Thermodynamics: Thermodynamics system (open, close, and isolated), Thermodynamic Properties: Definition and Units of -Temperature, Pressure (atmospheric, absolute and gauge). Volume. Internal energy, Enthalpy, Concept of Mechanical work, Thermodynamics Laws with example- Zeroth Law, First Law, Limitations of first law. Concept of heat Sink. Source, heat engine, heat pump, refrigeration engine. 2nd Law of Thermodynamics statements (Kelvin Plank, Claussius), Numerical on 2" law only. Measurement: Measurement of Temperature (Thermocouple - Type according to temperature range and application), Measurement of Pressure (Barometer, Bourdon pressure gauge, Simple U tube Manometer with numerical).

1. Basic Mechanical Engineering
By
Nitin G Shekapure
Unit V
Thermal Engineering (L29)
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2. Unit V
Thermal Engineering
Thermodynamics: Thermodynamics system (open, close, and isolated), Thermodynamic Properties:
Definition and Units of -Temperature, Pressure (atmospheric, absolute and gauge). Volume. Internal
energy, Enthalpy, Concept of Mechanical work, Thermodynamics Laws with example- Zeroth Law, First
Law, Limitations of first law. Concept of heat Sink. Source, heat engine, heat pump,
refrigeration engine. 2nd Law of Thermodynamics statements (Kelvin Plank, Claussius), Numerical
on 2" law only.
Measurement: Measurement of Temperature (Thermocouple - Type according to temperature range
and application), Measurement of Pressure (Barometer, Bourdon pressure gauge, Simple U tube
Manometer with numerical).
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3. Definition of Thermodynamics
Thermodynamics is a branch of science concerned with heat and temperature and their
relation to energy and work.
Thermodynamics is a branch of physics which deals with the energy and work of a
system.
thermo = heat (energy)
dynamics = movement, motion
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4. Thermodynamic System
The word system is very commonly used in thermodynamics;
let us know what it is.
Certain quantity of matter or the space which is under thermodynamic study or analysis
is called as system.
Let us say for example we are studying the engine of the vehicle, in this case engine is
called as the system. Similarly, the other examples of system can be complete
refrigerator, air-conditioner, washing machine, heat exchange, a utensil with hot water
etc.
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5. Suppose that we have to analyze the performance of engine in different conditions.
Here, we will feed the engine with fuels of different grades and load it with different
loads to find out its efficiency. We will also find its performance during idling,
acceleration, varying speed, slow speed and high speed. A thorough analysis of the
engine is carried out; hence it is called as system.
Thermodynamic System
The system is covered by the boundary and the area beyond the boundary is called as
universe or surroundings. The boundary of the system can be fixed or it can be movable.
Between the system and surrounding the exchange of mass or energy or both can
occur.
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6. Types of Thermodynamic Systems
There are three mains types of system: open system, closed system and isolated system.
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7. Open system
Types of Thermodynamic Systems
The system in which the transfer of mass as well as energy can take place across its boundary is called as
an open system.
Our previous example of engine is an open system. In this case we provide fuel to engine and it produces
power which is given out, thus there is exchange of mass as well as energy. The engine also emits heat
which is exchanged with the surroundings.
The other example of open system is boiling water in an open vessel, where transfer of heat as well as
mass in the form of steam takes place between the vessel and surrounding.
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8. Closed system
The system in which the transfer of energy takes place across its boundary with the surrounding, but no
transfer of mass takes place is called as closed system.
The closed system is fixed mass system. The fluid like air or gas being compressed in the piston and
cylinder arrangement is an example of the closed system.
In this case the mass of the gas remains constant but it can get heated or cooled.
Another example is the water being heated in the closed vessel, where water will get heated but its mass
will remain same.
Types of Thermodynamic Systems
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9. Isolated system
The system in which neither the transfer of mass nor that of energy takes place across its boundary with
the surroundings is called as isolated system.
For example if the piston and cylinder arrangement in which the fluid like air or gas is being compressed
or expanded is insulated it becomes isolated system. Here there will neither transfer of mass nor that of
energy.
Similarly hot water, coffee or tea kept in the thermos flask is closed system. However, if we pour this fluid
in a cup, it becomes an open system.
Types of Thermodynamic Systems
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10. Applications of Thermodynamics
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11. A quantity of the matter or part of the space which is under thermodynamic study is
called as system. There are three types of system: closed system, open system and
isolated system.
System
Surroundings or environment
Everything external to the matter or space, which is under thermodynamic study is
called surroundings or environment.
Boundary
The boundary that separates the system and surrounding is called as system boundary.
The system boundary may be fixed or moving.
