| Summary: | 碩士 === 國立臺北科技大學 === 能源與冷凍空調工程系碩士班 === 100 === Solidification of liquid binary alloys is found in various industrial applications, such as marine science, silicon crystal growth process, the ice storage system in HVAC, the food processing and cold storage in food industry, the metal alloys casting and low-temperature biotechnology applications. The natural convection phenomenon, also known as double-diffusive convection, which occurs during the solidification process owing to the effects of temperature and concentration gradients, is likely to cause poor quality of alloy castings. The factors contributing to the formation of double-diffusive convection and the means to eliminate or weaken such phenomenon have been the focus of research in the past. This study focused on the effect of slanted lateral cooling wall with negative slope on the formation of double-diffusive convection during the solidification of a 25 wt. % hyper-eutectic binary solution (NH4CL-H2O). Particle Image Velocimetry (PIV) techniques, thermochromic liquid crystal (TLC) and Schlieren method were employed to observe the flow development of the binary solution in the liquid. The experimental results showed that the water-rich fluid was continuously released through the mushy layer during solidification, resulting in the formation of a red color layer on the thermochromic liquid crystal. The image processing software was used for temperature field visualization. The experimental results also indicated that the lateral cooling wall with different slope has significant effects on the formation of double-diffusive convection during solidification. The growth process of double-diffusive convection varies apparently between the lateral cooling walls with higher slopes, such as in the case of 0 and 5 degrees compared to those with lower slopes, such as in the case of 10 and 15 degrees. As the slope of lateral cooling wall decreases, the filling-box process becomes faster and the time for the flow development to reach steady state becomes shorter.
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