新型相分離冷凝器相變傳熱強化機理研究

徐進良

摘 要：該研究針對有機工質朗肯循環系統中的關鍵部件冷凝器，創新性地提出了流型調控的新概念，通過采用相分離概念，在冷凝管內插入柱狀金屬絲網，在毛細力的作用下，液體被自動吸入到金屬網內，而氣相在管內壁和金屬網之間的環形間隙內流動，達到了流型調控的目的。該研究通過無相變空氣-水兩相流型調控實驗和數值研究發現：（1）水平光滑管內的分層流，經過新型結構管后，液體被全部吸入金屬絲網而導出，氣體則全部保留在了環形間隙內；（2）水平光滑管內的間隙流，經過新型結構管后，部分液體被吸入金屬絲網而導出，氣泡則在環形間隙內轉變為馬鞍形，從而大大增大了氣相與管內壁的接觸面積，形成大面積薄液膜傳熱，同時氣相被加速，強化了對流傳熱；（3）垂直光滑管內的間歇流，經過新型結構管后，由于絲網表面張力作用，氣彈進入環隙區域，形成拉長的環形氣彈，氣彈與管內壁的接觸面積變大，液膜厚度大幅減薄，同時氣彈上升速度大幅提高，引起環隙區域和核心區域內的流體通過網孔面進行強烈的質量與動量的交換并在核心區域產生自維持脈動流，以上因素均有利用提高設備換熱性能。 該研究通過光管與內插絲網管的R123水平管內冷凝對比實驗以及光管與內插銅粉燒結管的R245fa傾斜內冷凝對比實驗研究，得出：不銹鋼絲網管和銅粉燒結管均通過流型調控強化了管內冷凝，實驗工況范圍內，最大傳熱強化比達兩倍以上，綜合評價因子達到1.7。

關鍵詞：冷凝器 相分離 金屬絲網 流型調控 強化換熱

Research on Heat Transfer Enhancement Mechanism of Phase Separation Condenser

Xu Jinliang

（North China Electric Power University）

Abstract：For enhancing the heat transfer performance of the condenser in the organic Rankine cycle system， a flow pattern modulation concept was proposed by our group. A mesh cylinder is suspended in the heat transfer tube. Based on the experimental and numerical researches on the air-water two-phase flow pattern modulation process， we can obtain the following conclusions. （1） For the stratified flow in the horizontal tube， all liquid can be captured by the mesh cylinder to form the “gas-floating-liquid” mode. Gas is kept in the annular region. （2） For the intermittent flow pattern in the horizontal tube， the slug bubbles are prevented from entering the mesh cylinder thus they flow in the annular region to form the saddle bubbles. The condensation can be significantly enhanced by the following two mechanisms： the significantly increased contact area between the tube inner wall and the vapor phase； the increased moving speed of the saddle bubble in the annular region. （3） For the intermittent flow pattern in the vertical tube， the slug bubble cannot completely breakthrough the mesh pores， forcing the bubble flowing in the annular region to form the elongated-ring-slug-bubble. It was found that the modulated liquid film thickness can be decreased largely； the modulated bubble traveling velocity can be doubled， causing the increased liquid velocity and velocity gradient in the annular region to weaken the fluid boundary layer； the significantly increased bubble traveling velocity in the annular region promotes the mass and momentum exchange between the annular region and the core region， and yields the self-sustained pulsating flow in the core region. The above factors are benefit for the performance improvement of the heat transfer facilities. R123 condensation performance in a horizontal tube compared with that in a tube with a mesh cylinder insert and R245fa condensation performance in a horizontal tube compared with that in a tube with sintered copper powder cylinder insert were investigated experimentally. Conclusions were drawn that condensation heat transfer can be augmented considerably by flow pattern modulation in a tube inserted by empty cylinder made up of mesh screen or sintered copper powder. The heat transfer can be enhanced more than two times of that in a conventional smooth tube for the entire experimental conditions， where the performance factors are about 1.7.

Key Words：Condenser； Phase separation； Metallic mesh screen； Flow pattern modulation； Heat transfer enhancement

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