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THERMODYNAMIC PROPERTIES
1. TEMPERATUREA temperature is a numerical measure of hot or cold. Its measurement is by detection of heat
radiation or particle velocity or kinetic energy, or by the bulk behavior of a thermometric
material. It may becalibrated in any of various temperature scales,Celsius, Fahrenheit, Kelvin,
etc. The fundamental physical definition of temperature is provided bythermodynamics.
A temperature is a numerical measure of hot or cold. Its measurement is by detection of heat
radiation or particle velocity or kinetic energy, or by the bulk behavior of a thermometric
material. It may becalibrated in any of various temperature scales,Celsius, Fahrenheit, Kelvin,
etc. The fundamental physical definition of temperature is provided bythermodynamics.
Temperature scales differ in two ways: the point chosen as zero degrees, and the magnitudes of
incremental units or degrees on the scale.
TheCelsius scale (C) is used for common temperature measurements in most of the world. It is
an empirical scale. It developed by a historical progress, which led to its zero point 0C being
defined by the freezing point of water, with additional degrees defined so that 100C was the
boiling point of water, both at sea-level atmospheric pressure. Because of the 100 degree
interval, it is called a centigrade scale. Since the standardization of the kelvin in the International
System of Units, it has subsequently been redefined in terms of the equivalent fixing points on
the Kelvin scale, and so that a temperature increment of one degree Celsius is the same as an
increment of one degree kelvin, though they differ by an additive offset of 273.15.
The United States commonly uses theFahrenheit scale, on which water freezes at 32 F and boils
at 212 F at sea-level atmospheric pressure.
Temperature is a measure of aquality of a state of a material[30]
The quality may be regarded as
a more abstract entity than any particular temperature scale that measures it, and is called hotness
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by some writers. The quality of hotness refers to the state of material only in a particular locality,
and in general, apart from bodies held in a steady state of thermodynamic equilibrium, hotness
varies from place to place. It is not necessarily the case that a material in a particular place is in a
state that is steady and nearly homogeneous enough to allow it to have a well-defined hotness or
temperature. Hotness may be represented abstractly as a one-dimensional manifold. Every valid
temperature scale has its own one-to-one map into the hotness manifold.[31][32]
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2. PRESUREPressure is a measure of the force exerted per unit area on the boundaries of a substance (or
system). It is caused by the collisions of the molecules of the substance with the boundaries of
the system. As molecules hit the walls, they exert forces that try to push the walls outward. The
forces resulting from all of these collisions cause the pressure exerted by a system on its
surroundings. Pressure is frequently measured in units of lbf/in2 (psi).
Pressure is force per unit area applied in a direction perpendicular to the surface of an object.
Pressure is measured in any unit of force divided by any unit of area. TheSI unit of pressure is
the newton per square metre, which is called the Pascal (Pa) after the seventeenth-century
philosopher and scientistBlaise Pascal.A pressure of 1 Pa is small; it approximately equals the
pressure exerted by a dollar bill resting flat on a table. Everyday pressures are often stated in
kilopascals (1 kPa = 1000 Pa).
Mathematically:
where:
is the pressure
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is thenormal force,
is the area of the surface on contact.
Pressure is ascalar quantity. It relates the vector surface element (a vector normal to the surface)
with the normal force acting on it. The pressure is the scalarproportionality constant that relates
the two normal vectors:
The SI unit for pressure is the Pascal (Pa), equal to one newton per square metre (N/m2 or
kgm1
s2
). This special name for the unit was added in 1971; before that, pressure in SI was
expressed simply as N/m2.
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3. DENSITYThe density of a substance is the total mass (m) of that substance divided by the total volume(V) occupied by that substance (mass per unit volume). It has units of pound-mass per cubic feet
(lbm/ft3). The density of a substance is the reciprocal of its specific volume (n).
The density, or more precisely, the volumetric mass density, of a substance is itsmassper unit
volume. The symbol most often used for density is (the lower case Greek letter rho).
