Thermodynamics: Dimensions and Units

Chapter 1: Introduction

• This chapter provides an overview of thermodynamics.

Dimensions and Units

• Any physical quantity can be characterized by dimensions.
• Dimensions are defined by a numerical value and a unit.
• For example, the distance between Rolla and STL is 106 miles:
  • Distance is the dimension and is length.
  • The numerical value is 106.
  • The unit is miles.
• The density of water (H₂O) is 1000 kg/m³:
  • Density is the dimension and is mass/length³.
  • The numerical value is 1000.
  • The unit is kg/m³.
• There are two sets of units in common use today, despite efforts to unify the world with a single unit system:
  • English (American) system
  • Metric International System (SI)
• Every valid equation must be dimensionally homogeneous.
• All additive terms on both sides of the equation must have the same dimensions.
• For example, if an equation is valid in ft, the constant with the variable time in seconds must be in ft/s.

Importance and Engineer Roles in Energy Fields

• Energy is observed in everyday life, used regularly, and exists in the world.
• Rising energy costs and carbon dioxide emissions from fossil fuel use are common concerns.
• Stressed Supplies include the limited availability of petroleum and electricity.
• Energy has been a key element in the development of civilizations.
  • Pros include technological advancement, economic growth, improved living standards, enhanced communication, and agricultural productivity.
  • Cons include environmental degradation, resource depletion, social inequality, energy conflicts, and health issues.
• Engineers can develop efficient Energy Conversion Systems.
• Integration of Conversion Technologies that use Renewable Energy.
• They can design efficient energy systems using strategies for improvement and sustainable practices.

Definition and History of Thermodynamics

• Thermodynamics is the study of energy, including the conversion of energy from one form to another to accomplish a specific purpose.
• Thermodynamics also looks at the effects of adding or removing energy from a system.
• Thermodynamics emerged from the human need to enhance the effect of human efforts.
• Evolution of Thermodynamics:
  • 1697: Development of steam engines by Thomas Savery.
  • 1712: Newcomen's steam engine improvement.
  • 1849: The term "thermodynamics" was coined by Lord Kelvin.
  • 1859: First thermodynamics textbook by William Rankine..
  • Exploration of gas behavior by Galileo and Boyle led to Early Foundations.
  • Carnot, Clausius, and Kelvin formulated thermodynamic laws leading to Classical Thermodynamics.
  • Boltzmann and Maxwell worked on Statistical Mechanics.
  • Introduction of Gibbs' free energy concept led to Chemical Thermodynamics.
  • Expansion into quantum and non-equilibrium thermodynamics marked Modern Advancements.

Basic Concepts and Terminology

• Key concepts in thermodynamics include:
  • Systems
  • State and Properties
  • Processes and Cycles
  • Steady State and Equilibrium
• Thermodynamic analysis is based on a construct known as a thermodynamic system.
• A system is a specific portion containing the object(s) that are the focus of thermodynamic analysis or modeling.
• The system is defined by the person performing the analysis and should be made as simble as possible.

System and Surroundings

• A system is outlined by a system boundary.
• Everything inside the boundary is the system, while everything outside is considered the surroundings.

Types of Systems

• Isolated System: Neither mass nor energy crosses the boundary, making it completely self-contained.
• Closed System: Allows energy transfer but not mass, also called control mass.
• Open System: Both mass and energy can cross the boundary, called control volume.

Properties and States

• A property is a measurable macroscopic characteristic of a system, such as pressure, temperature, density, mass, and volume.
• Not all system properties are considered thermodynamic properties; thermodynamic properties are related to the energy of the system.
• System properties can be classified as extensive or intensive.
• Extensive properties depend on the size of the system, such as mass (m) and volume (V).
• Intensive properties are independent of the size of the system, such as temperature (T) and density (ρ).
• Extensive properties can be converted into intensive properties by dividing the extensive property by the mass or mole of the system.

