Pharmaceutical Engineering Unit -2, Chapter -4 Heat transfer, Chapter -5 Evaporation, Chapter -6 Distillation

1. PHARMACEUTICAL ENGINEERING
B. Pharma
3rd Semester
Unit -2
Presented by – Nikita Gupta
(Assistant Professor )

2. Chapter - 4
Heat Transfer

3. Syllabus:
• Objectives
• Applications
• Heat transfer mechanisms
• Fourier’s law
• Heat transfer by conduction, convection
&radiation
• Heat interchangers
• Heat exchangers.

4. HEAT TRANSFER
When two objects at
different temperatures
are brought into
thermal contact, heat
flows from the object
at higher temperature
to the object at lower
temperature.

5. The mechanisms by which the heat may
flow are
(i) conduction,
(ii) convection
(iii) radiation.
Mode of
Heat Transfer
Conduction
Convection
Natural
Convection
Forced
Convection
Radiation

6. Conduction
When heat flow through a body without
any observable motion of matter, the type
of heat flow is called conduction.
Mechanism :
In metallic solids, thermal conduction
results from the unbound electrons
(which is similar to the electrical
conductivity).

7. In solids that are poor conductor of heat
and in liquids the heat is conducted by
the transport of momentum of the
individual molecules along the
temperature gradient.
In gases the conduction occurs by the
random motion of the molecules, so that
heat is “diffused” from hotter regions to
the colder ones.

8. Examples:
Heat flow through the brick wall of a
furnace or the metal wall of a tube.

9. Convection
When heat flows by the transfer of
matter, the type of heat flow is called
convection.
In this case the heat flows by actual
mixing of warmer portions with the
cooler portions of the same material.

10. Examples
Transfer of heat by the bodies of
turbulent flow and by the current of
warm air from a room heater flowing
across the room

11. Radiation
When heat is transferred through the space by electromagnetic
waves the type of flow of heat is called radiation heat flow.
When radiation is passing through empty space, it is not
transformed into heat or any other form of neither energy,
nor it is diverted from its path. If the radiation falls on a matter
the radiation energy will be transmitted (i.e. pass
through the matter), reflected or absorbed. Only the energy that
is absorbed is converted into heat energy.

12. CONDUCTION
The basic law of heat transfer by
conduction can be written in the form of
the rate equation:
Rate = Driving force
Resistance
The driving force is the temperature
gradient.

13. Fourier’s law
Fourier’s law states that the rate of heat flow
through a uniform material is proportional to the
area perpendicular to the heat flow (A), the
temperature drop (dt) and inversely proportional
to the length of the path of flow.

14. q =
k AΔt
L
or
q =
Δt
L /kA
Δt = driving force
L/kA = the resistance

15. HEAT EXCHANGERS
• These devices are used for transferring heat from a
fluid (Hot Gas or Steam) to another fluid (Liquid)
through a metal wall.
The equipment’s used for heat transferring are known as
heat exchangers.

16. Tubular heater
Tubular heaters consists of circular tubes, one
fluid flows through the inner tube, while the
other flows through the outside space. The heat
transfer takes place across the wall
of the tube.

17. Single Pass Tubular heater

18. Floating-head two-pass heater –
It is structurally independent, hence known as
floating head.
The ends of the tubes are fitted with the
floating head.

19. Floating-head two-pass heater

20. Heat Interchangers:
These devices are used for transferring
heat from a One liquid to another liquid or
one gas to another gas through a metal
wall.

21. Liquid-to-liquid heat interchanger -
Construction is same as that of single-pass
tubular heater, only difference is that it
contains baffles to lengthen the path of flow
of outer liquid.