Mathematically, density is defined as mass divided by volume:
where is the density, m is the mass, and V is the volume. In some cases (for instance, in the
United States oil and gas industry), density is loosely defined as its weight per unit volume
although this is scientifically inaccuratethis quantity is more properly calledspecific weight.
density
Common symbol(s):
SI unit: kg/m3
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HISTORY
In a well-known but probably apocryphal tale, Archimedes was given the task of determiningwhetherKing Hiero'sgoldsmith was embezzlinggold during the manufacture of a goldenwreath
dedicated to the gods and replacing it with another, cheaper alloy. Archimedes knew that the
irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily
and compared with the mass; but the king did not approve of this. Baffled, Archimedes is said to
have taken an immersion bath and observed from the rise of the water upon entering that he
could calculate the volume of the gold wreath through thedisplacement of the water. Upon this
discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!"
(! Greek "I have found it"). As a result, the term "eureka"entered common parlance and
is used today to indicate a moment of enlightenment.
The story first appeared in written form inVitruvius'books of architecture,two centuries after it
supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other
things that the method would have required precise measurements that would have been difficult
to make at the time.
From the equation for density (= m/ V), mass density has units of mass divided by volume. As
there are many units of mass and volume covering many different magnitudes there are a large
number of units for mass density in use. TheSI unit ofkilogrampercubic metre (kg/m3) and the
cgs unit of gramper cubic centimetre (g/cm3) are probably the most commonly used units for
density. (The cubic centimeter can be alternately called a milliliter or a cc.) 1,000 kg/m3equals
one g/cm3. In industry, other larger or smaller units of mass and or volume are often more
practical andUS customary units may be used. See below for a list of some of the most common
units of density.
Measurement of density
The density at all points of a homogeneous object equals its total mass divided by its total
volume. The mass is normally measured with a scale or balance;the volume may be measured
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directly (from the geometry of the object) or by the displacement of a fluid. To determine the
density of a liquid or a gas, ahydrometer or daisy meter may be used, respectively. Similarly,
hydrostatic weighing uses the displacement of water due to a submerged object to determine the
density of the object.
If the body is not homogeneous, then its density varies between different regions of the object. In
that case the density around any given location is determined by calculating the density of a
small volume around that location. In the limit of an infinitesimal volume the density of an
inhomogeneous object at a point becomes: (r) = dm/dV, where dV is an elementary volume at
position r. The mass of the body then can be expressed as
In contrast, the density of gases is strongly affected by pressure. The density of anideal gas is
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4. INTERNAL ENERGYInternal energy is defined as the energy associated with the random, disordered motion of
molecules. It is separated in scale from the macroscopic ordered energy associated with moving
objects; it refers to the invisible microscopic energy on the atomic and molecular scale. For
example, a room temperature glass of water sitting on a table has no apparent energy, either
potential orkinetic .But on the microscopic scale it is a seething mass of high speed molecules
traveling at hundreds of meters per second. If the water were tossed across the room, this
microscopic energy would not necessarily be changed when we superimpose an ordered large
scale motion on the water as a whole.
Uis the most common symbol used for internal energy.
The internal energy is the total energy contained by a thermodynamic system.It is the energy
needed to create the system but excludes the energy to displace the system's surroundings, any
energy associated with a move as a whole, or due to external force fields. Internal energy has two
major components,kinetic energy andpotential energy.The kinetic energy is due to the motion
of the system's particles (translations,rotations,vibrations), and the potential energy is associated
with the static rest mass energy of the constituents of matter, static electric energy of atoms
within molecules or crystals,and the static energy of chemical bonds.The internal energy of a
system can be changed by heating the system or by doing work on it;[1]
the first law of
thermodynamics states that the increase in internal energy is equal to the total heat added and
work done by the surroundings. If the system is isolated from its surroundings, its internal energy
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cannot change. For practical considerations in thermodynamics and engineering it is rarely
necessary or convenient to consider all energies belonging to the total intrinsic energy of a
sample system, such as the energy given by the equivalence of mass. Typically, descriptions only
include components relevant to the system under study. Thermodynamics is chiefly concerned
only with changes in the internal energy.
