發(fā)布時間：2018-06-06 10:17

  本文選題：析晶污垢 + 換熱表面��； 參考：《華北電力大學》2015年博士論文

【摘要】：換熱設(shè)備污垢不僅影響了換熱器的換熱效率,還可能引發(fā)出很多技術(shù)和經(jīng)濟問題。當前業(yè)內(nèi)已將換熱表面污垢作為換熱器設(shè)計中的主要參考指標。本文采用數(shù)值模擬與實驗相結(jié)合的方法,系統(tǒng)分析換熱面上析晶污垢形成過程中的影響因素。根據(jù)先前污垢沉積機理研究的基礎(chǔ)上,結(jié)合連續(xù)性方程、動量方程、能量方程和傳質(zhì)方程,將污垢沉積過程以Fortran計算語言進行描述,編寫出污垢主要沉積量的計算程序,并于數(shù)值模擬軟件結(jié)合進行計算。為了使計算過程更加快捷和準確,分別將不同的離散格式和湍流模型應用于計算程序中,得出適用于計算的離散格式和湍流模型。通過分析表明,模擬數(shù)據(jù)和實驗數(shù)據(jù)吻合情況良好,且二階迎風格式模擬結(jié)果比一階迎風格式的結(jié)果更準確。RNG κ-ε模型比標準κ-ε 模型更接近于實際,計算的穩(wěn)定性和收斂性優(yōu)于標準κ-ε模型。針對所研究的換熱管以及換熱表面,分別在兩個實驗系統(tǒng)中進行實驗研究。將實驗結(jié)果與模擬結(jié)果進行對比。經(jīng)過對比可知,在忽略誘導期影響的情況下,模擬方法適用于文中研究的所有物理模型。將指定的工況分別經(jīng)過實際實驗和程序計算,將得出的結(jié)果—污垢熱阻進行對比,在忽略誘導期影響的情況下,模擬結(jié)果與實驗結(jié)果基本一致,可以說明該計算方式的可靠性。驗證過程除了在圓管中進行之外,還在矩形通道,以及部分含渦流發(fā)生器的換熱通道內(nèi)進行了驗證。將各流動工況分別在圓管和矩形通道內(nèi)進行計算,研究分析表明,光管內(nèi)析晶污垢的結(jié)垢情況和壁面溫度、溶質(zhì)濃度、流體溫度以及流體速度都有關(guān)系：隨著速度的增大,結(jié)垢量減少；隨著壁面溫度、入口溫度的升高,結(jié)垢量增多；隨著入口濃度的增大,結(jié)垢量增多。在縮放管和不連續(xù)雙斜向內(nèi)肋管中,其熱阻值小于圓管,入口速度和壁溫的變化趨勢與圓管一致,但是強化管的熱阻差值變化較圓管更加均勻。根據(jù)渦流發(fā)生器結(jié)構(gòu)的強化換熱理論,將其布置于換熱表面,研究其不同結(jié)構(gòu)對析晶污垢沉積的影響。為了能夠有效的評價渦流發(fā)生器對污垢沉積的影響,本文通過熱阻抑垢率來評價其抑垢的效果。經(jīng)研究在本文研究范圍內(nèi),三角翼型渦流發(fā)生器的抑垢效果最佳,而浮點型的渦流發(fā)生器的抑垢最差。最后通過實驗的方法,研究了氯離子和硝酸根離子種類及其濃度對析晶污垢沉積的影響。由于氯離子易吸附于硫酸鈣晶體表面,使得換熱表面污垢不易凝結(jié),導致含氯離子循環(huán)水的污垢熱阻小于含硝酸根離子的污垢熱阻。在兩種陰離子濃度變大情況下,污垢熱阻呈現(xiàn)變大的趨勢。通過實驗獲取的實際循環(huán)水中的水質(zhì)參數(shù)和污垢熱阻進行關(guān)聯(lián)分析得出,兩種強化換熱管的參數(shù)關(guān)聯(lián)順序相同,圓管與強化管的關(guān)聯(lián)順序不相同。強化換熱管結(jié)構(gòu)對水質(zhì)參數(shù)變化有影響,也會影響水質(zhì)參數(shù)與污垢熱阻的關(guān)聯(lián)。
[Abstract]:The fouling of the heat exchanger not only affects the heat exchange efficiency of the heat exchanger, but also may cause many technical and economic problems. At present, the fouling in the heat exchange surface has been used as the main reference index in the design of heat exchanger. The influence of the numerical simulation and experiment on the formation of crystallization fouling on the heat exchange surface is systematically analyzed in this paper. On the basis of the previous research on the mechanism of fouling deposition, combining the continuity equation, momentum equation, energy equation and mass transfer equation, the fouling deposition process is described in Fortran language, and the calculation program of the main deposition amount of fouling is written, and the numerical simulation soft parts are combined to make the calculation process more fast. Different discrete schemes and turbulence models are applied to the calculation program, and the discrete and turbulent models are obtained. The results show that the simulated data are in good agreement with the experimental data, and the two order upwind scheme is more accurate than the results of the first order upwind scheme. The.RNG kappa - epsilon model is more accurate than the standard kappa - epsilon model. The model is more close to the reality, the stability and convergence of the calculation are better than the standard kappa - epsilon model. For the heat transfer tube and the heat exchange surface, the experimental research is carried out in two experimental systems. The experimental results are compared with the simulation results. The comparison shows that the simulation method is suitable for Yu Wen in the case of neglecting the effect of the inducement period. All the physical models studied in the study. The results are compared with the results of the actual experiment and the program calculation. The results are basically consistent with the experimental results in the case of neglecting the effect of the induction period. It is verified in a rectangular channel and a heat transfer channel with some eddy current generator. The flow conditions are calculated in a circular tube and a rectangular channel respectively. The analysis shows that the scale of the fouling in the tube and the wall temperature, the concentration of the solute, the temperature of the fluid and the velocity of the fluid are all related to the velocity. With the increase of the inlet temperature, the scale of scale increases with the increase of the wall temperature and the inlet temperature. With the increase of the inlet concentration, the scale of scale increases. In the scaling tube and the discontinuous double inclined inner ribbed tube, the thermal resistance is less than the circular tube, the change trend of the inlet velocity and wall temperature is the same as that of the circular tube, but the change of the thermal resistance of the reinforced tube is more uniform than that of the circular tube. According to the theory of enhanced heat transfer of the structure of the eddy current generator, it is arranged on the heat exchange surface, and the influence of its different structures on the deposition of crystallization fouling is studied. In order to effectively evaluate the influence of the eddy current generator on the fouling deposition, this paper evaluates the effect of the scale inhibition by the rate of thermal resistance and inhibition. The inhibition effect of the eddy current generator is the best, while the floating point type vortex generator has the worst scale inhibition. Finally, the effect of the types and concentrations of chloride ions and nitrate ions on the deposition of crystallization fouling is studied. The fouling resistance of the subcycle water is less than that of the nitrate containing ion. In the case of two kinds of anion concentration, the fouling resistance tends to become larger. The correlation analysis of the water quality parameters and the fouling resistance of the actual circulating water obtained by the experiment shows that the correlation order of the parameters of the two kinds of enhanced heat transfer tubes is the same, the circular tube and the reinforcement are strengthened. The correlation order of pipes is different. Enhanced heat exchanger tube structure has an impact on the change of water quality parameters, and also affects the correlation between water quality parameters and fouling resistance.
【學位授予單位】：華北電力大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TK172

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本文編號：1986177