22. Liquid-to-liquid heat interchanger

23. Double - pipe heat interchanger

24. Chapter - 5
Evaporation

25. Syllabus
• Evaporation
• Objectives
• Applications
• Factors influencing evaporation,
• Differences between evaporation and other heat process

26. • Principles, construction, working, uses, merits and
demerits of –
• Steam jacketed kettle
• Horizontal tube evaporator,
• Climbing film evaporator
• Forced circulation evaporator
• Multiple effect evaporator& Economy of multiple
effect evaporator

27. Evaporation
It maybe definedas the vaporization of aportion of solvent
from a solution of a solid, leaving a concentrated liquid
residue.

28. Objectives:
1. Liquid, soft and dry extracts are prepared employing
evaporation process.
2. It is also used in the concentration of blood plasma and
serum.
3. Used inthepreparation of medicaments containing enzymes,
hormones,antibiotics and many other agents.

29. Applications of Evaporation
1.Evaporation process is used in the manufacture of bulk
drugs, particularly in pharmaceutical industries.
2.Evaporation is used in the manufacture of biological
products. e.g. Insulin, enzymes and hormones.
3.In demineralization of water.

30. 4. Liquid extracts, soft extracts & dry extracts.
5. In the concentration of blood plasma & serum.
6. It is also used in the manufacture of drugs containing,
antibiotics, enzymes, hormones & many other substances.
7. Used in purification of vitamins.
8. Concentration of proteins.
9. Concentration of biological products.
10. Stripping of solvents from vegetable & plant or herbal
extracts.
11. Removal of water & solvents from fermentation broths. 12.
Concentration of penicillin & related products

31. General Principles of Evaporation
Various factors influencing the heat transfer co-efficient
of an evaporator are;
1. Vapor pressure
2. Boiling point
3. Effect of dissolved substances
4. Heat supply and vapor removal
5. Heat transfer

32. Various factors influencing the rate of evaporation
Various factors influencing the rate of evaporation are;
 Temperature
 Temperature and time of evaporation
 Temperature and moisture content
 Type of product required
 Effect of concentration

33. EVAPORATION DISTILLATION DRYING
Components are Components are Components are
heated below their heated at their heated above their
boiling points respective boiling boiling points
points
Vaporization takes Vaporization takes Vaporization takes
place from surface of place from entire body place from entire solid
liquid of liquid bed
Condensation of vapors Condensation of vapors Condensation of vapors
are not required are required to get are not necessary
purified product
Differences between Evaporation,Distillation & Drying

34. Classification of Evaporators
They areclassifiedbased upon themovement of heat transfer.
They are;
1. Natural circulation evaporators
They are of three types;
A. Evaporating pans or Steam jacketed pans
B. Evaporating stills
C. Short tube evaporator
2.Forced circulation evaporators
3.Film evaporators
A. Climbing film evaporator
B. Falling film evaporator

35. Evaporating pans or Steam jacketed pans orSteam jacketed
kettle
Principle : The movement of the liquid results from
convection currents set up by the heating process.
Convection currents: The process in which heat moves
through a gas or liquid as the hotter parts rises and the
cooler part sinks.

37. Horizontal tube evaporator
In a Horizontal tube evaporator, the steam is passed
through tubes placed horizontally. As a result solvent
outside tubes gets evaporated and passed from the top and
concentrated liquid is discharged from the bottom.

39. Vertical evaporator or long tubes or climbing film
evaporators –
Long tube evaporators a large number of vertical tubes
about 7 meters in length and 50 mm in diameter are
enclosed in an outer jacket to which steam is supplied.
The pre-heated feed liquid is admitted at the base. Here
it boils and the vapours formed take the liquid up the
tube at a velocity of about 6-7 meters/second. The
liquid takes only a few seconds to travels the length of
the tube, so the evaporator is very suitable for heat-
sensitive substances

41. Forced circulation evaporators
Principle : Feed is introduced through the liquor inlet.
Pump will force the liquid through the calendria.
Steam heats the liquid inside the calendria . As it is
under pressure in the tubes the boiling point is
elevated and no boiling takes place. As the liquor
leaves the tubes and enters the body of the evaporator
through the tangential inlet there is a drop in pressure
and vapor flashes off from the superheated liquor. The
concentrated liquid is pumped out through the product
outlet and the vapor is collected through the vapor
outlet.

