激光干涉法在自然对流圆管测温和换热中的应用

发布时间：2018-05-26 16:25

  本文选题：水平圆管 + 自然对流　； 参考：《湖北工业大学》2015年硕士论文

【摘要】：自然对流圆管温度检测及换热分析对能源动力和生产安全具有重大的推动作用。激光干涉法将温度场激发的非均匀折射率编码于条纹的光强中,结合Gladstone-Dale关系式,实现从折射率到密度、浓度、温度等的无损全场检测。首先,对比各类干涉法的原理及应用,横向剪切类和全息类的竞争力较强。横向剪切类共光路的结构紧凑,抗振性优良,无需高精度的光学元件,条纹实时输出,条纹是剪切前后的两波面在重叠区的综合效果。大剪切量时则得到完全错开的两个类似于双曝光全息的简单条纹,无需要迭代还原。剪切干涉条纹易受光学像差的影响,出现背景条纹,条纹复杂度增加。双曝光全息干涉在同一全息干板上分别曝光畸变前后的波面,复位再现后易输出直观显示畸变波面信息的无限宽条纹。完全抵消了外界干扰产生的附加相位,只需一张干涉图就能重建畸变波面。综合考虑,本文拟以横向大剪切干涉和双曝光全息为实验手段,检测2种尺寸的自然对流水平圆管温度场。其次,模拟和细化横向大剪切(无待测圆管)纯背景干涉条纹。根据初级像差理论,利用MATLAB软件模拟光学像差和附加相位差对纯背景条纹的影响,验证了实际光学系统中存在的离焦和球差。以入射——出射偏转角为切入点,探讨剪切量对成像复杂度的影响,得出最佳常规偏转角60°。根据图像形态学理论,利用MATLAB软件细化暗条纹,实现条纹中心提取的多样性。然后,利用横向大剪切干涉仪纪录1号水平圆管(长度直径之比8.4)从高壁温425℃自然降至室温15.88℃的420幅干涉图系列。利用MATLAB自编编程快速提取干涉图的Red分量,通过峰谷点辅助确定条纹中心。采用有无圆管的两张干涉图法获得畸变波面相位,完全抵消了光学系统误差。反演圆管周围的二维温度场,与热电偶测量误差在0.19%以内。采用多项式和指数函数拟合温度场,50℃低温稳态拟合时两者结果均较好,400℃高温拟合时多项式优于指数。最后,利用双曝光全息术探索2号水平圆管(长度直径之比14.0)从壁温82℃降至室温22.1℃的换热规律。利用MATLAB程序快速辅助确定条纹中心,直接从一张干涉图中提取相位分布,重建二维温度场。提取壁面的温度梯度,计算表征换热强度的局部和平均Nu,拟合出的Nu经验公式与已有结果基本一致。
[Abstract]:The measurement of natural convection tube temperature and heat transfer analysis play an important role in promoting energy power and production safety. The nonuniform refractive index excited by the temperature field is encoded into the intensity of the fringe by laser interferometry, and the nondestructive full-field detection from refractive index to density, concentration and temperature is realized by combining the Gladstone-Dale relation. Firstly, compared with the principle and application of various kinds of interferometry, transverse shearing and holography are more competitive. The transverse shearing common optical path is compact in structure, excellent in vibration resistance, and no high precision optical element is needed. The fringe is the real time output of the stripe, and the fringe is the comprehensive effect of the two wavefront before and after shear in the overlapping region. Two simple fringes like double exposure holography are obtained with large shearing, and there is no need for iterative reduction. The shearing interference fringes are easily affected by optical aberration, and the background fringes appear and the fringes complexity increases. Double exposure holographic interference on the same holographic dry plate before and after exposure distortion of the wavefront, after reset and reproduction easy to output visual display distortion wave surface information infinite wide fringe. It completely cancels the additional phase generated by external interference and can reconstruct the distorted wave surface with only one interferogram. In this paper, the temperature field of two kinds of natural convection horizontal tube is measured by means of transverse large shear interference and double exposure holography. Secondly, the pure background interference fringes are simulated and refined. Based on the primary aberration theory, the effects of optical aberration and additional phase aberration on pure background fringes are simulated by using MATLAB software, and the defocus and spherical aberrations in practical optical systems are verified. The influence of shearing on the imaging complexity is discussed by using the incident-exit deflection angle as the starting point, and the optimal conventional deflection angle of 60 掳is obtained. According to the theory of image morphology, MATLAB software is used to refine dark fringes to realize the diversity of fringes center extraction. Then, a series of 420 interferograms of horizontal tube No. 1 (ratio of length and diameter, 8.4) from high wall temperature 425 鈩，

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