轴向变热流密度管外强化沸腾实验研究

发布时间：2018-04-20 04:05

  本文选题：管外沸腾强化 + Turbo-EHP　； 参考：《天津大学》2016年硕士论文

【摘要】：有机朗肯循环(ORC)是中低温资源有效利用的主要途径之一。在ORC系统之中,蒸发器部件的传热效率直接影响ORC系统整体的热效率,而ORC蒸发器内主要以管外沸腾传热为主。本文从这一点出发,分别做了两类实验即单管管外沸腾实验以及管壳式换热器实验。在单管实验中,选用了4种管型,分别为光管、波纹管、烧结管(HIGH-FLUX)和Turbo-EHP型多孔管,以及选用了两种实验工质,分别为R245fa和R601a,通过单管实验,得到了每种工质在各种管型管外沸腾的实验现象以及其管外局部换热系数、管外平均换热系数和压降。通过单管实验,对比分析后,在管壳式换热器实验中,选用了Turbo-EHP型多孔管作为实验管,采用了叉排的结构布置,实验结果得到管外沸腾的局部换热系数以及LMTD对数平均换热系数,得到如下结论:在单管实验中,通过观察实验现象,汽化核心最多的为HIGH-FLUX烧结管,其次为Turbo-EHP多孔管,之后为波纹管,最差的为光管。在波纹管实验中,发现气泡多数集中在波谷的前半部分,从侧面论证了Turbo-EHP型多孔管的优势。从LHTC数值比较来看,四种管型的LHTC均呈现先增后减的趋势与实验现象保持一致。从AHTC数值比较来看,四种管型的AHTC多数呈现了先线性增大后缓慢减小的趋势。特别地,多数R601a实验的AHTC值大于R245fa实验值。从对比光管的AHTC实验数值来看,Turbo-EHP型管为其4.82~7.75倍,波纹管为其1.1~1.2倍。从压降来看,所有实验的压降均随着热源温度的增大而线性增大。四种管型的R245fa实验的压降均大于R601a实验。其次对比四种管型可以发现ΔPTurbo-EHPΔP波纹管ΔP烧结管ΔP光管。通过单管实验的实验现象和换热系数,大致可以将换热器内部从下至上方向划分为三个区域,即液相区、气液区以及气相区,过冷液态工质进入第一个区域,热流密度较低,适宜采用HIGH-FLUX烧结管;其次饱和液进入气液区,此时热流密度较高,适宜Turbo-EHP型管,加快核态沸腾;而在气相区,工质多为气态,从强化换热的角度来看,宜加大换热面积,从而提高换热效率,宜采用高翅片管增加换热面积。管壳式换热器选用Turbo-EHP管作为实验用管,并采用R245fa作为实验工质。从上下管的LHTC来看,热源温度为50~60℃之间时,沿管长方向,LHTC先减后增的趋势,上下两管的换热系数十分接近;在热源温度为60~100℃时,沿管长方向,LHTC值先增后减,由于热源温度的升高从整个实验数据来看,局部换热系数为3027.96~8936.80W/(m2·K),当热源温度为100℃时,下管中0.2m处取得最大值。通过计算LMTD对数平均换热系数,LMTD对数平均换热系数值为1529.76~2271.63W/(m2·K),给采用Turbo-EHP型多孔管的换热器提供数值参考,具有一定的工程实际意义。
[Abstract]:Organic Rankine Recycling (ORC) is one of the main ways for the efficient utilization of medium and low temperature resources. In the ORC system, the heat transfer efficiency of the evaporator components directly affects the overall thermal efficiency of the ORC system, while the boiling heat transfer inside the ORC evaporator is mainly outside the tube. From this point of view, two kinds of experiments have been carried out, that is, the boiling experiment outside the single tube and the experiment of the shell and tube heat exchanger. In the single tube experiment, four kinds of tube types were selected, namely, light tube, corrugated tube, sintered tube HIGH-FLUX) and Turbo-EHP type porous tube, and two kinds of working fluids, R245fa and R601a, were selected respectively. The experimental phenomena of boiling of each kind of working fluid outside the tube, the local heat transfer coefficient, the average heat transfer coefficient and the pressure drop outside the tube are obtained. After the comparison and analysis of single tube experiment, in the experiment of shell and tube heat exchanger, the Turbo-EHP porous tube is selected as the experimental tube, and the structure arrangement of fork row is adopted. The experimental results show that the local heat transfer coefficient of boiling outside the tube and the logarithmic average heat transfer coefficient of LMTD are obtained as follows: in the single tube experiment, the most vaporized core is the HIGH-FLUX sintered tube, followed by the Turbo-EHP porous tube. Then the bellows, the worst is the light tube. In the experiment of bellows, it is found that most of the bubbles are concentrated in the front half of the trough. The advantages of the Turbo-EHP type porous tube are demonstrated from the side. From the comparison of LHTC values, the LHTC of the four types of tubes showed a trend of increasing first and then decreasing, which was consistent with the experimental phenomenon. From the comparison of AHTC values, most of the AHTC of the four types of tubes showed a trend of linear increase and then slow decrease. In particular, the AHTC values of most R601a experiments are higher than those of R245fa experiments. From the AHTC experimental value of the contrasted light tube, the Turbo-EHP type tube is 4.82 ~ 7.75 times higher than that of the corrugated tube, and the corrugated tube is 1.1 ~ 1. 2 times as high as that of the corrugated tube. From the point of view of pressure drop, the pressure drop of all experiments increases linearly with the increase of heat source temperature. The pressure drop of the four tube R245fa experiments is higher than that of R601a experiment. Then, the 螖 PTurbo-EHP 螖 P corrugated tube 螖 P sintered tube 螖 P light tube can be found by comparing four kinds of tube types. Through the experimental phenomenon and heat transfer coefficient of single tube experiment, the inner heat exchanger can be roughly divided into three regions from the bottom to the top, that is, the liquid region, the gas-liquid region and the gas region. The supercooled liquid fluid enters the first region and the heat flux density is low. It is suitable to adopt HIGH-FLUX sintered tube, then saturated liquid enters the gas-liquid zone, at this time the heat flux is relatively high, and the heat flux is suitable for Turbo-EHP tube to speed up the nucleation boiling. In the gas phase region, the working fluid is mostly gaseous, so from the point of view of enhanced heat transfer, the heat transfer area should be increased. In order to improve heat transfer efficiency, high finned tube should be used to increase heat transfer area. Turbo-EHP tube and R245fa are used as experimental tube and working medium in tube and shell heat exchanger. From the LHTC of the upper and lower tubes, when the heat source temperature is between 50 鈩，

本文编号：1776144