1 Engineering Thermodynamics Dr. Arif Al-Qassar 2016-2017 Definitions Adiabatic process is a process during which there is no heat transfer. The word adiabatic comes from the Greek word adiabatos, which means not to be passed. Bar is the unit of pressure equal to 10 5 pascal. Barometer is a device that measures the atmospheric pressure; thus, the atmospheric pressure is often referred to as the barometric pressure. Bernoulli equation for frictionless flow, it states that the sum of the pressure, velocity, and potential energy heads is constant. It is also a form of the conservation of momentum principle for steady-flow control volumes. Boiler is basically a large heat exchanger where the heat originating from combustion gases, nuclear reactors, or other sources is transferred to the water essentially at constant pressure. Boundary work (PdV work) is the work associated with the expansion or compression of a gas in a piston-cylinder device. Boundary work is the area under the process curve on a P-V diagram equal, in magnitude, to the work done during a quasi-equilibrium expansion or compression process of a closed system. Bourdon tube, named after the French inventor Eugene Bourdon, is a type of commonly used mechanical pressure measurement device which consists of a hollow metal tube bent like a hook whose end is closed and connected to a dial indicator needle. British thermal unit BTU is the energy unit in the English system, representing the energy needed to raise the temperature of 1 lbm of water at 68F by 1F. Calorie (cal) is the amount of energy in the metric system needed to raise the temperature of 1 g of water at 15 C by 1C. Classical thermodynamics is the macroscopic approach to the study of thermodynamics that does not require knowledge of the behavior of individual particles. Clausius statement of the second law is expressed as follows: 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. Closed system consists of a fixed amount of mass (control mass), and no mass can cross its boundary. But energy, in the form of heat or work, can cross the boundary.
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Engineering Thermodynamics Dr. Arif Al-Qassar 2016-2017
Definitions
Adiabatic process is a process during which there is no heat transfer. The word adiabatic
comes from the Greek word adiabatos, which means not to be passed.
Bar is the unit of pressure equal to 105 pascal.
Barometer is a device that measures the atmospheric pressure; thus, the atmospheric
pressure is often referred to as the barometric pressure.
Bernoulli equation for frictionless flow, it states that the sum of the pressure, velocity,
and potential energy heads is constant. It is also a form of the conservation of momentum
principle for steady-flow control volumes.
Boiler is basically a large heat exchanger where the heat originating from combustion
gases, nuclear reactors, or other sources is transferred to the water essentially at constant
pressure.
Boundary work (PdV work) is the work associated with the expansion or compression
of a gas in a piston-cylinder device. Boundary work is the area under the process curve
on a P-V diagram equal, in magnitude, to the work done during a quasi-equilibrium
expansion or compression process of a closed system.
Bourdon tube, named after the French inventor Eugene Bourdon, is a type of commonly
used mechanical pressure measurement device which consists of a hollow metal tube bent
like a hook whose end is closed and connected to a dial indicator needle.
British thermal unit BTU is the energy unit in the English system, representing the
energy needed to raise the temperature of 1 lbm of water at 68F by 1F.
Calorie (cal) is the amount of energy in the metric system needed to raise the
temperature of 1 g of water at 15 C by 1C.
Classical thermodynamics is the macroscopic approach to the study of thermodynamics
that does not require knowledge of the behavior of individual particles.
Clausius statement of the second law is expressed as follows: 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.
Closed system consists of a fixed amount of mass (control mass), and no mass can cross
its boundary. But energy, in the form of heat or work, can cross the boundary.
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Compression ratio (r ) of an engine is the ratio of the maximum volume formed in the
cylinder to the minimum volume. Notice that the compression ratio is a volume ratio and
should not be confused with the pressure ratio.
Compressor is a device that increases the pressure of a gas to very high pressures
(typical pressure ratios are greater than 3).
Conduction is the transfer of energy from the more energetic particles of a substance to
the adjacent less energetic ones as a result of interaction between particles.
Conservation of energy principle states that, energy can change from one form to
another but the total amount of energy remains constant. That is, energy cannot be
created or destroyed (see first law of thermodynamics).
Convection is the mode of energy transfer between a solid surface and the adjacent fluid
that is in motion, and it involves the combined effects of conduction and fluid motion.
