# 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 c c} \hline \hline
**Authors** & **Nanomaterials** & **Applications** & **Results and Remarks** & **Model or Method** \\ \hline \multirow{4}{*}{[PERSON] et al. [37]} & \multirow{4}{*}{\(CNTs\), \(LTEG\), Ag, Al, and Cu} & Thermal conductive & It is recommended to add \(LTEG\) & \\  & & polymer composites & composite as a suitable filter to the & HDPE polymer. With a 10 wt\% of \\  & & and Cu & applied to HDPE pipes to & \(LTEG\), the length of the GHE was & for U-Tube GHE [47]. \\  & & & reduce the pipe length of & reduced near to 10\% of the total \\  & & & the borehole GHE & borehole pipe \\ \hline \multirow{4}{*}{[PERSON] et al. [4]} & \multirow{4}{*}{TE} & \multirow{4}{*}{\begin{tabular}{} \end{tabular} } & A performance comparison of different \\  & & Different GHE & GHE configurations. GLHEPro used to \\  & & configurations: single & calculate different parameters. The use \\  & & U-pipe, double U-pipe & of TE pipes instead of HDPE pipes & \\  & & and coaxial, each with & allowed a reduction in the Bore \\  & & and standard HDPE pipes and & Thermally Resistance (BTR) of between 22.3 and 24.4\%, a reduction in the total \\  & & thermally enhanced (TE) & CHE length of between 9.0 and 14.8\% \\  & & pipes & and a reduction in construction costs of \\  & & & between 3.3 and 8.6\% \\ \hline \multirow{4}{*}{[PERSON] et al. [38]} & \multirow{4}{*}{HDPE-aluminum wires} & \multirow{4}{*}{\begin{tabular}{} \end{tabular} } & Improvement of thermal conductivity \\  & & HDPE pipes with & depending on the number of \\  & & aluminum wires used for & aluminum threads used in HDPE. \\  & & ground source & Increasing the number of wires \\  & & applications & increases the outer surface \\  & & applications & temperature, which can save heat \\  & & & exchanger piping length \\ \hline \multirow{4}{*}{[PERSON] et al. [10]} & \multirow{4}{*}{Nanoparticles} & \multirow{4}{*}{Nanoparticles} & Improve the thermal & Geometrical optimization with the use \\  & & properties of elements in & of different diameters, numbers, \\  & & geothermal piles to & and configuration piles. To improve \\  & & improve the thermal & material, nanofluids and highly \\  & & conductivity of HDPE & thermally conductive material fillers \\  & & pipes & are used. GEOPerform pipe is 75\% \\  & & & higher than the conventional HDPE \\  & & & pipe \\ \hline \multirow{4}{*}{[PERSON] et al. [41]} & \multirow{4}{*}{Nanobubbles} & Distinct types of heat & \multicolumn{2}{c}{Introducing the new term} \\  & & pipes classified into three & \multicolumn{2}{c}{\"nanobubbles\". This is a recent} \\  & & groups, sintered, groove & technology with few studies available. \\  & & and mesh, applied in & The applications using nanoparticles in \\  & & GSHP, thermal diodes, & heat pipes are still in the initial stages \\  & & and rotating heat pipes & and future works may explore hybrid \\  & & technologies with nanotechnology & \\ \hline \multirow{4}{*}{[PERSON] et al. [42]} & \multirow{4}{*}{TE-HDPE} & Performance of the coaxial & The coaxial GHE configurations & Dimensional thermal \\  & & pipe configuration in a & decrease the total borehole length from \\  & & vertical GHE & 9\% to 23\% using TE-HDPE. & [PERSON]’s method \\ \hline \multirow{4}{*}{[PERSON] and [PERSON] [43]} & \multirow{4}{*}{Nanothermo-dynamics} & \multirow{4}{*}{Introduce the concept of \begin{tabular}{} \end{tabular} } & This is an extension of the classic \\  & & thermodynamics theory to the \\  & & nanothermodynamics & nanometer scale. The developed model & Nanothermodynamics \\  & dynamics & & predicts macroscopic, mesoscopic, \\  & & and nanoscopic properties of materials & \\ \hline \multirow{4}{*}{[PERSON] and [PERSON] [44]} & \multirow{4}{*}{\
\begin{tabular}{} \end{tabular} } & \multirow{4}{*}{
\begin{tabular}{} \end{tabular} } & The use of different nanoparticles in \\  & & \(CNTs\) and their polymer & HDPE filled with 7 vol.\% \\  & & nanocomposites to replace & nanometer-size expanded graphite has \\  & & metal parts in several & a TC of 1.59 W/mK, twice that of \\  & & applications, power & microcompposites, which have a TC of \\  & & electronics, electric motors, & 0.78 W/mK at the same volume. \\  & & generators and heat & The \(CNT\) becomes the best promising \\  & & exchangers & candidate material for thermally \\  & & conductive composites. & \\ \hline \multirow{4}{*}{[PERSON] et al. [45]} & \multirow{4}{*}{CNTs} & To reduce the cost of GHE & The average COP for heating was quite \\  & & using U-shaped and & high, 3.9, and the seasonal reduction \\  & & double-shaped pipe & rate of primary energy compared to a \\ \cline{1-1}  & & configurations & typical air conditioning system \\ \cline{1-1}  & & & reached 23.2\% \\ \hline \hline \end{tabular}
\end{table}