Thermodynamics is the branch of physics that deals with heat, work, and temperature, and their relation to energy, radiation, and physical properties of matter. It explains interactions of variables in an system in terms of conservation of energy. The four main concepts are heat, temperature, entropy, and the laws of thermodynamics. Heat is energy transferred between objects at different temperatures. Temperature is a measure of average kinetic energy. Entropy represents disorder and waste heat. The laws govern energy transfer and conservation.

1. Thermodynamic
The branch of physical science that deals with the relations between heat and other forms of
energy (such as mechanical, electrical, or chemical energy), and, by extension, of the
relationships between all forms of energy.
Heat
Thermodynamics, then, is concerned with several properties of matter; foremost among these is
heat. Heat is energy transferred between substances or systems due to a temperature difference
between them, according to Energy Education. As a form of energy, heat is conserved, i.e., it
cannot be created or destroyed. It can, however, be transferred from one place to another. Heat
can also be converted to and from other forms of energy. For example, a steam turbine can
convert heat to kinetic energy to run a generator that converts kinetic energy to electricalenergy.
A light bulb can convert this electrical energy to electromagnetic radiation (light), which, when
absorbed by a surface, is converted back into heat.
Temperature
The amount of heat transferred by a substance depends on the speed and number of atoms or
molecules in motion, according to Energy Education. The faster the atoms or molecules move,
the higher the temperature, and the more atoms or molecules that are in motion, the greater
the quantity of heat they transfer.
Temperature is "a measure of the average kinetic energy of the particles in a sample of matter,
expressed in terms of units or degrees designated on a standard scale," according to
the American Heritage Dictionary. The most commonly used temperature scale is Celsius, which
is based on the freezing and boiling points of water, assigning respective values of 0 degrees C
and 100 degrees C. The Fahrenheit scale is also based on the freezing and boiling points of water
which have assigned values of 32 F and 212 F, respectively.

2. Scientists worldwide, however, use the Kelvin (K with no degree sign) scale, named after William
Thomson, 1st Baron Kelvin, because it works in calculations. This scale uses the same increment
as the Celsius scale, i.e., a temperature change of 1 C is equal to 1 K. However, the Kelvin scale
starts at absolute zero, the temperature at which there is a total absence of heat energy and all
molecular motion stops. A temperature of 0 K is equal to minus 459.67 F or minus 273.15 C.
Specific heat
The amount of heat required to increase the temperature of a certain mass of a substance by a
certain amount is called specific heat, or specific heat capacity, according to Wolfram Research.
The conventional unit for this is calories per gramper kelvin. The calorie is defined as the amount
of heat energy required to raise the temperature of 1 gram of water at 4 C by 1 degree. The
specific heat of a metal depends almost entirely on the number of atoms in the sample, not its
mass. For instance, a kilogram of aluminum can absorb about seven times more heat than a
kilogram of lead. However, lead atoms can absorb only about 8 percent more heat than an equal
number of aluminum atoms. A given mass of water, however, can absorb nearly five times as
much heat as anequal mass of aluminum. The specificheat of agas is more complex and depends
on whether it is measured at constant pressure or constant volume.
Thermal conductivity
Thermal conductivity (k) is “the rate at which heat passes through a specifiedmaterial, expressed
as the amount of heat that flows per unit time through a unit area with a temperature gradient
of one degree per unit distance,” according to the Oxford Dictionary. The unit for k is watts (W)
per meter (m) per kelvin (K). Values of k for metals such as copper and silver are relatively high
at 401 and 428 W/m·K, respectively. This property makes these materials useful for automobile
radiators and cooling fins for computer chips because they can carry away heat quickly and
exchange it with the environment. The highest value of k for any natural substance is diamond at
2,200 W/m·K, Other materials are useful because they are extremely poor conductors of heat;
this property is referred to as thermal resistance, or R-value, which describes the rate at which
heat is transmitted through the material. These materials, such as rock wool, goose down and
Styrofoam, are used for insulation in exterior building walls, winter coats and thermal coffee
mugs. R-value is given in units of square feet times degrees Fahrenheit times hours per British
thermal unit (ft2·°F·h/Btu) for a 1-inch-thick slab.
Newton's Law of Cooling
In 1701, Sir Isaac Newton first stated his Law of Cooling in a short article titled "Scala graduum
Caloris" ("A Scale of the Degrees of Heat") in the Philosophical Transactions of the Royal Society.
Newton's statement of the law translates from the original Latin as, "the excess of the degrees
of the heat ... were in geometrical progression when the times are in an arithmetical
progression." Worcester Polytechnic Institute gives a more modern version of the law as "the
rate of change of temperature is proportional to the difference between the temperature of the
object and that of the surrounding environment." This results in an exponential decay in the
temperature difference. For example, if a warm object is placed in a cold bath, within a certain
length of time, the difference in their temperatures will decrease by half. Then in that same
length of time, the remaining difference will again decrease by half. This repeated halving of the
temperature difference will continue at equal time intervals until it becomes too small to
measure.

