Particles flowing process across aligned tubes in a moving bed
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摘要: 工業中常用帶埋管的移動床來加熱或冷卻固體顆粒物料,其過程涉及顆粒流與管壁間的復雜傳熱,而顆粒繞流圓管的流動過程對其傳熱效果起著決定性作用.為簡化描述顆粒的流動過程,通過分析顆粒繞流圓管的特性,建立了擬漏斗流模型,并給出了模型所需顆粒繞流圓管描述參數的取值范圍,模型可用以求取顆粒繞流圓管的速度場和時長等參數.建立了埋管移動床實驗系統,考察了顆粒繞流順排管束的過程;同時利用離散單元法(DEM)對該過程進行數值模擬,獲得了顆粒繞流圓管的流動過程,并利用移動床實驗結果對比驗證了離散單元法數值模擬結果;最后,對比了基于擬漏斗流模型的計算結果和離散單元法數值模擬結果,并根據此結果對擬漏斗流模型的描述參數進行了確定.Abstract: Many solid particles in industrial processes require heating or cooling, such as calcinated petroleum coke, blast furnace slag, and steel slag. A moving bed with tubes is a viable design for facilitating such complex heat transfer processes. As particles are the primary heat carriers in this flow, the flow pattern of particles across the tubes in a moving bed is the main determinant of the heattransfer mechanism. The characteristics of particle flows across a tube structure are vastly different from those of a continuous-medium flow. Therefore, the flow pattern of particles moving across a bed of tubes must be studied prior to the heat-transfer mechanism. A simple pseudo-funnel flow model that can calculate parameters such as velocity field and residence time was established in this study for particle-flow modeling, and the range of parameters required to describe particles flowing across tubes was discussed. Using a movingbed test device made of transparent PMMA material, the flow of particles across aligned tubes banks was measured and a set of experimental results were obtained. Simultaneously, the discrete element method (DEM) was used for numerical simulations of the particleflow distribution in the system, and the obtained results were compared and verified by experimental results. Computational results from the quasi-funnel flow model were then compared with the DEM numerical simulation results to find the set of parameters required to describe particles flowing across aligned tube banks in the pseudo-funnel flow model. By setting appropriate values of the abovementioned parameters, the relative error between the two models could be reduced to 3%. This study provides a foundation for future studies on heat transfer processes in moving granular beds and the design and optimization of similar heat exchange devices.
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Key words:
- granular flow /
- flow characteristic /
- moving bed /
- discrete element method /
- residence time
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參考文獻
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