# Performance Study and Efficiency Improvement of Ice Slurry Production by Scraped-Surface Method
## 2 Experimental
### Materials  
The purity of sodium chloride is over 99.5%. The silica nanofluid with average particle diameter of 25 nm used in the experiments was supplied directly by Shenzhen Jingcai Co., Ltd (Shenzhen, China) at an original concentration of 30 wt%. The base fluid of the silica nanofluid provided by the manufacturer is deionized. We were unable to determine the different surfactants or dispersants the manufacturer employed as additives to stabilize the nanofluids, because this is proprietary information. During the experiment, a certain amount of deionized water and sodium chloride were added to dilute the mother nanofluids to obtain the desired concentration of the silica nanofluids. Each time 1 kg of nanofluid was prepared and the composition is shown in Table 3. The diluted nanofluids \begin{table}
\begin{tabular}{c c c} \hline
**No.** & **Variable** & **Uncertainty** \\ \hline
1 & Temperature & 0.2 K \\
2 & Volume flow rate & 0.04 m\({}^{3}\)/h \\
3 & Power consumption & 0.01 kWh \\
4 & Weight & 0.01 g \\
5 & Particle size of nanosilica & 0.5 nm \\
6 & IPF & 0.05–0.25\% \\
7 & COP & 0.006–0.013 \\ \hline \end{tabular}
\end{table} 
Table 2: Value of uncertainties. were subjected to ultrasonic vibration for 2 h. In order to verify whether agglomerated particles were present in the diluted nanofluids, the nanofluids were examined for particle size distribution under a transmission electron microscope (TEM, TECNAI G2F20, FEI, Hillsboro, OR, USA). Figure 3 shows a TEM image of 0.5 wt% silica nanofluid with an average size of 25 nm. The particle size result for this nanofluid is consistent with the data provided by the manufacturer. We noticed from the TEM image that a majority of nanoparticles fell near this average size, with a few smaller and a few larger particles, which should yield an overall average particle size of 25 nm. From similar TEM images of the other nanofluids with different particle size and different mass concentration, no agglomeration was observed. This was due to: (a) the nanofluid manufacturers have developed successful surfactants or dispersants that are already present in these purchased nanofluids, making them stably suspended and free from agglomeration or coagulation; (b) the sonication of the dilute sample ensured breaking off of agglomerated particles. The main variation parameters involved in the calculation of IPF include the specific heat of aqueous sodium chloride solution and silica nanofluid, which vary with the concentration of the additive. The specific heat of the aqueous sodium chloride solution also changes with temperature. During the process of the measurement of IPF, the average temperature before and after the ice slurry melts is approximately 273.1 K, so the specific heat at 273.1 K is used as the basis for IPF calculation. And the specific heat can be obtained by querying the handbook of physical property parameter. The specific heat of aqueous sodium chloride solution at different concentrations is shown in Table 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mass Concentrations (\%)** & **Deionized Water (g)** & **Sodium Chloride (g)** & **Parent Nanofluid (g)** \\ \hline
0.05 & 958.33 & 40 & 1.67 \\
0.1 & 956.67 & 40 & 3.33 \\
0.2 & 953.33 & 40 & 6.67 \\
0.5 & 943.33 & 40 & 16.67 \\
0.75 & 935 & 40 & 25.0 \\
1 & 926.67 & 40 & 33.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The composition of different concentrations of silica nanofluids. Figure 3: TEM image of silica nanofluid with an average size of 25 nm. The specific heat of the nanofluid is evaluated according to the formula [36]:  
\[C_{\rm p,nf}=\psi\times C_{\rm p,n}+(1-\psi)\times C_{\rm p,f}, \tag{3}\]  
where \(C_{\rm p,nf}\) is the specific heat of the nanofluid, \(\psi\) is the mass fraction of the nanosilica, \(C_{\rm p,n}\) is the specific heat of the nanosilica, and \(C_{\rm p,f}\) is the specific heat of the base fluid. This formula has been found appropriate for use with nanofluids as validated by [PERSON] et al. and [PERSON] et al [36; 37].