影响换热表面析晶污垢形成因素研究

发布时间：2018-06-06 10:17

本文选题：析晶污垢 + 换热表面　；参考：《华北电力大学》2015年博士论文

【摘要】：换热设备污垢不仅影响了换热器的换热效率,还可能引发出很多技术和经济问题。当前业内已将换热表面污垢作为换热器设计中的主要参考指标。本文采用数值模拟与实验相结合的方法,系统分析换热面上析晶污垢形成过程中的影响因素。根据先前污垢沉积机理研究的基础上,结合连续性方程、动量方程、能量方程和传质方程,将污垢沉积过程以Fortran计算语言进行描述,编写出污垢主要沉积量的计算程序,并于数值模拟软件结合进行计算。为了使计算过程更加快捷和准确,分别将不同的离散格式和湍流模型应用于计算程序中,得出适用于计算的离散格式和湍流模型。通过分析表明,模拟数据和实验数据吻合情况良好,且二阶迎风格式模拟结果比一阶迎风格式的结果更准确。RNG κ-ε模型比标准κ-ε 模型更接近于实际,计算的稳定性和收敛性优于标准κ-ε模型。针对所研究的换热管以及换热表面,分别在两个实验系统中进行实验研究。将实验结果与模拟结果进行对比。经过对比可知,在忽略诱导期影响的情况下,模拟方法适用于文中研究的所有物理模型。将指定的工况分别经过实际实验和程序计算,将得出的结果—污垢热阻进行对比,在忽略诱导期影响的情况下,模拟结果与实验结果基本一致,可以说明该计算方式的可靠性。验证过程除了在圆管中进行之外,还在矩形通道,以及部分含涡流发生器的换热通道内进行了验证。将各流动工况分别在圆管和矩形通道内进行计算,研究分析表明,光管内析晶污垢的结垢情况和壁面温度、溶质浓度、流体温度以及流体速度都有关系：随着速度的增大,结垢量减少；随着壁面温度、入口温度的升高,结垢量增多；随着入口浓度的增大,结垢量增多。在缩放管和不连续双斜向内肋管中,其热阻值小于圆管,入口速度和壁温的变化趋势与圆管一致,但是强化管的热阻差值变化较圆管更加均匀。根据涡流发生器结构的强化换热理论,将其布置于换热表面,研究其不同结构对析晶污垢沉积的影响。为了能够有效的评价涡流发生器对污垢沉积的影响,本文通过热阻抑垢率来评价其抑垢的效果。经研究在本文研究范围内,三角翼型涡流发生器的抑垢效果最佳,而浮点型的涡流发生器的抑垢最差。最后通过实验的方法,研究了氯离子和硝酸根离子种类及其浓度对析晶污垢沉积的影响。由于氯离子易吸附于硫酸钙晶体表面,使得换热表面污垢不易凝结,导致含氯离子循环水的污垢热阻小于含硝酸根离子的污垢热阻。在两种阴离子浓度变大情况下,污垢热阻呈现变大的趋势。通过实验获取的实际循环水中的水质参数和污垢热阻进行关联分析得出,两种强化换热管的参数关联顺序相同,圆管与强化管的关联顺序不相同。强化换热管结构对水质参数变化有影响,也会影响水质参数与污垢热阻的关联。
[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.
【学位授予单位】：华北电力大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TK172

【参考文献】