本文選題：臥式螺旋管　切入點：流動沸騰　出處：《重慶大學》2015年碩士論文

【摘要】：螺旋管因其具有良好的傳熱性能、制造簡單和結構緊湊等優(yōu)點被廣泛應用于動力、低溫與制冷技術、化工、食品醫(yī)藥等工業(yè)行業(yè)中。同直管相比,螺旋管強化傳熱的機理是:由于彎曲通道內的流體受到了離心力的作用,在螺旋管內的流道橫截面上產生了二次回流,管內的主流與二次回流的疊加使得流體在管內沿著管道軸向螺旋運動,從而增強了換熱效果。前人已經對螺旋管內單相和兩相流動與傳熱進行了大量的研究,然而這些研究主要針對的是螺旋管外壁為均勻熱邊界條件下的,對管外壁施加非均勻熱邊界條件的螺旋管內流動和傳熱性能的研究則鮮有報道。本文搭建了兩相流動與傳熱實驗臺,以制冷劑R22為工質對臥式螺旋管在非均勻熱邊界條件下的兩相流動與傳熱特性進行了實驗研究;另一方面還對非均勻熱邊界條件下螺旋管內單相湍流流動與傳熱進行了數值模擬研究。實驗方面,在熱流密度q=3.88-19.4 k W/m2,質量流速G=182-303 kg/(m2s),質量干度x=0.07-0.53范圍內,分別對三種熱邊界條件下的臥式螺旋管內流動沸騰換熱特性進行了實驗研究。三種熱邊界條件分別為:管外壁周向均勻熱流條件,管外壁外側均勻熱流、內側絕熱條件和管外壁內側均勻熱流、外側絕熱條件。三種熱邊界條件下的螺旋管內局部流動沸騰傳熱系數均是隨著熱流密度和質量流速的增大而增大。在本文實驗的干度范圍內,局部沸騰傳熱系數隨著質量干度的增大而增大。在三種熱邊界條件下對螺旋管外壁所施加的熱量相同的基礎上,將三種熱邊界條件下管內局部流動沸騰傳熱系數進行了對比,發(fā)現(xiàn)螺旋管外壁內側均勻熱流外側絕熱條件下管內沸騰傳熱系數最大,管外壁均勻熱流條件下次之,管外壁外側均勻熱流內側絕熱條件下最小。數值模擬計算方面,建立了三種不同幾何結構的螺旋管模型,以單相水為工質,通過改變進口雷諾數和熱邊界條件對螺旋管內單相湍流流動與傳熱特性進行了模擬計算,得到了不同熱邊界條件對管內流體溫度分布、速度分布和管內二次流的影響,且三種不同熱邊界條件下管內單相湍流流動傳熱系數的大小規(guī)律為:內側均勻熱流外側絕熱最大,均勻熱流條件下次之,外側均勻熱流內側絕熱時最小。總之,本文對非均勻熱邊界條件下螺旋管內單相和兩相流動與傳熱進行了探索研究,為螺旋管在非均勻熱邊界下的應用提供了設計依據和基礎數據。
[Abstract]:Spiral tubes are widely used in power, low temperature and refrigeration, chemical, food and pharmaceutical industries because of their good heat transfer performance, simple fabrication and compact structure. The mechanism of heat transfer enhancement in spiral tube is that the fluid in the curved channel is subjected to centrifugal force and secondary reflux occurs on the cross section of the channel in the spiral tube. The superposition of the main stream and secondary reflux in the tube makes the fluid move along the pipe axis, thus enhancing the heat transfer effect. Many researches have been done on the single-phase and two-phase flow and heat transfer in the helical tube. However, these studies mainly focus on the condition that the outer wall of the helical tube is uniform heat boundary. There are few reports on the flow and heat transfer performance in a helical tube with non-uniform heat boundary conditions applied to the outer wall of the tube. A two-phase flow and heat transfer experiment bench has been set up in this paper. The two-phase flow and heat transfer characteristics of a horizontal spiral tube under non-uniform heat boundary conditions were investigated experimentally with refrigerant R22 as working medium. On the other hand, numerical simulation of single-phase turbulent flow and heat transfer in helical tube under non-uniform heat boundary condition is carried out. Experimental results show that in the range of heat flux (Q) 3.88-19.4 k W / m ~ (2), mass velocity G _ (18) ~ (303) kg / m ~ (2) / s ~ (2) and mass dryness x ~ (0.07-0.53), The flow boiling heat transfer characteristics of horizontal helical tube under three kinds of heat boundary conditions are studied experimentally. The three heat boundary conditions are as follows: uniform heat flow around the outer wall of the tube, uniform heat flux outside the outer wall of the tube, The inner adiabatic condition and the uniform heat flux inside the outer wall of the pipe, The local boiling heat transfer coefficient of spiral tube increases with the increase of heat flux and mass flow rate under three kinds of heat boundary conditions. The local boiling heat transfer coefficient increases with the increase of mass dryness. On the basis of the same heat applied to the outer wall of the helical tube under three kinds of heat boundary conditions, the local boiling heat transfer coefficient in the tube under three kinds of heat boundary conditions is compared. It is found that the internal boiling heat transfer coefficient is the largest under the condition of uniform heat flux on the outer wall of the helical tube, followed by the uniform heat flux on the outer wall of the tube, and the minimum under the condition of the inner adiabatic heat flux on the outside of the outer wall of the tube. In the aspect of numerical simulation, Three kinds of helical tube models with different geometry are established. The flow and heat transfer characteristics of single-phase turbulent flow in helical tube are simulated by changing the inlet Reynolds number and heat boundary conditions with single-phase water as working medium. The effects of different heat boundary conditions on the temperature distribution, velocity distribution and secondary flow in the tube are obtained. The heat transfer coefficient of the single-phase turbulent flow in the tube under three different heat boundary conditions is as follows: the maximum adiabatic heat outside the inner uniform heat flux is obtained. Under uniform heat flow condition, the inner adiabatic time of outer uniform heat flux is the least. In a word, the single-phase and two-phase flow and heat transfer in helical tube under non-uniform heat boundary condition are studied. The design basis and basic data are provided for the application of helical tube under non-uniform thermal boundary.
【學位授予單位】：重慶大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TK124

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