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首页> 外文期刊>International Journal of Heat and Mass Transfer >Experimental evaluation of the convection heat transfer coefficient of large particles moving freely in a fluidized bed reactor
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Experimental evaluation of the convection heat transfer coefficient of large particles moving freely in a fluidized bed reactor

机译：在流化床反应器中自由移动的大颗粒对流传热系数的实验评价

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Heat transfer is a key aspect in the performance of fluidized bed reactors. In particular, the dense phase heat transfer coefficient, which determines the heat exchanged between the bed and fuel particles, is of special relevance. This work presents a study on the heat transfer that occur when introducing pel-letized particles of dry ice in a fluidized bed. The convection heat transfer coefficient is experimentally evaluated by means of the sublimation of dry ice particles using a novel methodology, which consists in a measurement system based on a macro-TGA fluidized bed and the corresponding evaluation of the acquired data. The system is capable of measuring the real time mass of the fluidized bed, which is a direct measure of the mass loss of the dry ice particles. The evaluation of such measurements allows to determine the convection heat transfer coefficient between the dry ice particles and the bed. Fixed and fluidized bed regimes, varying the excess gas velocity from -0.03 m/s up to 0.35 m/s, were tested for two different bed materials, namely Ballotini glass beads and alumina. The results of the sublimation and heat transfer coefficients are in good agreement with values reported in the literature, confirming the reliability of the experimental and postprocessing methodologies. In general, higher gas velocities enhance the dry ice particles mixing in the bed up to a limit in which the sublimation and convection heat transfer coefficients do not further increase. Additionally, the influence of the buoyancy behaviour of the dry ice particles in the bed on the convection heat transfer coefficient is discussed. The convection heat transfer coefficient decreases substantially if the dry ice particles present a flotsam behaviour and the gas velocity is not sufficiently high to ensure a proper circulation of the particles in the whole bed.
机译：传热是流化床反应器性能的关键方面。特别地，决定在床和燃料颗粒之间交换的热量的密集相传热系数具有特殊的相关性。这项工作提出了一种关于在流化床中引入干冰颗粒时发生的热传递的研究。通过使用新方法的干冰颗粒的升华试验对流传热系数通过新方法进行升华，该方法包括基于宏TGA流化床的测量系统和对所获取的数据的相应评估。该系统能够测量流化床的实时质量，这是干冰颗粒的质量损失的直接测量。对这种测量的评估允许确定干冰颗粒和床之间的对流传热系数。固定和流化床制度，对两种不同的床材料，即Ballotini玻璃珠和氧化铝测试了高达0.35m / s的过量气体速度。升华和传热系数的结果与文献中报道的值吻合良好，确认了实验和后处理方法的可靠性。通常，较高的气体速度增强干燥的冰颗粒在床中混合到升华和对流传热系数不会进一步增加的极限。另外，讨论了干冰颗粒在床上的浮力行为对对流传热系数的影响。如果干冰颗粒存在浮点行为，则对流传热系数基本上降低，并且气体速度不足以确保整体床中的颗粒的适当循环。

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