Terminology used in Thermodynamics
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12. Terminology used in Thermodynamics
Heat
• Heat is energy transferred between substances or systems due to a temperature difference
between them.
• 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 electrical energy.
• A light bulb can convert this electrical energy to electromagnetic radiation (light), which, when
absorbed by a surface, is converted back into heat.
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13. Temperature
• Temperature is "a measure of the average kinetic energy of the particles in a sample of matter,
expressed in terms of units or degrees
• 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.
• The most commonly used temperature scale is Celsius, which is based on the freezing and boiling
points of water, assigning respective values of 0°C and 100°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.
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14. 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.
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 an equal mass of aluminum. The
specific heat of a gas is more complex and depends on whether it is measured at constant pressure or
constant volume.
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15. Thermal conductivity
Thermal conductivity (k) is “the rate at which heat passes through a specified material,
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”
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16. State of the system
The present status of the system described in terms of properties such as pressure,
temperature, and volume is called the state of system.
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.
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17. Heat transfer
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.
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18. N
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19. Entropy
Entropy (S) is defined as "a measure of the disorder or randomness in a closed system," which
also unavoidably 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.
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 (Long–lasting) motion
machines."
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20. Pressure
Continuous physical force exerted on or against an object by something in contact with it.
The pressure exerted by the earth's atmosphere at any given point,
being the product of the mass of the atmospheric column of the unit
area above the given point and of the gravitational acceleration at the given point.
Also called barometric pressure
Atmospheric Pressure
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21. Atmospheric Pressure
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22. The amount by which the pressure measured in a fluid exceeds that of the atmosphere
Gauge Pressure
Gauge pressure is the additional pressure in a system relative to atmospheric pressure. It is a
convenient pressure measurement for most practical applications.
Absolute Pressure a perfect vacuum as its reference. This type of pressure reference is the
gauge pressure of the media plus the pressure of the atmosphere. As locations change,
especially when dealing with elevation changes, the reference point can change because of
atmospheric pressure differences. Using an absolute pressure sensor eliminates the reference
to a varying atmospheric pressure and relying on a specific pressure range for reference.
Absolute Pressure
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23. N
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24. Quantity Unit Symbol
Fundamental
Length Meter m
Mass Kilogram kg
Time Second s
Electric Current Ampere A
Temperature Kelvin K
Amount of substance Mole Mol
Derived
Force Newton N (Kg m/s²)
Pressure Pascal Pa (N/m²)
Energy Joule J (N m)
Power Watt W (J /s)
Units (SI)
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25. Volume
Volume is the quantity of three-dimensional space enclosed by a closed surface, for example,
the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains.
The SI unit of volume is cubic meter (m³). It is also express in liters. 1m³ = 10³ Liter
Container is generally
understood to be capacity of
the container
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26. Energy and Forms of Energy
• Energy is the ability to do work.
• Everything that happens in the world uses energy!
• Most of the time we can’t see energy, but it is everywhere around us!
What is Energy?
• Is NEVER created or destroyed!
• Can only be STORED or TRANFERRED.
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27. Batteries store energy! This car uses a lot of energy
Even this sleeping puppy is using stored energy We get our energy from FOOD!
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28. How is all energy divided?
All Energy
Potential
Energy
Kinetic
Energy
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29. Potential Energy is…
• The energy stored in an object.
• "Potential" simply means the energy has the ability to do something
useful later on.N
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30. Examples of Potential Energy:
A stretched rubber band..
Water at the top of a waterfall..
Yo–Yo held in your hand..
A drawn Bow and Arrow…
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31. • The higher an object, the more potential energy.
• The more mass an object has, the more potential energy it has
Which object has more potential energy?
A
B
(A) The brick has more mass than the feather; therefore more potential energy!
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32. Changing an objects’ height can change its potential energy.
• If I want to drop an apple from the top of one of these three things,
where will be the most potential energy?
A
B
C
• The higher the object, the more potential energy!
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33. Potential Energy Converted to Kinetic Energy…
• When stored energy begins to move, the object now transfers from potential energy
into kinetic energy.
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34. Kinetic Energy Is…
• The energy of a moving object.
• "Kinetic" means movement!
• When stored energy is being used up, it is making things move or happen.
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35. • The faster the object moves, the more kinetic
energy is produced.
The greater the mass and speed of an object, the more kinetic
energy there will be.
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36. When these objects move at the same speed, which will
have more kinetic energy?
The truck has more mass;
therefore, more kinetic energy!
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37. N
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38. • All energy is divided into two types: potential and kinetic.
• Potential Energy: The energy stored in an object.
• Kinetic Energy: The energy of a moving object.
