迭代法ECT对循环流化床底部固体浓度的测量

在矩形循环流化床底部固体浓度的测量中首次采用了迭代电容层析成象方法,比通用的线性逆映射方法明显提高了成象质量。通过层析成象分析得到了床层中固体浓度分布、平均固体浓度随时间的变化和频谱特性。     

流化床颗粒制备过程层析成像测量和优化控制

本文基于电容层析成像方法对气固流化床干燥、混合过程进行测量分析,研究循环流化床干燥过程固体颗粒浓度分布、湿度等主要参数随时间的变化规律。其中电容传感器包括8电极圆形传感器,用于流化床颗粒包衣过程浓度分布测量,12-4组合电极用于环核区域颗粒浓度分布测量,基于电容层析测量手段,对制药行业与流化反应有关的过程进行了系统研究,对典型过程进行了优化分析和控制。     

应用电容层析成象和压差对比法对流化床内固体颗粒浓度分布的测量研究

本文报告了一种可以用于对流化床内固体浓度分布测量的电容层析成象技术。应用这一技术的测量结果,与目前常用的压差法测量结果进行了对比。对在鼓泡流化床的测量结果,二者吻合较好,偏差在８．５％以内;随着流化速度增加,二种测量结果的差距逐渐增加,偏差最大值产生在腾涌流化状态。本文分析了造成偏差的原因,并对二种测量方法的特性进行了讨论。     

循环流化床多分离器返料系统颗粒分布特性实验研究

多旋风分离器及返料系统是保证循环流化床锅炉高效燃烧的关键设备,是循环流化床大型化研究的关键部件之一。本文采用电容层析成像技术结合压力测量,对多旋风分离器返料系统内部气固两相流场进行实验研究。通过六旋风分离器冷态循环流化床电容层析成像浓度分布和压力测量,揭示循环流化床多分离返料系统颗粒流动分配特性,为循环流化床锅炉大型化,特别是超临界锅炉多旋风分离器的优化布置提供科学依据,基础实验数据库和技术手段,研究内容将电容层析成像技术的应用扩展到工程设计中,对实际工程起到理论指导的作用。     

粉粒体两相流的电容层析成象测量

粉粒体系统中的固相浓度分布的在线测量是十分困难的问题．电容层析成象技术是一种近年来发展起来的非侵入式快速浓度场测量技术．它不干扰流场，不受流动中颗粒浓度、加速度、不透明等因素的制约．本文讨论其测量原理、应用、近期进展、存在的主要问题及其解决的对策．     

循环流化床多旋风分离器入口电容层析成像测量

旋风分离器是循环流化床锅炉的关键部件之一,其分离性能将直接影响整个循环流化床锅炉的总体设计及锅炉的运行性能.大型循环流化床锅炉采用多个旋风分离器与炉膛出口并联布置实现气固分离.研究其分离系统的气固两相流动特性可进行旋风分离器的分离性能分析。本文针对600 MW超临界循环流化床锅炉的冷态模型,采用电容层析成像测量技术进行旋风分离器入口烟道内气田两相流固相颗粒浓度测量,在不同床料量和炉膛表观风速下,研究多个旋风分离器入口固体颗粒分布特性,得到不同分离器入口处固体颗粒浓度随流化风速、初始物料量的变化,分析了电容原始信号的波动特性,研究结果对流化床大型化多分离器优化布置提供了支持.     

循环流化床返料系统固体颗粒微波多普勒测量

本文基于微波多普勒速度测量和电容层析成像浓度测量技术,研究循环流化床多分离器系统固体颗粒流量分配特性。其中微波多普勒测量系统主要由微波信号发射和接受天线、微波信号采集系统和分析软件组成.电容层析成像系统由电容传感器和电容采集模块构成。通过微波测量得到颗粒的平均速度,电容层析成像得到颗粒平均浓度分布,将上述两个参数结合,得到固体颗粒的流量。实验结果证实了电容和微波相结合对颗粒返料流率测量的可行性.     

