超声波热量表非定常数值模拟及性能研究

发布时间：2018-03-07 10:04

本文选题：U型超声波热量表　切入点：k系数　出处：《山东大学》2014年硕士论文　论文类型：学位论文

【摘要】：为应对能源短缺和环境污染问题,除了开发新能源外还有一项有力措施就是节能减排,供暖作为耗能和环境污染的大户,实行供热分户计量可以有效的改善现有按平方收费的弊端。推行供暖分户计量首先要有性能优良的热量表,本文针对影响超声波热量表测量精度的几个问题进行了研究,并提出相应的优化意见。现在超声波热量表流量部分的测量精度是热量表研制的关键点也是难点,影响热量表流量部分测量精度原因有三个方面：一是热量表电路对流量测量信号的采集；二是热量表基表内水流分布；三是超声波热量表检测装置的可靠性。本文采用理论分析和数值模拟相结合的方法从这三个方面对U型超声波热量表基表进行了非定常数值模拟并对影响其测量精度的几个问题进行分析,并用实验验证了所选的数值模拟方法的正确性。在测量原理方面,考虑到热量表工作环境温度变化范围较大,通过引进相关修正公式,减小了温度对流体粘度和超声波在流体中传播速度的影响,从而提高信号采集的准确度和流量修正系数选择的合理性。基表结构方面,利用软件FLUENT对户用DN25型超声波热量表基表采用RNGk-ε模型进行数值模拟计算,根据模拟计算结果分析超声波热量表基表内线面速度关系及流场状况。为减小反射装置对基表内流场的扰动,针对流场质量差、压损偏大的基表,可以通过加装整流片进行优化,加装整流片后反射装置中心面上的漩涡减小,基表内流场变得均匀,不同流量点下的压损均有减小。检测装置方面,为提高热量表的检测生产效率,以实验测量误差和k系数为评价依据,发现超声波热量表检测装置试验段的弯管及变截面管段对测试管段表位一的热量表测量精度影响很大,在弯管处加装导流片后可以明显消除弯管二次流,提高测量精度。在热量表入口安装过滤网,可以减小变截面管道对表位一热量表测量误差的影响。另外,本文通过非定常数值模拟方法,研究了超声波热量表管道阀门开启后流量增大过程中热量表基表内水流状态,并与稳定流量下的热量表进行对比,分析了阀门开启过程中水流状态的变化对k系数和基表内部流场的影响,对提高不同工作状态下超声波热量表的测量精度提供了理论依据。本文研究方法正确,并配有大量的实验及模拟数据和分析图表,结果分析清晰正确,对研究超声波热量表流量部分测量精度和提高热量表检测装置的可靠性及检测效率,具有一定的指导意义和理论价值。
[Abstract]:In order to deal with the problems of energy shortage and environmental pollution, in addition to the development of new energy sources, there is also a powerful measure to save energy and reduce emissions. Heating, as a major user of energy consumption and environmental pollution, Household heating metering can effectively improve the existing shortcomings of square charge. In order to carry out household heating metering, it is necessary to have a heat meter with good performance. In this paper, several problems affecting the measurement accuracy of ultrasonic heat meter are studied. And put forward the corresponding optimization advice. At present, the measurement accuracy of the flow part of the ultrasonic heat meter is the key point and the difficulty in the development of the heat meter. There are three reasons that affect the measurement accuracy of the heat meter flow part: the first is the acquisition of the flow measurement signal by the heat meter circuit; Second, the distribution of water flow in the heat meter; The third is the reliability of ultrasonic calorimeter. The unsteady numerical simulation of U-type ultrasonic calorimeter is carried out from these three aspects by the combination of theoretical analysis and numerical simulation. Several problems of accuracy are analyzed. The correctness of the numerical simulation method is verified by experiments. In terms of measurement principle, considering the large range of temperature variation in the working environment of the heat meter, the influence of temperature on the viscosity of the fluid and the velocity of ultrasonic wave propagation in the fluid is reduced by introducing the relevant correction formula. In order to improve the accuracy of signal acquisition and the reasonableness of the choice of flow correction coefficient, the software FLUENT is used to simulate and calculate the DN25 type ultrasonic calorimeter with RNGk- 蔚 model. Based on the results of simulation, the velocity relationship and flow field status of ultrasonic heat meter are analyzed. In order to reduce the disturbance of flow field in the base table by the reflector, the base table with poor flow field mass and large pressure loss is used to reduce the disturbance of the flow field in the base table. It can be optimized by adding rectifier. After the rectifier is installed, the vortex on the center surface of the reflector is reduced, the flow field in the base table becomes uniform, and the pressure loss at different flow points is reduced. In order to improve the efficiency of measuring heat meter, based on the error and k coefficient of experimental measurement, it is found that the bend pipe and variable section pipe section of the test section of ultrasonic heat meter test device have great influence on the measuring accuracy of the heat meter. The secondary flow can be eliminated obviously and the measurement accuracy can be improved by installing the guide plate at the bend. The influence of the variable section pipeline on the measurement error of the surface-heat meter can be reduced by installing a filter net at the entrance of the heat meter. In addition, by using unsteady numerical simulation method, the flow state in the heat meter is studied in the process of increasing the flow rate after the valve of the ultrasonic heat meter is opened, and compared with the heat meter under the steady flow rate. The influence of the change of the flow state on the k coefficient and the internal flow field of the base meter during the valve opening is analyzed, which provides a theoretical basis for improving the measuring accuracy of the ultrasonic heat meter under different working conditions. The research method of this paper is correct, with a large number of experimental and simulation data and analysis charts, the results are clear and correct. It can improve the reliability and efficiency of the measuring device for the ultrasonic heat meter. It has certain guiding significance and theoretical value.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TK31;TB559

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