# Study on Heat Transfer Performance and Anti-Fouling Mechanism of Ternary Ni-W-P Coating
## 2 Experimental Section
### Fouling Experiments and Heat Transfer Performance  
Figure 2 displays the schematic of the flowing fouling experimental rig. The experimental system is primarily composed of a water heating system (red line), a fouling solution system, and a data acquisition system. First of all, the water in the water tank was heated to 343 K by the heating rod, and then was pumped in the inner tube of the heat exchanger through the transmission of the water pump. The flow and temperature of the hot water were adjusted by the two-way regulating valve and the water tank power controller, respectively. When the inlet and outlet water temperatures in the heat exchanger were kept constant, 0.1 g/L CaCl\({}_{2}\) solution and 0.1 g/L NaHCO\({}_{3}\) solution in pear-shaped separating funnel were mixed to 0.1 g/L supersaturated solution through magnetic stirring apparatuses. With the increase of temperature and the change of flow rate, the crystals of calcium carbon in the supersaturated solution precipitate, resulting in the fouling deposition. The use of CaCl\({}_{2}\) and NaHCO\({}_{3}\) can be hydrolyzed into Ca\({}^{2+}\), Cl\({}^{-}\), Na\({}^{+}\), and HCO\({}_{3}\)\({}^{-}\) in fouling solution [27], and then further electrolysis can occur. The dynamic reaction is as follows,  
\[\mathrm{HCO}_{3}^{-}\rightleftharpoons\mathrm{H}^{+}+\mathrm{CO}_{3}^{2-} \tag{1}\]  
\[\mathrm{HCO}_{3}^{-}+\mathrm{H}^{+}\rightleftharpoons\mathrm{H}_{2}\mathrm{CO} _{3} \tag{2}\]  
\[\mathrm{H}_{2}\mathrm{CO}_{3}\rightleftharpoons\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \tag{3}\]  
\[\mathrm{H}_{2}\mathrm{O}\rightleftharpoons\mathrm{OH}^{-}+\mathrm{H}^{+} \tag{4}\]  
\[\mathrm{Ca}^{2+}+\mathrm{CO}_{3}^{2-}\rightleftharpoons\mathrm{CaCO}_{3} \tag{5}\]  
Then, the mixed 0.1 g/L supersaturated solution of fouling is transported to the shell side of the heat exchanger with the function of peristaltic pump (Table 4). In Figure 3, the experimental heat exchange device is similar to a double-pipe (heat) exchanger. The inner tube of the heat exchanger is connected with the heating circulating water of 343 K, which is to keep the temperature constant in fouling solution system. Meanwhile, the outer tube is filled with the fouling solution and heated by the water temperature of the inner tube. Before the experiment, the specimens of the fouling test are embedded into the foam board and placed in the detachable lids of the measurable anti-fouling heat exchanger. So, the working surfaces of the specimens are parallel to the pipe centerline, which can reduce the effect of obstruction of the specimen surfaces on the water \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Item**} & **Water** & **Water and Solution** & **Concentration of** & **Recording** & **Experimental** \\  & **Temperature/K** & **Velocity/m.s\({}^{-1}\)** & **CaCO\({}_{3}\) Solution/g.L\({}^{-1}\)** & **Interval/s** & **Time/h** \\ \hline Parameter & 343 & 0.15 & 1.0 & 120 & 72 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Experimental parameters of flow fouling. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{ \begin{tabular}{c} **Specimen** \\ **Number** \\ \end{tabular}  } & **Nickel** & **Ammonium** & **Sodium** & **Lactic Acid** & **Sodium** & **Sodium** \\  & **Sulfate (g/L)** & **Acetate (g/L)** & **Citrate (g/L)** & **(g/L)** & **Hypophosphite (g/L)** & **Tungstate (g/L)** \\ \hline \hline \(1\) & 18 & 12 & 35 & 20 & 20 & 25 \\ \(2\) & 18 & 12 & 35 & 20 & 20 & 30 \\ \(3\) & 18 & 12 & 35 & 20 & 20 & 35 \\ \(4\) & 18 & 12 & 35 & 20 & 20 & 40 \\ \(5\) & 18 & 12 & 35 & 20 & 20 & 45 \\ \hline \hline \end{tabularflow in the pipe and ensure that the specimens do not have galvanic effect with other metal surfaces. At the same time, the screw in the inner tube was used to fix the chip thermocouple in the nearby area of each specimen and the temperature of the fouling solution can be measured continually.