# Performance Study and Efficiency Improvement of Ice Slurry Production by Scraped-Surface Method
## 2 Experimental  
### Experimental Apparatus  
The surface-scrapped ice slurry generation system, as shown in Figure 1, includes an ice slurry generator, a condenser, a compressor, an expansion valve, a rotating blade, a circulating pump, and an ice slurry storage tank. The height of the ice slurry storage tank is 750 mm. The inner diameter is 780 mm and the outer diameter is 800 mm. The ice-making solution stored in the ice slurry storage tank is sent to the annular pipe at the top of the ice slurry generator by the circulation pump and sprayed on the inner wall surface of the scraping tank. The ice slurry generator consists of a circular shell-and-tube type heat exchanger, cooled on its outer shell side by an evaporating refrigerant, and attached with spring loaded rotating blades on its inner side to scrape the ice and prevent any crystal deposits on the cooled surface, as shown in Figure 2. The height of the heat exchanger is 400 mm. The inner diameter of the inner tube is 340 mm and the wall thickness is 10 mm. The inner diameter of the outer shell is 420 mm and the wall thickness is 40 mm. The detail description of scraping system is presented in Table 1. During the experiment, the rotating blades are driven by the motor reducer, and the rotation speed can be adjusted.  
\begin{table}
\begin{tabular}{c c c} \hline
**No.** & **Variable** & **Value** \\ \hline
1 & Scraping speed & 0–29 rpm \\
2 & Number of rotating blade & 2 \\
3 & Height of rotating blade & 180 mm \\
4 & Width of rotating blade & 32 mm \\
5 & Thickness of rotating blade & 12 mm \\
6 & Material of rotating blade & Teflon \\
7 & Distance between rotating blade and the inner wall & 0.2 mm \\ \hline \end{tabular}
\end{table}
Table 1: The detail description of scraping system.  
Figure 1: Schematic diagram of experimental apparatus.  
The solution height of the ice storage tank is about 220 mm. There are three Pt100 thermometer probes (Toprie, Shenzhen, Guangdong, China) within the tank, which are set at a height of 40 mm, 120 mm and 200 mm from the bottom respectively. The tank is equipped with a stirring paddle. During the ice making process, the stirring paddle automatically opened for 30 s every 570 s, so that the ice slurry solution was evenly mixed. At this time, the real-time temperature was recorded, and it was found that the display temperatures of the three Pt100 thermometer probes were almost the same. Therefore, the measured temperature was the actual temperature of the ice slurry. The volume flow rate of nanofluids was measured by a turbine flowmeter (LWGYB-15, Fanyang, Shanghai, China). The energy consumption of the total system, and that of the rotational scraping system were measured by two separate digital watt-hour meters (DTS1330-LCD, Zhnqi, Suining, Jiangsu, China).  
The reliability of the measurement results is represented through the uncertainty analysis. The uncertainties of direct measurement parameters given by the manufacturers are listed in Table 2, including temperature, volume flow rate, power consumption and weight. The sources of measurement errors were analyzed and the uncertainties of derivation parameters, such as COP and ice packing fraction (IPF), were evaluated [35]. The uncertainty of particle size of nanosilica was obtained through the analysis of the TEM images. The values of the uncertainty of these derivation parameters are also given in Table 2.  
Figure 2: Schematic of a scraped surface ice slurry generator.