# Heat Transfer Enhancement of Nanofluids with Non-Spherical Nanoparticles: A Review
## 2 Thermal Conductivity of NSN Nanofluids
### Experimental Data Evaluation
#### 2.1.3 Platelets/Blades/Bricks/Diamonds/Polygons  
Platelet/blade-shaped particles have a large section area. The data plotted in Figure 2 reveal a relatively small TCE of this nanofluid type. [PERSON] et al. [38] measured a TCE of approximately 29.51% at a high volume fraction of SiC-water nanofluid of 7%. [PERSON] et al. [34] compared the effects of the particle shapes of platelets, blades, and cylinders on TCE by eliminating the material and agglomeration effect. They discovered that although the sphericities of blades and platelets are larger than those of cylinders, the measured TCE of blades and platelets is smaller than that of cylinders. The classical H-C model considers the sphericity of non-spherical particles and cannot estimate the shape effect on the TCE of nanofluids. Similar results were obtained by [PERSON] et al. [39] in a comparison of platelet-, brick-, and blade-shaped particles. [PERSON] and [PERSON] [40] and [PERSON] et al. [41] investigated nanofluids with diamond-like particle shapes; however, these particles are treated as spheres. Their findings showed that TCE linearly increases with particle volume fraction. [PERSON] et al. [42] tested nanofluids with polygonal nanoparticles and discovered a slight difference between nanofluids and base fluid. Notably, particle sizes differ among these studies, which could also influence the TCE. Enhancement per concentration as a function of particle size at room temperature is illustrated in Figure 4. Experimental data reported in Table 1 are plotted, except for those of [PERSON] et al. [25; 26], whose findings were two orders of magnitude higher than other results. As shown in Figure 4, most of the enhancement per concentration is smaller than 10, indicating a relatively weak shape effect of these particles on TCE. From the data of diamond and platelet particles, the enhancement per concentration increases with increasing particle size. Nonetheless, the materials of nanoparticles as additives dispersed in the nanofluids are different, and studies demonstrated a different behavior in particle size effect [43]. [PERSON] et al. [44] recently argued that there is insufficient evidence that smaller nanoparticles increase ETC more than larger nanoparticles. Heat conductivities of nanofluids with blade- or brick-shaped nanoparticles measured by [PERSON] et al. [39] and [PERSON] et al. [34] are close and lower than those of other shapes due to the sphericity of bricks being close to 1. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Authors** & **Nanofluid Type** & \
\begin{tabular}{l} **Particle Shape and Size** \\ **(nm as Default)** \\ \end{tabular} &
\begin{tabular}{l} **Volume Fraction \(\phi\)** \\ **(Vol. as Default)** \\ \end{tabular} & **Temperature** & **Maximum TCE** \\ \hline [PERSON] et al. [30] & SiC–water/EG & Cylindrical & & & \\  & 600 (_d_) & & & 4 °C & 22.9\% \\ [PERSON] et al. [22] & CNTs–DE/EG/DW & Nanotube & & & 19.6\% in DE, 12.7\% in DE, 12.7\% in DE, 7.0\% in DW \\ [PERSON] et al. [45] & CNTs–water & Nanotube, 30 to 250 (_d_), & & 0.6\% & Room & 38\% \\ [PERSON] et al. [2] & TiO\({}_{2}\)–water & Nanorod & & & \\  & 10 (_d_) \(\times\) 40 (_l_) & & & & \\ [PERSON] and [PERSON] [31] & Bi\({}_{2}\)Te\({}_{3}\)–perfluoro–n & Nanorod & & & 7.7\% at 3 °C, 6.3\% at 50 °C \\  & hexane & 20 (_d_) \(\times\) 170 (_l_) & & & 6.1\% at 20 °C, 3.9\% \\ [PERSON] and [PERSON] [31] & Bi\({}_{2}\)Te\({}_{3}\)–hexadecane oil & Nanorod & & & 20–50 °C & 6.1\% at 20 °C, 3.9\% \\  & 20 (_d_) \(\times\) 170 (_l_) & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of experiments data for heat conductivity of NSN nanofluids. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline