【作者】 李言钦；

【导师】 周怀春；

【作者基本信息】 华中科技大学 ， 热能工程， 2006， 博士

【摘要】 炉内空气动力场是决定锅炉安全、经济运行的重要因素,但一直以来,大型锅炉炉膛空气动力场的测量尚没有一种非接触式的实时、在线检测技术。目前电厂及工业锅炉中一般采用飘带法结合风速表或热线风速仪等对锅炉进行冷态条件下的空气动力场测量。传统的测量方法是接触式、逐点测量,显然在人、财、物方面需要较大投入,而且时间长,准确度低。声波法测量炉内空气动力场是一种非接触式、全场测量的方法,本文在前人研究的基础上丰富和发展了声波法检测炉内气体速度场的方法与理论,并自主开发了较为初步的声波法测量系统。最后进行了炉内空气速度场测量的实验研究,国际上尚没有类似的报道。在展开声波法检测炉内气体速度场的讨论前,文中先给出了传统方法测量一次风管射流流场的实验。通过五孔探针法、PIV法测量及CFD模拟,在一定程度上验证了传统方法的优势与不足。五孔探针法的优点是直接,在速度值不太小时测量可靠,是常用的流场测量方法,其缺点是灵敏度不高,不易测出较弱流场区域的速度值;PIV法准确性好、灵敏度高,但工作量大,测量条件苛刻;CFD模拟对于给定条件的流场,可以详细地模拟出其速度分布,但计算时间长,且不能反映流场的实时变化。因此,对于实际的炉内测量,传统的流场测量方法很难满足要求,找到一种新的、更为适合和优越的炉内速度场检测方法是必要和迫切的。声波是一种机械波,在气体介质中传播将受所在介质物性及运动的影响,这是声波法测量炉内空气动力场的物理学基础。为验证声波法测量气体流速的基本可行性,首先进行了声波法测量单路径空气速度场的实验。实验设计为:根据传感器布置合理性,在一开放的圆管空气水平射流场中选取一与射流轴线成一定夹角的直线区间,进行声波法单路径测量。实验中分别用声波法和五孔探针法测量了该区间内的空气流速,通过对比分析,验证了声波法用于测量气体流速的可行性与可靠性。声波法检测炉内二维气体动力场,是在所测场四周边界布置适当数量的声传感器,形成网状交叉的声传播路径,测出各条路径上相反两方向的声信号传播时间,即可由矢量层析算法重建出所测场内连续的气体速度分布。模拟研究中,首先建立了由6个参数确定的简化四角切圆速度场模型,通过正问题和逆问题的研究,并进行相应的误差分析,验证了声波法测量二维速度场的实现性和可用性。对于实际的四角切圆速度场,本文开发了基于矢量层析算法的一般二维速度场重建程序。该程序在前述简化四角切圆模型的基础上进行了不同复杂程度的仿真实验,结果表明程序在一定程度上是准确和可靠的。本文最后给出了声波法测量炉内二维速度场的冷模实验研究。该实验是在一座自行设计搭建的炉膛模型台架上进行的,其尺寸为1.0m×1.0m×2.45m。实验研究了对称供风和非对称供风条件下切圆流场的声波法测量情况,分别得出了比较满意的重建结果,其计算程序即为前述一般二维速度场重建程序。完成一次声波法测量需要约5秒钟时间。作为对比,对称条件速度场分别用热线风速计和CFD软件进行了测量及模拟;非对称条件下的速度场用CFD进行了模拟。对上述结果分别作了相应的定性和定量分析。结果表明,声波法测量结果与两种传统方法得到的结果能够较好地相符。不过,因为没有足够可靠并适于实验条件的测量方法,声波法测量的可靠度并没有得到充分证明,这需要进一步的工作来完成。而当前的实验结果仍然在一定程度上说明了声波法测量炉内速度场的可行性并体现了明显的先进性。声波法作为一种有前景的炉内动力场检测技术,其最终目标是很好地应用于工程实践,本文在冷模实验研究的基础上还讨论了其用于热态炉内测量时的影响因素与改进设想;另外也提到了其用于测量锅炉水平烟道内烟气流速及温度沿横截面分布的可能性。更多还原

【Abstract】 The aerodynamic field in furnaces is an important factor determining the safe and economical operation. But all along, there’s no a nonintrusive, real-time and online technique on measurement of the aerodynamic field in large-scale furnaces. For the present, generally the cold aerodynamic fields are measured in power or industrial boilers. In the measurements, the ribbons are mainly adopted together with the anemometer or hot-line anemometer. Since the traditional methods are intrusive and pointwise, there needs quite much expense, nevertheless with long time and low accuracy. However, the acoustic method is nonintrusive and full-field to measure the aerodynamic field in furnaces. Based on the reseach of the predecessors, the paper amplified and developed the theory on acoustic velocity field measurement. The primitive acoustic measurement system and method have been developed creatively for cold measurement. And with the system, the velocity field measurements are performed. The related reports haven’t been found in the world, with only relavant theoretic research.Before the discussion on acoustic measuring the aerodynamic field in furnaces, an experiment on the traditional methods testing is carried out. The measured objection is a horizontal jet flow field of a newtype burner. By the practice of five-hole probe, PIV and simulation with CFD software, the faults of trandional techniques as well as the advantages are acquainted. Among the preceding methods, five-hole probe approach is immediate and relatively easy. But because of insufficient sensitivity, it can hardly measure the weak flow area. PIV method has perfect accuracy and sensitivity, however, it needs a great deal of work, and is particular at the measuring conditions. And for flow fields with difined conditions, CFD simulation can give detaild description. But it’s hard to trace the real-time variation of flow fields for CFD. So, for the aerodynamic field measurement in real furnaces, it’s requisite to find a new monitoring method that is more fit and advantageous.Sound wave is a kind of mechanical wave. Its propagation is effected by the attributes of the medium and the movement as well. This is the physical base of the acoustic measuring the aerodynamic fields in furnaces. Firstly, the measurement of a singular path in an air flow field by acoustic method is performed. This experiment can give an essential and direct argument of acoustic method used for measuring the air velocity field. By the practical situation, a relatively reasonable air flow field is designed. It is a proper linear interval taken in an open air jet flow from a horizontal circular tube. Acoustic and five-hole probe methods are used respectively to measure the flow field. The comparison between the results proved the feasibility of acoustic method for the measurement of the gas flow field.For the acoustic measurement of 2-D aerodynamic field in furnace, a right number of sound sensors are configured on the boundary of the measured field, and reticular sound projections are formed. By measuring the transit times of the sound waves in the reciprocal directions on the paths, the continuous velocity distribution can be reconstructed with a vector tomography algorithm. Regarding the simulation research, we firstly build up a simplified tangential flow field model. By calculation of the direct problem and reconstruction of the inverse problem, and also error analysis of different levels with the results, the performance and availability of the acoustic method in measuring the 2-D velocity fields is validated. Concerning the real tangential flow field, a reconstruction program of 2-D velocity field is developed. The program is examined with different degrees of phantom based on the preceding simplified tangential model. The result showed that the program is accurate and reliable to some extent, so it’s promising to be used to reconstruct the real tangential aerodynamic field in furnace.Based on the simulating study, the cold model experiment is performed on the 2-D flow field measurement with acoustic method. For that, a bench-scale furnace model of 1.0m×1.0m×2.45m is designed and built. In the experiment, the flow fields under the symmetrical and unsymmetrical air-supply conditions are measured respectively by acoustic method. Both have relatively satisfactory results. As comparison, the first case is also measued with a hot-wire anemometer, and simulated by CFD as well. For the second case, only the CFD simulation is used. With the measurement simulation results, qulitive and quantitative analyses are given. It is proved that, under relatively stable air conditions, the acoustic measuring results accord well with those by the other two methods. The experiment shows the feasibility of acoustic measuring flow fields in furnace, and also the obvious superiority. It’s prosperous to become an advanced and effective technique of aerodynamic field measurement, which is online and realtime. For the present, the measuring scheme of the acoustic system is each transducer emitting sound wave by turns, with about 5s for an integral measurement.As a prosperous monitoring technique of furnace aerodynamic field, the paper also discusses the impact factors and corresponding reforms with it for the measurement in hot furnace. What’s more, due to its great characteristics, its use on the gas speed and the temperature distributions in the horizontal flue is also mentioned.更多还原