Chemical engineering Interview by A K Verma

FLUID MECHANICS:
Fluid mechanics is defined as the science that deals with the behaviour of fluid at rest or in motion and the interaction of fluid with solid or other fluid at boundaries.
Fluid:
Fluid is a substance which has ability to flow. Fluid deform continuously under the influence of shear stress no matter how small.
Types of fluid:
●     Newtonian Fluid
●     Non-Newtonian Fluid
Studies of behaviour of non-newtonian fluid is called Rheology.
Newtonian Fluid: 
The fluid which obeys the newton’s law of viscosity is called Newtonian fluid. A fluid where the shearing stress is linearly related to the rate of shearing strain - is designated as a Newtonian Fluid.
Non-Newtonian fluid classified into two parts:
●     Time dependent
●     Time independent
Time dependent Non-Newtonian Fluid Classified into two Parts:
●     Thixotropic
●     Rheopectic
Thixotropic Fluids:
The viscosity of a thixotropic fluid decreases with increasing time at a constant shear rate.
Rheopectic:
The viscosity of a Rheopectic fluid increases with increasing time at a constant shear rate.

Time independent Non-Newtonian Fluid classified into three parts:
●     Bingham Plastic
●     Pseudo Plastic
●     Dilatant
Shear-thinning or Pseudoplastic Fluids:
A Shear-thinning or pseudo-plastic fluid is a fluid where viscosity decreases with increasing shear rate.
Dilatant Fluids:
A Shear Thickening Fluid - or Dilatant Fluid - increases the viscosity with agitation or shear rate.
Bingham Plastic Fluids:
A Bingham Plastic Fluid has a yield value which must be exceeded before it will start to flow like a fluid. 
Viscosity and Temperature:
●     For liquids viscosity decreases with temperature
●     For gases viscosity increases with temperature
Ideal Fluid:
Fluid which viscosity is zero. 
What is the Driving force for fluid flow:
Driving force for fluid flow is Energy per unit mass or total head
available at the point of location.

Viscosity:
Viscosity is measure of transport capacity of momentum disturbance within the fluid and it is acting as a messenger of momentum transport within the fluid.

Viscosity is caused by cohesive force between the molecules in liquids and by molecular collision in gas.
Density:
Density is measure of restoration capacity of momentum disturbance within the fluid.
Momentum diffusivity:
It is defined as relative importance of momentum transport within the fluid to the momentum stored by the fluid.
Viscous Flow:
Flow in which the frictional effects are significant are called viscous flow.
Laminar Flow:
The highly ordered fluid motion characterised by smooth layers of fluid. laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by smooth, constant fluid motion.
Turbulent Flow:
The highly disordered fluid motion that typically occurs at high velocity and is characterised by velocity fluctuations is called turbulent. turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce chaotic eddies, vortices and other flow instabilities.
Creeping Flow:
These are flow in which the reynolds number is very small.


Surface tension:
Liquid droplets behaves like small spherical balloons filled with the liquid and the surface of the liquid act like a stretched elastic membrane under tension. The pulling force that cause this tension acts parallel to the surface and is due to the attractive force between the molecules of the liquid. The magnitude of this force per unit length is called surface tension.
Capillary effects:
Capillary effect is the rise or fall of a liquid in a small diameter tube inserted into the liquid.
Streamline:
A streamline is a curve that is everywhere tangent to the instantaneous local velocity vectors.
Pathline:
It is actual path traveled by an individual fluid particle over some time period.
Bernoulli’s equation:
The sum of K.E, P.E,and flow energy of a fluid particle is constant along a streamline during steady flow.
Assumptions:
●     Steady state flow
●     Incompressible flow
●     Inviscid

Boundary Layer:
The region of the flow in which the effects of the viscous shearing forces caused by fluid viscosity are felt is called boundary region and that thickness is called boundary layer.
Hydrodynamic entrance length:
The region from the inlet of the pipe to the point at which boundary layer merges at the centreline is called hydrodynamic entrance region and length of this region is called hydrodynamic entrance length.
Turbulent Flow in Pipes:
Turbulent flow along a wall can be considered to consist of four regions, Characterised by the distance from the wall. The very thin layer next to the wall where viscous effect are dominated is the viscous sublayer. The velocity profile in this layer vary linearly and the flow is streamlined. Next to the viscous sublayer is the buffer layer in which turbulent effects are becoming significant but the flow is still dominating by viscous effects. Above the buffer layer is transition layer, also called the inertial sublayer in which the turbulent effect are much more significant but still not dominating. Above that is the outer layer in the remaining part of the flow in which turbulent effect dominate over molecular diffusion effects.
The Moody charts:
This is used to find friction factor
The friction factor in laminar flow is inversely proportional to Reynolds number and in fully developed turbulent pipe flow depends on the reynolds number and the relative roughness.



Types of control Valve:
Check Valve:
Check Valves are used when unidirectional flow is desired.They are automatic in operation and prevent flow in one direction but allow in the other.
Globe Valve:
The essential features of these valves is a globular body with a horizontal internal partition having a circular passageway. The glove valve is ordinarily used in smaller size. It is generally considered a poor practice to use a globe valve in a size larger than 2 inch. Globe valve are widely used for controlling flow. The fluid passes through a restricted opening and changes direction several times. As a result the pressure drop in this of valve is large.
Gate Valve:
Gate valves are universally used in larger size. Gate valve are not recommended for controlling flow and are usually left fully open or fully closed.
Types of Flowmeters:
A)   Variable Area Flowmeter
A variable area meter is a meter that measures fluid flow by allowing the
cross sectional area of the device to vary in response to the flow,
causing some measurable effect that indicates the rate.

Rotameter:
Some important features of Rotameters
●     Pressure drop is constant
●     These rotameters can be used for liquids and gases.
Rotameter consists of a gradually tapered tube, it is arranged in vertical position. The tube contains a float, which is used to indicate the flow of the fluid. This float will be suspended in the fluid while fluid flows from bottom of the tube to top portion. The entire fluid will flow through the annular space between the tube and float. The float is the measuring element. The tube is marked with the divisions and the reading of the meter is obtained from the scale reading at the reading edge of the float. Here to convert the reading to the flow rate a calibration sheet is needed.
Advantages:
●     Pressure drop is constant
●     No special fuel or external energy is required to pump
●     Very easy to construct and we can use a wide variety of materials to construct.
Disadvantages:
●     Due to its use of gravity, a rotameter must always be vertically oriented and right way up, with the fluid flowing upward.
●     Rotameters normally require the use of glass (or other transparent material), otherwise the user cannot see the float. This limits their use in many industries to benign fluids, such as water.
B) Constant Area flowmeters
1) Venturi meter
Working:
When a fluid, whose flow rate is to be determined, is passed through a Venturi meter, there is a drop in the pressure between the Inlet section and Cylindrical Throat of Venturi meter. The drop in pressure can be measured using a differential pressure measuring instrument. Since this differential pressure is in direct proportion to the flow rate as per the Bernoulli's Equation hence the differential pressure instrument can be configured to display flow rate instead of showing differential pressure.
Correction in Flowrate:Recalling the fact that the measured value of the piezometric pressure drop for a real fluid is always more due to friction than that assumed in case of an inviscid flow, a coefficient of discharge CD(always less than 1) has to be introduced to determine the actual flow rate.
Advantage of venturi meter:
●      The Venturi tubes can be used to handle fluids that contain slurries / sludges (for example: Sugar Cane Mill) , because these Venturi tubes contain no sharp corners and do not project into the fluid stream.
●      Negligible possibility of clogging with deposits or sludge.
●      A higher Coefficient of discharge obtainable.
●      Operational response can be designed with perfection.
●      Installation direction possibilities: Vertical / Horizontal / Inclined.
Limitations of venturi meter:
●      Venturi meters are expensive
●      Cannot be used in space constrained application because of their significant size.
●      Flow straighteners are required at the inlet and the outlet to attain streamline flow thereby increasing the cost and space for installation further.
●      Minimum line size for Installation of Venturi meter is limited to 1/2" (0.5 inch).

2) Orifice meter
Construction: An orifice meter provides a simpler and cheaper arrangement for the measurement of flow through a pipe. An orifice meter is essentially a thin circular plate with a sharp edged concentric circular hole in it.

Working:
When a liquid / gas, whose flow-rate is to be determined, is passed through an Orifice Meter, there is a drop in the pressure between the Inlet section and Outlet Section of Orifice Meter. This drop in pressure can be measured using a differential pressure measuring instrument. Since this differential pressure is in direct proportion to the flow-rate as per the Bernoulli's Equation hence the differential pressure instrument can be configured to display flow-rate instead of showing differential pressure.
Correction in Flow Rate:
Recalling the fact that the measured value of the piezometric pressure drop for a real fluid is always more due to friction than that assumed in case of an inviscid flow, a coefficient of velocity Cv(always less than 1) has to be introduced to determine the actual Flow Rate.
If a coefficient of contraction Cc is defined as, Cc= Ac /A0, where A0is the area of the orifice,Ac is the area of vena-contracta.
Vena contracta is the point in a fluid stream where the diameter of the stream is the least, and fluid velocity is at its maximum
Advantage of Orifice meter:
●     The Orifice meter is very cheap as compared to other types of flow meters.
●     Less space is required to Install and hence ideal for space constrained applications
●     Operational response can be designed with perfection.
●     Installation direction possibilities: Vertical / Horizontal / Inclined.
Limitations of Orifice meter:
●      Easily gets clogged due to impurities in gas or in unclear liquids
●      The minimum pressure that can be achieved for reading the flow is sometimes difficult to achieve due to limitations in the vena-contracta length for an Orifice Plate.
●      Unlike Venturi meter, downstream pressure cannot be recovered in Orifice Meters. Overall head loss is around 40% to 90% of the differential pressure .
●      Flow straighteners are required at the inlet and the outlet to attain streamline flow thereby increasing the cost and space for installation.
●      Orifice Plate can get easily corroded with time thereby entails an error.
●      Discharge Coefficient obtained is low.
Pitot Tube:
Pitot tube is used to measure point velocity or local velocity in a open channel or closed channel.

 Velocity Profiles:
●     Pseudoplastic shows flater profile compare to profile to newtonian
●     For extreme Pseudoplastic fluid the plug flow profile is obtained across the entire pipe
●     For dilatant fluid the profile is more pointed and narrower
●     For extreme dilatant fluid the velocity profile is linear function of radius.
●     For Bingham plastic fluid is parabolic near the surface and it is flat near the center

Differences between pipe and tube:
Pipes and tubes are specified in terms of their diameter and wall thickness.
Pipes:
 Heavy walled
 Relatively large in diameter
 comes in moderate lengths (20 to 40 ft)
 Threading is possible
 Pipe walls are rough
 Lengths of pipes are joined by screwed, flanged and welded
Tubes:
 Thin walled
 Less diameter
 available in the form of coils also, several hundred meters
 Cannot be threaded
 Tube walls are smooth
 These are joined by compression fittings, flare fittings, or soldered
Types of pumps:
A pump is a device that moves fluids by mechanical action. Pumps can be classified into three major groups according to the method they use to move the fluid: dynamics and displacement.
Positive displacement pumps:
A positive displacement pump makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe.

1)   Rotary positive displacement pumps
These pumps move fluid using a rotating mechanism that creates a vacuum that captures and draw in the liquid.

Rotary positive displacement pumps fall into three main types:
Gear pumps:
A simple type of rotary pump where the liquid is pushed between two gears
Screw pumps:
The shape of the internals of this pump is usually two screws turning against
each other to pump the liquid
Rotary vane pumps:
Similar to scroll compressors, these have a cylindrical rotor encased in
a similarly shaped housing. As the rotor orbits, the vanes trap fluid between the rotor and the casing, drawing the fluid through the pump.

2) Reciprocating pumps
Reciprocating pumps move the fluid using one or more oscillating pistons, plungers, or membranes (diaphragms), while valves restrict fluid motion to the desired direction.
Reciprocating pumps fall into three main types:
Plunger pumps:
A reciprocating plunger pushes the fluid through one or two open valves, closed by suction on the way back.
Diaphragm pumps:
Similar to plunger pumps, where the plunger pressurizes hydraulic oil which is used to flex a diaphragm in the pumping cylinder. Diaphragm valves are used to pump hazardous and toxic fluids.
Piston pumps displacement pumps:
Usually simple devices for pumping small amounts of liquid or gel manually. The common hand soap dispenser is such a pump.
Centrifugal Pumps:
A centrifugal pump is a pump consisting of an impeller fixed on a rotating shaft and enclosed in a casing.
Major components of centrifugal pumps
●      Volute casing
●      diffuser/guide vanes
●      rotors/impeller

Volute:
It is the gap between the casing and the impeller. In this volute kinetic energy is converted into pressure energy. As the cross section area increases, the volute reduces the velocity of the liquid and increases the pressure of the liquid.
Operating Principle:
As the fluid enters at the eye of the impeller it thrown radially outward via centrifugal force. As the fluid passes through impeller, the area of the flow increases which reduces the velocity of the fluid and consequently increase the pressure energy of the fluid. The fluid at the exit of the impeller enter into diffuser vanes which provide increasing area for the fluid to flow hence it convert more K. E. into pressure energy.
NPSH:
Net positive suction head is defined as minimum amount of head that must be available at the suction to avoid the cavitation.
There are two types of NPSH
●      NPSH available
●      NPSH required

All pump have different value of NPSH required and it can be obtained from the manufacturer.

(NPSH)R is defined as the minimum suction pressure required at the pump inlet for the pmp to avoid the cavitation.

To avoid the cavitation, the (NPSH)A should be greater than (NPSH)R.
Cavitation:
Cavitation takes place when the liquid get converted into vapour because of lower available head at suction of the pump in compare to the saturation or vapour pressure head of liquid at constant temperature.
As vapour forms enters in the impeller where the pressure is high, due to high pressure the vapour get implode/explode and high velocity jet is going to form which strike on the wall of the impeller, hence the impeller will get crode and unique sound is going to generate due to striking of the gas to the impeller.

