermal conductivity is enhanced abnormally only for nanofluids containing carbon nanotubes/nanofibers/nanowires. On the other hand, thermal conductivity enhancement per concentration is larger for nanorods/ellipsoids with small aspect ratios. The enhancement of the network effect on heat transfer is limited. Polygonal particles enhanced the thermal conductivity least due to the sphericity being close to 1. The approximate enhancement effect by three types of non-spherical nanoparticles on thermal conductivity is 4.5:2.5:1. However, the particle size effect on nanofluids' thermal conductivity is unclear. The convective heat transfer coefficient is increased by suspending non-spherical nanoparticles in the base fluid. Due to the increase in pumping power, no significant thermohydraulic performance was found for convective heat transfer of NSN nanofluid  
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**Authors** & **Nanofluid** & **Particle Shape and Size (nm)** & **Particle Loading** & **Flow State** & **CHT Enhancement** \\ \hline \multirow{10}{*}{ \begin{tabular}{} \end{tabular}  } & & Cylinder, AR = 1:8 & & & \\  & & Brick, & & & Cylinder \textgreater{}brick \textgreater{} \\  & & and water & AR = 1:1:1 & \textless{}1 vol.\% & In shell and tube heat exchanger & sphere, for \(h\), entropy generation, and heat transfer rate of nanofluid \\  & & & AR = 1:6:1/12 & & & \\  & & Platelet, AR = 1:1/8 & & & \\  & & Platelets, AR = 0.125 & & Flat-plate solar & \\  & & Bades, 1:6:1.12 & & collector tube & Brick-shape particles have the highest Nusselt number \\  & & glycol & Cylinders, AR = 8 & 12,000 \(<\) Re \(<\) & the highest Nusselt number \\  & & Bricks, 1:1:1 & & 25,000 & \\  & & & Oblate spheroid, & \textless{}20 vol.\% & Natural convection in a square cavity as flow resistance \\  & & & & Marangoni & \\  & & & Cube, rod, lamina, & \textless{}6 vol.\% & boundary layer flow & Sphere nanoparticles have the best CHT enhancement \\  & & & & & Nusselt number increases with \(\Phi\), \\  & & & & 100 \(<\) Re \(<\) 2000 & derived Nu formula based on the numerical data \\  & & & & & N\textless{}n_{\textgreater{}}/\text{Nu}\) increases when \(\Phi\) \\  & & & & Turbulent, & \\  & & & & 2500 \(<\) Re \(<\) 15,000 & Reynolds number, AR and \(\  
flow. NSN nanofluid is uneconomical for turbulent flows, and the temperature and particle concentration effect on convective heat transfer remains unclear. In addition, there is no perfect model to precisely predict the thermal conductivity and convective heat transfer of NSN nanofluids. Conceptualization, X.L. and F.Y. ; investigation, D.W.; resources, X.Y. ; data curation, W.T. ; writing--original draft preparation, C.D. ; writing--review and editing, X.L. ; visualization, J.D. ; supervision, W.Y. ; project administration, H.Y. ; funding acquisition, F.Y. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (No. 12172152, 11802105). The authors  
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