State vs. Path-Dependent Properties

• State properties describe the condition of a system at a particular time.
• State properties are independent of how the system reached that condition, such as temperature, pressure, internal energy, enthalpy, and entropy.
• Path-dependent properties depend on how the system changes from one state to another, such as heat and work.
• Examples of most common properties used are:
  • Density (ρ)
  • Pressure (P)
  • Temperature (T)
  • Internal energy (U)
  • Enthalpy (H)
  • Specific heat (Cv or Cp)
  • Entropy (S)
  • Gibbs free energy (G)

State and Properties

• To describe a thermodynamic system at a given moment, determine the state of the system.
• A thermodynamic state is defined by the values of all the system properties at a given moment.

Process

• If the system undergoes a change in state, it is undergoing a thermodynamic process.
• A process involves the action of changing a system when mass and/or energy is added or removed.

Types of Processes

• Isochoric: Processes occur at constant volume.
• Isobaric: Processes occur at constant pressure.
• Isothermal: Processes occur at a constant temperature.
• Adiabatic: Processes occur with no heat entering or leaving the system.
• Cycle: A special case where the initial state of the first process is the same as the final state of the last process.

Steady State and Equilibrium

• These are fundamental concepts applicable to systems and processes.
• A system is at steady state when all properties of the system are constant with respect to time.

Equilibrium

• Defined as a state of balance due to the canceling of actions by opposing forces.
• There are three possible driving forces:
  • Mechanical
  • Thermal
  • Chemical
• Thermal equilibrium exists when temperature is balanced throughout a system.
  • Two or more systems are at the same temperature.
  • A single system has a uniform temperature.
• Mechanical equilibrium exists when forces (or pressure) are balanced throughout the system.
  • System undergoes no acceleration.
• Chemical equilibrium exists when the chemical composition does not change with time.
  • A system is not at chemical equilibrium if there is chemical reaction(s) or phase change presents.
• If a system involves two phases, it is in phase equilibrium when the mass of each phase reaches an equilibrium level and stays there.

Forms of Energy

• A substance with energy can produce an effort, move, do work, or heat another substance.
• Energy is a property of a substance that can be classified into:
  • Energy Stored in a System
    • Internal Energy
    • Kinetic Energy
    • Potential Energy
  • Energy Transferred Between System and Surroundings
    • Heat
    • Work
• Forms of energy:
  • Clausius and Rankine developed the concept of 'internal energy' in the late 19th century.
  • Lord Kelvin proposed the use of 'energy' in thermodynamics in 1852.
  • Thomas Young introduces the term 'energy' in 1807.
  • Types include mechanical, chemical, nuclear, thermal, electromagnetic, and electrical.

Forms of Energy: Force

• Newton's 2nd law of motion quantifies the force (F) acting on an object (body).

Forms of Energy: Pressure

• Pressure (P) is the Force (F) acting on a surface divided by the area (A) of that surface.

Forms of Energy: Dynamic Interactions

• Heat (Q) is the form of energy that is transferred between two systems (or a system and its surrounding) by virtue of a temperature difference.
• Heat is transferred by: Conduction, Convection, and Radiation.

Forms of Energy: Work

• Work (W) is the product of the distance moved (Δx) times the magnitude of the force (F) opposing the motion.
• It is convenient to calculate the power (P or W) which is the rate at which work is done.
• Types of work include:
  • Work of expansion/contraction
  • Flow work
  • Shaft work
• The total energy (E) of a system is the sum of the internal, kinetic, and potential energies.
• Since total energy is an extensive property, it can be converted into an intensive property by calculating the specific energy (e).

Energy Types: Magnitudes

• The internal energy is much larger than the kinetic energy.
• The kinetic energy in turn larger than the potential energy.
• When become gases or vapors, the specific internal energy increases rapidly.
• KE and PE can be neglected compared to the internal energy.

Fundamental Laws of Thermodynamics

• These include:
  • Zeroth Law (temperature)
  • First Law (conservation of energy)
  • Second Law (entropy and direction of natural processes)
  • Third Law (absolute zero and system behavior).

Thermodynamics in Chemical Engineering

• Thermodynamics in the Chemical Manufacturing can use the following process:

1. Understanding, with Thermodynamic Properties
2. Analysis, with Heat transfer efficiency
3. Design, with Energy conservation methods
4. Operation, with Energy consumption calculations
5. Can be optimized through: Reactor Conditions, Catalyst effectiveness, Raw Material and Energy Requirements, and Material cost analysis