To avoid the cavitation the total head available at the suction of the pump should larger than the saturation pressure head of that liquid at given temperature.
Methods to avoid cavitation:
●     By changing the location of the pump
●     By lowering the temperature of process fluid
●     By Pressurizing the vessel
●     By proper installation of the system or by reducing the number of fittings and joints
●     By reducing the speed of the impeller
Does excessive amount of air at the pump suction cause cavitation:
No. Air has nothing to do with it. Cavitation is caused by the collapsing (imploding) vapor (not air) bubbles. These bubbles are simply a vaporized liquid in the region where static pressure dropped below vapor pressure.
Priming:
When the pump is at stop condition or not in operation, then suction pipe, discharge pipe, casing should be filled with process fluid. If it is not so then those section is going to filled with air. Hence enough pressure will not able to create to suck the liquid from reservoir to impeller. To avoid this problem, these section should be filled with process fluid when the pump are not in use and that is called priming.
Pump Characteristics Curve:
It is the curve of head, Power and efficiency versus discharge at the constant speed of the Impeller.
Break horse power(BHP): It is power supplied to the pump.
Water horse power(WHP): it is power supplied to the fluid by the pump.
Impeller:
An impeller is a part of a pump or compressor that rotates at a high speed and acts as a proper to increase a fluid pressure and flow rate.
Types of impeller:
  1. Forward curved
  2. Backward curved
  3. Radial curved
Most widely used is backward curved impeller.
 Which type of pump used For highly viscous fluid ?
 Reciprocating pumps used for viscous fluid. Centrifugal pumps cannot be used for highly viscous fluid as increased viscosity will lead to the consumption of more power. The head and pump performance will decrease.
What is centrifugal pump?
A centrifugal pump is a pump consisting of an impeller fixed on a rotating shaft and enclosed in a casing.
What is positive displacement pump?
A positive displacement pump is a pump which makes a fluid move by trapping a fixed amount of fluid and forcing that fluid to discharge pipe.
MASS TRANSFER:
Those operation in which transfer of mass or mole take place from one point to another point in a phase or one phase to another phase due to chemical deriving force and results some changes occurs.
Chemical driving force can be concentration difference, Partial pressure difference or mol fraction difference.
Mass transfer occurs if resistance and driving force both exists.
Example:Drying of clothes under the sun, Lumps of sugar added into a cup of tea.
Industrial examples:
●     Separation of C02 from flue gas by absorption
●     Separation of ethanol from ethanol water mixture by distillation
●     Separation of toluene from toluene water mixture by extraction operation using benzene as solvent
Absorption:
Unit operation in which solute/pollutant of gas is removed from gas with the help of suitable liquid solvent on the basis of solubility.
Absorption/Stripping:
Unit operation in which solute/pollutant of liquid is removed from liquid with the help of suitable gas on the basis of solubility.
Humidification:
It is defined as transfer of liquid vapour into gas.
Humidity:
Humidity is defined as amount of water vapour in dry air.
Dehumidification:
The removal of vapour from a gas is called Dehumidification.

Distillation:
Distillation is the Process of separation of two or more component on the basis of relative volatility with the help of reboiler followed by condensation.
Drying:
Drying is removal of moisture from substance by supplying heat and making use of driving force for the mass transfer.
Adsorption:
Adsorption is surface phenomena in which solute transferred from fluid to surface of solid.
Adsorbate:
It is the transferring component or solute which has to be adsorbed on surface of solid.
Adsorbent:
The solid material on which the solute is going to transfer is called adsorbent.
Adsorber:
The equipment in which the adsorption is going to take place is called adsorber.
Leaching:
In leaching solute is transferred from solid phase to liquid phase.
Crystallization:
Process of removal of solute from a liquid solution by heating or cooling.

Molecular Diffusion:
The Molecular mass transfer is due to molecular diffusion by virtue of thermal energy of the molecules.
How to increase rate of molecular diffusion:
●     By increasing the temperature. K.E of the molecules get increases, that will increase the net movement, that increase the rate of molecular diffusion.
●     By lowering the pressure. The mean free path get decreases, that implies that number of collision get decreases which increase the net movement.
Convective mass transfer:
It is due to random and macroscopic or bulk movement of the molecules and it predominant in the turbulent flow.
Driving force for Mass Transfer:
In a single phase, the driving force for mass transfer is concentration difference while for more than one phase the driving force is chemical potential.
Chemical Potential:
The chemical potential of the i-component of a thermodynamic system in a given phase is a thermodynamic state function. It defines changes of the Gibbs energy and other thermodynamic potentials when the number of particles of a corresponding component is changed. Chemical potential of the ith-component of the system is the derivative of any thermodynamic potential divided by the quantity (or number of molecules) of this component when the values of the other thermodynamic variables, given a thermodynamic potential, are constant, e.g., μi= (G/ni)T,p,nj, where G is the Gibbs energy of the phase; ni, the number of moles of the i-component of the phase; T, the absolute temperature; p, pressure, and nj, the number of moles of all other components (j = i).


Fick’s First Law of diffusion:
The flux of any species i w.r.t. Molar average velocity is Proportional to concentration gradient in that direction.
Fick’s First Law of diffusion:
The rate of change of concentration at a point in a space is proportional to second derivative of concentration with space.
Interphase Mass transfer:
●     Transfer of solute from bulk of the gas to interphase
●     At the interphase the solute comes to the equilibrium with solute in the liquid phase and this assumed that at the interphase mas is going to transfer from gas phase to liquid phase those of suddenly reached to the equilibrium.
●     There is transfer of solute from interphase to bulk of liquid.
Film Theory:
●     Whitman in 1923
●     Steady state molecular diffusion
●     Concentration gradient lies in hypothetical film
Penetration Theory:
●     Given by Higbie in 1935.
●     Unsteady state mass transfer occurs at gas-liquid interphase and this is given by Fick’s 2nd Law.
●     Equilibrium is immediately attained at the interface.
●     Each liquid element is in contact with the gas at interface for same length of time.
Surface Renewable Theory:
●     Given by Bankward.
●     The liquid element at the gas-liquid interface are being randomly replaced by fresh liquid element.
●     Unsteady state mass transfer occurs at liquid-gas interface.
●     At any moment, each of the liquid element at gas-liquid interface has same probability of being replaced by fresh element.

Distillation:
Distillation is the Process of separation of two or more component on the basis of relative volatility with the help of reboiler followed by condensation.

We know that mixture is the combination of more than one substance which may or may not be in same phase. There are several techniques which can be used to separate the components of a mixture. The mixtures which have all components in same phase are called as homogenous mixture like water in ethanol. On the contrary, if components of a mixture are present in different phase, it is called as heterogeneous mixture. Distillation, chromatography, separating funnel are some common methods of separation of components of mixture. Out of all these methods, distillation is one of the most common methods of separation of components of a mixture. This method is mainly used for liquid mixtures which contains components with different boiling points. 

