gpat online classes · agitated film evaporators –elevation of boiling point is not observed in...
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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.
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Topics going to cover in this session
1. Fluid flow
2. Heat transfer
3. Evaporation
4. Distillation
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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
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Types of flow
• Laminar flow
• Transitional flow
• Turbulent flow
Reynolds number
𝜌𝐷
Re=
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Concept of boundary layer
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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)
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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
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GATE VALVE GLOBE VALVE
CHECK VALVE BUTTERFLY VALVE NEEDLE VALVE
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Measurement of flow rate
• Direct weighing
• Hydrodynamic methods
• Direct displacement
• Miscellaneous methods dilution method
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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
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Venturi meter Orifice meterRotameters
Vortex-sheddingTurbine
Positive displacement
meters
Full- bore meters
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Ultrasonic meters
Coriolis flow meters
floats Full- bore meters
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Insertion meters
Thermal
Pilot tube
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Manometers
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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
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Source of heat
• Sun
• Chemical
• Electrical
• Nuclear
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Mechanism of heat transfer
• Conduction Thermal and electrical
• Convection natural and forced
• Radiation
• Thermal radiation corresponding to 0.8- 400 µ
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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
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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
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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
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Steam pressure
• The saturation temperature will be dependent on
pressure
• Temperature increase with pressure
• Steam tables are available
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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
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• 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
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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
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Contents
• Basic concept of phase equilibrium
• Factors affecting evaporation
• Evaporators
• Multiple effect evaporators
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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
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• 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
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• 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
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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
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Evaporators
• The steam heated tubular evaporators are
– Long tube vertical evaporators
a. Upward flow
b. Downward flow
c. Forced circulation
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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
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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.
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Multiple effect evaporators• Forward feed
• Backward feed
• For high viscous materials backward feed is preferred
• Mixed feed
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Contents
• Phase diagram
• Volatility
• Simple distillation
• Flash distillation
• Rectification/ fractional distillation
• Azeotropic distillation
• Extractive distillation
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Phase diagram
• It is a graphical representation of the physical states of a
substance under different conditions of temperature and
pressure.
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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):
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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
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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
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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
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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
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Extractive distillation
• Less volatile extraneous material
• Miscible with both components
• Structurally similar to one component
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