43. Multiple effect evaporator& Economy of multiple effect
evaporator -
Two evaporators are connected together with a piping
arrangement so that the vapour from the calandria of first
effect (which is heated by steam) is used to heat the calandria
of the second effect. This means that the calandria of the
second effect is used as condenser for the first effect, so that
latent heat of vaporisation is used to evaporate more quantity
of the liquid instead of its going as waste.

45. Chapter - 6
Distillation

46. Syllabus
• Distillation
• Basic Principles and methodology of simple
distillation
• Flash distillation
• Fractional distillation
• Distillation under reduced pressure
• Steam distillation
• Molecular distillation

47. Distillation - Distillation, process involving the conversion of
a liquid into vapour that is subsequently condensed back to
liquid form.
Uses of Distillation - Distillation is used for many commercial
processes, such as the production of gasoline, distilled water,
xylene, alcohol, paraffin, kerosene, and many other liquids.
Gas may be liquefied and separate. For example: nitrogen,
oxygen, and argon are distilled from air.

48. Basic Principles and methodology of simple distillation
Simple distillation may be used when the boiling points of
two liquids are significantly different from each other or to
separate liquids from solids or non volatile components.
In simple distillation, a mixture is heated to change the most
volatile component from a liquid into vapor.
The vapor rises and passes into a condenser.
Usually, the condenser is cooled to promote condensation of
the vapor, which is collected.

50. Flash distillation
Principle - Flash distillation uses vaporization to separate
the compounds.
Hot liquid mixtures get vaporized in flash vaporization
when they pass from high-pressure zones to low-pressure
zones.
Liquid vaporizes as pressure is reduced, which reduces
the boiling point.

51. The process of vaporization leads to a decrease in
temperature as the liquid vaporizes.
Vapour molecules with low boiling points become
condensed while vapour molecules with high boiling
points remain in the vapour phase.
These two phases are in contact until saturation occurs.
Vapours are allowed to condense further at the bottom,
while liquids fall to the bottom and are collected.

53. Fractional distillation
Fractional distillation is used when the boiling points
of the components of a mixture are close to each other,
as determined using Raoult's law.
A fractionating column is used to separate the
components used a series of distillations called
rectification.

54. In fractional distillation, a mixture is heated so vapor
rises and enters the fractionating column.
As the vapor cools, it condenses on the packing
material of the column.
The heat of rising vapor causes this liquid to vaporize
again, moving it along the column and eventually
yielding a higher purity sample of the more volatile
component of the mixture.

56. Distillation under reduced pressure or Vacuum
distillation -
Vacuum distillation is used to separate components that have
high boiling points.
Lowering the pressure of the apparatus also lowers boiling
points.
Otherwise, the process is similar to other forms of
distillation.
Vacuum distillation is particularly useful when the normal
boiling point exceeds the decomposition temperature of a
compound.

58. Steam distillation
Steam distillation is used to separate heat-sensitive
components.
Steam is added to the mixture, causing some of it to
vaporize.
This vapor is cooled and condensed into two liquid fractions.
Sometimes the fractions are collected separately, or they may
have different density values, so they separate on their own.
An example is steam distillation of flowers to yield essential
oil and a waterbased distillate.

60. Molecular distillation
Molecular Distillation Molecular distillation is a type of
short-path vacuum distillation, characterized by
extremely low vacuum pressure (≈ 0.01 torr).
It is a process of separation, purification, and
concentration of natural products, complex and
thermally sensitive molecules.

61. Principle of Molecular distillation - Molecular distillation is
considered the safest mode of separation and to purify the
thermally unstable molecules and related compounds with
low volatility and elevated boiling points.
The separation principle of molecular distillation is based on
the difference of molecular mean free path. The passage of a
free path for molecules should be collision-free. Langmuir
and Knudsen derived an equation that describes the yield of
distillate for molecular distillation.

63. Thank You
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