Perry’s Chemical Engineers’ Handbook Eighth Edition

Posted by admin on June 25, 2009 under Chemical Process Calculation | 10 Comments to Read

Electronic version of a well-known print handbook…This program is most useful for users who do most of their work in the field or on the road, where they would carry laptop computers but would not want to take books with them…One advantage of the software is the ability to print specific pages, allowing users to write notes on the pages without the guilt of defacing a book. Upper-division undergraduates and up. (Choice )

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Entropy Examples

Posted by admin on June 21, 2009 under Thermodynamics | Be the First to Comment

Some websites that discuss examples of entropy.

1. Examples of entropy changes – Examples of entropy changes
2. WikiAnswers – What is an example of entropy – Chemistry question: What is an example of entropy? Ice melting is a good example – energy is used to melt the ice but no work is done so it is sometimes called useless energy – check Wika Dictionary def.
3. Entropy – Examples of Entropy
4. GME: Generalized Entropy Methods Example – Generalized Entropy Methods Example
5. Entropy Usage Examples – entropy usage examples. Usage example using the word entropy.
6. Entropy example: Kilometer long jam for no real reason – Let us see what it says.
7. GME: Generalized Entropy Methods Example – By Shazam GME: Generalized Entropy Methods Example

Entropy – Second Law Of Thermodynamics

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Entropy is central to the. Second law of thermodynamics. The second law in conjunction with the. Fundamental thermodynamic relation. Places limits on a system’s ability to do.

Entropy is one of the three basic Thermodynamic potentials. Entropy is a measure of the uniformity of the distribution of energy. The thermodynamic entropy. , often simply called the entropy in the context of thermodynamics, can provide a measure of the amount of energy in a physical system that cannot be used to do work.

Entropy is not something that is fundamentally intuitive, but something that is fundamentally defined via an equation, via mathematics applied to physics. Remember in your various travails,that. Entropy is what the equations define it to be. There is no such thing as an “entropy”,without an equation that defines it. Entropy was born as a state variable in classical thermodynamics. But the advent of statisticalmechanics in the late 1800′s created a new look for entropy. It did not take long for claudeshannon to borrow the boltzmann-gibbs formulation of entropy, for use in his own work, inventingmuch of what we now call.

Entropy is to say that it is a measure of the “multiplicity” associated with the state of the objects. If a given state can be accomplished in many more ways, then it is more probabable than one which can be accomplished in only a few ways. “, throwing a seven is more probable than a two because you can produce seven in six different ways and there is only one way to produce a two. So seven has a higher multiplicity than a two, and we could say that a seven represents higher “disorder” or higher entropy. For a glass of water the number of molecules is astronomical. The jumble of ice chips may look more disordered in comparison to the glass of water which looks uniform and homogeneous. But the ice chips place limits on the number of ways the molecules can be arranged. The water molecules in the glass of water can be arranged in many more ways; they have greater “multiplicity” and therefore greater.

Refereces on What is Entropy?

1. What is Entropy? -
2. Entropy – Wikipedia, the free encyclopedia -
3. What is Entropy? – Brief and Straightforward Guide: What is Entropy?
4. What is Entropy? – Special Maths and Science Articles – What is Entropy?
5. What is Entropy? What is thermodynamic entropy? – The term entropy was first used by Rudolf Clausius to state the second law of thermodynamics. Though entropy is a simple term, many people find it difficult to understand its exact meaning. Let us see what is entropy, and its relation to second law of thermodynamics

Calculation Of Standard Heat Of Reaction

Posted by admin on June 18, 2009 under Chemical Process Calculation | Read the First Comment

Heat of reaction is easy to measure because it simply represents the amount of heat that is given off if the reactants are mixed together in a beaker and allowed to react freely without doing any useful work. The above definition for enthalpy and its physical significance allow the equation for î”. To be written in the particularly illuminating and instructive form. Both terms on the right-hand side represent heats of reaction but under different sets of circumstances.

Heat of reaction is negative then the reaction is exothermic, if it is posititve then the reaction is endothermic.

Heat of reaction is a difference between the intrinsic energy in the products of a chemical reaction and the intrinsic energy in the reactants, and it is either adsorbed or released during the course of the chemical reaction.

Heat of reaction is the heat liberated or absorbed when a chemical reaction takes place. Reaction liberates heat, temperature of the reaction mixture increases. Reaction absorbs heat, temperature of the reaction mixture decreases. The heat of reaction for a neutralisation reaction is known as the heat of neutralisation.

Heat of reaction is determined on-line for a simulated reaction with first order kinetics and for the hydrolysis of acetic anhydride.

Heat of reaction is substantially greater than the amount of sensible heat which would be absorbed by simply passing the materials through the fuel cell, a large amount of heat can be removed with a small amount of material, thus reducing the size of the fuel cell passages, and the size of the fuel cell, while maintaining optimum temperature conditions.

References – Calculation Of Standard Heat Of Reaction

1. Heat of Reaction of Hydrogen and Coal – From Industrial & Engineering Chemistry Process Design and Development (ACS Publications)
2. Calculating Heat of Reaction – Calculate HOR
3. Enthalpies of Reaction – Enthalpy of a Reaction

Calculation Of Absolute Humidity

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Absolute humidity is generally defined in chemical engineering as mass of water vapor per unit mass of dry air, also known as the mass mixing ratio (see below), which is much more rigorous for heat and mass balance calculations. Mass of water per unit volume as in the equation above would then be defined as. Bs 1339 (revised 2002) suggests avoiding the term “absolute humidity”. Most humidity charts are given in g/kg or kg/kg, but any mass units may be used. The engineering of physical and thermodynamic properties of gas-vapor mixtures is named.

-- Wikipedia

Facts about Absolute humidity

Absolute humidity is :

1. Never negative, but relative (to the dew point) it might if the air is cold and dry.
2. The weight of water vapor in a unit volume of air expressed, for example, as. Humidity mixing ratio is the weight of water vapor mixed with unit mass of dry air, usually expressed as grams per.
3. The mass of water vapor in a given volume of air (this measurement is not influenced by the mass of the air). Normally expressed in grams of water vapor per cubic meter of atmosphere at a specific temperature. The mass of water vapor in the atmosphere per unit of volume of space.
4. The actual mass of water vapor -. In si-units the absolute humidity may be expressed in kilograms of water vapor (kg). In imperial units the absolute humidity may be expressed in lbs of water vapor (lbs).

Absolute humidity Calculators

1. How do I convert relative humidity to absolute humidity? – How do I convert relative humidity to absolute humidity?
2. Humidity formulas – List of formula for humidity conversion
3. Temp, Humidity, Dew Point ONA – Dew Point Calculation
4. Calculate Humidity Online with Web HumiCalc: Thunder Scientific – Web HumiCalc automatically calculates humidity factors and does humidity conversions under different conditions after you enter variables. This is a free, online, limited version of Thunder Scientific’s desktop humidity calculation software.
5. Absolute Humidity Calculation – Software – absolute humidity calculation.
6. Humidity Calculator – Use radio button selectors to let readers calculate humidity.

Emissivity Values Definition and Coefficients

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The emissivity of a material is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature. It is a measure of a material’s ability to radiate absorbed energy. A true black body would have an e = 1 while any real object would have e < 1 . Emissivity is a dimensionless quantity (does not have units).

In general, the duller and blacker a material is, the closer its emissivity is to 1. The more reflective a material is, the lower its emissivity. Highly polished silver has an emissivity of about 0.02.

Emissivity depends on factors such as:

• Temperature
• Emission Angle
• Wavelength

A typical engineering assumption is to assume that a surface’s spectral emissivity and absorptivity do not depend on wavelength, so that the emissivity is a constant. This is known as the “grey body assumption”

When dealing with non-black surfaces, the deviations from ideal black body behavior are determined by both the geometrical structure and the chemical composition , and follow Kirchhoff’s law of thermal radiation : emissivity equals absorptivity (for an object in thermal equilibrium), so that an object that does not absorb all incident light will also emit less radiation than an ideal black body.

Emissivity Values – Emissivity Coefficients of some Materials

References on Emissivity Values Definition and Coefficients

1. Emissivity
2. Emissivity Coefficients

Systems of Units for Chemical Engineers

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Most engineering problems use one of three systems of units :

1. SI (Systeme Internationale, mks) – is commonly used by scientists. It is in everyday use in most of the world. The so-called “metric system” is a subset/variant of the SI system, which was officially standardized in 1960.
2. cgs – Engineering (American, English, fps) is the traditional system of the US and UK. Although the UK changed official systems in the 1970s, the US has not.
3. The vast majority of US industrial concerns still specify parts and equipment using these “Engineering” units.

Every system of units has a set of “basic units” for :

1. Absolute Temperature
2. And Amount Of Substance
3. Dimensions Of Mass
4. Electric Current
5. Length
6. Luminous Intensity
7. Time

derived units, which are special combinations of units or units used to describe combination dimensions (energy, force, volume, etc.) unit multiples, which are multiples or fractions of the basic units used for convenience (years instead of seconds, kilometers instead of meters, etc.). Often these are not “official” parts of the unit system (liters). Traditional unit systems were based on customary quantities (yard was distance from King’s thumb to his nose), but today all systems use basic units defined in terms of measurable physical constants. 1 meter is the distance equal to 1.65076373×106 wavelengths in vacuum of the radiation corresponding to the transition between two levels of the krypton 86 atom

SI System

Common derived units include:

The “liter” (cubic decimeter) is commonly used, although it hasn’t any “official” status.

A multiple system is used based on powers of 10: tera- (T) 1012, giga- (G) 109, mega- (M) 106, kilo- (k) 103, centi- (c) 10-2, milli- (m) 10-3, micro- (greek mu) 10-6, nano- (n) 10-9 pico- (p) 10-12.

cgs System

Other basic units and the multiple prefixes are the same as used in SI. Most of the derived units are the same, although

Engineering Units

with most others the same as SI. Multiples are a little tricky, and sort of fun, since they are based on tradition — yds, inches, miles, rods, acres, tons, and so on.

There are others that are used to varying degrees. Of particular interest are the energy units expressed in terms of heat, such as the BTU (British Thermal Unit): the heat required to raise the temperature of 1 lb of water by 1 degree Rankine.

These units have been standardized, since all English units such as the inch, pound, etc. are now officially defined in terms of SI units.

Reference: http://www.cbu.edu/~rprice/lectures/systems.html

Kirchhoff’s Law Of Thermal Radiation

Posted by admin on June 17, 2009 under Heat Transfer, Thermodynamics | Be the First to Comment

In thermodynamics , Kirchhoff’s law of thermal radiation, or Kirchhoff’s law for short, is a general statement equating emission and absorption in heated objects, proposed by Gustav Kirchhoff in 1859, following from general considerations of thermodynamic equilibrium and detailed balance .

An object at some non-zero temperature radiates electromagnetic energy . If it is a perfect black body , absorbing all light that strikes it, it radiates energy according to the black-body radiation formula. More generally, it is a “grey body” that radiates with some emissivity multiplied by the black-body formula.

Kirchhoff’s law states that:

At thermal equilibrium, the emissivity of a body (or surface) equals its absorptivity.

Here, the absorptivity (or absorbance) is the fraction of incident light (power) that is absorbed by the body/surface. In the most general form of the theorem, this power must be integrated over all wavelengths and angles. In some cases, however, emissivity and absorption may be defined to depend on wavelength and angle, as described below.