The internal energy is astate function of asystem,because its value depends only on the current
state of the system and not on the path taken or process undergone to arrive at this state. It is an
extensive quantity. The SI unit of energy is the joule (J). Some authors use a corresponding
intensive thermodynamic property called specific internal energy which is internal energy per
unit of mass (kilogram)of the system in question. The SI unit of specific internal energy is J/kg.
If intensive internal energy is expressed relative to units ofamount of substance (mol), then it isreferred to as molar internal energy and the unit is J/mol.
Internal Energy Example
When the sample of water and copper are both heated by 1c, the addition to the kinetic energy is
the same, since that is what temperature measures. But to achieve this increase for water, a much
larger proportional energy must be added to the potential energy portion of the internal energy.
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So the total energy required to increase the temperature of the water is much larger, i.e., its
specific heat is much larger.
5. ENTHALPYEnthalpy is a measure of the total energy of a thermodynamic system.It includes the
system'sinternal energy orthermodynamic potential (astate function), as well as itsvolume and
pressure (the energy required to "make room for it" by displacing its environment,which is an
extensive quantity). The unit of measurement for enthalpy in theInternational System of Units
(SI) is the joule, but other historical, conventional units are still in use, such as the British
thermal unit and thecalorie.
Formal definition
The enthalpy of a homogeneous system is defined as:
Where
His the enthalpy of the system
Uis theinternal energy of the system
pis thepressure of the system
Vis thevolume of the system.
The enthalpy is anextensive property.This means that, for homogeneous systems, the enthalpy
is proportional to the size of the system. It is convenient to introduce the specific enthalpy h
=H/mwhere mis the mass of the system, or the molar enthalpy Hm= H/n, where nis the number
of moles (h and Hm are intensive properties). For inhomogeneous systems the enthalpy is the
sum of the enthalpies of the composing subsystems
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where the label krefers to the various subsystems. In case of continuously varying p, T, and/or
composition the summation becomes an integral:
where is the density.
The enthalpy H(S,p) of homogeneous systems can be derived as a characteristic function of the
entropy Sand the pressure pas follows: we start from thefirst law of thermodynamics for closed
systems for an infinitesimal process
Here, Q is a small amount of heat added to the system and W a small amount of work
performed by the system. In a homogeneous system only reversible processes can take place so
the second law of thermodynamics gives Q = TdS with T the absolute temperature of the
system. Furthermore, if only pV work is done, W= pdV. As a result
Adding d(pV) to both sides of this expression gives
or
So
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Applications
In thermodynamics, one can calculate enthalpy by determining the requirements for creating a
system from "nothingness"; the mechanical work required, pV, differs based upon the constancy
of conditions present at the creation of thethermodynamic system.
Internal energy,U, must be supplied to remove particles from a surrounding in order to allow
space for the creation of a system, providing that environmental variables, such as pressure (p)
remain constant. This internal energy also includes the energy required for activation and the
breaking of bonded compounds into gaseous species.
This process is calculated within enthalpy calculations as U + pV, to label the amount of energy
or work required to "set aside space for" and "create" the system; describing the work done by
both the reaction or formation of systems, and the surroundings. For systems at constant
pressure, the change in enthalpy is the heat received by the system.
Therefore, the change in enthalpy can be devised or represented without the need for
compressive or expansive mechanics; for a simple system, with a constant number of particles,
the difference in enthalpy is the maximum amount of thermal energy derivable from a
thermodynamic process in which the pressure is held constant.
The term pV is the work required to displace the surrounding atmosphere in order to vacate the
space to be occupied by the system.
Heat of reaction
The total enthalpy of a system cannot be measured directly; the enthalpy change of a system is
measured instead. Enthalpy change is defined by the following equation:
where
is the "enthalpy change"
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is the final enthalpy of the system, expressed in joules. In a chemical reaction, is the
enthalpy of the products.
is the initial enthalpy of the system, expressed in joules. In a chemical reaction, is the
enthalpy of the reactants.