CFB顶部固体浓度的小波降噪ECT测量

应用电容层析成像(ECT)方法对循环流化床(CFB)顶部的固体浓度分布进行了测量;应用小波分析进行信号降噪和图像重建的改善.研究发现小波分析有双重作用:(1)降低ECT重建图像中的噪声;(2)对粗像素划分造成的图像粗燥边界产生平滑作用.数据显示了循环流化床顶部的固体浓度分布,尤其是角部和出口处的较高固体浓度.     

加压循环流化床CPFD数值模拟及电容层析成像测量

数值计算与实验测量相结合,对一套加压循环流化床返料系统内气固流场特性展开研究。基于CPFD方法,以Barracuda软件为计算平台,建立三维全循环数值模型,揭示系统内气固流场特性及颗粒循环流率相关信息。采用电容层析成像技术,对旋风分离器料腿内流场分布状况进行在线实时监测,通过双层电极同步测量结合相关性分析,得到颗粒流速与循环流率。研究表明:数值计算与实验测量所得不同操作压力下颗粒循环流率较为吻合,说明了CPFD三维全循环数值模型的可靠性,ECT结合相关性分析能够不破坏流场条件下实现加压循环流化床颗粒循环流率的测量。     

流化床干燥过程压力和电容层析成像测量分析

流化床干燥过程中床料物质属性和流动状态发生改变较大,单一的压力测量难以提供过程的全面信息。本研究将压力和电容层析成像(ECT)结合,用于干燥过程在线监测,探究不同工况下流化床的波动特性及不同参数对干燥过程的影响。结果表明,压差频谱分布可以反映颗粒密相和气泡相的波动特征;电容层析成像可以用于测量床料湿度和浓度分布。压差和电容层析成像的结合为流化床干燥过程关键参数提取、流动状态在线测量提供了一种新的方法。     

Three-phase flow pattern recognition in horizontal pipelines using electrical capacitance tomography

An experimental study was performed to evaluate the suitability of using an electrical capacitance tomography (ECT) system to visualise three component mixtures of crude oil, water and gas. The performance of the ECT system was examined over a range of three-phase flow conditions and regimes. The flow visualisations from the tomography system were compared with the images filmed using a CCD camera aligned with a Perspex pipe section. Results indicated that ECT was most successful in flow pattern identification for low water fraction flows. However, slug and stratified regimes could be identified for high water fraction flows. A critical factor in the quality and reliability of the generated image was the image reconstruction scheme used.     

一种基于电势分布的电容成像敏感分布计算方法

系统分析了电容成像（Electrical capacitance tomography，简称ECT）系统敏感分布和电势分布的关系，统一了计算公式，该方法简单且计算量小．仿真表明，采用该方法计算的ECT敏感分布，与采用定义计算的结果吻合。     

油气两相流空隙率测量系统

本文基于ECT技术和偏最小二乘回归方法建立了一套新型的两相流空隙率测量系统.该系统的数据采集单元以DSP处理器为核心,并采用USB2.0技术进行数据通讯,克服了目前ECT实时数据采集速度的瓶颈.同时,本文直接使用测量电容值并基于偏最小二乘回归方法建立了空隙率测量模型,克服了以往ECT空隙率测量时需要复杂费时的精确图像重建的缺点,提高了测量速度.实验研究表明,本文的系统是成功的,其测量精度和速度都满足实际应用的要求.     

Experimental investigation on the flame front resistance of gas channel growth with melt formation in iron ore sinter beds

The resistance of the flame front within the solid bed constitutes a fundamental and crucial area in porous bed combustion as the flame front propagation is highly related to the productivity and product quality. This paper focuses on the iron ore sintering, a thermal agglomeration process in steel mills. The results from a detailed experimental study of the pilot-scale pot tests under the conditions of a wide range of fuel rate are presented. The primary objective is to provide better understanding of the growth of gas channels relating to melt formation in the flame front and its resistance to flow. The sintering bed was divided into several zones based on the temperature profile and component distribution. Even though there is a continuous one-to-one replacement of humidified zone with porous sintered zone, a constant air flow rate during sintering could be obtained, indicating the ～100?mm high-temperature zone has a controlling effect on sintering bed permeability. The specific pressure drop value in high-temperature zone increases from ～3?kPa in upper bed to ～7?kPa in bottom bed, which varies with the bed temperature and structure properties. Both the green bed and sintered bed were scanned by X-ray computed tomography, the reconstruction and image analysis showed that the sintered bed has large gas channels and many more closed pores due to solid-melt-gas coalescence. More melt is generated when the heat is accumulated along the bed or input higher coke content, showing a propensity to suppress the gas channel growth and amplify the mismatch of gas transportation along the bed. Higher coke rate leads to a higher resistance in flame front, resulting in a slower flame front speed. These results are aimed to provide quantitative validation for improvements of a numerical sintering model in a future work.     

