gpat online classes · agitated film evaporators –elevation of boiling point is not observed in...

PHARMACEUTICAL ENGINEERING

PRESENTED BYDR. T.E.G.K.MURTHY

PROFESSOR & PRINCIPAL BAPATLA COLLEGE OF PHARMACY

BAPATLA, ANDHRA PRADESH.

GPAT ONLINE CLASSES

In collaboration with A.P govt.

Topics going to cover in this session

1. Fluid flow

2. Heat transfer

3. Evaporation

4. Distillation

1. Fluid Flow• Contents:

– Types of Fluid flow

– Concept of boundary layer

– Basic equations of fluid flow

– Study of valves

– Measurement of flow rate

– Flow meters

– Manometers

Types of flow

• Laminar flow

• Transitional flow

• Turbulent flow

Reynolds number

𝜌𝐷

Re=

Concept of boundary layer

Basic equations of fluid flow

• Conservation of mass (continuity equation)

• Rate of mass flow in – rate of mass flow out= rate of mass

accumulation

• Conservation of momentum (Cauchy equation, Navier- stokes,

Ealers equation)

• Rate of momentum accumulation=rate of momentum entering-

rate of momentum leaving +sum of forces acting on the

system

• Conservation of energy (Bernoulli equation)

Study of valves

• Plug cocks are used for compressed air

• Most common types are gate and globe valves

• The direction of flow does not change in gate valve and not recommended

for controlling flow

• Automatic control valves are similar to globe valves

• Check valves are for unidirectional flow

GATE VALVE GLOBE VALVE

CHECK VALVE BUTTERFLY VALVE NEEDLE VALVE

Measurement of flow rate

• Direct weighing

• Hydrodynamic methods

• Direct displacement

• Miscellaneous methods dilution method

Flow meters• Full- bore meters

– Venturi meter

– Orifice meter

– Variable area meters such as rotameters

– V-element

– Magnetic

– Vortex-shedding

– Turbine

– Positive displacement meters

– Ultrasonic meters

– Mass flow devices such as Coriolis flowmeters

– Stainless steel floats are common

• Insertion meters

– Pitot tube

– Thermal meters

Venturi meter Orifice meterRotameters

Vortex-sheddingTurbine

Positive displacement

meters

Full- bore meters

Ultrasonic meters

Coriolis flow meters

floats Full- bore meters

Insertion meters

Thermal

Pilot tube

Manometers

2. Heat Transfer• Contents

– Source of heat

– Mechanism of heat transfer

– Laws of heat transfer

– Steam as source of heating media

– Determination of requirement amount of steam

– Steam pressure

– Boiler capacity

– Steam trap

Source of heat

• Sun

• Chemical

• Electrical

• Nuclear

Mechanism of heat transfer

• Conduction Thermal and electrical

• Convection natural and forced

• Radiation

• Thermal radiation corresponding to 0.8- 400 µ

Laws of heat transfer

• Fourier’s law

dq/dA = -K dT/dx

• Coefficient of thermal conductivity depends on the material of the body and

temperature

K=a+bt

• Accurate k values with water, mercury among liquids and silver, lead or

copper among the solids

• Newton’s law of cooling

q/A= h (Ts- T f )

• Stefan- Boltzmann law

q= bAT4

b=0.174X10 -8 Btu/ hr.ft2F

• Radiation of actual body

q=ɛbAT4

Steam as source of heating media

• Cheap and plentiful raw material

• Easy to generate and distribute

• Cheaper than electricity

• Clean, odorless and taste less

• High heat content, heat materials quickly

• Heat is given up at a constant temperature

• 2-3 times higher than atmosphere, potential safety problems

• Use of high strength piping and equipment

Determination of requirement amount of steam

• The quantity of heat required to raise the

temperature of a material Q=MS∆t

• The quantity of heat required to cause vaporization

Q=M/L

Steam pressure

• The saturation temperature will be dependent on

pressure

• Temperature increase with pressure

• Steam tables are available

Boiler capacity

• Steam is generated at 600- 800 kpa and 160- 1700c

• Boiler efficiency= (steam value per hour.kg) x(h 2- h 1 )x100

________________________________________________________________________________________________________

Fuel consumption per hour. Kg x fuel low calorific heating value

• Combustion efficiency

– Burner’s ability to burn the fuel

– Un burnt fuel quantities in exhaust, excess oxygen in exhaust

• Thermal efficiency

– Effectiveness of heat exchanger

– Affected by scale formation soot formation

– Steam is used at 150-300 KPa and 110- 1350c

– Reducing valve to reduce, adjust, and control the pressure to the

desired level operated manually or automatically

– Safety valve is positioned before the control valve to operate

against the pressure

Steam trap

• To remove condensate and air

• Mechanical traps are based on density difference

and not useful to remove air

• Thermostatic devices based on sensible heat.

