Question

In flow through a packed bed, the specific surface of a particle is defined as

A. The ratio of surface area of the particle to the surface area of an equivalent spherical particle
B. The surface area of a particle divided by the void fraction
C. Volume fraction of particles in the bed divided by (one minus the void fraction)
D. The ratio of surface area of the particle to the volume of the particle

Answer 1

In a packed bed, the specific surface of a particle is the ratio of its surface area to its volume, which is crucial for efficiency in diffusion processes.

Step-by-step explanation:

In flow through a packed bed, the specific surface of a particle is defined as the ratio of surface area of the particle to the volume of the particle. This is because any three-dimensional object has a surface area and a volume; hence the surface-to-volume ratio is a critical factor in processes involving mass transfer, such as diffusion. The higher this ratio, the more efficient the diffusion process as there is more surface area available for interaction per unit volume of particle.

For a sphere, as described in the question, the surface-to-volume ratio is mathematically computed as 3/r, where 'r' represents the radius of the sphere. As the radius increases, this ratio decreases, indicating less surface area is available per unit volume, making diffusion less efficient. This principle applies similarly in packed beds, where the goal often involves optimizing contact between fluid phases and the solid particles.