Cycle is a process, or series of processes, that allows a system to undergo state changes
and returns the system to the initial state at the end of the process. That is, for a cycle the
initial and final states are identical.
Density is defined as mass per unit volume.
Enthalpy H (from the Greek word enthalpien, which means to heat) is a property and is
defined as the sum of the internal energy U and the PV product.
Entropy can be viewed as a measure of molecular disorder, or molecular randomness. is
a property designated S and is defined as dS =(Q/T)int rev.
Equation of state is an equation that relates the pressure, temperature, and volume of a
substance, (PV=mRT).
Equilibrium implies a state of balance. In an equilibrium state there are no unbalanced
potentials (or driving forces) within the system. A system in equilibrium experiences no
changes when it is isolated from its surroundings.
First law of thermodynamics is simply a statement of the conservation of energy
principle; it may be expressed as follows: Energy can be neither created nor destroyed; it
can only change forms.
Gage pressure is the difference between the absolute pressure and the local atmospheric
pressure.
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Heat transfer (heat) is defined as the form of energy that is transferred between two
systems (or a system and its surroundings) by virtue of a temperature difference.
Ideal gas is a gas that obeys the ideal-gas equation of state.
Ideal gas specific heat relation is R = Cp - Cv
Internal energy (U) of a system is the sum of all the microscopic forms of energy.
Irreversible processes are processes which, once having taken place in a system, cannot
spontaneously reverse themselves and restore the system to its initial state.
Irreversibilities are the factors that cause a process to be irreversible. They include
friction, unrestrained expansion, mixing of two gases, heat transfer across a finite
temperature difference, electric resistance, inelastic deformation of solids, and chemical
reactions.
Isentropic process is an internally reversible and adiabatic process. In such a process
the entropy remains constant.
Iso prefix is often used to designate a process for which a particular property remains
constant.
Isobaric process is a process during which the pressure P remains constant.
Isochoric process (isometric process) is a process during which the specific volume v
remains constant.
Isolated system is a closed system in which energy is not allowed to cross the boundary.
Isothermal process is a process in which the temperature is maintained constant.
Joule (J) is a unit of energy and has the unit (N·m).
kelvin is the temperature unit of the Kelvin scale in the SI, (T=t+273).
Kinetic energy (KE) is energy that a system possesses as a result of its motion relative to
some reference frame. When all parts of a system move with the same velocity, the
kinetic energy is expressed as KE = m V2/2.
Mach number, named after the Austrian physicist Ernst Mach (1838–1916), is the ratio
of the actual velocity of the fluid (or an object in still air) to the speed of sound in the
same fluid at the same state.
Manometer is a device based on the principle that an elevation change of z of a fluid
corresponds to a pressure change of P/ g, which suggests that a fluid column can be
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used to measure pressure differences. The manometer is commonly used to measure
small and moderate pressure differences.
Mass flow rate (m.) is the amount of mass flowing through a cross section per unit time.
Open system is any arbitrary region in space through which mass and energy can pass
across the boundary.
Polytropic process is a process in which pressure and volume are often related by
PVn= C, where n and C are constants, during expansion and compression processes of
real gases.
Potential energy (PE) is the energy that a system possesses as a result of its elevation in
a gravitational field and is expressed as PE = mgz.
Power is the work done per unit time is called and has the unit kJ/s, or kW.
Pressure is defined as the force exerted by a fluid per unit area.
Pressure ratio is the ratio of final to initial pressures during a compression process.
Process is any change that a system undergoes from one equilibrium state to another. To
describe a process completely, one should specify the initial and final states of the
process, as well as the path it follows.
Pump is a steady flow device used to increase the pressure of a liquid while compressors
increase the pressure of gases.
Pure substance is a substance that has a fixed chemical composition throughout.
Radiation is the transfer of energy due to the emission of electromagnetic waves (or
photons).
Refrigerator is a cyclic device which causes the transfer of heat from a low-temperature
region to a high-temperature region. The objective of a refrigerator is to maintain the
refrigerated space at a low temperature by removing heat from it.
Specific heat is defined as the energy required to raise the temperature of a unit mass of a
substance by one degree. In general, this energy will depend on how the process is
executed.
Specific heat at constant pressure (Cp)is the energy required to raise the temperature of
the unit mass of a substance by one degree as the pressure is maintained constant.
