Decoupling fluidization‐induced structural resistance and shear‐induced relaxation in gas–solid fluidized beds

Conventional measurement methods of apparent viscosity of fluidized gas–solid systems conflate the resistance associated with the fluidization state and the additional resistance variation induced by measurement‐imposed shear. Here, we characterize the coupled viscosity response to separately prescribed gas velocity and spindle rotation using in situ rotational rheology, pressure‐fluctuation analysis, particle image velocimetry, and fiber‐optic measurements. The low‐shear boundary viscosity decreased markedly with increasing gas velocity, whereas the terminal viscosity remained within 0.19–0.26 Pa·s, demonstrating distinct fluidization‐ and shear‐dependent resistance contributions. A structural relaxation index quantified their relative contrast. After finite‐range normalization, the Geldart B data collapsed onto a common Cross‐type curve with K = 24.91 s (characteristic time parameter) and m = 1.4 (dimensionless shear‐thinning index), yielding R 2 = 0.9992. This decoupling framework provides a quantitative basis for interpreting startup resistance, operating torque, and power demand in mechanically agitated or internally equipped fluidized beds.