# Nanotechnology Applications in Ground Heat Exchanger Pipes: A Review
## 2 Literature Review
### Nanomaterials
#### 2.2.1 Theoretical and Numerical Simulations
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Authors** & **Nanofluids** & **Applications** & **Results and Remarks** \\ \hline [PERSON] and [PERSON] [11] & Al\({}_{2}\)O\({}_{3}\)-\(EG\)-water & Using the nanofluid Al\({}_{2}\)O\({}_{3}\)/ethylene glycol-water (EG-water) in two HGHE systems and one GSHP system & The results showed that with a 0.1\% nanofluid concentration in the U-type GHE, the heat exchanger improved the performance by 19\% compared to glycol-water and increased performance by 17.7\% with a concentration of 0.2\%. The setup was based on the ASHRAE book. \\ \hline [PERSON] et al. [33] & Ag, MgO, \(MWCNT\), and \(DWCNT\) & Experimental data of efficiency of different nanofluids are reviewed and an efficiency-price index is proposed & An economic analysis concluded that nanofluids do not have economic justification except in high-tech devices with critical application \\ \hline [PERSON] et al. [34] & Graphite, Al\({}_{2}\)O\({}_{3}\), CuO, TiO\({}_{2}\), Fe\({}_{2}\)O\({}_{2}\), SiO\({}_{2}\), SiC, and \(CNTs\) & Viscosity and thermal conductivity improvement of nanofluids & Graphene, \(CNTs\), Au, and Ag are more conductive than the TiO\({}_{2}\) SiC, and SiO\({}_{2}\) nanofluids. Most of the results reveal that the viscosity and thermal conductivity increase as the particle charge increases. \\ \[PERSON] [35] & Al\({}_{2}\)O\({}_{3}\), TiO\({}_{2}\), and Fe\({}_{2}\)O\({}_{3}\) & Patented nanofluid to introduce nanoparticles into the GHE of GSHP & A new parameter called the Mourntseff (Mo) number is introduced, which is a function of the \(\mu\), \(\kappa\), \(\rho\), and \(Cp\). Heat transfer is improved, GHE size is reduced and pumping cost is reduced; therefore, installation cost is reduced \\ \hline [PERSON] et al. [36] & Refrigerant \(R11\) & Closed circuit of cold water using a storage tank, with the refrigerant (R11) used as base working fluid with a mixture of titanium nanoparticles of 21 nm size & The results indicate that the heat transfer capacity of the pipe depends on the fluid transport properties; that is, the efficiency of the heat pipe tends to increase with increasing heat flow. Increasing the temperature between the evaporator and condenser sections results in a higher rate of heat transfer. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of experimental studies on heat exchanger pipes using nanofluids. 22.3 and 24.4%, a reduction in the total GHE length of between 9.0 and 14.8% and a reduction in the construction cost of between 3.3 and 8.6%. GSHP fitted with TE pipes can be a financially feasible and environmentally beneficial solution, even though the current typical commercial cost of TE pipes is almost twice that of conventional HDPE pipes. The authors proposed to work with the development of a tool to quickly and easily carry out size, performance and cost comparison analyses for a wide range of situations to present a more accurate and realistic view of the advantages and disadvantages of using TE pipes in the construction of GHE. A new idea to improve the thermal conductivity of HDPE pipes, which are resistant to oxidation but have low thermal conductivity and are used in many land source applications, was presented by [38]. The computational analysis presents a new fabrication composed of HDPE with aluminum wires that are distributed circumferentially and equally in the thickness of the pipe. Using a finite volume method and FORTRAN, a model comparing the pure HDPE and the new material was developed. The results shows an enhancement in the equivalent thermal conductivity of the composite by almost 25% for the 2 mm aluminum wires, and 150% for the 3 mm wires depending on the number of wires. Similarly, in [39] is realized research on the effect of adding aluminum powder to an HDPE with different volumetric concentrations. A numerical model shows that the thermal conductivity of the composite was less than 10% by volume, while [40] proposed a model using an aluminum nitride-HDPE mix, increasing the thermal conductivity.