In the distillation of mixture of liquids, the liquid can be heated to convert them to gaseous state. Since they have different boiling points, they condense back at different rate and can easily separate. Similarly reverse process can be used to separate gases in which different gases liquefy at different rate by changing temperature or pressure. Distillation has several applications in different fields like it is widely used in the production of gasoline, distilled water, xylene, alcohol, paraffin and kerosene. Distillation can be different types such as fractional distillation, destructive distillation, vacuum distillation etc. 
Applications of distillation:
The application of distillation can roughly be divided in four groups: laboratory scale, industrial distillation, distillation of herbs for perfumery and medicinals (herbal distillate), and food processing.
Batch distillation:
Simple distillation is mainly used for the separation of liquid from a mixture. In this method, liquid is evaporated and condensed back to separate from its mixture. 
For example, if we want to separate to separate pure water from a salt solution, take a beaker of the salt solution and heat it to the boiling point. At boiling point, liquid will convert into vapour state and vapour will pass through condenser that is connected to another beaker or collector. By continuing this process, liquid or pure water will collect at another side of apparatus and salt will remain in beaker.
Example of Distillation:
Distillation is mainly used for the separation of
●      different fractions from petroleum products,
●      mixture of methanol and ethanol,
●      acetone and water,
●      impurities from alcohol,
●      Water from salt.
Fractional distillation:
Principle of Fractional Distillation:
The miscible liquids boil at different temperature and evaporate at different temperature. When the mixture is heated, the liquid with lower boiling point boils and turns into vapours. So the mixture is heated to a temperature at which one or two components of the mixture will vaporise. Fractional distillation involves repeated distillations and condensations.
Fractional Distillation Uses:
There are number of uses of fractional distillation.
●      One of the important use of using fractional distillation is to separate the crude oil into its various components such as gasoline, kerosene oil, diesel oil, paraffin wax, liberating oil.
●      Fractional distillation is also used for the purification of water. Water contains many dissolved impurities; these can be removed by this process.
●      It is also used for separating acetone and water.
●      Industrial use of fractional distillation is in petroleum refineries, chemical plants, natural gas processing and separation of pure gases from mixture of gases.
●      It has other industrial uses as it is used for purification and separation of many organic compounds.
Fractional Distillation of Crude Oil:
Fractional distillation is used to separate the various components of crude oil. Various components of crude oil such as gasoline, paraffin wax, lubricating oil, diesel oil, fuel oil, naphtha, kerosene are separated. Crude oil is heated and the mixture stars boiling. Hydrocarbon gases are introduced into the column. 
 
The temperature decreases in going up the fractionating column.  The hot vapours rise up in the fractionating column. Therefore vapours with higher boiling point condense in the lower part and the vapours of components with low boiling point condense at the top. The condensed vapours are removed from the sides of the column.









Tx-y Diagram:
●     Mixture of vapour and liquid remain at its saturation curve, it doesn’t leave saturation curve until complete vaporization or condensation occurs.
●     Liquid and vapour coexists.


Px-y Diagram:
In order to avoid getting confused about what you're looking at, think: what causes a liquid to vaporize? Two things should come to mind:
●      Increasing the temperature
●      Decreasing the pressure
Therefore, the region with the higher pressure is the liquid region, and that of lower pressure is vapor, as labeled.
The distillation operation can not carried out at high pressure. If pressure reach to the critical pressure of anyone component then the mixture will behave as non ideal because it is very difficult to differentiate between the liquid and vapour at critical pressure or above critical pressure and no further separation take place.

Some Important points:
●     When we provide heat to water, temperature increase from 50°C to 100°C, internal energy of water molecules increase. The water molecule at surface of water has tendency to leave but molecule within the bulk which is surrounded by 360° can’t leave bulk. At 100°C each and every molecules of water has tendency to leave the bulk. When we continue give heat, temperature will remain 100°C and phase change will occurs. Temperature will be still 100°C till complete vaporization happen. Now if we give more heat then it will increase the temperature of vapour.
●     For the mixture boiling point doesn’t exist, boiling range exists.
●     For mixture dew point doesn’t exists, dew point range exists.
●     Initial phase of vaporization is governed by more volatile component.
●     At a particular temperature, the component exerting more vapour pressure is more volatile      component.
●     During boiling more volatile component governed the process.
●     Less volatile component is easily condensable.
●     More volatile component are easily vaporizable.
●     During condensation less volatile component govern the process.


Flash or equilibrium Distillation:
●     Flash distillation is used often extensively in petroleum refinery in order to reduce the load on main fractionating column.
●     In Flash distillation, the petroleum fraction are heated in pipe still and heated fluid is flashed into vapour via pressure reducing valve.
●     After flashing vapour and liquid are separated to each other and each containing many components.
Flash or equilibrium distillation is generally used for the component which has very large difference in boiling point or have large relative volatility.
The equilibrium composition only depends upon temperature and pressure and it remain as it no matter even if we change the feed composition.
Vacuum Distillation:
Vacuum distillation method is mainly used in refineries. It involves expanding oil to produce high surface area that facilitates the vaporous extraction of water and other contaminants.  The distillation includes heating, vaporization, condensation and cooling of vapors. It separates all the components of a liquid mixture with the help of partial vaporization. It results the separation of vapor and liquid residue. 
In this process, the more volatile components like water vaporized and less volatile components remain in the oil. The water vapors can be condensed and back to liquid state. Various properties of components of mixture and efficiency of the distillation process will determine the completeness of separation of components.

Steam Distillation:
distillation of a liquid in a current of steam, used especially to purify liquids that are not very volatile and are immiscible with water.


Azeotropic distillation:
Azeotropes are mixtures of two or more different liquids which can either have a higher boiling point than either of the components or they can have a lower boiling point. Unlike azeotropes, ideal solutions have uniform mixtures of components. Ideal solutions always follow Raoult’s law. 

Mixture of benzene and toluene is good example of ideal solution. Azeotropes do not follow Raoult’s law because during boiling, the ratio of component in solution and vapor is same. Azeotropic distillation can be defined as the technique of addition of another component to form a new low boiling point azeotropic solution such as benzene can be added to the solution of ethanol and water in azeotropic distillation. Let’s discuss the azeotropic distillation method.

Azeotropic Distillation Method:
 


The azeotropic distillation unit consists of a container to feed the azeotrope, decanter and steamer. For example; the mixture of acetic acid and water can be separate out with the addition of an ester like n-butyl acetate. Remember the boiling point of acetic acid is 118.1oC and water is 100oC. Addition of ester whose boiling point is 125oC forms a minimum-boiling azeotrope with water with boiling point 90.2oC. Hence azeotropic mixture will be distilled over as vapor and leave acetic acid at bottoms. The overhead vapor is condensed and collected in a decanter. 

Here it forms two insoluble layers in which the top layer contains pure butyl acetate with water, and a bottom layer contains pure water saturated with butyl acetate. The top layer is returned to the distillation column and bottom layer is sent to another column for the recovery of the ester by steam stripping. 



