Abstract 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 pelletized 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.

中文翻译：

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大颗粒在流化床反应器中自由运动对流换热系数的实验评价

摘要 传热是流化床反应器性能的一个关键方面。特别是，决定床和燃料颗粒之间热交换的密相传热系数特别重要。这项工作对在流化床中引入干冰颗粒时发生的传热进行了研究。对流传热系数是通过使用一种新的方法通过干冰颗粒的升华进行实验评估的，该方法包括基于宏观 TGA 流化床的测量系统和对所获得数据的相应评估。该系统能够实时测量流化床的质量，这是对干冰颗粒质量损失的直接测量。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。对于两种不同的床材料，即 Ballotini 玻璃珠和氧化铝，测试了固定床和流化床制度，将过量气体速度从 -0.03 m/s 变化到 0.35 m/s。升华系数和传热系数的结果与文献中报道的值非常一致，证实了实验和后处理方法的可靠性。通常，较高的气体速度会增强床中干冰颗粒的混合，达到升华和对流传热系数不会进一步增加的极限。此外，讨论了床中干冰颗粒的浮力行为对对流传热系数的影响。如果干冰颗粒呈现漂浮物行为并且气体速度不足以确保颗粒在整个床中的适当循环，则对流传热系数显着降低。