T型管路設計在工業中有著廣泛的應用。其中冷熱水混合之應用較為常見，過程中冷熱流體分別利用主管與支管注入，並在T型管下游區進行混流。由於主管路長期流經高溫熱水，因此管壁上處於高溫環境，而支管注入之流體為冷卻流體，經冷熱混合後，主管管壁將產生十分不穩定溫度震盪(thermal fluctuations)現象，造成管壁產生強烈熱應力，結果會導致管道破損並發生失水事故。對核能工業而言，近幾十年來，許多議題集中在核電廠內之管路應用，探討熱應力可能引發的管路失效或洩漏事故，使國際間對T型管內的熱水流現象探討極為重視。本研究主要探討T型管中流體之冷熱水混合現象。我們設計垂直支管支流體為冷水且固定流量，並將熱水注入水平主管且調整其流量，最終觀測冷熱水於主管與支管交界處混合後，對於主管管壁之影響及管內溫度分佈。本研究設計兩套模組進行實驗，首先是可進行較高壓力，高溫差研究之不銹鋼管實驗；其次是透明且可觀測流場變化之壓克力管實驗，從實驗結果中得知，於第一個實驗模組中，在試驗條件I下，發現固定支管流率下，較低之主管流率將呈現更佳之混合效果。在條件II和III中，較高的注水流速度將使紊流效應增強，導致冷熱混合之效應更加均勻。第二個實驗模組中，透過調整支管與主管流速下，發現當支管流速與主管流速比(Vb/Vm)大於7.8時，會於T型管混合區上游0.5D壁面位置量測到溫度降低之現象，其主要顯示該處有冷水撞擊主管底部並產生迴流現象所致。此回流是由於一定程度之支管高流速冷水沖擊到主管之底部所造成，而此撞擊到主管底部之冷水會對主管管壁產生較大之熱應力。因此主管支管之流速比與熱水流混合現象是本研究中欲探討之重點。

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.

[1] Andersson, U., Westin, J., Eriksson, J., Thermal Mixing in a T-junction. Technical Report U 06-66, Vattenfall Research and Development AB, 2006.
[2] McFarland, B.L.,Landy,D.G., Turbulent mixing of two streams in a 90 tee. AIChE Symposium76,351–358, 1980.
[3] S. Chapuliot, C. Gourdin, T. Payen, J.P. Magnaud, A. Monavon., Hydro-thermal- mechanical analysis of thermal fatigue in a mixing tee. Nuclear Engineering and Design 235, 575–596, 2005.
[4] K.-J. Metzner, U. Wilke., Nuclear Engineering and Design 235, 473–484, 2005.
[5] Aizawa, T., Masuda, Y., Minami, K., Kanakubo, M., Nanjo, H., Smith, R.L., Direct observation of channel-tee mixing of high-temperature and high-pressure water. J. Supercrit. Fluids 43, 222–227, 2007.
[6] C.Walkera, M. Simianoa, R. Zboray, H.-M. Prasser, Investigations on mixing phenomena in single-phase flow in a T-junction geometry, Nuclear Engineering and Design 239, 116–126, 2009.
[7] Nobuyuki Kimura, Hiroshi Ogawa, Hideki Kamide, Experimental study on fluid mixing phenomena in T-pipe junction with upstream elbow, Nuclear Engineering and Design 240, 3055–3066, 2010.
[8] Shouxu Qiao, Hongfang Gu, Haijun Wang , Yushan Luo, Dasheng Wang, Pan Liu, Qingli Wang, Qing Mao, Experimental investigation of thermal stratification in a pressurizer surge line, Annals of Nuclear Energy 73, 211–217, 2014.
[9] Kamide, H., Igarashi, M., Kawashima, S., Kimura, N., Hayashi, K., ‘‘Study on mixing behavior in a tee piping and numerical analyses for evaluation of thermal striping’’, Nucl. Eng. Des. 239, 58－67, 2009.
[10] Kimura, N., Ogawa, H., Kamide, H., ‘‘Experimental study on fluid mixing phenomena in T-pipe junction with upstream elbow ’’, Nucl. Eng. Des. 240, 3055－3066, 2010.
[11] Hosseini, S.M., Yuki, K., Hashizume, H., ‘‘Classification of turbulent jets in a T-junction area with a 90-deg bend upstream’’, Int. J. Heat Mass Transfer 51, 2444－2454, 2008.
[12] C.Walkera, M. Simianoa, R. Zborayb, H.-M.Prassera, “ Investigations on mixing phenomena in single-phase flow in a T-junction geometry,” Nuclear Engineering and Design 239, 116–126, 2009.
[13] Smith, B.L., Mahaffy, J.H., Angele, K., ‘‘A CFD benchmarking exercise based on flow mixing in a T-junction’’, Nucl. Eng. Des. 264, 80－88, 2013.
[14] Gao, K., Wang, P., Lua, T., Song, T., ‘‘Experimental investigation and numerical simulation for weakening the thermal fluctuations in a T-junction’’, Ann. Nucl. Energy 78, 180－187, 2015.
[15] Zughbi, H.D., Khokhar, Z.H., Sharma, R.N., ‘‘Mixing in Pipelines with Side and Opposed Tees’’, Ind. Eng. Chem. Res. 42, 5333－5344, 2003.
[16] Hu, L.W., Kazimi, M.S. ‘‘LES benchmark study of high cycle temperature fluctuations caused by thermal striping in a mixing tee’’, Int. J. Heat Fluid Fl. 27, 54－64, 2006.
[17] Ayhan, H., Sökmen, C.N., ‘‘CFD modeling of thermal mixing in a T-junction geometry using LES model’’, Nucl. Eng. Des. 253, 183－191, 2012.
[18] New, T.H., Lim, T.T., Luo, S.C., ‘‘Effects of jet velocity profiles on a round jet in cross-flow’’, Exp. Fluids 40, 859－875, 2006.
[19] Zughbi, H.D., ‘‘Effects of Jet Protrusion on Mixing in Pipelines with Side-tees’’, Chem. Eng. Res. Des. 84, 993－1000, 2006.
[20] Lee, J.I., Hu, L.W., Saha, P., Kazimi, M.S., ‘‘Numerical analysis of thermal striping induced high cycle thermal fatigue in a mixing tee’’, Nucl. Eng. Des. 239, 833－839, 2009.
[21] de Tilly, A., Sousa, J.M.M., ‘‘An experimental study of heat transfer in a two-dimensional T-junction operating at a low momentum flux ratio’’, Int. J. Heat Mass Transfer 51, 941－947, 2008.
[22] Walker, C., Simiano, M., Zboray, R., Prasser, H.M. ‘‘Investigations on mixing phenomena in single-phase flow in a T-junction geometry’’, Nucl. Eng. Des. 239, 116－126, 2009.
[23] Naik-Nimbalkar, V.S., Patwardhan, A.W., Banerjee, I., Padmakumar, G., Vaidyanathan, G., ‘‘Thermal mixing in T-junctions’’, Chem. Eng. Sci. 65, 5901－5911, 2010.
[24] Zboray, R., Prasser, H.M., ‘‘On the relevance of low side flows for thermal loads in T-junctions’’, Nucl. Eng. Des. 241, 2881－2888, 2011.
[25] Kuschewski, M., Kulenovic, R., Laurien, E., ‘‘Experimental setup for the investigation of fluid–structure interactions in a T-junction’’, Nucl. Eng. Des. 264, 223－230, 2013.