Effect of Particle Size on Carbon Nanotube Aggregates Behavior in Dilute Phase of a Fluidized Bed

Abstract

Fluidized bed reactors have been increasingly applied for mass production of Carbon Nanotube (CNT) using catalytic chemical vapor deposition technology. Effect of particle size (d p = 131 µm and 220 µm) on fluidization characteristics and aggregation behavior of the CNT particles have been determined in a fluidized bed for its design and scale-up. The CNT aggregation properties such as size and shape were measured in the dilute phase of a fluidized bed (0.15 m-ID × 2.6 m high) by the laser sheet technique for the visualization. Two CNT particle beds showed different tendency in variations of the aggregates factors with gas velocity due to differences in factors contributing to the aggregate formation. The CNT particles with a larger mean size presented as relatively larger in the aggregate size than the smaller CNT particles at given gas velocities. The aggregates from the large CNT particles showed a sharp increase in the aspect ratio and rapid decrease in the roundness and the solidity with gas velocity. A possible mechanism of aggregates formation was proposed based on the variations of aggregates properties with gas velocity. The obtained Heywood diameters of aggregates have been firstly correlated with the experimental parameter.

Visualization of Carbon Nanotube Aggregates in Dilute Phase of a Fluidized Bed

“…The CNT with average diameter of 0.25mm is a type of the entangled CNT. The CNT particle is macroscopically seen as a black powder whereas microscopically the nanotubes on the particle surface are randomly oriented in an entangled spaghettilike configuration [6]. Experiments were carried out in a fluidized bed unit made of transparent Plexiglas column as shown in figure 1.…”

“…The non-intrusive methods such as digital image analysis methods combined with laser sheet, tomography and nuclear magnetic resonance techniques measure the whole image of the particles flow in a wide range [5]. The imaging based on laser sheet technique has been used to measure aggregation phenomena at different flow regime in fluidized beds with advantages of easy installation and in-situ measurement [4,[6][7][8]. More recently, a few studies [4,6] has used the laser-based image analysis method to measure sizes of multi-walled CNT aggregates.…”

“…The imaging based on laser sheet technique has been used to measure aggregation phenomena at different flow regime in fluidized beds with advantages of easy installation and in-situ measurement [4,[6][7][8]. More recently, a few studies [4,6] has used the laser-based image analysis method to measure sizes of multi-walled CNT aggregates. Jeong and Lee [4] measured the sizes of aggregates just above the bed surface for inferring particles behavior in the dense bed.…”

“…Jeong and Lee [4] measured the sizes of aggregates just above the bed surface for inferring particles behavior in the dense bed. Kim [6] measured the aggregates properties at a point in the dilute phase of reactor. However, the lack of information on variation in the aggregates size and shape along height of the reactor exists for understanding the macro and microscopic structure of the aggregates in the freeboard of the fluidized bed.…”

Numerical Investigation of Design and Operating Parameters of Thermal Gradient Continuous-Flow PCR Microreactor Using One Heater

“…PCR is one of the most commonly used enzymatic processes that involve discrete thermal cycling, making it a good option to study heat transport characteristics in microfluidic chips. Thermal modeling is a key element of many biochemical analysis systems, involving operations, such as kinetics analysis [2][3][4], enzyme catalytic mechanism [5][6][7], and biochemical interaction analysis [8][9][10]. Due to lateral thermal diffusion process in microfluidic chips, the thermal profile in microchannel can be accurately captured by using a three-dimensional conjugate heat transfer model.…”