共查询到19条相似文献,搜索用时 250 毫秒
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为了探寻速度进口边界条件对边壁进风鼓泡流化床床内气泡行为的影响,根据欧拉-欧拉双流体模型,应用标准kε-方程模型处理气体湍流流动,分别采用均匀进风速度边界条件、脉动项按正态分布和脉动项按正弦分布的脉动进风速度边界条件,对鼓泡床内的气固两相流动过程进行了数值模拟.结果表明:采用脉动进风速度边界条件时,在非射流孔道处气体可形成气泡,气泡的上升速度比匀速进风时小;气体能够充分地与固体颗粒相互作用,床层中的空隙率主频较小;在设置边界条件时考虑脉动能够更合理地预测和分析床内气泡的尺寸、速度等特性. 相似文献
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笔者根据两相流化理论,提出了流化床膨胀度的计算公式,用来估算燃煤流化床的膨胀高度。由于直接测量气泡群的上升速度很困难,为此曾在沸腾床面积为0.33米~2的冷态试验台上,测取了流化床的膨胀度R、气体床截面平均流速W_f和床临界流化速度 相似文献
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实现流化床内气泡参数实时在线测量与表征,对深入了解流化床内气固流动特性以及反应过程调控具有重要意义。本文提出一种非接触静电传感阵列的气泡参数测量方法,通过静电传感器结合互相关法测量气泡上升速度,进一步利用气泡流经传感器的时间差,可获得气泡直径。开发了非接触式多路检测系统,并在二维流化床上开展了气泡特性实验研究。结果表明:静电传感器阵列结合互相关技术可实现在流化床内气泡上升速度、直径的同时测量;不同工况下,二维流化床中气泡的流动特性基本满足Davidson半经验公式,气泡的上升速度与流化风速及气泡直径的平方根成线性关系。非接触静电传感阵列对气泡流动不产生干扰,在表征流化床内部气泡流动特性具有重要的工程应用价值。 相似文献
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循环流化床锅炉流体动力学研究 总被引:1,自引:0,他引:1
在循环流化床锅炉炉膛内,分为湍流床和快床两个区域。本文论述了由鼓泡流化床与从气力输送状态向循环流化床转化过程中的流体动力学现象。研究了湍流床开始出现到完全转化为湍流床及快床时,炉内气体速度变化的规律和相应的计算公式。对转化过程中的主要影响因素,如床的当量直径,床温及固体颗粒供给速度等进行了深入试验研究,对循环流休床锅炉的设计和运行有一定的指导意义。 相似文献
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在循环流化床锅炉炉膛内,分为湍流床与快床两个区域。本文论述了由鼓泡流化床和从气力输送状态向循环流化床转化过程中的流体动力学现象。研究了湍流床开始出现到完全转化为湍流床及快床时,炉内气体迅速变化的规律和相应的计算公式。对转化过程中的主要影响因素,如床的当量直径、床的温度以及固体颗粒供给速度等进行了试验研究。 相似文献
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为了研究流化床锅炉低速床内水平埋管周围的两相运动规律,采用光偶测试元件和计算机数据采集系统,对流化床内的水平单管和顺排管速进行了测试,根据4种颗粒、3种管径以及不同水平和垂直管间距的不同组合的实验结果,得出了平均气泡附壁时间分率和平均乳化团贴壁时间的分区数据关联式,对它们的影响因素作了分析。 相似文献
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气泡和颗粒在流化床水平理管周围的运动行为与埋管传热和埋管磨损关系十分密切。采用光偶测试元件和计算机数据采集系统,对流化床内的水平埋管进行了测试,研究了不同粒径、不同角度、不同管径以及不同流速条件下气泡附壁时间分布规律。研究发现:气泡附壁时间服从指数分布,在所研究的诸条件中,粒径对分布函数形态的影响最为明显。 相似文献
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《International Journal of Heat and Mass Transfer》1987,30(6):1095-1101
Bubble properties in a three-dimensional, freely-bubbling, gas fluidized bed are reported in the presence and the absence of a horizontal tube-bundle. The tube-bundle is a staggered-array of tubes 1.9cm in diameter, with a pitch: diameter ratio of 3.5. Two different gas distributor plates, one made from sintered metal and one a simple perforated plate, were used and results compared under identical fluidizing conditions. Bubble rise velocities, bubble size and frequency distributions are measured and reported. Greater bubble rise velocities are recorded in a bed free of solid obstacles with both distributor plates. Bubble size distributions do not seem to be greatly affected by the presence of a horizontal tube-bank in the bed. 相似文献
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Shuji Furui Hisashi Umekawa Kouichi Hayashi Mamoru Ozawa Nobuyuki Takenaka 《亚洲传热研究》2003,32(8):727-739
Fluidized bed combustion is one of the advantageous technologies for coal and/or incineration firing especially with respect to the environmental protection of emissions, such as NOx/SOx. Bed material movement in such a fluidized bed has a prime importance in the heat transfer process. Thus, quantitative measurement of the bed material movement and the void fraction are indispensable for better understanding of the fluidized bed. In this investigation, neutron radiography is applied to visualize the bed material movement in a simulated fluidized bed heat exchanger installed with vertical tubes. Bubble behavior and void fraction profile are obtained by the image processing technique. Bubble movement is highly restrained by these vertical tubes, so that the bubbles rise up along the tube. The bubble diameter is well correlated by the modified Mori and Wen's correlation taking into account the pitch of the tube arrangement. The bubble rise velocity and void fraction are well correlated by applying the drift‐flux model. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(8): 727–739, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10127 相似文献
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基于小波变换的鼓泡流化床压力波动信号的分析 总被引:2,自引:0,他引:2
运用小波变换对鼓泡流化床内压力信号进行多尺度分解 ,并计算各尺度高频信号的功率谱积分 ,由此来对鼓泡床压力波动信号所含的丰富信息进行分析 ,这种分析方法充分体现了小波分析的优越性。通过对GeldartD类床料的实验、研究得出分解时选用的最佳小波基随流化速度变化的规律 ;尺度 6及尺度 5对应的高频信号分别可以表征气泡在床表面的破裂及在布风板附近的形成 ,尺度 4的高频信号是由气泡沿床层上升而引起的 ,这在以往使用傅立叶变换或只用功率谱分析是无法得出的。结果表明 ,小波变化结合功率谱分析是一种分析鼓泡流化床内压力脉动信号的有效方法 相似文献
