Thermodynamics Basics

Thermodynamics Definition and Scope

• Thermodynamics is the study of energy, energy transformations, and its relation to matter.
• It involves the analysis of thermal systems using conservation equations, including Conservation of Mass, Conservation of Energy (1st law of thermodynamics), the 2nd law of thermodynamics, and property relations.

Laws of Thermodynamics

• The 1st law of thermodynamics states that energy can change forms, but the total amount remains constant during an interaction.
• The 2nd law of thermodynamics states that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy.

Energy Characteristics

• Energy can be viewed as the ability to cause changes.
• Energy has both quantity and quality.

Dimensions and Units

• Any physical quantity can be characterized by dimensions.
• There are two types of dimensions: primary (fundamental) and secondary (derived).
• Primary dimensions are: mass, length, time, and temperature.
• Secondary dimensions are derived from primary dimensions, such as velocity and pressure.
• There are two unit systems: SI (International System) and USCS (United States Customary System).
• SI units are used exclusively in this course and are based on decimal relationships between units.

System Definitions

• A system is a quantity of matter or a region in space chosen for study.
• The surroundings are the mass or region outside the system.
• The boundary is the real or imaginary surface that separates the system from its surroundings.
• Closed systems consist of a fixed amount of mass, and no mass can cross its boundary.
• Open systems or control volumes are properly selected regions in space that enclose devices with mass flow.
• Isolated systems are closed systems that do not communicate with the surroundings by any means.
• Rigid systems are closed systems that communicate with the surroundings by heat only.
• Adiabatic systems are closed or open systems that do not exchange energy with the surroundings by heat.

Energy Types

• Total energy of a system can be assigned a value of zero at some reference point.
• Total energy of a system has two groups: macroscopic and microscopic.
• Macroscopic forms of energy are related to motion and external effects such as gravity, magnetism, and electricity.
• Microscopic forms of energy are related to molecular structure and are independent of outside reference frames.
• The sum of microscopic energy is called the internal energy, U.