| Summary: | 碩士 === 國立臺北科技大學 === 能源與冷凍空調工程系碩士班 === 96 === Phase change materials were employed in industrial applications very often. The solidification of a binary solution is one of them (for example, casting of binary alloys). In the past, one of the main issues to study the solidification of a liquid binary alloy focused on how to remove or weaken the “double-diffusive convection” because it is the main reason to cause the poor quality of alloys. The objective of this paper is to investigate the effect of periodic forced convection on the development of double-diffusive convection and to find a method to erase or reduce the double-diffusive convection. A hypereutectic aqueous ammonium chloride (NH4Cl-H2O) solution was adopted as the test sample in this paper and it was put into an enclosure cooled from the bottom, known as unidirectional solidification process, to investigate the heat and mass transport phenomena during solidification. The measurement of the flow visualization by shadowgraph technique, movement of liquid-mush interfaces, temperature distribution and concentration distribution were conducted during solidification. Experimental results revealed that with increasing period forced convection, the double-diffusive convection became weak, the plume appeared rather late and the time of developing double-diffusive convection became short. For periodic lid-driven velocity with 4 cm/sec, the number of plumes was reduced by 60% as compared to that of UDS without externally imposed forced convection.
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