離子態水溶液及去離子水穩態池沸騰實驗研究

Steady-state pool boiling in ionic solution and deionized water

黃子振(Tzu-Chen Huang)

指導教授 ： 潘欽

國立清華大學/原子科學院/核子工程與科學研究所/碩士(2017年)

摘要

池沸騰實驗一直以來都是研究沸騰熱傳與雙相流最基本的研究方法之一。過去我們團隊以不鏽鋼金屬圓球及鋯球在海水及去離子水中進行1000℃高溫淬冷實驗，模擬當核電廠發生爐心裸露事故時以緊急爐心注水系統注水的移熱能力。實驗結果顯示當以海水做為冷卻液體時可以大幅降低淬冷的時間，因為海水內的離子成分會防止蒸汽膜的產生，進而讓高溫表面持續與液體接觸而提高移熱效率。本實驗由此為出發點，以穩態池沸騰來觀察離子態水溶液及去離子水之間的差異以及背後的物理因素。

本研究以白金熱阻絲作為測試段，線徑為0.3 mm 且長度為11.3 cm。在其上方塗有絕緣保護膠以防止進行離子態實驗時會有氧化還原等反應。實驗水槽為一個長23 cm寬22 cm高20 cm的不鏽鋼水槽。白金線表面溫度則由四線式量測法量測電阻並由溫度電阻校正曲線回推其平均表面溫度，藉此便可以推得沸騰曲線。每次實驗皆以盛裝6 L(相當於11.5 cm水位高度)的測試液體並以下方的恆溫控制加熱盤控制液體溫度。本研究以4支T-type熱電偶連接到數據截取器MX100量測液體的溫度。

由實驗結果可發現，在相同熱通率下，去離子水氣泡尺寸明顯大於海水和氯化鈉水溶液，而隨著功率上升去離子水的氣泡也會顯著的成長，然而在離子態水溶液的實驗中，氣泡的尺寸幾乎維持不變，亦即氣泡不會合併。在氯化鈉水溶液中，高頻率且不合併的氣泡將製造劇烈的擾動，因而提高熱傳效率以及臨界熱通率。然而在海水的實驗中，因為其測試段靠近陰極沉積的含鎂鹽類將提高熱阻，進而導致壁溫上升，最終熱傳效果甚至比去離子水還要差。去離子水的沸騰實驗往往伴隨著大量氣泡的合併，因此在測試段上也比較容易形成穩定的氣膜。相較於其它兩種工作流體，在較低熱功率下，去離子水便有可能已徑達到臨界熱通率。

關鍵字

池沸騰 ； 離子態水溶液 ； 氣泡合併 ； 臨界熱通率

並列摘要

Pool boiling experiment is one of the most fundamental methods to study boiling heat transfer and two phase flow phenomena. Our team used to conduct a quench experiment by quenching stainless steel ball and zircaloy ball with initial temperature at 1000℃ in seawater and deionized water to simulate the situation that the emergency core cooling system in nuclear power plant injects water to the core when the core uncovered accident occurs. The results demonstrate that seawater can significantly reduce the quenching time because the ions in it may inhibit the formation of vapor film at ultra-high temperature during quenching. In other words, the extreme hot surface can still contact with the liquid coolant and enhance the heat transfer coefficient. In this experiment, we design a steady-state pool boiling experiment to explore the different phenomena and the physics involved between ionic solution and deionized water.

The test section is a platinum wire heater with a diameter of 0.3 mm and a length of 11.3 cm. It is coated with electronic insulation adhesive to prevent electrochemical reaction in ionic solution. A stainless steel tank with a length of 23 cm, width of 22 cm and height of 20 cm is employed as the pool for the boiling experiments. The pool is always filled with 6 L, equivalent to a depth of 11.5 cm of test working fluid in each test. A hot plate below the tank is used to control the bulk liquid temperature, which is measured by four T-type thermocouples connected to MX100 data acquisition system. The wall superheat can be acquired by the Kelvin 4-wire measurement method. The boiling curve can then be acquired.

The results demonstrate that the bubbles for boiling in deionized water are usually much bigger than that in seawater or sodium chloride solution at the same heat flux. As the heating power is increased, the bubbles in deionized water may grow up obviously due to frequent bubble coalescence, while the bubble diameter approximately the same in ionic solution owing to lack of bubble coalescence. In sodium chloride solution, high departure frequency and non-coalescence bubbles may induce significant disturbance to the liquid near the surface and result in much better heat transfer performance and higher critical heat flux. In seawater, however, some magnesium salt may deposit on the heating wire, especially near the cathode and thus increase the thermal resistance. This may deteriorate heat transfer and heat transfer coefficient may be smaller than that in deionized water at high heat flux. In deionized water, the frequent bubble coalescence may eventually form a stable vapor film on the test section and heat transfer mode changes from nucleate boiling to film boiling. Compare with the other two working fluids, the critical heat flux in deionized water is much lower than that in seawater and sodium chloride solution.

並列關鍵字

Pool boiling ； Ionic solution ； Bubble coalescence ； Critical heat flux

參考文獻

[2] S. Nukiyama, "The maximum and minimum values of the heat Q transmitted from metal to boiling water under atmospheric pressure", International Journal of Heat and Mass Transfer, 9(12), 1966, pp. 1419-1433.

[3] F.P. Incropera, D.P. deWitt, T.L. Bergman, A.S. Lavine, Principles of Heat and Mass Transfer, 7 ed., John Wiley & Sons, NY, 2012.

[5] D. Zhong, J.a. Meng, Z. Li, Z. Guo, "Experimental study of saturated pool boiling from downward facing surfaces with artificial cavities", Experimental Thermal and Fluid Science, 68, 2015, pp. 442-451.

[7] S.-H. Hsu, Y.-H. Ho, M.-X. Ho, J.-C. Wang, C. Pan, "On the formation of vapor film during quenching in de-ionized water and elimination of film boiling during quenching in natural sea water", International Journal of Heat and Mass Transfer, 86, 2015, pp. 65-71.

[9] C.-K. Huang, V.P. Carey, "The effects of dissolved salt on the Leidenfrost transition", International Journal of Heat and Mass Transfer, 50(1–2), 2007, pp. 269-282.