Corollary Of Kirchhoff’s Law

The emissivity cannot exceed one (because the absorptivity cannot, by conservation of energy ), so it is not possible to thermally radiate more energy than a black body, at equilibrium. In negative luminescence the angle and wavelength integrated absorption exceeds the material’s emission, however, such systems are powered by an external source and are therefore not in thermal equilibrium.

This theorem is sometimes informally stated as a poor reflector is a good emitter, and a good reflector is a poor emitter. It is why, for example, lightweight emergency thermal blankets are based on reflective metallic coatings : they lose little heat by radiation.

References on Kirchhoff’s law of thermal radiation

1. Evgeny Lifshitz and L. P. Pitaevskii, Statistical Physics: Part 2, 3rd edition (Elsevier, 1980).
2. F. Reif, Fundamentals of Statistical and Thermal Physics (McGraw-Hill: Boston, 1965).
3. Kirchhoff’S Law Of Thermal Radiation

Websites on Kirchhoff’s Law of Thermodynamics

1. Kirchhoff’s Laws Thermal Derived Circuits Thermodynamics – Kirchhoff’s Laws Thermal Derived Circuits Thermodynamics Economy.
2. Kirchhoff’S Law Of Thermal Radiation Articles In thermodynamics, Kirchhoff’s law – In thermodynamics, Kirchhoff’s law of thermal radiation, or Kirchhoff’s law for short, is …
3. Kirchhoff’s Law definition by Babylon’s free dictionary – Definition of Kirchoff Law

History Of Chemical Engineering

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Chemical engineering as a discipline is a little over one hundred years old. It grew out of mechanical engineering in the last part of the 19th century, because of a need for chemical processors. Before the Industrial Revolution (18th century), industrial chemicals were mainly produced through batch processing.

• Batch processing is similar to cooking. Individuals would mix ingredients into a vessel, heat or pressurize the mixture, test it, and purify it to get a salable product.
• Batch processes are still performed today on expensive products, such as perfumes, or pure maple syrups, where one can still turn a profit, despite batch methods being slow and inefficient.

Most chemicals today are produced through a continuous “assembly line” chemical process. The Industrial Revolution was when this shift from batch to continuous processing occurred.

Chemical Engineering Timeline

In 1824, French physicist Sadi Carnot , in his On the Motive Power of Fire was the first to study the thermodynamics of combustion reactions in steam engines .

In the 1850s, German physicist Rudolf Clausius began to apply the principles developed by Carnot to chemical systems at the atomic to molecular scale.

During the years 1873 to 1876 at Yale University , American mathematical physicist Josiah Willard Gibbs , the first to be awarded a Ph.D. in engineering in the U.S., in a series of three papers, developed a mathematical-based, graphical methodology, for the study of chemical systems using the thermodynamics of Clausius.

In 1882, German physicist Hermann von Helmholtz , published a founding thermodynamics paper, similar to Gibbs, but with more of an electro-chemical basis, in which he showed that measure of chemical affinity , i.e. the “force” of chemical reactions , is determined by the measure of the free energy of the reaction process. Following these early developments, the new science of chemical engineering began to develop.

The following timeline shows some of the key steps in the development of the science of chemical engineering:

References on History Of Chemical Engineering

1. History of Chemical Engineering
2. Chemical Engineering

Heat Transfer by Jack Holman

Posted by admin on under Heat Transfer | 7 Comments to Read

As one of the most popular heat transfer texts, Jack Holman’s HEAT TRANSFER is noted for its clarity, accessible approach, and inclusion of many examples and problem sets. The new Ninth Edition retains the straight-forward, to-the-point writing style while covering both analytical and empirical approaches to the subject.

Throughout the book, emphasis is placed on physical understanding while, at the same time, relying on meaningful experimental data in those situations that do not permit a simple analytical solution. New examples and templates provide students with updated resources for computer-numerical solutions.

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