• Balanced pressure thermostatic steam trap

Contents

• Basic concept of phase equilibrium

• Factors affecting evaporation

• Evaporators

• Multiple effect evaporators

Basic concept of phase equilibrium

• Homogeneous and physically distinct part of a system

separated from other parts by definite boundaries

• Number of components

• Degree of freedom

– One component system

– Two component system

• One component system

• Melting point, boiling point, triple point, sublimation and

polymorphism

• Two component system

• Solid- vapour system of two components

• Liquid- liquid systems of two components

• Liquid- gas system of two components

• Solid- solid system of two components

• Solid- liquid system of two components

• Solid- vapour system of two components– Hydration and dehydration of salts

– Efflorescence and exsiccation

– Deliquescence and hygroscopicity

• Liquid- liquid systems of two components– Completely miscible liquids

– Partially miscible liquids

– Immiscible liquids

• Liquid- gas system of two components– Solution of gases in liquids

• Solid- solid system of two components– Solution of solids in solids

• Solid- liquid system of two components– Solution of solids in liquids

– Formation of eutectic mixtures

Factors affecting evaporation

Liquid characteristics

• Concentration

• Foaming

• Temperature sensitivity, temperature and time of evaporation and

temperature and moisture content

• Scale

Materials of construction

Single and multiple effect operation

Type of product required

Evaporators

• The steam heated tubular evaporators are

– Long tube vertical evaporators

a. Upward flow

b. Downward flow

c. Forced circulation

Agitated film evaporators

– Evaporating pan, evaporating still and short tube evaporator are examples of

natural circulation evaporators

– Hemispherical shape pan fabricated with either copper or stain less steel for

best surface/ volume ratio

– A receiver and vacuum pump may be connected to still

– Calandria is a part occupied by a nest of tubes within the evaporator

– Short tube evaporator is preferred for a continuous process operated for one

product like cascara

– Length to diameter ratio in long tube evaporator is 140 : 1

Agitated film evaporators

– Elevation of boiling point is not observed in film evaporator due to hydrostatic

head and also suitable for foam forming materials (climbing film evaporator

– Spider or spray nozzles are used in falling film type for uniform flow in tubes

– For highly heat sensitive materials, ) falling film evaporators are used

– Combination of climbing and falling film evaporators are used for high viscous

materials and for high percentage of evaporation

– Wiped film or rotary film evaporators provide mechanical agitation for too

viscous materials.

Multiple effect evaporators• Forward feed

• Backward feed

• For high viscous materials backward feed is preferred

• Mixed feed

Contents

• Phase diagram

• Volatility

• Simple distillation

• Flash distillation

• Rectification/ fractional distillation

• Azeotropic distillation

• Extractive distillation

Phase diagram

• It is a graphical representation of the physical states of a

substance under different conditions of temperature and

pressure.

Volatility• In order to separate a binary mixture using distillation process, there must be

differences in volatilities of the components.

• A measure for this is termed the relative volatility.

• Volatility of component-A as: partial pressure of component-A divide by mole

fraction component-A in liquid

• For a binary mixture of A and B, therefore:

• Volatility of A = pA / xA

• Volatility of B = pB / xB

• Relative volatility is the ratio of volatility of A (MVC) over volatility of B (LVC):

Simple distillation

• Controlled by Rayleigh’s equation

• Known as differential distillation

– It consists of distillation flask, condenser and receiver

– Below 100, water/ steam bath, above 220, woods or Rose metal

bath, more than 250, oil bath

– Preparation of Water for injection and purified water

Flash distillation

• Vaporization of entire liquid as flash as passes from high to low pressure

• Known as equilibrium distillation

• Continuous and used for multi component systems of narrow boiling range

Rectification/ fractional distillation• Reflux: Part of condensate back to the still

• Reflux ratio: ratio of reflux to the product

• Scrubbing and stripping

• Feed plate, rectifying section and stripping

section

• Plate columns (bubble cap and sieve plate

columns) and packed columns

• General purpose (ring and saddle type)

and high efficiency type

• Raschig type ring and berl type saddles

and structured grid packing are popular

• McCabe- Thiele method assumes the

composition in each plate is decided by the

mole fraction of one of the two

components

Azeotropic distillation

• More volatile extraneous material

• Forms low boiling point azeotrope with one of the key

component

• 96.4% ethanol

• Use of benzene, heptanes or cyclohexane

Extractive distillation

• Less volatile extraneous material

• Miscible with both components

• Structurally similar to one component

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