• Energy is never created or destroyed. It is always stored or transferred.
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39. The internal energy U of a system is
increased by the transfer of either heat or
work into the system.
Internal Energy
The internal energy of the system is the sum of the kinetic and potential energies of the
atoms and molecules making up the system.
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40. If A is in thermal equilibrium with B, and B is in thermal equilibrium with C, then C will be in
thermal equilibrium with A.
Zeroth Law of Thermodynamics
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41. When a body is brought into contact with another body that is at a different
temperature, heat is transferred from the body at higher temperature to the one at
lower temperature until both bodies attain the same temperature (thermal
equilibrium)
Zeroth Law of Thermodynamics
Observation
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42. The first law of thermodynamics is the application of the conservation of energy principle to
heat and thermodynamic processes:
This means that heat energy cannot be created or destroyed. It can, however, be transferred
from one location to another and converted to and from other forms of energy.
First Law of Thermodynamics
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43. First Law of Thermodynamics
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44. N
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45. A container has a sample of nitrogen gas and a tightly fitting movable piston that does
not allow any of the gas to escape. During a thermodynamics process, 200 joules of heat
enter the gas, and the gas does 300 joules of work in the process.
What was the change in internal energy of the gas during the process described above?
ΔU=Q+W ( start with the first law of thermodynamics)
ΔU=(+200 J) + (-300 J)
The heat Q will be a positive number if heat enters the gas, since it increases the internal energy of the gas.
we use is that the work is a positive number if work is done on the gas, since that adds energy to the gas.
But since in this problem work was done by the gas, we plug in a negative number for the work done,
since this subtracts energy from the gas.
ΔU=-100
Note: Since the internal energy of the gas decreases, the temperature must decrease as well.
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46. Example:
Four identical containers have equal amounts of helium gas that all start at the same initial
temperature. Containers of gas also have a tightly fitting movable piston that does not
allow any of the gas to escape. Each sample of gas is taken through a different process as
described below:
Sample 1: 500 J of heat exits the gas and the gas does 300 J of work
Sample 2: 500 J of heat enters the gas and the gas does 300 J of work
Sample 3: 500 J of heat exits the gas and 300 J of work is done on the gas
Sample 4: 500 J of heat enters the gas and 300 J of work is done on the gas
Sample 1 Sample 2 Sample 3 Sample 4
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47. Limitation of First Law of Thermodynamics
• A cup of hot coffee left in a cooler room eventually cools off. The reverse of this process- coffee
getting hotter as a result of heat transfer from a cooler room does not take place.
• Consider heating of a room by passage of electric current through an electric resistor. Transferring of
heat from room will not cause electrical energy to be generated through the wire.
• Consider a paddle-wheel mechanism operated by fall of mass. Potential energy of mass decreases
and internal energy of the fluid increases. Reverse process does not happen, although this would not
violate first law.
• Water flows down hill where by potential energy is converted into K.E. Reverse of this process does
not occur in nature.
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48. Need Of Second Law of Thermodynamics
• Processes proceed in a certain direction and not in the reverse direction. The first law places
no restriction on direction.
• A process will not occur unless it satisfies both the first and second laws of thermodynamics.
• Second law not only identifies the direction of process, it also asserts that energy has quality
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49. The second law of thermodynamics asserts that processes occur in a certain direction and
that the energy has quality as well as quantity. The first law places no restriction on the
direction of a process, and satisfying the first law does not guarantee that the process will
occur. Thus, we need another general principle (second law) to identify whether a process can
occur or not.
Heat transfer from a hot container to the cold surroundings is possible; however, the reveres process
(although satisfying the first law) is impossible
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50. A cup of coffee dose not get hotter in a cooler room
Transferring heat to paddle
wheel will not cause it to rotate
Transferring heat to a wire will
not generate electricity.
These processes
cannot occur even
though they are not
in violation of first
law
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51. N
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52. Thermal Energy Reservoirs
Bodies with relatively large thermal masses can be
modeled as thermal energy reservoirs
• A hypothetical body with a relatively large thermal energy capacity (mass x specific heat) that
can supply or absorb finite amounts of heat without undergoing any change in temperature is
called a thermal energy reservoir, or just a reservoir.
• In practice, large bodies of water such as oceans, lakes, and rivers as well as the atmospheric
air can be modeled accurately as thermal energy reservoirs because of their large thermal
energy storage capabilities or thermal masses.
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53. Heat Engines
The devices that convert heat to work.
• They receive heat from a high temperature
(Source energy, solar energy, oil furnace, nuclear
reactor, etc.)
