共查询到18条相似文献,搜索用时 125 毫秒
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引 言流动沸腾传热广泛存在于石油、化工、轻工、动力及能源等各个领域 ,但三相流动沸腾传热的研究极少 .李修伦等[1]在流动沸腾系统中加入惰性固体粒子 ,进行了汽 -液 -固三相流沸腾传热的初步研究 .李修伦、闻建平[2 ,3]进一步将三相流和沸腾换热相结合 ,较好地解决了沸腾传热强化和防垢、除垢问题 .李修伦、张利斌等[4 ]又采用循环流化床技术 ,结合粒子在沸腾系统中的强化特性 ,开发了汽 -液 -固三相循环流化床蒸发器 ,它具有良好的强化传热和防、除垢性能 .上述研究均属于单组分三相流动沸腾传热 ,而关于二元物系三相流动沸腾传热的研… 相似文献
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研究了汽液固循环流化床蒸发器的防垢与传热性能。实验表明,在防垢的同时,可有效地强化传热,提高蒸发能力,节约投资。 相似文献
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结合当前有关超声波强化传热及除垢防垢的研究形势,介绍了超声波强化传热及防垢除垢的技术研究成果,全面阐述了该技术在强化传热及防垢除垢方面的原理及进展,并就该技术的应用前景与研究方向进行了分析和展望。 相似文献
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引 言结垢是蒸发器加热壁面上经常遇到的问题 .垢层严重地降低了换热效率 ,使传热过程迅速恶化 ,蒸发器的防、除垢问题受到人们的普遍重视 .张利斌、李修伦等[1] 研究了汽液固三相循环流化床蒸发器沸腾传热和防、除垢性能 ,本文进一步考察该蒸发器的防、除垢机理 ,并对其进行了分析 .1 汽液固三相流剪应力“混相流”模型根据文献 [1],蒸发管内的汽液固三相流动呈现“混相流”的特性 ,因此为便于分析及突出问题的基本特征 ,假设 :(1)温度场引起的物性变化忽略不计 ;(2 )蒸发管内的汽液两相流动视为均相流动 ,蒸汽的惟一效果是改变了“流体… 相似文献
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汽液固三相循环流化床蒸发器已应用到盐化、烧碱、中药和造纸等工业中,表现出良好的防除垢性能。文中研究了这种新型流化床蒸发器的防、除垢机理。首先揭示出汽液固三相流剪应力对延长污垢的诱导期起主要作用,并对汽液固三相流剪应力和三相流剪应力增长率进行了定量计算,分析其影响因素。其次从污垢附着和剥蚀的角度,考察了固体颗粒的除垢作用。根据理论分析指出三相流剪应力对污垢附着需要的时间和污垢剥蚀比率的影响,从而计算了剥蚀比例和剥蚀速率及其影响因素。 相似文献
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对多相流化床换热器流固分布装置的发展情况进行了综合分析,为进一步优化流化床换热器流固分布装置,使流化床换热器更好地传热和防垢、除垢,提供了有益的参考。 相似文献
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In order to enhance heat transfer and solve the fouling problems in boiling processes, a boiling system was designed by adding solid particles to the boiling liquid. In this paper, both theoretical analyses and experimental studies on the flow boiling heat transfer in a vapor-liquid-solid three-phase circulating fluidized bed evaporator were carried out. Based on the analysis of the heat transfer characters of this three-phase flow boiling, a mathematical model for predicting the flow boiling heat transfer coefficients of the vapor-liquid-solid three-phase circulating fluidized bed evaporator was developed. The experiments show that, in the presence of solid particles the flow boiling heat transfer is enhanced and is about 2 times that of the vapor-liquid two-phase one. The predicted results of the flow boiling heat transfer coefficients agreed well with the experimental data. 相似文献
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P. Pronk C.A. Infante Ferreira G.J. Witkamp 《Chemical Engineering and Processing: Process Intensification》2008,47(12):2140-2149
Eutectic freeze crystallization is a promising separation technique to produce salt and ice crystals with very high purities and requires less energy than competitive evaporative crystallization techniques. A drawback of this technique is crystallization fouling, which seriously reduces heat transfer rates. Solid–liquid fluidized bed heat exchangers may be attractive crystallizers for this purpose, since they have demonstrated to prevent severe crystallization fouling, for example of ice crystals. This paper presents crystallization experiments with a single-tube fluidized bed heat exchanger. A first experimental series showed that fluidized beds are also able to prevent salt fouling during cooling crystallization from KNO3 or MgSO4 solutions. A second series revealed that fouling during eutectic freeze crystallization is more severe than during separate