Mechanical Engineering: Introduction to Thermodynamics

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Questions and Answers

What is the characteristic feature of a quasi-static process?

High pressure

Infinite slowness (correct)

Finite slowness

Fast reaction rate

Which of the following is an example of a reversible process?

Frictional adiabatic expansion of a fluid

Frictionless isothermal expansion of a fluid (correct)

Frictional isothermal expansion of a fluid

Frictional compression of a fluid

What is the result of an irreversible process?

No change in the Universe

Net change in the Universe (correct)

No effect on the surrounding

Reversible process

What is the formula for calculating work done?

W=F·d·cos(?) Signup and view all the answers

What is pressure-volume work commonly known as?

PV work Signup and view all the answers

What is the sign convention for work done by the system on the surroundings?

Positive Signup and view all the answers

What is the relation between internal energy, heat, and work?

?U=Q-W Signup and view all the answers

What is chemical equilibrium related to?

Chemical potential Signup and view all the answers

What is the definition of thermodynamic work?

Work involves energy transfer that occurs when a system undergoes a change in volume or pressure Signup and view all the answers

What is the unit of work in the International System of Units (SI)?

Joule (J) Signup and view all the answers

What is the primary focus of thermodynamics?

Energy and its transformation Signup and view all the answers

What is the term for the quantity of matter or a region in space chosen for study?

Thermodynamic system Signup and view all the answers

In a closed system, what can cross the boundary?

Energy in the form of heat or work Signup and view all the answers

What is the term for the boundary of a control volume?

Control surface Signup and view all the answers

Which approach considers the events occurring at the molecular level?

Microscopic approach Signup and view all the answers

What is the primary focus of the macroscopic approach?

Overall behavior of the system Signup and view all the answers

What is the benefit of the macroscopic approach?

Requires simple mathematical formulae Signup and view all the answers

What is an example of an open system?

Both A and B Signup and view all the answers

What is a characteristic of a closed system?

Fixed amount of mass Signup and view all the answers

What is the term for the real or imaginary surface that separates the system from the surrounding?

Boundary Signup and view all the answers

What is a quasi-equilibrium process?

A process that remains infinitesimally close to an equilibrium state at all times Signup and view all the answers

What is a point function?

A quantity that is independent of the path Signup and view all the answers

What is a path function?

A quantity that depends on the path Signup and view all the answers

What is a cycle in thermodynamics?

A process that returns to its initial state at the end of the process Signup and view all the answers

What is temperature?

A measure of degree of hotness or coldness Signup and view all the answers

What is the relation between Kelvin and Celsius scales?

T(K) = T(C) + 273.16 Signup and view all the answers

What is pressure?

Force per unit area Signup and view all the answers

What is the unit of pressure in the SI system?

Pa Signup and view all the answers

What is thermodynamic equilibrium?

A state where no changes in macroscopic property are observed if the system is isolated Signup and view all the answers

What is mechanical equilibrium?

Equality of pressure Signup and view all the answers

What is the main characteristic of the microscopic approach?

Studying the motion of molecules and their interactions Signup and view all the answers

What is an intensive property of a system?

A property that is independent of the size of the system Signup and view all the answers

What is the specific volume of a substance?

The volume of the substance per unit mass Signup and view all the answers

What is the state of a system described by?

Its properties and their values Signup and view all the answers

What is a process in thermodynamics?

A change in the state of a system Signup and view all the answers

What is the characteristic of a system in thermal equilibrium?

The temperature is same throughout the system Signup and view all the answers

What is the continuum idealization?

A continuous, homogeneous matter with no holes Signup and view all the answers

What is an extensive property of a system?

A property that depends on the size of the system Signup and view all the answers

What is the specific gravity of a substance?

The ratio of its density to the density of a standard substance Signup and view all the answers

What is equilibrium in thermodynamics?

