Unit 2 Overview: Thermodynamics

Unit 2 Overview: Thermodynamics

Introduction

Thermodynamics is the study of energy transfer between systems and its transformation into different forms. This unit explores essential topics:

• Heat and Temperature: Fundamental concepts of heat and temperature, including temperature scales and the first and second laws of thermodynamics.

• Work and Energy: Examining various forms of energy (kinetic, potential, and internal) and their relation to work.

• Heat Transfer: Mechanisms of heat transfer (conduction, convection, and radiation) and the concept of thermal conductivity.

• The Carnot Cycle: Introduction to the theoretical Carnot cycle, efficiency of heat engines, entropy, and the second law of thermodynamics.

• Thermodynamic Processes: Exploration of isothermal, adiabatic, and isobaric processes with derived equations.

• Applications: Practical applications, including refrigeration, air conditioning, power cycles, and combustion.

Students will apply thermodynamic principles to solve real-world problems and understand energy transformations in practical contexts.

2.1 Thermodynamic Systems

A system is a defined region or quantity of matter under study. Systems can be classified as:

1. Closed System: Exchanges energy (heat or work) but not matter with surroundings.

2. Open System: Exchanges both energy and matter with surroundings.

3. Isolated System: No exchange of energy or matter; total energy remains constant.

The system’s boundary separates it from its surroundings and can be real (e.g., container walls) or imaginary (e.g., control surfaces).

2.2 Pressure, Thermal Equilibrium, and the Ideal Gas Law

Pressure:

Pressure is the force per unit area exerted on a surface. Units include Pascals (Pa), atmospheres (atm), or pounds per square inch (psi).

Thermal Equilibrium:

A state where two systems have no net heat transfer, indicating uniform temperature.

Ideal Gas Law:

The behavior of ideal gases is described by:

Where:

• : Pressure

• : Volume

• : Number of moles

• : Universal gas constant

• : Absolute temperature

The Ideal Gas Law predicts gas behavior under varying conditions but may not be accurate for real gases deviating from ideal behavior.

2.3 Thermodynamics and Forces

• Gravitational Forces: Influence fluid behavior, such as atmospheric and ocean circulation.

• Electromagnetic Forces: Affect internal energy and can do work (e.g., in circuits).

• Pressure Forces: Drive fluid movement and are essential in engines and compressors.

2.4 Thermodynamics and Free-Body Diagrams

Free-body diagrams (FBDs) simplify force analysis in thermodynamic systems. Key applications include:

• Representing forces acting on pistons or heat exchangers.

• Analyzing energy transfer in engines and mechanical systems.

2.5 Thermodynamics and Contact Forces

• Pressure: Defined as force per unit area, critical in fluid and gas behavior.

• Work: The product of force and displacement; essential for energy transfer in systems like engines and compressors.

2.6 Heat and Energy Transfer

Mechanisms of Heat Transfer:

1. Conduction: Heat transfer through molecular collisions.

2. Convection: Heat transfer via fluid movement.

3. Radiation: Heat transfer through electromagnetic waves.

Energy transfer also occurs via:

• Mechanical Work

• Chemical Reactions

• Nuclear Reactions

2.7 Internal Energy and Energy Transfer

Internal energy includes all forms of energy within a system (kinetic, potential, chemical). Changes in internal energy result from:

• Heat Transfer: Increases or decreases internal energy.

• Work: Transfers energy to or from a system.

First Law of Thermodynamics:

Where:

• : Change in internal energy

• : Heat added to the system

• : Work done by the system

2.8 Thermodynamics and Elastic Collisions

• Elastic Collisions: Total kinetic energy and momentum are conserved.

• Conservation of Momentum: Essential for analyzing particle and material behavior during collisions.

Applications include safety equipment design (e.g., airbags) and fluid flow analysis.

2.9 Thermodynamics and Inelastic Collisions

• Inelastic Collisions: Kinetic energy is not conserved; some energy transforms into heat, sound, or deformation.

• Momentum Conservation: Still applies, enabling analysis of collision outcomes.

Applications include studying material properties and impact energy dissipation.

2.10 Thermal Conductivity

Thermal conductivity measures a material’s ability to conduct heat. It depends on:

• Material composition

• Structure

• Temperature

Examples:

• High Conductivity: Metals like copper (used in heat exchangers).

• Low Conductivity: Insulators like plastic or fiberglass (used in building insulation).

2.11 Probability, Thermal Equilibrium, and Entropy

Entropy:

A measure of a system’s disorder. Entropy increases as systems evolve towards thermal equilibrium.

Second Law of Thermodynamics:

Entropy of an isolated system always increases over time.

Applications include energy system design, chemical reactions, and statistical mechanics to model large particle systems.

Thermodynamics bridges the gap between microscopic particle interactions and macroscopic energy systems. Mastery of these principles enables practical problem-solving in engineering, environmental science, and beyond.