For an exothermic reaction at constant pressure, the system's change in enthalpy equals the
energy released in the reaction, including the energy retained in the system and lost through
expansion against its surroundings. In a similar manner, for an endothermic reaction, the
system's change in enthalpy is equal to the energy absorbed in the reaction, including the energy
lost by the system and gained from compression from its surroundings. A relatively easy way to
determine whether or not a reaction is exothermic or endothermic is to determine the sign of H.If H is positive, the reaction is endothermic, that is heat is absorbed by the system due to the
products of the reaction having a greater enthalpy than the reactants. On the other hand if H is
negative, the reaction is exothermic, that is the overall decrease in enthalpy is achieved by the
generation of heat.
Although enthalpy is commonly used in engineering and science, it is impossible to measure
directly, as enthalpy has no datum (reference point). Therefore enthalpy can only accurately be
used in aclosed system.However, few real-world applications exist in closed isolation, and it is
for this reason that two or more closed systems cannot correctly be compared using enthalpy as a
basis.
Specific enthalpy
As noted before, the specific enthalpy of a uniform system is defined as h = H/m where m is the
mass of the system. TheSI unit for specific enthalpy is joule per kilogram. It can be expressed in
other specific quantities by h = u + pv, where u is the specificinternal energy,p is the pressure,
and v is specific volume, which is equal to 1/, where is the density.
http://en.wikipedia.org/wiki/Exothermic_reactionhttp://en.wikipedia.org/wiki/Chemical_reactionhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Endothermichttp://en.wikipedia.org/wiki/Closed_systemhttp://en.wikipedia.org/wiki/SI_unithttp://en.wikipedia.org/wiki/Internal_energyhttp://en.wikipedia.org/wiki/Internal_energyhttp://en.wikipedia.org/wiki/SI_unithttp://en.wikipedia.org/wiki/Closed_systemhttp://en.wikipedia.org/wiki/Endothermichttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Chemical_reactionhttp://en.wikipedia.org/wiki/Exothermic_reaction -
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6. ENTROPYEntropy is a measure of the number of specific ways in which a system may be arranged,
often taken to be a measure of disorder, or a measure of progressing towards
thermodynamic equilibrium. The entropy of an isolated system never decreases, because
isolated systems spontaneously evolve towards thermodynamic equilibrium, which is the
state of maximum entropy.
Entropy was originally defined for athermodynamically reversible process as
where the entropy (S) is found from the uniform thermodynamic temperature (T) of a closed
system dividing an incremental reversible transfer of heat into that system (dQ). The above
definition is sometimes called the macroscopic definition of entropy because it can be used
without regard to any microscopic picture of the contents of a system. In thermodynamics,
entropy has been found to be more generally useful and it has several other formulations.
Entropy was discovered when it was noticed to be a quantity that behaves as a function of state.
Entropy is anextensive property,but it is often given as anintensive property of specific entropy
as entropy per unit mass or entropy per mole.
http://en.wikipedia.org/wiki/Reversible_process_%28thermodynamics%29http://en.wikipedia.org/wiki/Thermodynamic_temperaturehttp://en.wikipedia.org/wiki/Closed_systemhttp://en.wikipedia.org/wiki/Closed_systemhttp://en.wikipedia.org/wiki/Function_of_statehttp://en.wikipedia.org/wiki/Intensive_and_extensive_properties#Extensive_propertieshttp://en.wikipedia.org/wiki/Intensive_and_extensive_properties#Intensive_propertieshttp://en.wikipedia.org/wiki/Intensive_and_extensive_properties#Intensive_propertieshttp://en.wikipedia.org/wiki/Intensive_and_extensive_properties#Extensive_propertieshttp://en.wikipedia.org/wiki/Function_of_statehttp://en.wikipedia.org/wiki/Closed_systemhttp://en.wikipedia.org/wiki/Closed_systemhttp://en.wikipedia.org/wiki/Thermodynamic_temperaturehttp://en.wikipedia.org/wiki/Reversible_process_%28thermodynamics%29 -
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7. COFFICIENT OF VISCOSITY
The viscosity of afluid is a measure of its resistance to gradual deformation byshear stress or
tensile stress. For liquids, it corresponds to the informal notion of "thickness". For example,
honey has a higher viscosity thanwater.
