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.
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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