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The different carbon nanotube (CNT) particles (@A and @V) were bed materials in the pseudo-2D tapered fluidized bed (TFB) with/without a distributor. A detailed investigation of the motion mechanism of bubbles was carried out. The high-speed photography and image analysis techniques were used to study bubble characteristic and mixing behavior in the tapered angle of TFB without a distributor. The fractal analysis method was used to analyze the degree of particles movement. Results showed that an S-shaped motion trajectory of bubbles was captured in the bed of @V particles. The population of observational bubbles in the bed of @V particles was more than that of @A particles, and the bubble size was smaller in the bed of @V particles than that of @A particles. The motion mechanism of bubbles had been shown to be related to bed materials and initial bed height in terms of analysis and comparison of bubble diameter, bubble aspect ratio and bubble shape factor. Importantly, compared to the TFB with a distributor, the TFB without a distributor had been proved to be beneficial to the CNT fluidization according to the study of bubble characteristic and the degree of the particle movement. Additionally, it was found that the mixing behavior of @V particles was better than @A particles in the tapered angle of TFB without a distributor.

In this work, a tapered fluidized bed (TFB) without a distributor for fluidizing carbon nanotube (CNT) was applied for improving the dead zone, blockage, and fracture of distributor, which occurred in actual production. Experiments were performed under different superficial gas velocities, static bed heights, CNT agglomerate size, and positions of pressure probe. To obtain multi-perspective and multi-scale understanding of fluidization dynamics of gas–CNT flow in the TFB without a distributor, the standard deviation, skewness, kurtosis, wavelet decompositions and homogeneous index analysis methods were adopted. Some noticeable phenomena were observed. Particle movements including inter-particle, gas–particle and particle–wall dominate dynamic characteristics. The amplitudes of pressure fluctuations of coarse agglomerated multi-walled CNT were more sensitive to the gas velocity than that of fine agglomerated multi-walled CNT. The sensitively of energy contribution of the meso- and macro-structures was that the sensitivity of the measured position was less than the sensitivity of the energy contribution by the changes of particle size, and the sensitivity of the energy contribution by the changes of particle size was less than the energy contribution by the changes of gas velocity. The fluidization quality of coarse agglomerated multi-walled CNT was better than that of fine agglomerated multi-walled CNT, which was verified by the skewness and wavelet analysis.

In this work, the fluidization characteristics of gas–agglomerated carbon nanotube (CNT) particles flow in a tapered fluidized bed (TFB) without a distributor were investigated between 180 and 680 °C for the first time. The objective of this work was to investigate the effect of temperature on minimum fluidization velocity (Umf) and dynamic characteristics of gas–agglomerated CNT particles flow at elevated temperature. To this end, the experimental work was divided into two phases. In the first phase, the influence of temperature on the Umf and the correlations of Umf for agglomerated CNT particles at different bed temperatures were investigated and obtained. In the second phase, the dynamic characteristics of gas-agglomerated CNT particles flow in the TFB without a distributor at elevated temperature were studied in detail via time-series analysis methods. Experimental results revealed that the Umf decreased for agglomerated CNT particles with the increase of temperature, and the correlations could be reasonable predicted the Umf over the range of variables investigated. The inhomogeneous dynamic characteristics were existed in the bed at elevated temperature in the meso-scale due to the stochastic features of small bubbles or cavities movement. Moreover, though the time-series parameters (standard deviation, wavelet energy distribution, and homogeneous index) of the dynamic characteristics were different, the gas- agglomerated CNT particles flow behaviors under different operating conditions showed a high sensitivity to the temperature from the fixed bed to the partial fluidization regime.

In this work, the tapered fluidized bed reactor (TFBR) without distributor is used for the first time in the production of carbon nanotubes (CNTs), in which, the periodic motion process of CNTs par...

In this work, an imaging processing technique was used to study bubble distribution and evolution in the carbon nanotube (CNT) growth process for the first time. The Fractal analysis method is used to analyze the degree of gas-solid mixing and particles movement. A superposition imaging method was proposed and used to investigate the effect of bubbles on gas-CNT particle mixing. Using a tapered fluidized bed reactor (TFBR) without a distributor, we found that bubbles play different roles in particle mixing at different stages of CNT growth in tapered fluidized bed reactor (TFBR) without a distributor. The degree of mixing of gas-CNT particles and the degree of particle movement are related to the growth time of the CNT. In the growth process of agglomerated multi-walled CNT (@A), strong gas-solid contact dominates in the 1-5 min and 15-20 min windows. Stable fluidization of @A plays an important role in 35-40 min and 45-50 min windows. The degree of dispersion of bubbles of vertical array multi-walled CNT (@A) decreases over time. Importantly, efficient heat and mass transfer are ensured in the three time periods before 15.28 min. After 35.28 min, the @V growth process exhibits stable fluidization. Based on the probability density and joint probability density of bubble aspect ratio and shape factor, we found that different growth time of CNT differentially influences the bubble characteristics in the bed. Additionally, the distribution tendency of @A particle and particle productivity were strikingly similar, confirming that the image processing technique and fractal analysis method adopted in this study are feasible and reliable.