數值模擬不同長短垂直倒Ｕ型管中單相流體的流場及熱傳之現象

Abstract

為模擬核電廠發生管路破裂導致卻水流失或停電導致供水幫浦無法供應冷卻水時，蒸氣產生器在自然循環下熱流現象的變化，以增進核能安全分析之能力。本文利用數值計算方法探討在已知管壁溫度分佈及進、出口流量條件下，核電廠內的蒸氣產生器倒U型管中的流動與熱傳現象。為簡化研究將30支倒Ｕ型管依等價原則簡化為2支。由於模擬的倒U型管形狀複雜，故用適合複雜計算邊界的有限元素法。壁面溫度由實際實驗量得，雷諾數由103開始逐漸下降至10。葛拉旭夫數隨雷諾數改變從兩管順流開始至發生逆流為止。結果顯示葛拉旭夫數增大，管內流體發生逆流現象越顯著，凈熱傳量則變劣。此外並發現外管較內管容易發生逆流現象。

The paper was to investigate of phenomena of flow field and heat transfer of inverted U-tubes in a steam generator of nuclear power plant under two known conditions of temperature distribution at tube wall and flow rates of inlet and outlet. For the convenience of analysis, an equivalent rule is adopoted to simplify 30 inverted U-tubes to 2 inverted U-tubes. Since the geometry of the steam generator is complicate, the finite element method which is convenient for the complex shape domain is utilized. for pratical prupose, the temperature distributions at tube walls are obtained from experimental results, and Reynolds numbers change from 103 to 10. At certain Reynolds number mentioned above, Grashof number varies from the normal current flows occuring in the 2 inverted U-tubes to the reverse flow appearing in any one of the inverted U-tubes. The results show that the higher the Grashof number is, the more apparent the reverse flow is, and the net heat transfer rate becomes worse. The net heat transfer rate becomes worse. The reverse flow appearing in the outer tube is easier than that appearing in the inner tube which is in agreement with the earlier experiment results.