Name the types of trays used for distillation operation?(Sieve Trays,Bubble cap Trays,Valve trays uses advantages and disadvantages)

Name the types of trays used for distillation operation?



The terms "trays" and "plates" are used interchangeably. There are many types of tray designs, but the most common ones are:

Sieve Trays

Sieve trays are simply metal plates with holes in them. Vapour passes straight upward through the liquid on the plate. The arrangement, number and size of the holes are design parameters.

Because of their efficiency, wide operating range, ease of maintenance and cost factors, sieve and valve trays have replaced the once highly thought of bubble cap trays in many applications.

Typical Schamtics of Sieve Trays:

Bubble cap Trays

A bubble cap tray has riser or chimney fitted over each hole, and a cap that covers the riser. The cap is mounted so that there is a space between riser and cap to allow the passage of vapour. Vapour rises through the chimney and is directed downward by the cap, finally discharging through slots in the cap, and finally bubbling through the liquid on the tray.


Typical Schamtics of Bubble Cap Trays:

Valve trays

In valve trays, perforations are covered by liftable caps. Vapour flows lifts the caps, thus self creating a flow area for the passage of vapour. The lifting cap directs the vapour to flow horizontally into the liquid, thus providing better mixing than is possible in sieve trays.

Typical Schamtics of Valve Trays:
 
 

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Define boiling point elevation?(what is boiling point elevation)

 Define boiling point elevation?


When we add solute to the solvent boiling point of solution will be more than that of pure solvent.

The difference between the boiling points of solution to that of solvent is known as boiling point elevation.

Example;

Aqueous sugar solution boiling point is more than that of pure water.

Phenomena:

We know that vapor pressure is directly proportional to the surface of the free liquid surface. When we add solute to the solvent free liquid surface decreases and in turn vapor pressure also decreases. So boiling point increases with the addition of solute to the solvent.

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What are the disadvantages of a fixed tube sheet heat exchanger?

 What are the disadvantages of a fixed tube sheet heat exchanger?


Fixed type heat exchanger is one type of shell and tube heat exchanger tube sheet i.e. tube sheet is permanently welded or attached to the shell.

Disadvantages:

It is not possible to clean on the shell side of this exchanger.

It is not possible clean the tube bundle outside portion.

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What is meant by induced draft in cooling tower? (Diagram, Schematic,operation principle of cooling tower)

What is meant by induced draft in cooling tower?


Induced draft means we create (induce) some pressure draft (difference) using I.D Fans (Induced draft Fans) on the top Cooling tower.

Here we use a high efficiency fans to suck the air from the bottom of the cooling tower and it discharges air to atmosphere at high velocities. Typical Induced Draft cooling tower is as shown in the figure.

During this movement of air from bottom to the top of cooling tower water comes in contact with air in counter current direction and cooling of water takes place by means of evaporation cooling.

“By using any of the cooling towers we can cool the water up to its wet bulb temperature of the environment.”

Typical Induced draft cooling tower is as shown in the figure:

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Why low pressure steam is used in evaporators?(Steam Economy and steam consumption)

Why low pressure steam is used in evaporators?

For steam (Go through steam tables) as pressure increases Latent heat decreases and specific heat increases. Latent heat can be recovered and where as specific heat cannot be utilized fully. So this leads to increase in steam consumption and decrease in steam economy.

"So for more steam economy low pressure steam is desirable"

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What are the differences between condenser and a reboiler?(Diagrams of reboiler and condensor)

 What are the differences between condenser and a reboiler?


Common Things:

In both the cases phase change takes place and both operations require some media i.e. in condenser for cooling and in reboiler for heating.

Differences:

In condensers latent heat removed from the vapor using a coolant and phase change takes place from vapor to liquid

In reboilers latent heat provided for the liquid using a heating media and phase change takes place from liquid to vapor

Reboiler:
 
An example of Kettle type reboiler is as shown in the below figure: Stem is Heting media
 

Condenser:

 
Typical condenser used in laboratory is as shown in the below figure: With cooling water as coolant.
 

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IUPAC definition of self-diffusion coefficient(This is measured using diaphragm-cell technique8 or the pulsed-gradient spin echo (PGSE) NMR method)

self-diffusion coefficient


According to IUPAC definition, self-diffusion coefficient is the diffusion coefficient of species i when the chemical potential gradient equals zero. It is linked to the diffusion coefficient Di by the equation:

Here, ai is the activity of the species i in the solution and ci is the concentration of i. This term is commonly assumed to be equal to the tracer diffusion determined by watching the movement of an isotope in the material of interest.

