Mixing (Blending) Flashcards
a process in which two or more ingredients in separate or roughly mixed conditions are treated so that each particle of any one ingredient is as nearly as possible adjacent to a particle of each of the other ingredients
Mixing (Blending)
This is usually accomplished utilizing paddles, revolving blades, or other devices within the mixer, arranged to move adjacent volumes of the fluid in different directions, thereby shuffling the system in three dimensions
Bulk transport
• velocity differences within the body of fluid produce randomization of the fluid molecules. For this reason, turbulence is a highly effective mechanism of mixing.
Turbulent mixing
highly viscous fluids are being processed.
Laminar mixing
Just read
When two different liquids are mixed through laminar flow, the generated shear stretches the interface between them
The primary mechanism responsible for mixing at the molecular level is ____ resulting from the thermal motion of the molecules.
diffusion
When it occurs in conjunction with laminar flow __ tends to reduce the sharp discontinuities at the interface between the fluid layers and, if allowed to proceed for sufficient time, results in complete mixing
Molecular diffusion
A system for liquid mixing commonly consists of two primary components:
- a tank or other container suitable for holding the material being mixed
- means supplying energy to the system to facilitate reasonably rapid mixing
The distinction between impeller types is often made based on
- type of flow pattern they produce
- the blades’ shape and pitch
In impellers the flow pattern may be analyzed in terms of three components:
radial, axial or longitudinal, tangential
perpendicular to the impeller shaft
radial
parallel to the impeller shaft
axial or longitudinal
tangential to the circle of rotation around the impeller shaft
tangential
- the segment of a multithreaded screw
- either right- or left-handed depending on the direction of slant of their blades
Propellers
• The three-blade design is most commonly used with fluids
• most efficient when they run at high speeds in liquids of relatively low viscosity
Propellers
the primary effect of a propeller is due to a __.
axial flow
With these types of impellers, a radial flow is induced by the centrifugal action of the revolving blades
Turbines
When radial-tangential flow is desired, turbines with blades set at a 90-degree angle to their shaft are employed
Turbines
can be operated satisfactorily in fluids 1000 times more viscous than fluids in which a propeller of comparable size can be used
Turbines
generally operated at low speeds of 50 rpm or less
Paddles
Their blades have a large surface area as compared to the tank in which they are employed, a feature that permits them to pass close to the tank walls and effectively mix viscous liquids and semisolids
Paddles
• involve sub-surface jets of air, or less commonly of some other gas, for adequate mixing of certain liquids
• The jets are usually arranged so that the buoyancy of the bubbles lifts liquids from the bottom to the top of the mixing vessel
• the intense turbulence generated by the jet produces intimate mixing
Air jets
They utilize liquids pumped at high pressure into a tank for mixing
Fluid jets
the fluids are pumped through nozzles arranged to permit a good circulation of material throughout the tank
Fluid jets