Extractive distillation:
A method of separating two components of very similar boiling point from a mixture. A third, miscible and high-boiling-point solvent is added to the mixture which causes a change in the volatilities of the components. These components are then vaporized by the application of heat and cooled by the action of cold water in a condenser.
Mccabe thiele method:
Assumptions:
●     Specific heat capacity of both the component must be same.
●     Only latent heat transport, no sensible heat transport.
This method uses the equilibrium curve diagram to determine the number of theoretical stages (trays) required to achieve a desired degree of separation. It is a simplified method of analysis making use of several assumptions, but nonetheless a very useful tool for the understanding of distillation operation.
The VLE data must be available at the operating pressure of the column.
In its essence, the method involves the plotting on the equilibrium diagram 3 straight lines: the rectifying section operating line (ROL), the feed line(also known as the q-line) and the stripping section operating line (SOL).
Each of these lines passes through the points representing the mole fractions of the more volatile component in the distillate, bottoms and feed (xD, xBand xF) respectively. These lines represent the relationship between the concentrations in the vapour phase (y) and the liquid phase (x).
The number of theoretical stages required for a given separation is then the number of triangles that can be drawn between these operating lines and the equilibrium curve. The last triangle on the diagram represents the reboiler.
To obtain the number of theoretical trays using the McCabe-Thiele Method, we shall used the "Parts-Whole Relationship": analysis is first carried out by partitioning the column into 3 sections: rectifying, feed and stripping sections as shown in left Figure below. These sections are then represented on the equilibrium curve for the binary mixture in question and re-combined to make a complete design, as shown in the Figure.
In the simplest case, the McCabe-Thiele Method to determine the number of theoretical stages follows the steps below:
  1. Analysis of the Rectifying section, and determine the ROL using xD and R
  2. Analysis of the Feed section, and determine the feed condition (q) 
  3. Determination of the feed line (q-line)using xFand q
  4. Locate the intersection point between ROL and q-line
  5. Analysis of the Stripping Section, and determine the SOL using (4) and xB
On the completed design (equilibrium diagram): The number of points on equilibrium curve = Number of theoretical trays + 1 Reboiler (last triangle).
●    Most reboilers are partial reboilers, that is they only vaporize part of the liquid in the column base. Partial reboilers also provide an ideal separation stage.
●    Only phase change occurs in total condenser, but phase change as well as separation occurs in partial condenser.
●    No heat loss, no heat gain. No heat of mixing.
●    As heat given to boiler is equal to heat taken from condenser.
●    Stream on the same side of the tray lies on the operating line.
Relative Volatility:
It is defined as concentration ratio of i to j in vapour phase to same ratio in the liquid phase. Relative volatility is a measure of the difference between the vapor pressure of the more volatile components of a liquid mixture and the vapor pressure of the less volatile components of the mixture.
The quantity α is unitless. When the volatilities of both key components are equal, it follows that α= 1 and separation of the two by distillation would be impossible under the given conditions. As the value of αincreases above 1, separation by distillation becomes progressively easier.

Variation of Relative Volatility with Column Pressure
In the case of Distillation column, Relative volatility is the main driving force. Relative volatility is strong function of temperature and as temperature increase, Relative Volatility increase.
As the column Pressure increase, Bubble point curve and Dew point curve come closer which in turn decreases the width of the tie line and in turn, it increase difficulty of separation.
Conclusion is increase in the column pressure, increase the difficulty of separation. That’s why Distillation column are always preferred to operate at atmospheric pressure or even at vacuum to enhance the ease of separation.

Some Points:
●    If relative volatility is very high, we need special refrigerator/coolant. In this case we use partial condenser instead of total condenser.
●    If we need product in the form of vapour then use partial condenser.
●    In case of non condensable component, use partial condenser.
Reflux Ratio:
It is defined as the number of moles feed back to column to the number of moles withdrawn.
Total Reflux ratio:
●     Slope of rectifying line merge with diagonal line.
●     Slope of striping line is 1, thus stripping line merge with diagonal line.
●     Feed line doesn’t exists, only point exists.
●     In this case we need equilibrium relationship to solve problems.
●     At total reflux condition, duty of reboiler is maximum, size of reboiler and condenser are maximum. Column diameter is maximum and the number of equilibrium stages desired for separation is minimum.



Minimum Reflux ratio:
The point where rectifying line, stripping line , feed line and equilibrium curve touch is known as pitch point.
●     In minimum reflux condition, reboiler duty decreases, diameter of column decreases, size decreases but number of theoretical trays increases.
Some Points:
●     As reflux ratio increase slope of rectifying line section increase and the rectifying operating line shift away from the equilibrium line.
●     Increase in reflux ratio, increase duty of condenser and reboiler, increasing the size of condenser and reboiler which increase column diameter.
●     As reflux increases, the number of equilibrium stages for separation decreases.
●     If reflux is cold, it will increase the mass transport at 1st tray. Cold liquid will cooled vapour steam and condense vapour, it will increase more volatile component in vapour stream. Initially flow rate of distillate decrease then it increase.
●     Cold reflux will act as same as that of maximum reflux.
●     Coold reflux will increase the duty of condenser which also increase the duty of reboiler and size of condenser and reboiler increases. Also it increase size of the column which decrease the number of tray to get same mass transport.
●     When vapour increase, it will make cold liquid to saturated liquid, because duty of condenser is fixed. So disturbance will come for a short time only.
Flooding:
The vapour velocity is more. It carries the liquid droplets with it. Which is known as entrainment. If this phenomena continue, a stage will come when the tray belonging to stripping section gets empty and liquid will transfer to rectifying section. Every tray of rectifying section holds more liquid than its capacity because of which condition of flood occurs. This is known as flooding.
To avoid flooding, decrease the reboiler duty which turn decrease the flow/generation of vapour in turn decrease the potential at trays which maintain the smooth runnability.
Wheeping:
If the vapour velocity is less than resistance offered by the vapour to the liquid to hold it on a tray is not enough and liquid gets come down through the holes which is known as wheeping.
Effect of pressure on distillation:
●     If pressure increase y decrease
●     If pressure increase, width of tie line decrease
●     As pressure decrease equilibrium curve shifted away from diagonal
●     As pressure decrease, number of equilibrium stages decreases
●     Pressure increases, relative volatility decreases and very high pressure relative volatility become unity.
Extraction
Extraction is a process of separating a solute from a solution via solvent on the basis of relative solubility.
●     Extraction is always an equilibrium phenomena.
●     Leaving streams are in equilibrium.
●     Only liquid-liquid-liquid mixture can be separated.
●     Minimum component id distillation is binary while trinary in extraction.
Why we use condenser in Distillation column?
Condenser is used to remove heat from column and condense vapour to liquid.
Why Reboiler?
It act as the pressure filler to column.
Why Partial reboiler not total reboiler?
It take less heat, Separation occurs, Purge capability, At initial more volatile component vaporized, less heat required to vaporize more volatile component, steam economy.
Raoult's Law:
Equilibrium Partial pressure of any species i in vapour phase or gas phase is proportional to mole fraction of that species in liquid phase and proportionality constant is vapour pressure in pure form at that temperature.