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Combustion of isolated bubbles was investigated with a laboratory-scale fluidized-bed reactor. Two different combinations of oxygen and argon were employed as the fluidizing gas. Single bubbles of methane were injected into an incipiently fluidized bed maintained at elevated temperatures. Gas composition inside the bubbles was measured using a suction probe connected to an on-line mass spectrometer, and the temperature of the bubbles was monitored using a fast-response thermocouple. The effects of bed particle type, particle size, bubble size, bed temperature, and oxygen concentration in the emulsion phase were examined for bed temperatures between 923 and 1203 K. A theoretical model of homogeneous combustion within the bubble phase was developed for comparison to the experimental results. The model accounted for the heat and mass transfer between bubble and emulsion phases, but only considered combustion within the bubble. The results indicated that small bubble size and high oxygen concentrations in the emulsion phase enhanced bubble-phase combustion. The bed temperature also proved to be an important parameter, with higher temperatures promoting bubble combustion, but unlike some other investigations, no critical ignition temperatures were observed in either experiments or model results. The fluidized bed's particle size and particle composition influence the heat and mass-transfer coefficients, and therefore the bubble-phase combustion, but these have a smaller influence than bed temperature and bubble size. Model results for bubble-phase gas composition and temperature compared favorably with the experimental measurements. 相似文献
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In the present study, the CFD model is based on a two‐fluid model extended with the kinetic theory of granular flow. The simulation results of bubble diameter and bubble rise velocity are compared to the Darton equation and the Davidson model in a free bubbling fluidized bed. The predicted values are in reasonable agreement with the values from the Darton bubble size equation and the Davidson model for isolated bubbles. It is shown that the break‐up and direct wall interaction effects influence the dynamic bubble behavior in the free bubbling fluidized beds. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Akira Nishimura Seiichi Deguchi Hitoki Matsuda Masanobu Hasatani Arun S. Mujumdar 《亚洲传热研究》2002,31(4):307-319
A pulsating fluidized bed is operated with two sequential durations designated as an on‐period with injecting fluidization gas and an off‐period without it. The heat transfer coefficient between a vertically immersed heater and bed in a pulsating fluidized bed is measured under various pulse cycles and fluidized particles. The obtained results are compared with those in a normal fluidized bed with continuous fluidization air injection. The relationship between heat transfer coefficients and bubble characteristics, evaluated using a digital video camera, has also been investigated. For certain fluidized particles and operating pulse cycles, the fluidization of particles and the increment of heat transfer coefficients can be obtained under a mean air velocity based on a pulse cycle duration smaller than the minimum fluidization air velocity in a normal fluidized bed. Under the pulse cycles where a static bed through the whole bed is formed in the off‐period duration, the improved heat transfer rate over that in a normal fluidized bed can be measured. This may be attributed to large bubble formation. As heat transfer in the pulsating fluidized bed is obstructed with increasing time to keep a static bed due to the excessive off‐period duration, it is indicated that there is an optimum off‐period duration based on the heat transfer rate. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 307–319, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10038 相似文献
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J. Kubie 《International Journal of Heat and Mass Transfer》1976,19(12):1441-1453
The influence of gas bubbles on heat transfer in gas fluidized beds has been investigated. A platinum wire has been used as a heat-transfer probe and the aggregative gas fluidized bed has been simplified by generating a single continuous stream of gas bubbles into an incipiently fluidized bed. It has been found that in the case of aggregative gas fluidized beds of small particles operating below the radiative temperature level, transient conduction into the emulsion phase is responsible for at least 90% of heat transfer and that the remainder is contributed by the superimposed gas convection. A theoretical model of the bubble induced heat transfer has been developed. Finally, experimental justification for the concept of the property boundary layer introduced in [2] is presented. 相似文献