Combined law of thermodynamics

Combined law of thermodynamics


In thermodynamics, the combined law of thermodynamics is simply a mathematical summation of the first law of thermodynamics and the second law of thermodynamics subsumed into a single concise mathematical statement as shown below:



Here, U is internal energy, T is temperature, S is entropy, p is pressure, and V is volume. In theoretical structure in addition to the obvious inclusion of the first two laws, the combined law incorporates the implications of the zeroth law, via temperature T, and the third law, through its use of free energy as related to the calculation of chemical affinities near absolute zero.

Third law of thermodynamics

Third law of thermodynamics


The third law of thermodynamics is an axiom of nature regarding entropy and the impossibility of reaching absolute zero of temperature. The most common enunciation of third law of thermodynamics is:“ As a system approaches absolute zero of temperature, all processes cease and the entropy of the system approaches a minimum value. ”


The essence of the postulate is that the entropy of the given system near absolute zero depends only on the temperature (i.e. tends to a constant independently of the other parameters).

History

The third law was developed by Walther Nernst, during the years 1906-1912, and is thus sometimes referred to as Nernst's theorem or Nernst's postulate. The third law of thermodynamics states that the entropy of a system at zero is a well-defined constant. This is because a system at zero temperature exists in its ground state, so that its entropy is determined only by the degeneracy of the ground state; or, it states that "it is impossible by any procedure, no matter how idealised, to reduce any system to the absolute zero of temperature in a finite number of operations".

An alternative version of the third law of thermodynamics as stated by Gilbert N. Lewis and Merle Randall in 1923:“ If the entropy of each element in some (perfect) crystalline state be taken as zero at the absolute zero of temperature, every substance has a finite positive entropy; but at the absolute zero of temperature the entropy may become zero, and does so become in the case of perfect crystalline substances. ”


This version states not only ΔS will reach zero at T = 0 K, but S itself will also reach zero.

Overview

In simple terms, the Third Law states that the entropy of a pure substance approaches zero as the absolute temperature approaches zero. This law provides an absolute reference point for the determination of entropy. The entropy determined relative to this point is the absolute entropy.

A special case of this is systems with a unique ground state, such as most crystal lattices. The entropy of a perfect crystal lattice as defined by Nernst's theorem is zero (if its ground state is singular and unique, whereby log(1) = 0). An example of a system which does not have a unique ground state is one containing half-integer spins, for which time-reversal symmetry gives two degenerate ground states. Of course, this entropy is generally considered to be negligible on a macroscopic scale. Additionally, other exotic systems are known that exhibit geometrical frustration, where the structure of the crystal lattice prevents the emergence of a unique ground state.

Real crystals with frozen defects obey this same law, so long as one considers a particular defect configuration to be fixed. The defects would not be present in thermal equilibrium, so if one considers a collection of different possible defects, the collection would have some entropy, but not actually have a temperature. Such considerations become more interesting and problematic in considering various forms of glass, since glasses have large collections of nearly degenerate states, in which they become trapped out of equilibrium.

Another application of the third law is with respect to the magnetic moments of a material. Paramagnetic materials (moments random) will order as T approaches 0 K. They may order in a ferromagnetic sense, with all moments parallel to each other, or they may order in an antiferromagnetic sense, with all moments antiparallel to each other.

Yet another application of the third law is the fact that at 0 K no solid solutions should exist. Phases in equilibrium at 0 K should either be pure elements or atomically ordered phases.

Second law of thermodynamics

Second law of thermodynamics


The second law of thermodynamics is an expression of the universal law of increasing entropy, stating that the entropy of an isolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium.

The second law traces its origin to French physicist Sadi Carnot's 1824 paper Reflections on the Motive Power of Fire, which presented the view that motive power (work) is due to the fall of caloric (heat) from a hot to cold body (working substance). In simple terms, the second law is an expression of the fact that over time, differences in temperature, pressure, and density tend to even out in a physical system that is isolated from the outside world. Entropy is a measure of how far along this evening-out process has progressed.

There are many versions of the second law, but they all have the same effect, which is to explain the phenomenon of irreversibility in nature.

Introduction

Versions of The Law

There are many statements of the second law which use different terms, but are all equivalent. [#wp-endnote_Fermi_ (Fermi, 1936)] Another statement by Clausius is:

Heat cannot of itself pass from a colder to a hotter body.

An equivalent statement by Lord Kelvin is:

A transformation whose only final result is to convert heat, extracted from a source at constant temperature, into work, is impossible.