Viscosity is due tofrictionbetween neighboring parcels of the fluid that are moving at different
velocities.When fluid is forced through a tube, the fluid generally moves faster near the axis and
very slowly near the walls, therefore somestress (such as apressure difference between the two
ends of the tube) is needed to overcome the friction between layers and keep the fluid moving.
For the same velocity pattern, the stress required is proportional to the fluid's viscosity. A liquid'sviscosity depends on the size and shape of its particles and the attractions between the particles.
Shear viscosity
Laminar shear of fluid between two plates. Friction between the fluid and the moving boundaries
causes the fluid to shear. The force required for this action is a measure of the fluid's viscosity.
http://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Drag_%28physics%29http://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Tensile_stresshttp://en.wikipedia.org/wiki/Honeyhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Frictionhttp://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Stress_%28physics%29http://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/File:Laminar_shear.svghttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Stress_%28physics%29http://en.wikipedia.org/wiki/Velocityhttp://en.wikipedia.org/wiki/Frictionhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Honeyhttp://en.wikipedia.org/wiki/Tensile_stresshttp://en.wikipedia.org/wiki/Shear_stresshttp://en.wikipedia.org/wiki/Drag_%28physics%29http://en.wikipedia.org/wiki/Fluid -
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In a general parallel flow (such as could occur in a straight pipe), the shear stress is proportional
to the gradient of the velocity The shear viscosity of a fluid expresses its resistance to shearing
flows, where adjacent layers move parallel to each other with different speeds. It can be defined
through the idealized situation known as a Couette flow, where a layer of fluid is trapped
between two horizontal plates, one fixed and one moving horizontally at constant speed . (The
plates are assumed to be very large, so that one need not consider what happens near their
edges.)
The magnitude of this force is found to be proportional to the speed and the area of each
plate, and inversely proportional to their separation . That is,
http://en.wikipedia.org/wiki/Couette_flowhttp://en.wikipedia.org/wiki/File:Laminar_shear_flow.svghttp://en.wikipedia.org/wiki/File:Laminar_shear_flow.svghttp://en.wikipedia.org/wiki/File:Laminar_shear_flow.svghttp://en.wikipedia.org/wiki/File:Laminar_shear_flow.svghttp://en.wikipedia.org/wiki/File:Laminar_shear_flow.svghttp://en.wikipedia.org/wiki/File:Laminar_shear_flow.svghttp://en.wikipedia.org/wiki/File:Laminar_shear_flow.svghttp://en.wikipedia.org/wiki/Couette_flow -
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The measure of the viscosity of a fluid, equal to theforceper unit area required to maintain a
difference of velocity of one unit distance per unit time between two parallel planes in the fluid
that lie in the direction of flow and are separated by one unit distance: usually expressed in poise
or centipoise.
http://dictionary.reference.com/browse/forcehttp://dictionary.reference.com/browse/force -
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8. THERMAL CONDUCTIVITYInphysics,thermal conductivity (often denoted k, , or ) is theproperty of a material toconduct
heat.It is evaluated primarily in terms ofFourier's Law forheat conduction.
Heat transfer occurs at a higher rate across materials of high thermal conductivity than across
materials of low thermal conductivity. Correspondingly materials of high thermal conductivity
are widely used in heat sink applications and materials of low thermal conductivity are used as
thermal insulation.Thermal conductivity of materials is temperature dependent. The reciprocal
of thermal conductivity is called thermal resistivity.
