Abstract
T-pipe designs have been widely used in the industry. Among them, mixing of hot and cold water is a common application. In the mixing process, cold and hot fluids are respectively injected through main and branch pipes, and are mixed in the downstream area of T-junction. High temperature hot water flows through the main pipe under normal operations; hence, the pipe wall is at high temperatures for long time. The fluid injected through the branch pipe into the main pipe is a cool fluid. After mixing, the wall of the main pipe is under high thermal fluctuations, which will cause strong thermal stresses generated in the main pipe wall. These stresses will eventually lead to pipe damage and water loss. There are two experimental designs in this study, the first one may sustain higher pressure and higher temperature difference with stainless steel pipes；and the second one is transparent and flow map observable acrylic made pipes. With the experimental results, some points can be addressed. Within the first experimental conditions, test condition I, it is concluded that lower main pipe flow rate leads to better mixing effect with constant branch pipe flow rate. In conditions II and III, higher injection flow velocity would enhance the turbulence effect which results in better thermal mixing. In the second experimental condition, through flow rate adjustments of the branch and main pipes, when the branch/main velocity ratio is greater than 7.8, which shows the cold water will hit the bottom of the main pipe and create a reverse flow. This reverse flow creates large thermal stresses on the wall. Hence, the branch/main velocity ratio and the hot-water-mixing phenomenon are the vital focusing of this study.