Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Zhu, Jesse

Abstract

Light particles are commonly utilized as the solid phase in reverse fluidized bed reactors, especially for applications in wastewater treatment and other chemical or biochemical processes. This is primarily due to their favorable buoyancy characteristics and their ability to enhance mass transfer and mixing within the reactor. The drag coefficient related to the particle terminal velocity is one of the vital parameters for fluidized bed operation and design. However, traditional drag coefficient models are mostly based on heavy particle settling experiments. The few free-rising particle experiments have only justified the constant drag coefficient values in the high Reynolds number region, but the drag coefficient predictions for the low Reynolds number region have been assumed to be the same as for heavy particles.

Thus, this study investigates the drag coefficient and movement phenomena of free-rising spherical particles in various fluid mediums. It focuses on understanding the complex interactions between spherical particles and fluid dynamics, particularly under different conditions of density differences and fluid types. The research encompasses experimental setups using spherical particles of various materials and sizes in fresh and salted water. High-speed video imaging and advanced tracking software were employed to analyze the particles' terminal velocities and movement behaviors. A new drag coefficient model for free-rising spherical particles was developed, offering improved accuracy over traditional models, especially at lower Reynolds numbers. The study's findings provide valuable insights into particle-fluid interactions, which have significant implications for fluidization technology and related industrial applications.

Summary for Lay Audience

In many industrial processes, including wastewater treatment and chemical manufacturing, special reactors called reverse fluidized bed reactors are used. These reactors contain suspended light particles that float downwards with the fluid direction down to the bottom of reactor through the liquid inside the reactor. The light particles help to enhance mass transfer and mixing within the reactor and make the treatment process more efficient.

One key aspect of designing these reactors is understanding how these particles move through the liquid, especially their speed as they rise, which is influenced by a factor called the drag coefficient. This drag coefficient helps engineers predict how particles will behave in different liquids.

Traditional models to predict this drag coefficient are based on experiments with heavy particles sinking in liquids. However, light particles, which float upwards, behave differently. Previous studies have shown that the drag coefficient for light particles in high Reynolds number conditions has similar tendence to that for heavy particles, but larger constant drag coefficient value. There has been little research on how this coefficient behaves at low Reynolds number for free-rising particles, which are more common in these reactors.

This research focuses on understanding how spherical light particles move through various liquids, such as fresh water and saltwater, under different conditions. By using advanced video technology and tracking software, the study observed and measured the movement and the speeds of these particles in great detail. The findings led to the development of a new model for predicting the drag coefficient of light particles, especially at low Reynolds number region. This new model is more accurate than traditional ones and can help improve the design and efficiency of fluidized bed reactors, benefiting industries that rely on these systems.

Download

Share

COinS