Fundamental of Multi-Phase Flows: a Quick Synopsis
Multi-Phase flows are special kind of flow which has more than one phase. This kind of flow is seen in manifold ways in industrial processes. Some examples of multiphase flows are solid-gas flows in pneumatic conveying, gas-liquid flows in condensers and evaporators, solid liquid gas flow in chemical reactors, etc. In Multiphase flow, solid, liquid, and gas phases show some typical characteristics which determine the fundamentals of Multi-Phase flow.
In computational Multi-phase Flows solid phases are found in the form of lumps and these lump type particles are found carried away with the direction of the flow. The uniqueness of the movement of these solid particles is abruptly dependent on the size of these particles and on the movement of the related fluids. Whereas larger particles are found non-responsive, tiny particles obeys the fluid motions.
In multi-phase flows with droplets and particles which has a liquid phase, it can be a continuous phase having dispersed solid elements in the form of particles, gases in the form of bubbles, and other liquids in the form of drops. This liquid phase can be discontinuous too as in the drop form remaining suspended either in the gas phase or in another liquid phase. Another property of this liquid phase is related to wet ability.
Gas as a fluid possesses similar properties like fluid. However it has an additional property of being highly compressive. Despite this property, in many instances of multiphase flow containing gas needs to be treated as fundamentally incompressible specifically if the pressure is found quite high and the Mach number in comparison gas phase is found considerably low.
Different types of multiphase flows are found. The most common types are two phase flows, which incorporate diverse types of flows like Gas liquid flow, liquid-liquid flow, gas-solid flow, and liquid -solid flow.
Three phase flows are also found quite commonly like gas-liquid-liquid flows, gas-liquid-solid flows, and solid Liquid-liquid flows. Gas-liquid-liquid flows are made of vapor mix and two non-homogenous liquid phases are often found in chemical plants. Gas-liquid-solid flows type of flow system is found two phase fluidized bed and gas lift chemical reactors where a liquid-gas reaction is supported and promoted by solid and catalyst kind of particles in suspended condition in mixture.
Four-phase multi-phase flows are also found. One of the most common examples of this 4-phase multi-flow system is direct-contact congeal crystallization where, for example, butane liquid is inserted into solution where from the crystals are to be shaped, and freezing takes place as a consequence of the desertion of the concerned liquid butane. In this example, these4 phases are butane liquid, vapor, solute phase, and the solid phase.
4 types of multi-phase flow models are found: empirical, multi-fluid, phenomenological, and interface tracking. Under simulated steady-state conditions, speed, stress, and phase fractions can be changed is aspect of time, but their disparity in regards to time is constant.
Multiphase flow problems are quite complicated that advanced computational and tentative methods are often needed to resolve the formula that describes them. The challenges consist of modeling nonlinear fluids, modeling and tracking of interfaces, fondling with multiple length-scales, characterizing phase structures, and treating drop breakup as well as coalescence. Models must be authenticated, which needs the use of costly and tricky experimental methods.