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《工程热物理学报》2016,(4)
针对水连续油水分散流流速测量问题,提出了一种基于连续波超声多普勒的测量方法。测量传感器主要由一对中心频率为1 MHz的压电陶瓷超声换能器构成。发射探头向被测流体中发射连续的超声波,受到流体内运动的分散液滴散射后的声波被接收探头接收。根据多普勒效应,发射声波和接收声波的频率差与测量区域内散射体的运动速度成正比。由于分散相和连续相之间存在相对滑动,因此利用漂移模型对最终结果进行修正。对漂移模型中的参数进行基于油水两相流实际流动状态的理论分析,并通过实验数据计算漂移速度。实验结果表明,该测量模型对流型的依赖性很高,且漂移速度随着含水率的变化而改变,通过测量数据对该测量模型进行修正,最终结果的相对误差小于5%。 相似文献
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研究了电容耦合式非接触电导检测技术(C~4D)应用于气液两相流测量的可行性,建立了一套基于非接触电导的毫米级气液两相流参数检测系统。利用所建立的系统,在内径为5 mm,9 mm的水平管上进行了气液两相流实验,获得了不同流型下的电导测量信号,并对段塞流、波状流、泡状流和环状流四种典型流型下的电导信号进行了分析与比较。研究结果表明,所建立的基于非接触电导的气液两相流参数检测系统是有效的,C~4D技术应用于气液两相流参数测量是可行的。不同流型下所获的电导信号特征均表现出明显差异,有望用于流型辨识。 相似文献
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声波法是多相流测量的一种有效方法,可靠的声速模型是其中时差法等测量的理论基础。该文系统总结了国内外不同学者所建立的气固两相声速模型。为直观地呈现其差异、发展与局限,该文以颗粒相浓度的影响为例,采用模拟计算和实验测量相结合的方法对其中不同典型声速模型进行了定量分析与比较。结果表明,传统的拟均相介质模型声速随颗粒浓度变化,与在其基础上考虑声波特性的改进模型,以及分别基于相间耦合和颗粒散射的声速模型差异均较大,且显著偏离实验测量值。其主要源于传统的拟均相介质模型未考虑两相间相对运动的影响;而考虑相间相互作用的声速模型间虽有不同差异,但均与实验测量值较为接近,根据稀相区实验研究,所得声速值均较实验值偏小。 相似文献
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在气粒两相流动问题中,颗粒间以及气体与颗粒间的传热问题不可忽略.光滑离散颗粒流体动力学(SDPH)模型作为一种新的求解气粒两相流动问题的方法,已经成功应用于模拟风沙运动等问题.在此基础上,提出了SDPH方法的热传导模型,模拟了气粒两相流动问题中的热传导过程以及颗粒蒸发过程.首先引入各相的能量方程,利用有限差分与光滑粒子流体动力学一阶导数相结合的方法,处理各相内部热传导项中的二阶导数问题,基于气粒两相间温度差及对流换热系数计算颗粒与气体间的热传导量,推导得到了含热传导模型的气粒两相流SDPH计算方程组,模拟计算了圆盘形颗粒团算例及鼓泡流化床内部热传导算例,并与双流体模型计算结果进行对比,结果基本符合;其次利用离散液滴模型中的颗粒蒸发传质传热定律计算颗粒的蒸发过程,数值模拟了颗粒射流蒸发过程,并与离散颗粒模型结果进行对比,两者符合得较好,验证了该方法的准确性及实用性. 相似文献
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本文从描述多维湍流气固两相流的两流体模型出发,导出了计算湍流气固两相流中固体颗粒扩散速度的计算模型,进而基于在一维流场中颗粒的终端速度是重力加速度gi的函数,提出在多维流场中颗粒相处于一个修正的加速度场g'i的作用下,该修正的加速度g'i包含了包括重力在内的各种力的作用,这些力对颗粒的加速作用与重力对颗粒的加速作用没有区别。根据这种观点,提出了用于模拟多维湍流气固两相流的改进的扩散模型。本文使用改进的扩散模型对台阶后方的气固两相流进行了数值模拟,并将数值计算结果与实验结果进行了比较,结果表明,改进的扩散模型的预报结果与实验结果符合得相当好。 相似文献
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Convective heat transfer coefficients were measured experimentally for a tube immersed vertically in a circulating fluidized bed. Circulating fluidized beds operate in the dilute transport regime of two-phase (solid/gas) flow. The dominant mechanism for heat transfer to surfaces is particle-induced convection. In this study, experiments were carried out in a circulating fluidized bed of15 cm diameter and 11 m height. An instrumented tube of 9.5 mm diameter and 1.3 m length was placed vertically at the centeriine of the fluidized bed to measure convective heat transfer coefficients at several different elevations in the bed. Three types of particles, with mean diameters ranging from 68 to 2S1 urn, were used in the experiments at superficial gas velocities in the range of 1.3 to 8.2 m/s. Results showed that the convective heat transfer coefficients with solid/gas two-phase circulation were two to three times greater than those for single-phase gas convection at the same velocity. For a given gas velocity, the coefficients increased with increasing solid mass flux, but decreased with elevation. It was demonstrated that the heat transfer coefficients for the immersed tube and for the bed wall could be correlated with different functional dependence on the two-phase suspension density. 相似文献
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针对气固流化床中风帽故障影响流化质量问题,本文提出一种能够快速精确地检测出风帽故障位置和类型的声发射检测方法;声发射技术是一种实时、在线、非侵入流场的声波检测方法,利用均匀安装在流化床分布板下方的声发射传感器进行定位测量;采集气固流化床内颗粒撞击分布板产生的声信号,对该信号进行多尺度小波包分解,找出特征频段,由各个测点声发射信号总能量对比可以直观反应风帽故障存在位置,而各尺度能量分率的变化能进行故障类型判断;这种实时测量方法能更早,更精确的对风帽破损情况进行准确的判断。 相似文献
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A mathematical model is proposed to show the evolution of temperature, chemical composition and energy release or transfer in slugs, clouds and particulate phase, in a fluidized bed where there are slugs, of a mixture of air and propane, moving up through the particulate phase previously set in the state of incipient fluidization with air. The analysis begins as the slugs are formed at the orifices of the distributor, until they explode inside the bed or emerge at the free surface. The model also makes the analysis of what happens in the gaseous mixture that leaves the free surface of the fluidized bed until the propane is thoroughly burnt. It is essentially built upon a simple quasi-global mechanism for the combustion reaction and the mass and heat transfer equations from the two-phase model of fluidization. The aim was not to propose a new modelling approach, but to combine classical models, one concerning the reaction kinetics and the other the bed hydrodynamic aspects, to obtain a better insight on the events occurring inside a fluidized bed reactor, enhancing the understanding of this type of reactor. Experimental data to balance with the numerical model were obtained through tests on the combustion of commercial propane, in a laboratory scale fluidized bed, using four sand particle sizes: 400–500, 315–400, 250–315 and 200–250 μ m. The mole fractions of CO2, CO and O2 in the flue gases and the temperature of the fluidized bed were measured and compared with the numerical results. 相似文献
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A mathematical model and a numerical algorithm are proposed for investigation of aerodynamics in an apparatus with a circulating fluidized bed. The model is based on the basic assumptions of the theory of interacting interpenetrating continua and two-dimensional nonstationary Navier-Stokes equations. Calculations of the motion of a two-phase mixture in the laboratory apparatus were performed. The computational results are in good agreement with the experimental data.Scientific-Research Institute of Applied Mathematics and Mechanics at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 63–68, April, 1993. 相似文献