3. Heat transfer
Heat can be transferred from one body to another or between a body and the environment by
three different means: conduction, convection and radiation. Conduction is the transfer of
energy through a solid material. Conduction between bodies occurs when they are in direct
contact, and molecules transfer their energy across the interface. Convection is the transfer of
heat to or from a fluid medium. Molecules in a gas or liquid in contact with a solid body transmit
or absorb heat to or from that body and then move away, allowing other molecules to move into
place and repeat the process. Efficiency can be improved by increasing the surface area to be
heated or cooled, as with a radiator, and by forcing the fluid to move over the surface, as with a
fan.Radiation is the emission of electromagnetic (EM) energy, particularly infrared photons that
carry heat energy. All matter emits and absorbs some EM radiation, the net amount of which
determines whether this causes a loss or gain in heat.
The Carnot cycle
In 1824, Nicolas Léonard Sadi Carnot proposed a model for a heat engine based on what has
come to be known as the Carnot cycle. The cycle exploits the relationships among pressure,
volume and temperature of gasses and how an input of energy can change form and do work
outside the system.Compressing a gas increases its temperature so it becomes hotter than its
environment. Heat can then be removed from the hot gas using a heat exchanger. Then, allowing
it to expand causes it to cool. This is the basic principle behind heat pumps used for heating, air
conditioning and refrigeration.Conversely, heating a gas increases its pressure, causing it to
expand. The expansive pressure can then be used to drive a piston, thus converting heat energy
into kinetic energy. This is the basic principle behind heat engines.
Entropy
All thermodynamic systems generate waste heat. This waste results in an increase in entropy,
which for a closed system is "a quantitative measure of the amount of thermal energy not
available to do work," according to the American Heritage Dictionary. Entropy in any closed
system always increases; it never decreases. Additionally, moving parts produce waste heat due
to friction, and radiative heat inevitably leaks from the system. This makes so-called perpetual
motion machines impossible. Siabal Mitra, a professor of physics at Missouri State University,
explains,"You cannot build an engine that is 100 percent efficient, which means you cannot build
a perpetual motion machine. However, there are a lot of folks out there who still don't believe it,
and there are people who are still trying to build perpetual motion machines."Entropy is also
defined as "a measure of the disorder or randomness in a closed system," which also inexorably
increases. You can mix hot and cold water, but because a large cup of warm water is more
disordered than two smaller cups containing hot and cold water, you can never separate it back
into hot and cold without adding energy to the system. Put another way, you can’t unscramble
an egg or remove cream from your coffee. While some processes appear to be completely
reversible, in practice, none actually are. Entropy, therefore, provides us with an arrow of time:
forward is the direction of increasing entropy.
The four laws of thermodynamics
The fundamental principles of thermodynamics were originally expressed in three laws. Later, it
was determined that a more fundamental law had been neglected, apparently because it

