# Heat Storage as a Way to Increase Energy Efficiency and Flexibility of NPP in Isolated Power System
## 2 Materials and Methods
### Experimental Verification of a Mathematical Model  
The verification of the compiled two-dimensional model (described in Section 2.4) by experiment was carried out (results in Section 3.2). The process of paraffin solidification around a tube with a cold heat transfer fluid was studied. The experiment was recreated using the model presented above. The results of the model and experiment were compared. A comparison was made between the temperatures at individual PCM points measured at the experimental setup and the temperatures at the same points obtained by the simulation. A comparison was made between the outlet water temperature measured at the experimental facility and the outlet water temperature obtained by the simulation.  
The scheme of the experimental installation is shown in Figure 7.  
Figure 6: Schematic of a simplified calculation using a one-dimensional model.  
The main part of the experimental installation was a container filled with paraffin, height--1000 mm, width and thickness: 150 \(\times\) 150 mm. A vertical metal tube with a nominal diameter of 50 mm was placed in the container. Four temperature sensors were located inside the container: T1--at a height of 750 mm, at a distance of 5 mm from the tube; T2--at a height of 700 mm, at a distance of 15 mm from the tube; T3--at a height of 350 mm, at a distance of 5 mm from the tube; T4--at a height of 300 mm, at a distance of 15 mm from the tube. Temperature sensors T5 and T6 were located at the inlet and outlet of the heat transfer fluid. The container with paraffin was thermally insulated.  
Before the experiment began, the paraffin melted due to the supply of steam through an internal metal tube. Steam was produced by an atmospheric pressure steam generator set. The paraffin in the container was completely melted and had an average temperature of about 80 \({}^{\circ}\)C at the start of the experiment. In the experiment, the water from the \"cold\" tank was pumped by a pump into a metal tube located inside the paraffin tank. In the tube, the water heated up and flowed into a \"hot\" tank. The water flow rate was determined using a flow meter. The water flow rate was regulated by changing the rotation speed on the pump and partially closing the valve. During the experiment, temperature sensors' readings and readings on the flow meter were recorded at intervals of 15 s. The water flow rate was 16.4-17.3 L/min, and the temperature of \"cold water\" at the inlet to the experimental installation was 19.5-20.3 \({}^{\circ}\)C (an average value of 20 \({}^{\circ}\)C is accepted).  
Food paraffin P-2 was used as the PCM in the experimental setup. The physical properties of this paraffin (according to the characteristics of the manufacturer) are presented in Table 3.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Melting Point, \({}^{\circ}\)C** & **Melting Heat,** & **Heat Capacity,** & **Thermal Conductivity,** & **Density, kg/m\({}^{3}\)** \\ \hline
60 & 198 & 2.5 & 0.24 & 800 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Thermophysical properties of paraffin P-2.  
Figure 7: The scheme of the experimental installation.