A state of balance in the system Signup and view all the answers

Study Notes

Introduction to Thermodynamics

Thermodynamics is the science of energy and its transformations, dealing with equilibrium and feasibility of processes.
It involves the relationship between heat and work, and the properties of systems in equilibrium.

Thermodynamic System

A thermodynamic system is a quantity of matter or a region in space chosen for study.
The system is separated from the surrounding by a boundary, which can be real or imaginary.
The system can be classified into two types: closed system and open system.

Closed System (Control Mass)

A closed system consists of a fixed amount of mass, and no mass can cross its boundary.
Energy in the form of heat or work can cross the boundary, but the volume of the system does not have to be fixed.
Example: piston-cylinder device.

Open System (Control Volume)

An open system is a properly selected region in space, and both mass and energy can cross its boundary.
The boundary of a control volume is called a control surface, which can be real or imaginary.
Example: compressor, turbine, nozzle.

Macroscopic and Microscopic Approaches

The macroscopic approach considers a system as a whole, without taking into account events at the molecular level.
The microscopic approach considers the system as comprising of many tiny particles, with molecular motion and random interactions.
The macroscopic approach is used in classical thermodynamics, while the microscopic approach is used in statistical thermodynamics.

Properties of a System

A property is a characteristic of a system, which can be independent or dependent.
Intensive properties are independent of the size of the system, such as temperature, pressure, and density.
Extensive properties depend on the size of the system, such as mass, volume, and total energy.
Specific properties are extensive properties per unit mass, such as specific volume, specific energy, and specific gravity.

State and Equilibrium

The state of a system is described by its properties, and a system is in equilibrium when there are no unbalanced potentials or driving forces within the system.
A system is in thermal equilibrium when the temperature is uniform throughout the system, and in mechanical equilibrium when there is no change in pressure at any point of the system.
A system is in chemical equilibrium when its chemical composition does not change with time.

Processes and Quasi-Equilibrium

A process is a change that a system undergoes from one equilibrium state to another.
A quasi-equilibrium process is an idealized process that proceeds in such a way that the system remains infinitesimally close to an equilibrium state at all times.
Quasi-equilibrium processes are easy to analyze and are used as standards to compare actual processes.

Point Function and Path Function

A point function is a quantity whose change is independent of the path, such as properties like pressure, volume, and temperature.
A path function is a quantity whose value depends on the path followed during a change of state, such as heat and work.

Cycle and Steady Flow Process

A cycle is a process in which the system returns to its initial state at the end of the process.
A steady flow process is a process in which a fluid flows through a control volume steadily.

Temperature and Pressure

Temperature is a measure of hotness or coldness, and it is a point function.
Pressure is defined as the force exerted by a fluid per unit area, and it is a point function.

Thermodynamic Equilibrium

A system is in thermodynamic equilibrium when no changes in macroscopic properties are observed when it is isolated from its surroundings.
The conditions for thermodynamic equilibrium are thermal equilibrium, mechanical equilibrium, and chemical equilibrium.

Quasi-Static and Reversible Processes

A quasi-static process is a process that is performed in such a way that the deviation from thermodynamic equilibrium is infinitesimal.
A reversible process is a process that can be executed in either direction, with no dissipative effects such as friction or loss of energy.

Irreversible Process

An irreversible process is a process that cannot be restored to its initial state, and the system and surroundings are affected by loss of work and gain of low-temperature heat.

Work and Heat Transfer

Work is the transfer of energy that occurs when a force is applied to an object, causing it to move.
Thermodynamic work involves energy transfer that occurs when a system undergoes a change in volume or pressure.
Pressure-volume work is the most common type of thermodynamic work, and it is given by W = PΔV.
Sign convention for work transfer: work done by the system is positive, and work done on the system is negative.

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Description

Learn about the basic concepts of thermodynamics, including energy transformation, equilibrium, and feasibility of processes, as well as the relationship between heat and work. Understand thermodynamic systems and their properties.