Difference between particulate and aggregative fluidization
Answers
A fluidised bed is a physical phenomenon occurring when a quantity of a solid particulate substance (usually present in a holding vessel) is placed under appropriate conditions to cause a solid/fluid mixture to behave as a fluid. This is usually achieved by the introduction of pressurized fluid through the particulate medium. This results in the medium then having many properties and characteristics of normal fluids, such as the ability to free-flow under gravity, or to be pumped using fluid type technologies.
The resulting phenomenon is called fluidisation.
Fluidization (or fluidisation) is a process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid (liquid or gas) is passed up through the granular material.
Answer:
Explanation:
Fluidization of solids by liquids is characterized by a minimum fluidization velocity at which the upward drag force exerted on the particles by the upflowing liquid is just balanced by the force due to gravity. However, unlike gas-solid systems, most of the liquid-fluidized beds do not give rise to bubbles formation as the liquid velocity is gradually raised and increased beyond the minimum fluidization velocity. Instead, the bed expands in a regular fashion with the bed voidage increasing, as the liquid velocity increases. Over and above, there exists a sharp interfacial boundary between the bed top surface and the liquid above it. Such a behavior is call particulate fluidization to differentiate it from the aggregative fluidization found in the gas-solid system.
Why most of the gas-solid systems subscribe to aggregative fluidization while most of the liquid-solid systems give rise to particulate fluidization is not at all understood. But it may be the fact that density ratio between the solid particles and the fluidizing fluid plays an important role in this regard. If the ratio is high, as with most gas-solid combinations, the aggregative behavior comes to play; if the ratio is low, as with most liquid-solid combinations, the system goes to behave the particulate fluidization