• They convert part of this heat to work (usually in
the form of a rotating shaft)
• They reject the remaining waste heat to a low-
temperature sink (the atmosphere rivers etc)
• They operate on a cycle
• Heat engines and other cyclic devices involve
transferring heat to and from a fluid which is
undergoing a cycle.
• This fluid is called the working fluid
Work can always be
converted to heat
directly and
completely, but
reverse is not true.
Part of heat received by a
heat engine is converted to
work, while the rest is
rejected to sink.
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54. Schematic of Heat Engine Even the most efficient heat
engines reject almost one-half of
the energy they receive as waste
heat
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55. A steam power plant
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56. Thermal efficiency
Some heat engines perform
more better than others
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57. The Second Law of Thermodynamics: Kelvin–Planck Statement
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.
No heat engine can have a thermal efficiency
of 100 percent, or as for a power plant to
operate, the working fluid must exchange
heat with the environment as well as the
furnace
A heat engine that violates the Kelvin–
Planck statement of the second law
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58. Refrigerators and Heat Pumps
The transfer of heat from a low temperature
medium to a high temperature one requires
special devices called refrigerators.
• Refrigerators, like heat engines, are cyclic
devices.
• The working fluid used in the refrigeration
cycle is called a refrigerant. (R12 – 29.8°C)
• The most frequently used refrigeration
cycle is the vapor compression refrigeration
cycle.
In a household refrigerator, the freezer compartment
where heat is absorbed by the refrigerant serves as
the evaporator, and the coils usually behind the
refrigerator where heat is dissipated to the kitchen
air serve as the condenser.
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59. Coefficient of Performance
The objective of a refrigerator is to
remove QL from the cooled space
The efficiency of a refrigerator is expressed in terms of
the coefficient of performance (COP).
The objective of a refrigerator is to remove heat (QL)
from the refrigerated space.
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60. The Second Law of Thermodynamics: Clasius Statement
It is impossible to construct a device that operates in a
cycle and produces no effect other than the transfer of
heat from a lower temperature body to a higher-
temperature body.
A refrigerator that violates the Clausius
statement of the second law.
• It states that a refrigerator cannot operate unless its
compressor is driven by an external power source, such as
an electric motor.
• This way, the net effect on the surroundings involves the
consumption of some energy in the form of work, in
addition to the transfer of heat from a colder body to a
warmer one.
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61. Perpetual-Motion Machines
A perpetual-motion machine that
violates the first law (PMM1)
A perpetual-motion machine that
violates the second law (PMM2)
Perpetual-motion machine: Any device that violates the first or the second law.
A device that violates the first law (by creating energy) is called a PMM1.
A device that violates the second law is called a PMM2.
Despite numerous attempts, no perpetual-motion machine is known to have worked. If something
sounds too good to be true, it probably is.
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62. REVERSIBLE AND IRREVERSIBLE PROCESSES
Reversible process: A process that can be reversed without leaving any trace on the
surroundings.
Irreversible process: A process that is not reversible.
….
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63. Problem: Heat is transferred to a heat engine from a furnace at a rate of 80 MW. If the rate of
waste heat rejection to a nearby river is 50 MW, determine the net power output and the thermal
efficiency for this heat engine.
Given: The rates of heat transfer to and from a heat engine are given. QH = 80 MW and QL = 50 MW
The net power output and the thermal efficiency are to be determined.
Assumptions Heat losses through the pipes and other components are negligible.
The net power output of this heat engine is
Wnet,out = QH – QL
= 80 – 50
= 30 MW
Then the thermal efficiency is easily determined to be
ηth = Wnet,out / QH
= 30 / 80
= 0.375 (or 37.5%)
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64. Problem: The food compartment of a refrigerator, shown in Fig., is maintained at 4°C by
removing heat from it at a rate of 360 kJ/min. If the required power input to the refrigerator is 2
kW, determine (a) the coefficient of performance of the refrigerator and (b) the rate of heat
rejection to the room that houses the refrigerator.
The power consumption of a refrigerator is given. The COP and the rate of heat
rejection are to be determined.
(a) The coefficient of performance of the refrigerator is
That is, 3 kJ of heat is removed from the
refrigerated space for each kJ of work supplied.
(b) The rate at which heat is rejected to the room that houses the refrigerator is determined from the
conservation of energy relation for cyclic devices,
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65. Problem: A heat pump is used to meet the heating requirements of a house and maintain it at
20°C. On a day when the outdoor air temperature drops to 2°C, the house is estimated to lose
heat at a rate of 80,000 kJ/h. If the heat pump under these conditions has a COP of 2.5,
determine (a) the power consumed by the heat pump and (b) the rate at which heat is absorbed
from the cold outdoor air.