Definitions
The reciprocal of thermal conductivity is thermal resistivity, usually expressed in kelvin-meters
per watt (KmW1
). For a given thickness of a material, that particular construction's thermal
resistance and the reciprocal property, thermal conductance, can be calculated. Unfortunately,
there are differing definitions for these terms.
Units of thermal conductivity
In SI units, thermal conductivity is measured in watts per meter kelvin (W/ (mK)). The
dimension of thermal conductivity is M1L
1T
3
1. These variables are (M) mass, (L) length, (T)
time, and () temperature. In Imperial units, thermal conductivity is measured in BTU/
(hrftF).
Other units which are closely related to the thermal conductivity are in common use in the
construction and textile industries. The construction industry makes use of units such as theR-
value (resistance) and theU-value (conductivity). Although related to the thermal conductivity of
a material used in an insulation product, R and U-values are dependent on the thickness of theproduct.
Likewise the textile industry has several units including the tog and the Klo which express
thermal resistance of a material in a way analogous to the R-values used in the construction
industry.
http://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/List_of_materials_propertieshttp://en.wikipedia.org/wiki/Heat_conductionhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Heat_conduction#Fourier.27s_lawhttp://en.wikipedia.org/wiki/Heat_conductionhttp://en.wikipedia.org/wiki/Heat_sinkhttp://en.wikipedia.org/wiki/Thermal_insulationhttp://en.wikipedia.org/wiki/International_System_of_Unitshttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Metrehttp://en.wikipedia.org/wiki/Kelvinhttp://en.wikipedia.org/wiki/Dimensional_analysishttp://en.wikipedia.org/wiki/Imperial_unitshttp://en.wikipedia.org/wiki/British_thermal_unithttp://en.wikipedia.org/wiki/Hourhttp://en.wikipedia.org/wiki/Foot_%28unit%29http://en.wikipedia.org/wiki/Fahrenheithttp://en.wikipedia.org/wiki/Fahrenheithttp://en.wikipedia.org/wiki/R-value_%28insulation%29http://en.wikipedia.org/wiki/R-value_%28insulation%29http://en.wikipedia.org/wiki/R-value_%28insulation%29#U-factorhttp://en.wikipedia.org/wiki/Tog_%28unit%29http://en.wikipedia.org/wiki/Thermal_Comforthttp://en.wikipedia.org/wiki/Thermal_Comforthttp://en.wikipedia.org/wiki/Tog_%28unit%29http://en.wikipedia.org/wiki/R-value_%28insulation%29#U-factorhttp://en.wikipedia.org/wiki/R-value_%28insulation%29http://en.wikipedia.org/wiki/R-value_%28insulation%29http://en.wikipedia.org/wiki/Fahrenheithttp://en.wikipedia.org/wiki/Foot_%28unit%29http://en.wikipedia.org/wiki/Hourhttp://en.wikipedia.org/wiki/British_thermal_unithttp://en.wikipedia.org/wiki/Imperial_unitshttp://en.wikipedia.org/wiki/Dimensional_analysishttp://en.wikipedia.org/wiki/Kelvinhttp://en.wikipedia.org/wiki/Metrehttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/International_System_of_Unitshttp://en.wikipedia.org/wiki/Thermal_insulationhttp://en.wikipedia.org/wiki/Heat_sinkhttp://en.wikipedia.org/wiki/Heat_conductionhttp://en.wikipedia.org/wiki/Heat_conduction#Fourier.27s_lawhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Heat_conductionhttp://en.wikipedia.org/wiki/List_of_materials_propertieshttp://en.wikipedia.org/wiki/Physics -
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Measurement
There are a number of ways to measure thermal conductivity. Each of these is suitable for a
limited range of materials, depending on the thermal properties and the medium temperature.
There is a distinction between steady-state and transient techniques.
In general, steady-state techniques are useful when the temperature of the material does not
change with time. This makes the signal analysis straightforward (steady state implies constant
signals). The disadvantage is that a well-engineered experimental setup is usually needed. The
Divided Bar (various types) is the most common device used for consolidated rock solids.