This is measured using diaphragm-cell technique8 or the pulsed-gradient spin echo (PGSE) NMR method


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What is water cluster? What happens if the cluster size of water increases? What is Bucky water? Tools requires for Experimental observation of structure of water? Bulk water models? Classification of water models?

What is water cluster?


In chemistry a water cluster is a discrete hydrogen bonded assembly or cluster of molecules of water.

These clusters have been found experimentally or predicted in silico in various forms of water; in ice, in crystal lattices and in bulk liquid water, the simplest one being the water dimer (H2O)2 . Ongoing academic research is important because the realization that water manifests itself as clusters rather than an isotropic collection may help explain many anomalous water characteristics such as its highly unusual density temperature dependence.

Water clusters are also implicated in the stabilization of certain supramolecular structures. So little is understood about water clusters in bulk water that it is considered one of the unsolved problems in chemistry

What happens if the cluster size of water increases?


In silico (see: water models), cyclic water clusters (H2O)n are found with n = 3 to 60. With increasing cluster size the oxygen to oxygen distance is found to decrease which is attributed to so-called cooperative many-body interactions: due to a change in charge distribution the H-acceptor molecule becomes a better H-donor molecule with each expansion of the water assembly.

What is Bucky water?

Many isomeric forms seem to exist for the hexamer: from ring, book, bag, cage, to prism shape with nearly identical energy. Two cage-like isomers exist for heptamers and octamers are found either cyclic or in the shape of a cube. Even larger clusters are predicted: the fullerene-like cluster W28 is called bucky water and even for a 280 water molecule monster icosahedral network (with each water molecule coordinate to 4 others) there is found a local energy minimum.

Tools requires for Experimental observation of structure of water?

The experimental observation of water clusters requires sophisticated spectroscopic tools such as Far-infrared (FIR) vibration-rotation-tunneling (VRT) spectroscopy (a infrared spectroscopy technique).

When the water is part of a crystal structure as in a hydrate, x-ray diffraction can be used. In a recent study the conformation of a water heptamer was determined (cyclic twisted nonplanar) using this method

Bulk water models?

According to the so-called in silico method quantum cluster equilibrium (QCE) theory of liquids W8 clusters dominate the liquid water bulk phase followed by W5 and W6 clusters. In order to facilitate a water triple point the presence of a W24 cluster is invoked. In another model bulk water is built up from a mixture of hexamer and pentamer rings containing cavities capable of enclosing small solutes. In yet another model equilibrium exists between a cubic water octamer and two cyclic tetramers. However, in spite of much model making all models are unable to reproduce the experimentally observed density maximum.

Classification of water models?

These models use the approximations of molecular mechanics. Many different models have been proposed:

They can be classified by

o The number of points used to define the model (atoms plus dummy sites)

o Whether the structure is rigid or flexible

o Whether the model includes polarization effects.

o An alternative to the explicit water models is to use an implicit solvation model, also known as a continuum model.


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Archimedes Number (Ar) and its physical significance and application(rato of)

Archimedes Number (Ar)

This represents the ratio of buoyancy and inertial forces


Formula:

where:

• g = gravitational acceleration (9.81 m/s²),

• ρl = density of the fluid, kg / m3

• ρ = density of the body, kg / m3

• μ = dynamic viscosity, kg / sm

• L = characteristic length of body, m

Application:

Used when dealing with Gravitational settling of particle in fluid

Physical significance:

This represents the ratio of buoyancy and inertial forces, which stands in for the contribution of natural convection. When Ar >> 1, natural convection dominates and when Ar << 1, forced convection dominates.

When analyzing potentially mixed convection of a liquid, the Archimedes number parametrizes the relative strength of free and forced convection by representing the ratio of Grashof number and the square of Reynolds number.


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What is a fsecond order system/Process? and Second system transfer function

A second-order system is one whose output, y(t), is described by the solution of a second-order differential equation. For example, the following equation describes a second-order system:

If a0 # 0, then eqn. yields

where

Equation  is in the standard form of a second-order system where

T = the natural period of oscillation of the system
ζ = the damping factor, and
KP = the steady state, or static, or simply gain of the system.

The physical meaning of the parameters r and 5 will become clear in the next two sections, while KP as the same significance as for the first-order system.

If eqn. is in terms of deviation variables, the initial conditions are zero and the Laplace transformation of eqn.  yields the following standard transfer function for a second-order system;