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Welcome CHE-1
For the above list, it seams to me you have some interest in the area of thermodynamic. So, to suit your request, check the following sites please
Chemical Engineering Thermodynamics
Basic Chemical Thermodynamics
< http://orac.sunderland.ac.uk/~hs0bcl/td1.htm >
Thermodynamics Notes
< http://lorien.ncl.ac.uk/ming/Webnotes/Main/main.htm >
THERMODYNAMICS - Basic Cycles and Components < http://filebox.vt.edu/eng/mech/scott/index.html >
Discussion - What is Entropy
< http://www.experts-exchange.com/Miscellaneous/Math_Science/Q_20309979.html >
Thermodynamics Demonstrations
< http://info.phys.uvic.ca/dbr/resman/thermodynamics.html >
Encyclopedia of Thermodynamics
< http://therion.minpet.unibas.ch/minpet/groups/thermodict/ >
Chemical Engineering Thermodynamics
< http://flory.engr.utk.edu/che330/ >
Also, you can check the following thermodynamics Books
Also, you asked for convection term
So, consult those links
Basics of Heat Transfer
< http://www.engr.uga.edu/service/extension/publications/extengrhndbk/Insulation%20and%20Heat%20Transfer/insulation%20and%20heat%20transfer.pdf >
Convection
< http://www.ecr.mu.oz.au/~mbrear/436-351/Tutorial%20B%20-%20Convection.pdf >
Heat conduction
< http://www.jhu.edu/~virtlab/conduct/conduct.htm >
Correlations for Convective Heat Transfer
< http://chemengineer.about.com/science/chemengineer/library/weekly/aa020298.htm >
Fundamentals of Heat Transfer Tutorial
< http://ce597nwww.ecn.purdue.edu/CE597N/1997F/students/regan.j.young.1/project/ .>
ChemTech
Finally, your last question was
Why do we have to use reflux rate in Distillation column ?1
Answer
what would it the case if you do not have reflux at all, assume that you have feed , top product (D), and bottom product without recycling any of the top or bottom back to the column.
: think what will happen with puritym… and to conclude that
As the reflux ratio is increased, the gradient of operating line for the rectification section moves towards a maximum value of 1. Physically, what this means is that more and more liquid that is rich in the more volatile components are being recycled back into the column. Separation then becomes better and thus less trays are needed to achieve the same degree of separation. Minimum trays are required under total reflux conditions, i.e. there is no withdrawal of distillate.
On the other hand, as reflux is decreased, the operating line for the rectification section moves towards the equilibrium line. The ‘pinch’ between operating and equilibrium lines becomes more pronounced and more and more trays are required.This is easy to verify using the McCabe-Thiele method.
The limiting condition occurs at minimum reflux ration, when an infinite number of trays will be required to effect separation. Most columns are designed to operate between 1.2 to 1.5 times the minimum reflux ratio because this is approximately the region of minimum operating costs (more reflux means higher reboiler duty).
ChemTech
:p:p:p
For detail explaination, let us start with the term “ENTROPY”
In classical thermodynamics, energy is constant and entropy never decreases. But entropy may stay constant.
Entropy is a really hard concept to understand. It is not a “thing” such as mass or lenght which can be measured more directly. The definition of entropy is:
dS = dQ / T
Where S is the entropy, Q is the energy (heat) and T is the teperatue.
The second law of thermodynamics state that entropy must either increase or stay constant on every fenomena. If it stays constant, it means that the process is reversible.
Entropy is a “thing” that you calculate, but can’t measure directly, to tell you if a process is reversible or not.
If you are converting a type of energy A to another type B and the entropy increases in the process, then you can’t convert it ALL back from B to A. If the entropy remains constant, then you can convert A to B and B to A with no loss of energy.
For example, a simple IDEAL pendulum. It converts gravitational energy into kinetic energy and vice versa, with no loss. Its entropy remais constant.
A engine of a car converts chemical energy from the gas to mechanical energy. But the entropy increases in the process, so you can’t convert all the mechanical energy back into the chemical energy stored in the gas. You lost some energy in the form of heat and sound and other kinds of energy.
Entropy is often called “the arrow of time”. It shows us in which direction the time is flowing. If we take a physical non-reversible process and reverse the time, entropy would decrease. And according to thermodynamics this is impossible. So we know in which direction the time is flowing.
Let’s take some examples on time reversal. If you watch a tape of a pendulum moving, you can’t tell if the tape is moving forward or backwards. The movement of the pendulum is the same if you hit “fast forward” or “rewind”. So, when you reverse the time, the process suffers no change. That means its entropy is constant and the process is reversible.
If you watch a film of a bomb exploding, or an egg falling to the ground, or a tea cup braking, you can easily tell if the tape is moving forward or backwards. That is possible because in this process the entropy is changing, and the reversal of time is not possible. You will never see a broken egg becoming whole again, as in the reversed tape.
Another great example my teacher gave me once is about life on earth. People think that life on earth is possible because the sun is giving energy to it. But the truth is that the sun is giving “negative entropy” to the earth.
If the sun was really giving energy to the earth, then the earth would heat up and up and up, with no limit. The same amount of energy the earth receivers from the sun it gives back to the rest of the universe. So the temperature of the earth remains approximately the same.