4. hadseemed soobvious that it did not need to be stated explicitly. To form acomplete setof rules,
scientists decided this most fundamental law needed to be included. The problem, though, was
that the first three laws had already been established and were well known by their assigned
numbers. When faced with the prospect of renumbering the existing laws, which would cause
considerable confusion, or placing the pre-eminent law at the end of the list, which would make
no logical sense, a British physicist, Ralph H. Fowler, came up with an alternative that solved the
dilemma: he called the new law the “Zeroth Law.” In brief, these laws are:
The Zeroth Law states that if two bodies are in thermal equilibrium with some third body,
then they are also in equilibrium with each other. This establishes temperature as a fundamental
and measurable property of matter.
The First Law states that the total increase in the energy of a system is equal to the increase
in thermal energy plus the work done on the system. This states that heat is a formof energy and
is therefore subject to the principle of conservation.
The Second Law states that heat energy cannot be transferred from a body at a lower
temperature to a body at a higher temperature without the addition of energy. This is why it
costs money to run an air conditioner.
The Third Law states that the entropy of a pure crystal at absolute zero is zero. As explained
above, entropy is sometimes called "waste energy," i.e., energy that is unable to do work, and
sincethere is no heat energy whatsoever at absolute zero, there can be no wasteenergy. Entropy
is also a measure of the disorder in a system, and while a perfect crystal is by definition perfectly
ordered, any positive value of temperature means there is motion within the crystal, which
causes disorder. For these reasons, there can be no physical system with lower entropy, so
entropy always has a positive value.
The science of thermodynamics has been developed over centuries, and its principles apply to
nearly every device ever invented. Its importance in modern technology cannot be overstated.
Fluid
A substance that has no fixed shape and yields easily to external pressure; a gas or (especially)
a liquid. In other words In physics and engineering, fluid dynamics is a subdiscipline
of fluid mechanics that describes the flow of fluids (liquids and gases). It has several
subdisciplines, including aerodynamics (the study of air and other gases in motion) and
hydrodynamics (the study of liquids in motion).

5. The different types of fluids
1. Ideal fluid
2. Real fluid
3. Newtonian fluid
4. Non-Newtonian fluid, and
5. Ideal plastic fluid
1. Ideal Fluid:
A fluid which can not be compressed and have no viscosity falls in the category of ideal
fluid. Ideal fluid is not found in actual practice but it is an imaginary fluid because all the
fluid that exist in the environment have some viscosity. there in no ideal fluid in reality.
2. Real Fluid:
A fluid which has atleast some viscosity is called real fluid. Actually all the fluids existing
or present in the environment are called real fluids. for example water.
3. Newtonian Fluid:
If a real fluid obeys the Newton's law of viscosity (i.e the shear stress is directly
proportional to the shear strain) then it is known as the Newtonian fluid.
4. Non-Newtonian Fluid:
If real fluid does not obeys the Newton's law of viscosity then it is called Non-
Newtonian fluid.
5. Ideal Plastic Fluid:
A fluid having the value of shear stress more than the yield value and shear stress is
proportional to the shear strain (velocity gradient) is known as ideal plastic fluid.

6. Mach Number
In fluid dynamics, the Mach number (M or Ma) is a dimensionless quantity representing the
ratio of flow velocity past a boundary to the local speed of sound.
M is the Mach number,
u is the local flow velocity with respect to the boundaries (either internal, such as an
object immersed in the flow, or external, like a channel), and
c is the speed of sound in the medium.
By definition, Mach 1 is equal to the speed of sound. Mach 0.65 is 65% of the speed of sound
(subsonic), and Mach 1.35 is 35% faster than the speed of sound (supersonic).
The local speed of sound, and thereby the Mach number, depends on the condition of the
surrounding medium, in particular the temperature. The Mach number is primarily used to
determine the approximation with which a flow can be treated as an incompressible flow. The
medium can be a gas or a liquid. The boundary can be traveling in the medium, or it can be
stationary while the medium flows along it, or they can both be moving, with different velocities:
what matters is their relative velocity with respect to each other. The boundary can be the
boundary of an object immersed in the medium, or of a channel such as
a nozzle, diffusers or wind tunnels channeling the medium. As the Mach number is defined as the
ratio of two speeds, it is a dimensionless number. If M < 0.2–0.3 and the flow is quasi-
steady and isothermal, compressibility effects will be small and simplified incompressible flow
equations can be used. The Mach number is named after Austrian physicist and
philosopher Ernst Mach, and is a designation proposed by aeronautical engineer Jakob Ackeret.
As the Mach number is a dimensionless quantity rather than a unit of measure, with Mach, the
number comes after the unit; the second Mach number is "Mach 2" instead of "2 Mach" (or
Machs). This is somewhat reminiscent of the early modern ocean sounding unit "mark" (a
synonym for fathom), which was also unit-first, and may have influenced the use of the term
Mach. In the decade preceding faster-than-sound human flight, aeronautical engineers referred
to the speed of sound as Mach's number, never "Mach 1.

7. Closed and open system
Open and closed systems :
In social science. ... An open system is defined as a “system in exchange of matter with its
environment, presenting import and export, building-up and breaking-down of its material
components.”
Closed systems:
On the other hand, are held to be isolated from their environment.