The COP of a heat pump is given. The power consumption and the rate of heat absorption
are to be determined.
(a) The power consumed by this heat pump, shown in Fig. is determined from the
definition of the coefficient of performance to be
(b) The house is losing heat at a rate of 80,000 kJ/h. If the house is to be maintained at a constant
temperature of 20°C, the heat pump must deliver heat to the house at the same rate, that is, at a
rate of 80,000 kJ/h. Then the rate of heat transfer from the outdoor becomes
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66. Temperature Measurement
Thermocouple
A thermocouple is an electrical device consisting of two dissimilar conductors forming electrical
junctions at differing temperatures. A thermocouple produces a temperature-
dependent voltage as a result of the thermoelectric effect, and this voltage can be interpreted to
measure temperature. Thermocouples are a widely used type of temperature sensor.
Thermocouples operate under the principle that a
circuit made by connecting two dissimilar metals
produces a measurable voltage (emf-electromotive
force) when a temperature gradient is imposed
between one end and the other.
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67. Summary of Different Types of Thermocouple
Type Conductor Combination Temperature Range
°F °C
B Platinum 30% Rhodium / Platinum 6% Rhodium 2500 to 3100 1370 to 1700
E Nickel-chromium / Constantan 32 to 1600 0 to 870
J Iron / Constantan 32 to 1400 0 to 760
K Nickel-chromium / Nickel-aluminum 32 to 2300 0 to 1260
N Nicrosil / Nisil 32 to 2300 0 to 1260
R Platinum 13% Rhodium / Platinum 1600 to 2640 870 to 1450
S Platinum 10% Rhodium / Platinum 1800 to 2640 980 to 1450
T Copper / Constantan -75 to +700 -59 to +370
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68. Pressure Measurement Devices
Absolute pressure: The actual pressure at a given position
Gage pressure: Difference between absolute and atmospheric pressure
Vacuum pressure: Pressure below atmospheric pressure
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69. Barometer
Atmospheric pressure is measured by a device called a barometer; thus, the atmospheric
pressure is often referred to as the barometric pressure.
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70. Bourdon Pressure Gauge
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71. Simple U Tube Manometer
Pressure is defined as a force per unit area - and the most accurate way to
measure low air pressure is to balance a column of liquid of known weight
against it and measure the height of the liquid column so balanced.
Fig. 2-1. In its simplest form the manometer is a U-tube about half filled with liquid. With both ends of the tube open,
the liquid is at the same height in each leg.
Fig. 2-2. When positive pressure is applied to one leg, the liquid is forced down in that leg and up in the other. The
difference in height, "h," which is the sum of the readings above and below zero, indicates the pressure.
Fig. 2-3. When a vacuum is applied to one leg, the liquid rises in that leg and falls in the other. The difference in height,
"h," which is the sum of the readings above and below zero, indicates the amount of vacuum.
Instruments employing this principle are called manometers. The simplest form is the basic and well-known U-tube
manometer. (Fig. 2-1). This device indicates the difference between two pressures (differential pressure), or between a
single pressure and atmosphere (gage pressure), when one side is open to atmosphere. If a U-tube is filled to the half
way point with water and air pressure is exerted on one of the columns, the fluid will be displaced. Thus one leg of
water column will rise and the other falls. The difference in height "h" which is the sum of the readings above and
below the half way point, indicates the pressure in inches of water column.
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72. • A manometer is comprised of a bulb containing a gas and a U-shaped tube.
• The U-shaped tube is partially filled with mercury. The weight of the mercury puts pressure on
the gas.
• If the U-tube is OPEN there is also air pressure acting on the gas.
• The gas molecules put pressure on the mercury.
Manometer
PHg
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73. Closed Manometers
There is a balance between the weight of the mercury on
the left (PHg) and the pressure of the gas on the right
(Pgas).
The difference between the heights of the mercury on
each side of the tube is a measure of the pressure of the
gas.
Pgas = Δh
vacuum
PHg
Open Manometers
• When gas pressure is greater than atmospheric pressure, the
mercury is pushed toward the open end.
• The balance is between the gas on the right, and the air plus
mercury on the left.
Pair + PHg = Pgas
• The weight of the mercury is measured as the height difference:
PHg = Dh
So Pgas = Pair + Dh
Pair
PHg
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74. PHg
Pair
Open Manometers
• When gas pressure is less than atmospheric pressure, the
mercury is pushed toward the gas reservoir.
• The balance is between the air on the left and the gas plus
mercury on the right:
Pair = Pgas + PHg
• The weight of the mercury is measured as the height difference:
PHg = Dh
So Pair = Pgas + Dh
Or Pgas = Pair- Dh
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