Pathway-dependent heat transfer in a fluidized bed reactor revealed by spatial and temporal measurements

Abstract

Efficient heat remove and uniform temperature distribution are critical for designing chemical reactors involving strongly exothermic gas-solid reactions, such as the various conversion of coal-based syngas to aromatics. Classical Fourier heat conduction theory implies that the effective heat transfer capability from spatial temperature gradients should be consistent with temporal temperature responses. However, whether this assumption remains in a gas-solid fluidized bed, as a typical heterogeneous multiphase system with complex dynamic structures remains unclear. In this study, the heat transfer behavior of fluidization was investigated spatially and temporally via steady-state temperature gradients and transient pulse method, respectively. Significant different equivalent heat transfer coefficients indicate an apparent spatiotemporal inconsistency in the effective heat transport of fluidization. Mechanistic analysis reveals that the spatial steady-state heat transfer process is mainly governed by the near-wall effective thermal-resistance region, whereas the temporal transient heat diffusion process is primarily affected by dynamic alternation between dilute and dense phases. Increasing the superficial gas velocity enhances both heat transfer processes, but the underlying enhancement mechanisms are fundamentally different. The former is mainly attributed to the weakening of the near-wall effective thermal-resistance region, while the latter is primarily caused by bubble-driven mixing enhancement. Further results demonstrate that modifying the heated-wall interfacial condition with thermally conductive grease markedly changes the spatial-domain heat-transfer response, highlighting the sensitivity of wall-dominated heat transfer to the near-wall interfacial state. These findings indicate that the effective heat transport capability in complex heterogeneous multiphase systems exhibits pronounced path dependence. This study provides a new theoretical basis for heat transfer pathways, thermal management optimization, and reactor design in strongly exothermic gas-solid reactors.

Graphical abstract

Keywords

gas-solid fluidized beds / heat transfer / syngas to aromatics / Fourier’s law of heat conduction

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