Absorption Factor:
It is defined as ratio of slope of operating lime to slope of equilibrium line.
●      A>>1, Effective separation
●      A=1, Limiting Separation
●      A<<1, No separation
Driving force is minimum at top of the tower and maximum at bottom of the tower.
Absorption is exothermic process, we decrease temperature from top to bottom of the tower.
Dalton's law:
Dalton's law states that the total vapor pressure is the sum of the vapor pressures of each individual component in the mixture.
Physical Meaning of NTU:
NTU is defined as ratio of actual change in composition(Y1-Y2) to the average mean driving force.
For desire separation(fixed value of Y1-Y2), if NTU increase it means average driving force is only a small fraction of actual desire change. That means larzer height of tower is required.
Absorption followed by chemical reaction in the liquid phase is generally used to completely removal of solute from gas mixture.
Why distillation, Why not adsorption or leaching:
In distillation the new phase generated is different from the original by phase, or heat content only. This heat can be removed or added by easy operations. But in case of adsorption or leaching the a foreign substance is introduced to separate the phases. The new phase generated using these processes is a new solution which in turn may be
separated using other separation methods unless the new solution is directly useful. This makes the distillation process to more economical.
Difference between partial condenser and total condenser:
In a total condenser, all of the vapor leaving the top of the column is condensed. Consequently, the composition of the vapor leaving the top tray y1 is the same as that of the liquid distillate product and reflux, xD.
In a Partial condenser, all of the vapor leaving the top of the column is Partially condensed. Consequently, the composition of the vapor leaving the top tray y1 is different from that of the liquid distillate product and reflux, xD.
A partial condenser functions as an equilibrium separation stage, so columns with a partial condenser effectively have an extra ideal stage.
If column Delta P decreases what happens to the purity:
Distillate Purity will increase and separation becomes more easier as driving force is going to increase if Pressure decrease and consequently relative volatility increase. 

When reflux ratio to the column is minimum, what will happen ?
When reflux ratio is minimum, Reboiler duty decrease, diameter of column decreases but number of theoretical trays increases.
What is dew point Temperature?
It is the temperature at which vapour is about to condense.
What is bubble point  Temperature?
It is the temperature at which liquid is about to vaporise.
What is Driving force for Evaporation?
The driving force for evaporation is the gradient of the water vapour pressure near the skin surface.
Dry Bulb Temperature:
The Dry Bulb Temperature refers basically to the ambient air temperature. It is called "Dry Bulb" because the air temperature is indicated by a thermometer not affected by the moisture of the air.
Wet Bulb Temperature:
The Wet Bulb temperature is the adiabatic saturation temperature. Wet Bulb temperature can be measured by using a thermometer with the bulb wrapped in wet muslin. The adiabatic evaporation of water from the thermometer bulb and the cooling effect is indicated by a "wet bulb temperature" lower than the "dry bulb temperature" in the air.
The rate of evaporation from the wet bandage on the bulb, and the temperature difference between the dry bulb and wet bulb, depends on the humidity of the air. The evaporation from the wet muslin is reduced when air contains more water vapor.
At 100% saturation :
Dry bulb temperature = wet bulb temperature = Dew point


HEAT TRANSFER:
Heat transfer:
Heat transfer is thermal energy in transit due to a spatial temperature difference.
Modes of heat transfer:
●    Conduction
●    Convection
●    radiation
Driving force for Heat Transfer:
Temperature gradient is the driving force for heat transfer.
Conduction Heat Transfer:
Conduction Heat transfer is the transfer of thermal energy between adjacent molecules in a substance due to temperature gradient. Conduction takes place in all forms of matter like solids,liquids, and gases.
In solids conduction heat transfer is due to combination of vibrations of molecules in the lattice and the energy transport by free electrons.
Fourier’s Law:
Heat flux is proportional to the temperature gradient.
q = − k ∇T
Thermal Conductivity:
Thermal conductivity (k) is the intrinsic property of a material which relates its ability to conduct heat. K is measure of propagation of thermal energy.
Effect of temperature on thermal conductivity
●     For Metals, K decrease with increasing temperature
●     For Nonmetals, K increase with increasing temperature
●     For Gases, K increase with increasing temperature
●     For Liquids, K decrease with increasing temperature except water
●     For alloy, value of K is less than that of pure metals
Factors affecting the thermal conductivity:
●     Chemical compositions
●     Temperature & Pressure(till critical)
●     Phase involved
●     Void fraction/porosity in solids
Thermal diffusivity:
It is defined as relative importance of transport capacity of thermal energy to storage capacity of thermal energy.

Convection:
Heat transfer by basic mode of conduction and advection. Advection refers transport due to bulk fluid motion.
The convection heat transfer mode is sustained both by random molecular motion and by the bulk motion of the fluid within the boundary layer. The contribution due to random molecular motion dominates near the surface where the fluid velocity is low.

Forced convection:
Forced convection when the flow is caused by external means such as by fan, a pump or atmospheric wind.
Free convection:
Free convection the flow is induced by buoyancy force, which are due to density difference caused by temperature variation in the fluid.
Nusselt number:
It is defined as dimensionless temperature gradient at wall.
Prandtl number:
It is defined as relative thickness of hydrodynamic boundary layer to thermal boundary layer or in other words, it is defined as relative importance of momentum diffusivity to thermal diffusivity.
Assumption involved in the derivation of LMTD:
●     Overall heat transfer coefficient is constant throughout the heat exchanger.
●     In case any fluid undergoes phase change, the phase change offers throughout the heat exchanger.
●     The specific heat and mass flow rate of each fluid is constant.
●     No heat loss to surrounding.
●     There is no conduction in the direction of flow neither in a fluid nor in the tube or shell wall.
Purpose of using buffle:
●     It is used to direct the shell side fluid.
●     It also provide support to the tubes.
●     It also increase the shell side heat transfer coefficient by reducing the distance between two adjacent baffles.
NTU:
NTU is a measure of effectiveness of heat exchanger.

Fins:
Fins are extended surface which is used to increase heat transfer rate due to increase in effective area.
Gray body:
The gray body is the body for which the monochromatic emissivity does not depends upon the wavelength.
Planck's Law:
It shows the relation between emissive power for black body with temperature and wavelength.
Reboiler:
Reboilers are heat exchangers typically used to provide heat to the bottom of industrial distillation columns. They boil the liquid from the bottom of a distillation column to generate vapors which are returned to the column to drive the distillation separation.
Types of Reboiler:
The most critical element of reboiler design is the selection of the proper type of reboiler for a specific service. Most reboilers are of the shell and tube heat exchanger type and normally steam is used as the heat source in such reboilers.
Commonly used heat exchanger type reboilers are:

Kettle Reboilers:
The layout of the kettle reboiler is illustrated schematically in Figure. Liquid flows from the column into a shell in which there is a horizontal tube bundle, boiling taking place from the outside this bundle. The vapor passes back to the column as shown. Kettle reboilers are widely used in the petroleum and chemical industries; their main problems are that of ensuring proper disentrainment of liquid from the outgoing vapor and the problem of the collection of scale and other solid materials in the tube bundle region over long periods of operation.
 