Specific heat at constant volume (Cv)is the energy required to raise the temperature of
the unit mass of a substance by one degree as the volume is maintained constant.
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Specific heat ratio (γ or k) is defined as the ratio Cp/Cv.
Steady implies no change with time. The opposite of steady is unsteady, or transient.
Surroundings are everything outside the system boundaries.
Thermal efficiency th is the ratio of the net work produced by a heat engine to the total
heat input, th = Wnet/Qin.
Thermodynamics can be defined as the science of energy. Energy can be viewed as the
ability to cause changes. The name thermodynamics stems from the Greek words therme
(heat) and dynamis (power), which is most descriptive of the early efforts to convert heat
into power. Today the same name is broadly interpreted to include all aspects of energy
and energy transformations, including power production, refrigeration, and relationships
among the properties of matter. (i.e. thermodynamics: the science that deals with heat and
work and those properties of matter that relate to heat and work).
Work is the energy transfer associated with a force acting through a distance.
Working fluid is the fluid to and from which heat and work is transferred while
undergoing a cycle in heat engines and other cyclic devices.
Zeroth law of thermodynamics states that if two bodies are in thermal equilibrium with
a third body, they are also in thermal equilibrium with each other.
Ministry of Higher Education and Scientific Research
University of Technology
Control and Systems Engineering Department
Third Year/ Control Engineering Branch
Engineering Thermodynamics
Asst. prof. Dr. Arif A. Al-Qassar
2016-2017
References:
Rayners Joel "Basic Engineering Thermodynamics in SI Units"
Yunus Çengel and Michael Boles "Thermodynamics: An Engineering Approach"
د. رحيم جوي "اساسيات ديناميك الحرارة "
الحرارية" واآلالتالثيرموديناميك د. مرتضى الكواكبي "
Chapter One
General Introduction
1.1. Introduction
Thermodynamics is a branch of physical science that treads with various phenomena
of energy and related properties of maters, especially the low of transformation of heat into
other forms of energy.
The name thermodynamics stems from the Greek words therme (heat) and dynamics
(power), which is most descriptive of the early efforts to convert heat into power. Today the
same name is broadly interpreted to include all aspects of energy and energy transformations,
including power production, refrigeration, and relationships among the properties of matter.
1.2. Working Substance
All thermodynamic systems require some working substance in order to perform
various operations. The working substances are, in general, fluids which are capable of
deformation in that they can readily be expanded and compressed. The working substance
also takes part in energy transfer. For example it can receive or reject heat energy or it
can be the means by which work i s d on e . Common examples of working substances
used in thermodynamic systems are air and steam.
1.3. Properties and State
Any characteristic of the substance which can be observed or measured is called a
property of the substance. Examples of properties are pressure, volume and temperature. This
type of property which is dependent upon the physical and chemical structure of the
substance is called an internal or thermostatic property.
Properties which are independent of mass, such as temperature and pressure, are said to be
intensive properties.
Properties which are dependent upon mass, such as volume and energy in its various forms,
are called extensive properties.
Knowledge of the various thermostatic properties of a substance defines the state of the
substance. If a property, or properties, are changed, then the state is changed.
1.4. Phase
When a substance is of the same nature throughout its mass it is said to be in a phase.
Matter can exist in three phases, solid, liquid and vapour or gas. If the matter exists in only
one of these forms then it is in a single phase. If two phases exist together then the substance
is in the form of a two-phase mixture. Examples of this are when a solid is being melted into
a liquid or when a liquid is being transformed into a vapour. In a single phase the substance is
said to be homogenous.
1.5. Process
When the state of a substance is changed by means of an operation or operations
having been carried out on the substance, then the substance is said to have undergone a
process. Typical processes are the expansion and compression of a gas or the conversion of
water into steam.
1.6. Cycle
If processes are carried out on a substance such that, at the end, the substance is
returned to its original state, then the substance is said to have been taken through a cycle.
This is commonly required in many engines. A sequence of events takes place which must be
repeated and repeated. In this way the engine continues to operate. Each repeated sequence of
events is called a cycle.
1.7. The System
All physical things in nature have some form of boundary whose shape in general
identifies it. Inside its boundary there are certain things with particular functions to carry
out. This inside arrangement is called a system. Outside the boundary of the object are the
surroundings.