The second law is only applicable to macroscopic systems. The second law is actually a statement about the probable behavior of an isolated system. As larger and larger systems are considered, the probability of the second law being practically true becomes more and more certain. For any system with a mass of more than a few picograms, the second law is true to within a few parts in a million.

The formulation of the second law that refers to entropy directly is due to Rudolf Clausius:
In an isolated system, a process can occur only if it increases the total entropy of the system.

Thus, the system can either stay the same, or undergo some physical process that increases entropy. (An exception to this rule is a reversible or "isentropic" process, such as frictionless adiabatic compression.) Processes that decrease total entropy of an isolated system do not occur. If a system is at equilibrium, by definition no spontaneous processes occur, and therefore the system is at maximum entropy.

Also due to Clausius is the simplest formulation of the second law, the heat formulation:
Heat cannot spontaneously flow from a material at lower temperature to a material at higher temperature.

Informally, "Heat doesn't flow from cold to hot (without work input)", which is obviously true from everyday experience. For example in a refrigerator, heat flows from cold to hot, but only when electrical energy is added. Note that from the mathematical definition of entropy, a process in which heat flows from cold to hot has decreasing entropy. This is allowable in a non-isolated system, however only if entropy is created elsewhere, such that the total entropy is constant or increasing, as required by the second law. For example, the electrical energy going into a refrigerator is converted to heat and goes out the back, representing a net increase in entropy.

A third formulation of the second law, the heat engine formulation, by Lord Kelvin, is:
It is impossible to convert heat completely into work.

That is, it is impossible to extract energy by heat from a high-temperature energy source and then convert all of the energy into work. At least some of the energy must be passed on to heat a low-temperature energy sink. Thus, a heat engine with 100% efficiency is thermodynamically impossible.

Microscopic systems

Thermodynamics is a theory of macroscopic systems at equilibrium and therefore the second law applies only to macroscopic systems with well-defined temperatures. No violation of the second law of thermodynamics has ever been observed in a macroscopic system. But on scales of a few atoms, the second law does not apply; for example, in a system of two molecules, it is possible for the slower-moving ("cold") molecule to transfer energy to the faster-moving ("hot") molecule. Such tiny systems are outside the domain of thermodynamics, but they can be investigated using statistical mechanics. For any isolated system with a mass of more than a few picograms, the second law is true to within a few parts in a million.

Energy dispersal

The second law of thermodynamics is an axiom of thermodynamics concerning heat, entropy, and the direction in which thermodynamic processes can occur. For example, the second law implies that heat does not spontaneously flow from a cold material to a hot material, but it allows heat to flow from a hot material to a cold material. Roughly speaking, the second law says that in an isolated system, concentrated energy disperses over time, and consequently less concentrated energy is available to do useful work. Energy dispersal also means that differences in temperature, pressure, and density even out. Again roughly speaking, thermodynamic entropy is a measure of energy dispersal, and so the second law is closely connected with the concept of entropy.

Overview

In a general sense, the second law says that temperature differences between systems in contact with each other tend to even out and that work can be obtained from these non-equilibrium differences, but that loss of heat occurs, in the form of entropy, when work is done.Pressure differences, density differences, and particularly temperature differences, all tend to equalize if given the opportunity. This means that an isolated system will eventually come to have a uniform temperature. A heat engine is a mechanical device that provides useful work from the difference in temperature of two bodies:

Heat engine diagram

During the 19th century, the second law was synthesized, essentially, by studying the dynamics of the Carnot heat engine in coordination with James Joule's Mechanical equivalent of heat experiments. Since any thermodynamic engine requires such a temperature difference, it follows that no useful work can be derived from an isolated system in equilibrium; there must always be an external energy source and a cold sink. By definition, perpetual motion machines of the second kind would have to violate the second law to function.

History

The first theory on the conversion of heat into mechanical work is due to Nicolas Léonard Sadi Carnot in 1824. He was the first to realize correctly that the efficiency of this conversion depends on the difference of temperature between an engine and its environment.

Recognizing the significance of James Prescott Joule's work on the conservation of energy, Rudolf Clausius was the first to formulate the second law in 1850, in this form: heat does not spontaneously flow from cold to hot bodies. While common knowledge now, this was contrary to the caloric theory of heat popular at the time, which considered heat as a liquid. From there he was able to infer the law of Sadi Carnot and the definition of entropy (1865).