Vertical Thermosyphon Reboiler:
This type is illustrated in Figure. The liquid passes from the bottom of the tower into the reboiler, with the evaporation taking place inside the tubes. The two-phase mixture is discharged back into the tower, where the liquid settles back to the liquid pool and the vapor passes up the tower as shown. The heating fluid (typically condensing steam) is on the outside of the tubes. The vertical thermosyphon reboiler is less susceptible to fouling problems and in general has higher heat transfer coefficients than does the kettle reboiler. However, additional height is required in order to mount the reboiler.

Horizontal Thermosyphon Reboiler:
Here, the liquid from the column passes in cross flow over a tube bundle and the liquid-vapor mixture is returned to the column as shown. The heating fluid is inside the tubes. This design has the advantage of preserving the natural circulation concept while allowing a lower headroom than the vertical thermosyphon type.
Condenser:
Condenser, device for reducing a gas or vapour to a liquid. Condensers are employed in power plants to condense exhaust steam from turbines and in refrigeration plants to condense refrigerant vapours, such as ammonia and fluorinated hydrocarbons. The petroleum and chemical industries employ condensers for the condensation of hydrocarbons and other chemical vapours. In distilling operations, the device in which the vapour is transformed to a liquid state is called a condenser.
Air-Cooled Condenser:
Air-Cooled types are usually used in the residential and small offices applications. They are used in small capacity systems below 20 tons. The advantages of using this design include not having to do water piping, not necessary to have water disposal system, saving in water costs and not much scaling problems caused by the mineral content of the water. It is also easier to install and has lower initial cost.
Water-Cooled Condenser:
There are 3 types commonly being used. 
●     Shell and tube, 
●     Shell and coil,
●     Double tube. 
The most commonly used is the shell and tube type and are usually available from two tons up to couple of hundred tons. This design has lower power requirements per ton of refrigeration and the compressors can last longer compared to the air-cooled type. A water cooling tower is frequently used for higher capacity application.

Evaporative Condenser:
Evaporative type which is a combination of water and air-cooled.
Types of compressors:
Two principal methods are used to compress gases. The first method is to trap a volume of gas and displace it by the positive action of a piston or rotating member; we call these machines positive-displacement compressors. The second method uses dynamic compression; it is accomplished by the mechanical action of contoured blades, which impart velocity and hence pressure to the following gas.
Where does the head gets developed in a centrifugal compressors:
Head is developed in the compressors partially in the impeller itself and partially in the diffuser / volute.
Pressure ratio of a compressor:
Ration of discharge pressure to suction pressure is known as pressure ratio.
What sort of bearings are used for high speed compressors:
Hydrodynamic type bearing like sleeve or tilting pad bearings are generally used for compressors.

Heat exchanger:
Heat exchangers are devices used to transfer heat energy from one fluid to another.
Fouling:
Material deposits on the surfaces of the heat exchanger tubes may add more thermal resistances to heat transfer. Such deposits, which are detrimental to the heat exchange process, are known as fouling.

Evaporator:
Evaporation is the removal of solvent as vapor from a solution, slurry or suspension of solid in a liquid. Solvent is mainly water.
Types of Evaporator:
Evaporator consists of a heat exchanger for boiling the solution with special provisions for separation of liquid and vapor phases. Most of the industrial evaporators have tubular heating surfaces. The tubes may be horizontal or vertical, long or short; the liquid may be inside or outside the tubes.
Why Don't we use odd number of tube passes in Shell and Tube Heat Exchanger:
Odd numbers of tube passes have more complicated mechanical stresses, etc. An exception: 1-1 exchangers are sometimes used for vaporizers and condensers.
BLOWERS:
Blowers develop little higher pressure in comparison to fans. They are used for pressure below 1.65 Psi. The centrifugal blower produces energy in the air stream by the centrifugal force and a velocity to the gas by the blades. The scroll shaped volute diffuses the air and creates an increase in the static pressure by reducing the gas velocity.


THERMODYNAMICS:
Thermodynamics is a fundamental subjects that describes law’s of the governing occurrences of physical process associated with transfer or transformation of energy.
Zeroth Law of thermodynamics:
When two systems are each in thermal equilibrium with a third system, the first two systems are in thermal equilibrium with each other.
First Law of thermodynamics:
The first law of thermodynamic is basically the law of conservation of energy and joule’s has derived expression for the conservation of energy.
The Algebraic sum of net heat and work interaction within system and surrounding in thermodynamic cycle is zero.
Second Law of thermodynamics:
Heat does not flow spontaneously from a colder region to a hotter region, or, equivalently, heat at a given temperature cannot be converted entirely into work. Consequently, the entropy of a closed system, or heat energy per unit temperature, increases over time toward some maximum value. Thus, all closed systems tend toward an equilibrium state in which entropy is at a maximum and no energy is available to do useful work.
Second Law also said that energy has not only quantity it has also quality.
Third Law of thermodynamics:
The entropy of a pure crystalline substance at absolute zero temperature is zero. Because there is no uncertainty about the state of the molecules at that instant.
Thermodynamic properties:
Identifiable and observable characteristics nature of the system by which a system can be specify is called thermodynamic property.

There are two types of thermodynamic properties:
●     Extensive properties
●     Intensive properties
Extensive property:
It Is defined as one which depends on quantity of matter specified in the system.
Intensive property:
It is defined as one which does not depends on the quantity of matter present in the system.
Thermodynamic State:
The system is said to be state when following two condition to be satisfied
●     Properties should be uniform throughout the system(All intensive properties should be uniform throughout the system).
●     They should be invariant with time at least temporarily for a moment when the state of the system is defined.
Thermodynamic System:
●     Control mass system
●     Control volume system
In control mass system the mass of the system is fixed as well as identity is fixed. It is also called close system and it involves energy interaction but no mass interaction.
In the control volume system, the volume of the system is fixed and it involved mas as well as energy interaction and the boundary control volume is called control surface. It is also called open system.
Thermodynamic equilibrium:
For the system to be in thermodynamic equilibrium, the system has to be in thermal, chemical as well as mechanically equilibrium.
If the system is in thermodynamic equilibrium it means there is no driving force for the process to be happen hence that system can be considered as a state. It means all states are in thermodynamic equilibrium always.
Quasi-static process:
Almost stop process or infinitely slow process is said to be quasi-static process.
Concept of degree of freedom:
To define the system at any state large number of variable are available but out of those variables only some of them are sufficient to define the system completely and it is defined as minimum number of independent intensive variable which should be fixed in order to define the system completely.
Different form of energy:
There are two form of energy
●     Energy in transit( it means energy that can be transfer), eg, Heat and work.
●     Energy in store(energy which are stored in the system)
Some points regarding Heat and Work
●     Heat and Work both are free phenomena, it mean it has to cross the boundary.
●     Both are inexact differential, it means heat and work both are path function.

Types of work
●     Displacement work
●     Paddle work
●     Flow work
●     Shaft work
Displacement work: The displacement work is only associated with control mass system because in control mass system, mass is fixed but volume can be change.
Paddle wheel work:If stirred is going to rotate in a container filled with fluid then the temperature of fluid get increase because of mechanical work is done by the stirred on the system and that types of work is called paddle wheel work. No change in volume but there is work.
Shaft work:In open system the shaft has to rotate against the resisting torque and that work is called as shaft work.
Shaft work is associated with open system.
Flow work:The flow work is work required to maintain the flow. It is only associated with open system.
Enthalpy:
Enthalpy is defined as summation of internal energy and pressure into volume. Enthalpy is used for open as well as for closed system. In open system, PV is called flow work. in closed system, PV is only pressure into volume.