Well, the amount of energy the sun gives to earth is the same the earth gives back to the universe, lets call it Q. So the entropy the sun is giving to the earth is Q/Ts (Ts is temperature of the sun) and the entropy earth is giving to the universe is Q/Te (Te is temperatue of the earth). Since Ts > Te, then Q/Te > Q/Ts.
So, the earth is receiving Q/Ts from the sun and is giving away Q/Te to the rest of the universe. So the change of entropy on the earth is Q/Ts - Q/Te < 0. So entropy on earth is decreasing.
Since life forms are more organized than a soup of atoms and molecules, to have life a planet must organize itself, ie, must decrease its entropy. That what is happening to the earth due to the sun. The sun is decreasing the entropy on earth.
Now you might ask “but how can entropy decrese on earth if it must always increase or remain constant?” The answer is that the entropy of the whole system (sun + earth + universe) is increasing. The entropy of parts of a system may decrese, since the total entropy of the system either increases or remains constant.
“Modified”
ChemTech
The Term of "convection
Heat energy transfers between a solid and a fluid when there is a temperature difference between the fluid and the solid. This is known as “convection heat transfer”. Generally, convection heat transfer cannot be ignored when there is a significant fluid motion around the solid
The temperature of the solid due to an external field such as fluid buoyancy can induce a fluid motion. This is known as “natural convection” and it is a strong function of the temperature difference between the solid and the fluid. Blowing air over the solid by using external devices such as fans and pumps can also generate a fluid motion. This is known as “forced convection”.
Fluid mechanics plays a major role in determining convection heat transfer. For each kind of convection heat transfer, the fluid flow can be either laminar or turbulent. Laminar flow generally occurs in relatively low velocities in a smooth laminar boundary layer over smooth small objects, while turbulent flow forms when the boundary layer is shedding or breaking due to higher velocities or rough geometries
ماشاء الله عليك أخوي chemtech
كفيت ووفيت :)
Fugacity (1) chemtech
Let use now move to the concept of Fugacity:
Formal definition
whenever we are dealing with the chemical potential of a component in a gas phase, or a component that MAY be in a gas phase , then we can use the fugacity to account for the difference between the chemical potential of interest µ(P,T), and the chemical potential of the pure substance at T,1 bar:
f(i) = exp{µ(t,p) - µ(t,1 bar, pure)]/RT}
qualitative concept:
Note that at a given T,there are only two variables in the above equation: f(i) and µ(T,P). Therefore, as, fi increases, so does µ. A high fugacity of water or oxygen means a high chemical potential of water or oxygen, respectively. A high chemical potential of water or oxygen indicates a “wet” or “oxidized” system, respectively.
BUT
what does it MEAN???
well, look at the most general equation for fugacity:
f(i) = j X(i) J P.
If a gas is ideal AND the mixture is ideal, then, f(i) = X(i) P, and fi is also equal to Pi .
So, if you ask:
“what is the fugacity, and how do I think about it”, ???
just think of it as a partial pressure: it is a strong function of the mole fraction of the component in the gas phase, and of the total pressure of the gas phase, just like a partial pressure; more precicely, remembering that chemical potential is a quantitative measure of the reactivity of a component in a phase, we can think of fiugacity as a measure of how much the chemical potential of the component in the gas deviates from the chemical potential of some reference, namely, the standard state, due to changes in P and/or the mole fraction of the component i.
ChemTech
D:D
Fugacity (2) chemtech
How is it different then, from partial pressure or total pressure?
Well, taking a pure gas first, we know that fi deviates from P by:
f(i) = J P.
WHY is this so, you ask?
Well, IT GOES BACK TO the fact that the rate of change of the chemical potential of a pure gas (i) with respect to changes in P (at a given T) is equal to the volume of the gas, V. For an ideal gas, V = RT/P; dµ = VdP, then becomes dµ = RT(dP/P), and integration yields µ(P) = µ(1 bar) + RtlnP, where the RtlnP term corrects the one-bar chemical potential up to the pressure of interest, P.
BUT
for a non-ideal gas, V has a different value from RT/P, so something other than RTlnP must be used as the “pressure correction” term. The solution to this problem, is, on the surface, a rather “unsatisfying” one: we use Rtlnf(i), instead of RTlnP. Now the pressure has been multiplied by the fugacity coefficient, which are tabulated, or are available as output from computer models, but which ultimately are based on experimental determinations made by by hard working experimental geochemists and others scientists by integrating the *difference* between the observed molar volume of the gas and the ideal molar volume (RT/P), with respect to pressure (dP) from one bar to the pressure of interest.
So, pressure is still pressure, and fugacity is not a “corrected pressure”.
Fugacity has meaning only when related to chemical potential, and the correction factor term RtlnF(i) corrects the chemical potential of gas for the fact that tabulated free energies of the gas are at a stated total pressure (usually one bar), and for the pure gas; because the chemical potentail is central to thermodynamics, fugacity becomes so also.
As µ(T,P, pure) = µ(T,1,pure) +Rtlnf(pure )i, we can, at a given T, use f(i)i as a proxy for the chemical potential, when we are thinking about how pressure will affect a reaction where we have a gas phase present (e.g., “ah yes, at T = 200 C, as we increase the fugacity of water in the gyp-anh-gas assemblage, we will definitely favor the stability of gypsum relative to anhydrite” ).
ChemTech
;););)