Established in the 19th century, the Kelvin-Planck statement of the Second Law says, "It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work." This was shown to be equivalent to the statement of Clausius.

The Ergodic hypothesis is also important for the Boltzmann approach. It says that, over long periods of time, the time spent in some region of the phase space of microstates with the same energy is proportional to the volume of this region, i.e. that all accessible microstates are equally probable over long period of time. Equivalently, it says that time average and average over the statistical ensemble are the same.

Using quantum mechanics it has been shown that the local von Neumann entropy is at its maximum value with an extremely high probability, thus proving the second law. The result is valid for a large class of isolated quantum systems (e.g. a gas in a container). While the full system is pure and has therefore no entropy, the entanglement between gas and container gives rise to an increase of the local entropy of the gas. This result is one of the most important achievements of quantum thermodynamics.

First law of thermodynamics

The first law of thermodynamics


The internal energy is essentially defined by the first law of thermodynamics which states that energy is conserved:



where
ΔU is the change in internal energy of a system during a process.
Q is heat added to a system (measured in joules in SI); that is, a positive value for Q represents heat flow into a system while a negative value denotes heat flow out of a system.
W is the mechanical work done on a system (measured in joules in SI)
W' is energy added by all other processes

The first law may be equivalently in infinitesimal terms as:



where the terms now represent infinitesimal amounts of the respective quantities. The d before the internal energy function indicates that it is an exact differential. In other words it is a state function or a value which can be assigned to the system. On the other hand, the δ's before the other terms indicate that they describe increments of energy which are not state functions but rather they are processes by which the internal energy is changed.

From a microscopic point of view, the internal energy may be found in many different forms. For a gas it may consist almost entirely of the kinetic energy of the gas molecules. It may also consist of the potential energy of these molecules in a gravitational, electric, or magnetic field. For any material, solid, liquid or gaseous, it may also consist of the potential energy of attraction or repulsion between the individual molecules of the material.

Zeroth law of thermodynamics

The zeroth law of thermodynamics


The zeroth law of thermodynamics is a generalized statement about bodies in contact at thermal equilibrium and is the basis for the concept of temperature. The most common enunciation of the zeroth law of thermodynamics is:“ If two thermodynamic systems are in thermal equilibrium with a third, they are also in thermal equilibrium with each other. ”


In other words, the zeroth law says that if considered a mathematical binary relation, thermal equilibrium is transitive.

History

The term zeroth law was coined by Ralph H. Fowler. In many ways, the law is more fundamental than any of the others. However, the need to state it explicitly as a law was not perceived until the first third of the 20th century, long after the first three laws were already widely in use and named as such, hence the zero numbering. There is still some discussion about its status in relation to the other three laws.

Overview

A system in thermal equilibrium is a system whose macroscopic properties (like pressure, temperature, volume, etc.) are not changing in time. A hot cup of coffee sitting on a kitchen table is not at equilibrium with its surroundings because it is cooling off and decreasing in temperature. Once its temperature stops decreasing, it will be at room temperature, and it will be in thermal equilibrium with its surroundings.

Two systems are said to be in thermal equilibrium when 1) both of the systems are in a state of equilibrium, and 2) they remain so when they are brought into contact, where 'contact' is meant to imply the possibility of exchanging heat, but not work or particles. And more generally, two systems can be in thermal equilibrium without thermal contact if one can be certain that if they were thermally connected, their properties would not change in time.

Thus, thermal equilibrium is a relation between thermodynamical systems. Mathematically, the zeroth law expresses that this relation is an equivalence relation.

Internal energy

Internal energy


A characteristic property of the state of a thermodynamic system, introduced in the first law of thermodynamics. For a static, closed system (no bulk motion, no transfer of matter across its boundaries), the change in internal energy for a process is equal to the heat absorbed by the system from its surroundings minus the work done by the system on its surroundings. Only a change in internal energy can be measured, not its value for any single state. For a given process, the change in internal energy is fixed by the initial and final states and is independent of the path by which the change in state is accomplished.

Overview

Internal energy does not include the translational or rotational kinetic energy of a body as a whole. It also does not include the relativistic mass-energy equivalent E = mc2. It excludes any potential energy a body may have because of its location in external gravitational or electrostatic field, although the potential energy it has in a field due to an induced electric or magnetic dipole moment does count, as does the energy of deformation of solids (stress-strain).

The principle of equipartition of energy in classical statistical mechanics states that each molecular degree of freedom receives 1/2 kT of energy, a result which was modified when quantum mechanics explained certain anomalies; e.g., in the observed specific heats of crystals (when hν > kT). For monatomic helium and other noble gases, the internal energy consists only of the translational kinetic energy of the individual atoms. Monatomic particles, of course, do not (sensibly) rotate or vibrate, and are not electronically excited to higher energies except at very high temperatures.

From the standpoint of statistical mechanics, the internal energy is equal to the ensemble average of the total energy of the system.

SILICONE RUBBER EXTRA HIGH VOLTAGE INSULATORS | MATCHLESS DESIGN

SILICONE RUBBER EXTRA HIGH VOLTAGE INSULATORS | MATCHLESS DESIGN


The automatic microprocessor controlled crimping machine ensures uniform crimping without any stress concentration.



STATE-OF-THE-ART SUPERIORITY


Self - Cleaning Function
The specially designed Polymeric material used in making the housing of these insulators have a self-cleaning property by recovering the Hydrophobic characteristic due to migration of low moleculor weight / oligomeric PDMS, making it possible to maintain anti-tracking performance over an extended period.


Shatter Resistance
Composite Insulators are practically unbreakable.


Hydrophobicity


Surface hydrophobicity is maintained throughout the lifetime of the insulator. This is very important in polluted environment.




High Tensile Strength
The composite FRP pultruded rod has a very high mechanical strength. Our special crimping technique allows this high strength to be maintained.


Light Weight
In a typical comparison, the Composite Insulator weighs 10-35% of a Ceramic Insulator. This ensures easy installation, less manpower, low transportation and installation cost.

SILICONE RUBBER EXTRA HIGH VOLTAGE INSULATORS | TESTINGS

SILICONE RUBBER EXTRA HIGH VOLTAGE INSULATORS | TESTINGS


The different tests that are carried out in our Laboratory:

Mechanical & Physical Tests on our Silicone Compound
Tensile Strength
Elongation at Break
Tear Strength
Hardness
Specific Gravity
Study of process ability and Curing Characteristics at a particular temperature with the help of Oscillating Disc Rheometer
The report from this study helps us to know the processing characteristics and total spectrum of curing characteristics of our Silicone rubber compound, which in turn guide the production department to maintain consistent quality
Electrical Tests on our Silicone compound
Volume Resistivity
Break down Voltage
Tracking and Erosion Resistance Test
Resistance to Corona
Here a cured sheet from our Silicone compound is put in a cell under
corona generating electrodes, thereby exposing the Silicone rubber under corona. In this test the Silicone rubber is subjected to combined stress from electrons, ozone, UV and high temperature simultaneously.
UV Resistance Test (ASTM G53)
The facility for exposing the vulcanized sheet made from Silicone rubber to UV light (315 nm) and dry heat simulating normal day condition.
Test for Hydrophobicity
Sophisticated camera based instrument for measuring contact angle of liquids on solids. This instrument is interfaced to PC. Liquid drop shape analysis makes the instrument an error free. By measuring contact angle, we can assess the state of hydrophobicity character of Silicone rubber under various conditions.
Facilities available for carrying out different tests on FRP rod & Viscosity of Resin Mixture:
Measurement of viscosity of epoxy mixture in the impregnated bath is very important, as the viscosity of resin mixture will control the impregnation of the bunch of glass fibers. Our quality control department in their process control collects samples from resin bath time to time and checks the viscosity and gives their feedback to the production department to maintain the required viscosity.
Glass Content


Dye Penetration Test

It is one of the very basic tests to assess the quality of the FRP rod. We regularly carry out this test on our FRP rod.

Water Diffusion Test

This is a critical test for FRP rod. Though it is quite time consuming, we are carrying out this tests on our FRP rod on regular basis.

Besides the above-mentioned tests, we carry out the following tests regularly on our FRP rods:
Water absorption test
Specific gravity

All these are to convey that we understand the importance of role of composite insulators in power transmission and the importance of their long term uninterrupted performance. We believe a thorough testing of components and in-process can ensure the quality of this new generation product to give service for years together.

SILICONE RUBBER EXTRA HIGH VOLTAGE INSULATORS

SILICONE RUBBER EXTRA HIGH VOLTAGE INSULATORS


Electrical insulator is a very important component in the electric power systems such as sub-stations and distribution & transmission lines. In the early days, insulators were made of ceramic and glass materials. But in 1963, polymeric insulators were developed and its improvements in design and manufacturing in the recent years have made them attractive to utilities. It consists of a fiberglass core rod covered by weather-sheds or skirts of polymer such as silicone rubber, equipped with metal end fittings. It is also called composite insulators, which means made of at least two insulating parts – a core and housing equipped with end fittings. Polymeric insulators have many advantages over the ceramic and glass insulators such as good performance in contaminated environment, light weight, easy handling, maintenance free, and considerably low cost etc. Because of these properties it is gaining popularity worldwide and replacing the conventional ceramic and glass insulators.

This write-up gives the salient features considered by GOLDSTONE in developing SILICONE RUBBER POLYMER INSULATORS. Two aspects are to be essentially considered in the development, one is the material suiting to the requirements and the other is design aspect. The following few lines will briefly describe the important aspects considered.

Insulator Construction


Silicone Rubber

Silicon rubber insulators give excellent performance in harsh polluted environment which is explained briefly in subsequent lines. The pollution problem is mainly due to the deposition of the pollutants on the insulator i.e. on the porcelain surface in the case of disc insulator strings. The pollutants, in nature, are hydrophilic, and hence chances of dry band arcing is more which may lead to a flashover and it is not a desired characteristic. Due to this reason periodical cleaning of the insulator is imperative. In case of silicone rubber insulator also, the pollutants will get deposited on the weather shed. But the hydrophobicity transfer characteristics of silicon rubber will play a major role in such circumstances. This property is controlled by proper selection of base Silicone rubber, dosage and particle size of ATH and degree of cross linking of Silicone rubber of the weather shed. The Silicone rubber compound used by Goldstone is having all the required properties to combat with the harsh environment.

The pollutants, which are hydrophilic in nature, are converted into hydrophobic nature due to the hydrophobicity recovery characteristics of silicon rubber which gives a good performance in harsh polluted environments in comparison to porcelain insulators which do not have such characteristic. The silicon rubber compound used by Goldstone has been tested for hydrophobicity after exposing the material to corona, UV radiation, arcing etc., and the results are very good. Hence, in view of the material characteristics, the silicon rubber compound used in manufacturing the insulators, will give good performance in the polluted environments as mentioned above.

In addition to corona, UV radiation, the prime importance of silicon rubber material is to possess good resistance to tracking and erosion. The material used by Goldstone has been tested for tracking and erosion as per IEC: 587.

FRP Rods

The FRP rods used as the core material in the manufacture of silicon rubber insulators is manufactured by pultrusion method using boron free ECR grade glass fibres. The FRP rods being Produced by Goldstone are having all the required mechanical and electrical characteristics required for the long term uninterrupted performance of High Voltage Composite Insulators. The FRP rods have been tested for Brittle Fracture Test. The rods met the requirements and passed in the test without even slight sign of brittle fracture.

Metal Fittings

Both the socket and ball fittings are of forged fittings in High Voltage Insulators, whose tensile strength, elongation, impact strength, melting temperature etc. are best suited for silicon rubber insulators for erecting in harsh polluted environments. Sharp corners have been avoided so as to avoid corona.

Dimensions

To suit the interchangeability, the overall length of the insulator has been kept within the range of overall length of tension and suspension insulator strings. The metal end fittings have been designed for 20mm designation in case of tension insulators and 16mm designation in case of suspension insulators for Extra High Voltage Insulators.


Creepage Distance

With reference to IEC: 60815, a specific creepage distance of 31mm/kV has been specified for very highly polluted condition. The description of polluted condition for Very High Level as per IEC: 60815 pertains to areas subjected to conductive dusts and to industrial smoke producing particularly thick conductive deposits, areas very close to the coast and exposed to sea-spray or to very strong and polluting winds from the sea and desert areas characterized by no rain for long periods, exposed to strong winds carrying sand and salt, and subjected to regular condensation. Hence our Polymer Insulators have been made to design for a specific creepage distance of 31mm/kV for High Voltage Insulators.

Shed Profile

Even though the profile parameters for the shed as well as whole insulator specified in IEC: 60815 are meant for porcelain insulators, the same have been followed for silicone rubber insulators. All the profile parameters given in IEC: 60815 have been obtained in the design of insulators.

Sheath Thickness

A normal sheath thickness of 3mm over the FRP rod is being adopted for silicone rubber insulators. But in our design, we have designed a sheath thickness of 5mm so as to get long time with standability of the sheath towards the pollution thus leading for a longer span of life of the silicon rubber insulator.