Thermodynamic process:
●     Isothermal Process
●     Adiabatic process
●     Isochoric Process
●     Isobaric process
●     Polytropic Process
Slope of adiabatic curve is more than an isothermal curve.
Adiabatic curve is much more stripper/vertical than the isothermal.
Throttling Process:
In throttling process, When a gas is allowed to flow through a porous plug/capillary tube/Partially open valve, there is a reduction in the pressure because of the resistance to flow.
The enthalpy remain constant during throttling process hence throttling process is called iso enthalpy process.
Joule’s and thomson effect:
●     At inversion point dT/dP=0
●     For an ideal gas dT/dP=0
 Application of throttling process:
●     In the refrigeration and air conditioning system to cool the gas.
●     To find out the dryness fraction of steam.
Free expansion:
●     w=0, Q=0, PdV can’t be zero
●     Free expansion is highly irreversible
●     Uf=Ui which implies Tf=Ti but it is not isothermal
●     n1=n2, P1V1=P2V2
Specific heat:
The specific heat is defined as amount of the heat supplied to the system to raise the temperature of unit mass of substance by unit degree centigrade.
Heat engine:
All device are not able to convert heat energy into work energy but there is a device which operate in cyclic manner called heat engine which able to convert some parts of heat energy into work and it store remaining energy in the form of internal energy then it transfer to the surrounding.
Thermal reservoir:
●     It is hypothetical body which relatively large thermal capacity.
●     Supply or absorbs infinite amount of heat without change in temperature.
●     The reservoir that supply energy in form of heat is called source or high temperature reservoir.
●     The reservoir that absorbs energy in form of heat is called sink or low temperature reservoir.
Properties of heat engines:
●     It operate in a cyclic manner
●     It receive energy in the form of heat from the source
●     It converts some parts of received heat into work
●     It reject remaining heat to sink
Internal Energy:
The sum of all microscopic form of energy is called internal energy.
Ideal solutions:
●     The average intermolecular forces of attraction and repulsion in the solution are unchanged on mixing the solution
●     The volume of the solution varies linearly with composition.
●     the total vapor pressure of the solution varies linearly with composition expressed as mole fraction


MECHANICAL OPERATIONS:
Mechanical operation is that unit operation in which we study about the force acting on the solids.
Rittinger’s Law(1867):
It states that work required for crushing is directly proportional to the new surface area created.
Kick’s Law(1885):
It states that work require for crushing a particle will be same for same reduction ratio irrespective of their initial size.
Bond’s Law(1952):
It states that work required to crushing a particle is directly proportional to the square root of surface area to volume ratio of product from a very large feed size.
Work index:
It is defined as the gross energy required in kwh/ton to reduce a very large feed to such a size that 80% of the product may pass through a 100 micrometer screen.
Suspension:
Random movement of solid particle in a Solid-liquid mixture.
Settling:
Vertically downward movement of solid particles in a Solid-liquid mixture.

Sedimentation:
Separation of fine size solids from S-L mixture by settling.
Drag force:
Force acting on a body opposite to the direction of flow is called drag force.
Terminal settling Velocity:
It is maximum attainable velocity by solid particles in a fluid at which force by solid particles become equal to resistive force.
Filtration:
It is defined as a unit operation of solid-liquid separation where we pass the slurry through a porous medium under the influence of pressure or vacuum where particulate undissolved suspended solid retain on the surface of the medium and liquid pass through it.
●     Deep bed filtration used for water purification.
●     Cross flow filtration used to concentrate the slurry.
●     Cake filtration used when solid concentration is high.
What is jigging and where it is used:
Jigging is a separation method in which the particle are separated by using the density difference between them. Usually it is used to separate metal slag form metals.

CHEMICAL TECHNOLOGY:
Crude Oil:Crude oil is a multicomponent mixture of hydrocarbons contain billions component and in distillation we get around 25 products.

Classification of crude oil:
●     Paraffinic crude oil 
●     Saturated(Olefinic) long chain hydrocarbons
●     Naphthene crude oil(Saturated ring compound )
●     Aromatic crude oil(unsaturated ring compound)

Products from Crude oil after distillation:
Refinery gas, Gasoline, naphtha, Aviation turbine fuel, Kerosene, Diesel, Gas oil, Lubricating Oil, Petroleum, Light fuel oil, Heavy fuel oil, Wax or Asphalt, Road making Bitumen, Residue
Flash Point/Fire point:
The minimum temperature at which an oil gives out sufficient vapours to form a flammable mixture with the air which catches fire.
If the flashes sustain for at least five seconds then it is known as fire point.
Cloud Point:
The temperature at which the oil become cloudy is known as cloud point of the oil.
Pour Point:
The temperature at which oil refuse to flow is called Pour point of the oil.
Octane Number:
Octane number is the characteristics properties of gasoline. It is defined as percentage by volume of isooctane in a mixture of iso-octane and n-heptane that have same knocking tendency as that of fuel. 

Cetane number:
Cetane number is the characteristics properties of diesel. It is defined as Percentage by volume of cetane in a mixture of cetane and methyl naphthalene which has same characteristics performance in the standard engine that of fuel.
Smoke Point:
Smoke point is characteristics properties of kerosene. It is the height of flame in mm without smoke formation when kerosene is burnt in a standard lamp under controlled condition.
Aniline Point:
It is the lowest temperature at which oil is completely miscible within equal volume of aniline. Aniline Point give qualitative analysis of the aromatic content.
Reid Vapor Pressure:
Reid vapor pressure (RVP)is a common measure of the volatility of gasoline. It is defined as the absolute vapor pressure exerted by a liquid at 37.8 °C (100 °F) as determined by the test method.
Anti-Knocking Agents:
Tetraethyllead, Alcohol,Toluene, Methylcyclopentadiene
Properties of Natural Gas:
Natural gas is a colourless, tasteless, odourless, and non-toxic gas. Because it is odourless, mercaptan is added to the natural gas, in very small amounts to give the gas a distinctive smell of rotten eggs. This strong smell can alert you of a potential gas leak.


Chemical Composition of Natural Gas:
Natural gas is primarily composed of methane, but also contains ethane, propane and heavier hydrocarbons. It also contains small amounts of nitrogen, carbon dioxide, hydrogen sulphide and trace amounts of water.
Chemical Composition of LPG:
LPG is composed mainly of propane and butane
Composition of water Gas:
It contain mainly CO and H2 in the ratio of 1:1
Composition of syngas:
It contain mainly CO and H2 in the ratio 1:2
Composition of producer gas:
It contain mainly CO and N2 in the ratio of 1:2
Cracking
Cracking is defined as conversion of higher boiling petroleum to lower boiling petroleum fraction under the effect of temperature and pressure. It is an endothermic process.
It is two types.1)Thermal cracking 2) Catalytic cracking