一种测量多相流流型的ECT图像重建算法

提出了一种新的电容层析成像图像重建算法-IMNSNOF算法.该算法在分析极小范数解的基础之上针对ECT逆问题的特点对其进行改进,并利用奇异值分解定理证明这种改进的数值稳定作用.在此基础上建立新的日标泛函,并在求解该泛函的过程中采用正则技巧对其进行改进确保数值解的稳定性.利用非闭合电极ECT传感器实测了多相流沿流向的流型...     

Potential measurement in ECT system

Potential measurement can be applied to electrical capacitance tomography (ECT) systems. However, the relationship between potential and the capacitance is not well understood. This paper reveals that a potential is dependent on the capacitance ratio for a given excitation voltage, independent of capacitance themselves. The conditions for using this method are discussed. Finally, image reconstruction based on the Generic Algorithm for Electrical Capacitance Tomography (GA-ECT) is implemented satisfactorily for square and circular sensors respectively.     

Analysis of the effect of stray capacitance on a charge/discharge-based electrical capacitance tomography system

The measurement circuit of electrical capacitance tomography (ECT) system mainly includes CMOS switches, C/V conversion circuit and Data processing circuit. In order to improve the image reconstruction quality, conversion circuit is very necessary to the small capacitance measurement circuit. A charge/discharge measurement circuit is one of the most suitable for the C/V conversion circuit in ECT. The stray capacitance between the measurement electrodes and earth can be large and have an effect on the capacitance measurement. This paper analyzes this effect, taking into account the ON-resistance of the COMS switch, the unit gain frequency of op-amp, and gain error in the measurement circuit. Finally, it is shown that if the range of stray capacitance is 150 ± 60 pF, overall error would be estimated. Comparing the effects of the circuit parameters, this charge/discharge-based capacitance is effectively stray-immune. It is a more efficient analysis to C/V circuit in ECT and offers a great benefit to information processing.     

Second law analysis of the flow of two immiscible micropolar fluids between two porous beds

This work investigates the effect of entropy generation rate within the flow of two immiscible micropolar fluids in a horizontal channel bounded by two porous beds at the bottom and top. The flow is considered in four zones. Zone IV contains the flow of viscous fluid in the large porous bed at the bottom, zone I and zone II contain the free flow of two immiscible micropolar fluids, and zone III contains the flow of viscous fluid in the thin porous bed at the top. The flow is assumed to be governed by Eringen’s micropolar fluid flow equations in the free channel. Darcy’s law and Brinkman’s model are used for flow in porous zones, namely, zone IV and zone III, respectively. The closed form expressions for entropy generation number and Bejan number are derived in dimensionless formby using the expressions of velocity, microrotation and temperature. The effect of physical parameters like a couple stress parameter and micropolarity parameter on velocity, microrotation, temperature, entropy generation number and Bejan number are investigated.     

倾斜上升管内气液两相弹状流壁面传质特性研究

采用VOF模型对倾角为45°、80°、85°三种情况下倾斜上升管内弹状流的壁面传质特性进行了研究.传质特性通过其与壁面切应力的类比关系来体现.数值模拟结果表明,低混合物流速时,上管壁面切应力在液膜区有明显波动,而下管壁面切应力分布则比较光滑.随着混合流速的增大,液膜区上下壁面切应力分布趋于一致.管子下壁面切应力平均值大于管子上壁面,在Taylor气泡运动速度较低时较为突出.随着Taylor气泡速度的增大,管子上下壁面的切应力平均值趋于相同.相同的混合流速下倾斜角度越大,上下管壁的切应力分布越趋于近似.下降液膜区的壁面切应力平均值大于Taylor气泡尾迹区域.根据Chilton-Colburn的类比关系,壁面切应力的规律完全适用于壁面传质系数.