salt or ice crystallization and is therefore difficult to prevent by the fluidized bed. The explanation for this phenomenon is that the salt crystallization process strongly reduces the solute mass transfer limitation for ice crystals growing on the wall resulting in an increased growth rate and more severe crystallization fouling. The addition of a non-crystallizing component strongly reduces fouling and enables to perform eutectic freeze crystallization in fluidized bed heat exchangers for industrial applications. 相似文献
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A model is proposed to predict boiling heat transfer coefficient in a three-phase circulating fluidized bed (CFB), which is a new type of evaporation boiling means for enhancing heat transfer and preventing fouling. To verify the model, experiments are conducted in a stainless steel column with 39 mm ID and 2.0 m height, in which the heat transfer coefficient is measured for different superficial velocities, steam pressures, particle concentrations and materials of particle. As the steam pressure and particle concentrations increase, the heat transfer coefficient in the bed increases. The heat transfer coefficient increases with the liquid velocity but it exhibits a local minimum.The heat transfer coefficient is correlated with cluster renewed model and two-mechanism method. The prediction of the model is in good agreement with experimental data. 相似文献
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设计并构建了一套冷模液-固下行循环流化床蒸发器,考察了颗粒对壁面的碰撞行为随轴向位置和操作参数的变化规律,以便更好地揭示循环流化床强化传热和防、除垢的机理。实验中,选用水和不同粒径的聚甲醛颗粒和玻璃珠作为工质,对不同颗粒加入量(0~2.0%)和循环流量(2.15~5.16 m3·h-1)下的碰撞加速度信号进行了功率谱密度、峰度和标准偏差等频域和时域分析。研究结果表明:液相和固相碰撞加速度信号的频率范围分别为0~2 000 Hz和6 000~16 000 Hz。沿着下行床的轴向位置从上到下,颗粒对壁面碰撞加速度信号的标准偏差先减小,后增大;峰度增大。随着颗粒加入量和循环流量的增加,标准偏差增大,峰度减小。颗粒加入量较低时,标准偏差随着聚甲醛颗粒粒径的增加先减小、后增大;而峰度随着粒径的增加明显增大。颗粒加入量较高时,标准偏差和峰度随着粒径的增加而增大,但增大的幅度较小。玻璃珠的标准偏差较小,但峰度明显高于聚甲醛颗粒。构建了操作参数对颗粒碰撞行为影响的三维图。研究结果有助于促进流化床换热防垢节能技术的工业化应用。 相似文献
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The particle collision behavior and heat transfer performance are investigated to reveal the heat transfer enhancement and fouling prevention mechanism in a Na2SO4 circulating fluidized bed evaporator. The particle collision signals are analyzed with standard deviation by varying the amount of added particles ε (1%–3%), circulation flow velocity u (0.37–1.78 m·s-1), and heat flux q (7.29–12.14 kW·m-2). The results show that the enhancement factor reach up to 14.6% by adding polytetrafluoroethylene particles at ε = 3%, u = 1.78 m·s-1, and q = 7.29 kW·m-2. Both the standard deviation of the particle collision signal and enhancement factor increase with the increase in the amount of added particles. The standard deviation increases with the increase in circulation flow velocity; however, the enhancement factor initially decreases and then increases. The standard deviation slightly decreases with the increase in heat flux at low circulation flow velocity, but initially increases and then decreases at high circulation flow velocity. The enhancement factor decreases with the increase in heat flux. The enhancement factor in Na2SO4 solution is superior to that in water at high amount of added particles. The empirical correlation for heat transfer is established, and the model results agree well with the experimental data. 相似文献