Krishak college of pharmacy Mirzapur UP By Tanu B.Pharm 2nd year

1. Krishak college of pharmacy
(Rajgarh Mirzapur).
Name :- Tanu Maurya B. Pharm(2nd Year)
Subject :- Pharmaceutical Engineering
Topic :- Mixing :
Introduction, Factor Affecting, mechanisms of Mixing

2. Introduction
Mixing is defined as a process in which two
or more components within a system are
converted into one mass or mixture. Ideal
Mixing indicates that different materials
are thoroughly combined to produce
homogenous product. Random Mixing
probability of finding same proportions of
component in the entire mixture. Ordered
Mixing yields the closest situation of the
perfect mix and it is achieved by use of
mechanical, adhesion or coating force.
(A) Ideal Mixing (B) Random Mixing
The term Mixing and Blending are often used
interchangeably but technically they are slight different.
Blending means to mix or intermingle smoothly or
inseparably.

3. FACTORS AFFECTING MIXING
OPERATION
1.Nature of the product: For effective mixing particle surface should be smooth.
Rough surface of one or more components lead to increase chances of entry of active
substance into the pores of another ingredient and further affect mixing.
2. Particle size: It is easier to mix powders of same particle size. Variation in particle
size lead to improper mixing. Increasing the difference in particle size will lead to
segregation (size separation). Since small particles can fall through the voids between
the larger paparticle
3. Particle shape: The particle should be spherical in shape to achieve uniform mixing
4. Particle charge: Some particles due to electrostatic charges exert attractive force
which lead to separation.

4. 5. Proportion of Material: It is easy to mix powders if available in equal quantities.
But to mix small quantities of powders with large quantities of ingredients is difficult
process.
6. Relative density: If the components have a different density, the denser material
will sink through lighter material, the effect of which will depend on the relative
positions of the material in the mixer.
7. Viscosity: The mixing is also affected by the viscosity. An increase in viscosity
reduces the extent of mixing. More viscous particles cause poor mixing.
8.Surface tension of liquids: The surface tension of the liquid is also an important
factor affecting the mixing. High surface tension reduces the extent of mixing.
9. Temperature: The temperature also affects the mixing because the viscosity
changes with the change of temperature.

5. 10.Mixer volume: The volume of the mixing also affects the mixing phenomena. The
blender volume should be such that overfilling should not be done as it decreases the
mixing efficiency.
11. Agitator type: The shape, size, location and type of agitator also affect the degree
of mixing achieved and the time required to mix specific components.
12. Speed/rpm of the impeller: The speed of the impeller affects the homogeneity
of the mixing. As mixing at less rpm is more homogeneous than at a higher rpm.
13. Mixing time: The mixing time is also very important for appropriate mixing.
There is always an optimal mixing time for the specific conditions in which the mixing
is taken place.

6. Mechanism of mixing
The mechanism of liquid mixing are:-
1. Bulk transport: It is the movement of large portion of material from one
location to another location. The movement is done by rotating blades or paddles.
2. Turbulent Mixing : In this, mixing is due to turbulence. Turbulence is a function
of velocity gradient between two adjacent layers of a liquid. In turbulent flow
there is random fluctuation in fluid velocity at a given point within the system. The
turbulent flow can be easily visualized as a composite of eddies of different sizes.
An eddy is defined as a part of the fluid moving as a unit in a direction often
contrary to that of the general flow.

7. 3. Laminar Mixing/Streamline Mixing: When two dissimilar liquids are mixed
through a laminar flow, the shear that is generated stretches the interface between
them. In this mechanism the layers folds on themselves. As a result the number of
layers, and therefore the interfacial area between them, increases exponentially with
time.
4. Molecular Diffusion: The mechanism responsible for mixing at the molecular
level is the diffusion resulting from the thermal movement of the molecules. The
process is described in terms of Fick’s law of diffusion:
Where, Dm/dt is the rate of transport of mass across an interface.
A is the area
de/dx is the concentration gradient across the interface
D is diffusion coefficient