本文選題：管外沸騰強化 + Turbo-EHP��； 參考：《天津大學(xué)》2016年碩士論文

【摘要】：有機朗肯循環(huán)(ORC)是中低溫資源有效利用的主要途徑之一。在ORC系統(tǒng)之中,蒸發(fā)器部件的傳熱效率直接影響ORC系統(tǒng)整體的熱效率,而ORC蒸發(fā)器內(nèi)主要以管外沸騰傳熱為主。本文從這一點出發(fā),分別做了兩類實驗即單管管外沸騰實驗以及管殼式換熱器實驗。在單管實驗中,選用了4種管型,分別為光管、波紋管、燒結(jié)管(HIGH-FLUX)和Turbo-EHP型多孔管,以及選用了兩種實驗工質(zhì),分別為R245fa和R601a,通過單管實驗,得到了每種工質(zhì)在各種管型管外沸騰的實驗現(xiàn)象以及其管外局部換熱系數(shù)、管外平均換熱系數(shù)和壓降。通過單管實驗,對比分析后,在管殼式換熱器實驗中,選用了Turbo-EHP型多孔管作為實驗管,采用了叉排的結(jié)構(gòu)布置,實驗結(jié)果得到管外沸騰的局部換熱系數(shù)以及LMTD對數(shù)平均換熱系數(shù),得到如下結(jié)論:在單管實驗中,通過觀察實驗現(xiàn)象,汽化核心最多的為HIGH-FLUX燒結(jié)管,其次為Turbo-EHP多孔管,之后為波紋管,最差的為光管。在波紋管實驗中,發(fā)現(xiàn)氣泡多數(shù)集中在波谷的前半部分,從側(cè)面論證了Turbo-EHP型多孔管的優(yōu)勢。從LHTC數(shù)值比較來看,四種管型的LHTC均呈現(xiàn)先增后減的趨勢與實驗現(xiàn)象保持一致。從AHTC數(shù)值比較來看,四種管型的AHTC多數(shù)呈現(xiàn)了先線性增大后緩慢減小的趨勢。特別地,多數(shù)R601a實驗的AHTC值大于R245fa實驗值。從對比光管的AHTC實驗數(shù)值來看,Turbo-EHP型管為其4.82~7.75倍,波紋管為其1.1~1.2倍。從壓降來看,所有實驗的壓降均隨著熱源溫度的增大而線性增大。四種管型的R245fa實驗的壓降均大于R601a實驗。其次對比四種管型可以發(fā)現(xiàn)ΔPTurbo-EHPΔP波紋管ΔP燒結(jié)管ΔP光管。通過單管實驗的實驗現(xiàn)象和換熱系數(shù),大致可以將換熱器內(nèi)部從下至上方向劃分為三個區(qū)域,即液相區(qū)、氣液區(qū)以及氣相區(qū),過冷液態(tài)工質(zhì)進入第一個區(qū)域,熱流密度較低,適宜采用HIGH-FLUX燒結(jié)管;其次飽和液進入氣液區(qū),此時熱流密度較高,適宜Turbo-EHP型管,加快核態(tài)沸騰;而在氣相區(qū),工質(zhì)多為氣態(tài),從強化換熱的角度來看,宜加大換熱面積,從而提高換熱效率,宜采用高翅片管增加換熱面積。管殼式換熱器選用Turbo-EHP管作為實驗用管,并采用R245fa作為實驗工質(zhì)。從上下管的LHTC來看,熱源溫度為50~60℃之間時,沿管長方向,LHTC先減后增的趨勢,上下兩管的換熱系數(shù)十分接近;在熱源溫度為60~100℃時,沿管長方向,LHTC值先增后減,由于熱源溫度的升高從整個實驗數(shù)據(jù)來看,局部換熱系數(shù)為3027.96~8936.80W/(m2·K),當(dāng)熱源溫度為100℃時,下管中0.2m處取得最大值。通過計算LMTD對數(shù)平均換熱系數(shù),LMTD對數(shù)平均換熱系數(shù)值為1529.76~2271.63W/(m2·K),給采用Turbo-EHP型多孔管的換熱器提供數(shù)值參考,具有一定的工程實際意義。
[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，

本文編號：1776144