If the mass of a system remains constant then the system is said to be a closed system,
for example a piston of a cylinder.
If the mass of a system changes, or is continuously changing, then the system is said to
be an open system. For example, an air compressor is an open system since air is
continuously streaming into and out of the machine, in other words, air mass is crossing its
boundary. This is called a two-flow boundary system. Another example is air leaving a
compressed air tank. This would be a one-flow boundary system since air is only leaving
the tank and none is entering. If the mass and energy cannot be transferred to or from the
surrounding, the system is said to be an insulated system. Closed and open systems are
illustrated in Fig. 1.1.
Fig. 1.1. Closed and Open Systems
1.8. Energy
Energy is defined as that capacity a body or working substance to do work in a
possess.
Here, work is defined, as in mechanics, as the result of moving a force through a distance.
The presence of energy can only be observed by its effects and these can appear in many
different forms.
An example where some of the forms in which energy can appear is in the motor car.
The petrol put into the petrol tank must contain a potential chemical form of energy
because by burning it in the engine, the motor car, through various mechanisms, is propelled
along the road. Thus, work, by definition. is being done because a force is being moved
through a distance.
As a result of burning the petrol in the engine, the general temperatures of the working
substances in the engine, and the engine, will be increased and this increase in
temperature must initially have been responsible for propelling the motor car.
Due to the increase in temperature of the working substances then. since the motor car is
moved and work is done, the working substance at the increased temperature must have
contained a form of energy resultant from this increased temperature. This energy content
resultant from the consideration of the temperature of a substance is called internal energy.
Some of this internal energy in the working substances of the engine will transfer to the
cooling system of the engine because the cooling water becomes hot. A transfer of energy in
this way, because of temperature differences, is called heat-transfer.
The motor car engine will probably have an electric generator which rotated by the engine and
is used to charge the battery. The battery, by its construction and chemical nature, stores
energy which can appear at the battery terminals as electricity. The electricity from the battery
can be used to rotate the engine starter which, in turn, rotates and starts the engine. By rotating
the engine to start it, the electric motor must be doing work and thus, electricity must have the
capacity for doing work, and hence is a form of energy.
To stop the motor car the brakes are applied. After the motor car has stopped the brake
drums are hot and thus, as discussed above, the internal energy of the brake drum
materials must have been increased. This internal energy increase resulted from the stopping
of the motor car and hence there must have been a type of energy which the motor car
possessed while it was in motion. This energy of motion is called kinetic energy.
From this discussion it will be seen that energy can appear in many forms and further, it
appears that energy, through the action of various devices, can be converted from one form
into another.
1.9. Temperature
Temperature is a measurement of the average kinetic energy of the molecules in an
object or system and can be measured with a thermometer or a calorimeter. It is a means of
determining the internal energy contained within the system.
The Celsius scale was the most commonly used scale in the countries using a metric
system of units. The thermodynamic temperature scale in the SI is the Kelvin scale. The
temperature unit on this scale is the kelvin, which is designated by K (not K).
The temperature scale in the America system is the Fahrenheit scale.
The Kelvin scale is related to the Celsius scale by
T(K) = T(C) + 273.15 --- (1.1)
T(F) = 1.8 T(C) + 32 --- (1.2)
Note that the magnitudes of each division of 1 K and 1C are identical. Therefore, when
we are dealing with temperature differences T, the temperature interval on both scales is the
same. T(K) = T(C) --- (1.3)
1.10. Pressure
Pressure is the force exerted normally on the unit area. We speak of pressure only
when we deal with a gas or a liquid. The counterpart of pressure in solids is stress. For a
fluid at rest, the pressure at a given point is the same in all directions. The pressure in
a fluid increases with depth as a result of the weight of the fluid. Since pressure is denned
as force per unit area (P =F/A), it has the unit of newton’s per square meter (N/m2), which
is called a Pascal (Pa). That is,
1 Pa = 1 N/m2
The pressure unit Pascal is too small for pressures encountered in practice. Therefore, its
multiples kilopascal (1 kPa = 103
Pa) and megapascal (1 MPa = 106
Pa) are commonly
used. Two other common pressure units are the bar and standard atmosphere: