Thermodynamics and Energy Concepts

Thermodynamics and Energy

• Thermodynamics is the science of energy, which is the ability to cause changes.
• The first law of thermodynamics states that energy cannot be created or destroyed, only transformed.
• The second law of thermodynamics states that, while energy is conserved, it loses quality when transformations from one form to another occur.
• Classical thermodynamics is a macroscopic approach that focuses on the overall behavior of systems.
• Statistical thermodynamics, on the other hand, takes a microscopic approach, focusing on the behavior of individual particles.

Importance of Dimensions and Units

• Any physical quantity has dimensions, which are assigned magnitudes called units.
• SI (International System of Units) is a decimal-based system, while the English system uses arbitrary relationships between units.

Systems and Control Volumes

• A system is a specific quantity of matter or a region in space under study.
• Surroundings refer to everything outside the system.
• The boundary separates the system from its surroundings and can be fixed or movable.
• A closed system, also known as a control mass, involves a fixed amount of mass with no mass crossing its boundary.
• An open system, or control volume, is a region in space that typically encloses a device involving mass flow (e.g., compressor, turbine).
• Both mass and energy can cross the boundary of a control volume.
• The control surface defines the boundaries of a control volume.

Properties of a System

• A property is a characteristic of a system.
• Intensive properties are independent of the system's mass (e.g., temperature, pressure, density).
• Extensive properties depend on the size of the system (e.g., volume, mass).
• Specific properties are extensive properties per unit mass, like specific volume and specific weight.
• Density is mass per unit volume, while specific volume is volume per unit mass.
• Specific gravity is the ratio of a substance's density to the density of a reference substance (usually water at 4°C).
• Specific weight is the weight of a unit volume of a substance.

State and Equilibrium

• Thermodynamics primarily deals with equilibrium states, where there are no unbalanced forces within the system.
• Thermal equilibrium: Uniform temperature throughout the system.
• Mechanical equilibrium: No pressure changes within the system over time.
• Phase equilibrium: The mass of each phase in a multi-phase system remains constant.
• Chemical equilibrium: No chemical reactions are happening within the system.

Processes and Cycles

• A process represents any change a system undergoes from one equilibrium state to another.
• The path illustrates the series of states a system passes through during a process.
• Describing a process requires knowing the initial and final states, the path taken, and interactions with the surroundings.
• A quasi-static process occurs when the system remains infinitesimally close to equilibrium throughout the process.
• Process diagrams use thermodynamic properties as coordinates (e.g., temperature, pressure, volume) to visualize processes.
• The prefix "iso-" denotes a process with a constant property:
  • Isothermal: Constant temperature (T).
  • Isobaric: Constant pressure (P).
  • Isochoric (or isometric): Constant specific volume (v).
• A cycle completes a process by returning to the initial state.

The Steady-Flow Process

• "Steady" implies no change with time.
• A steady-flow process refers to fluid flowing steadily through a control volume (continuous operation).
• Continuous operation devices like turbines, pumps, boilers, condensers, and heat exchangers approximate steady-flow conditions.

Temperature and the Zeroth Law of Thermodynamics

• The 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.
• In simpler terms, if two objects have the same temperature reading on a thermometer, they are in thermal equilibrium.

Temperature Scales

• Temperature scales are based on reproducible states (e.g., freezing and boiling points of water).
• The ice point refers to the equilibrium between ice, water, and saturated air at atmospheric pressure (0°C or 32°F).
• The steam point refers to the equilibrium between liquid water and water vapor at atmospheric pressure (100°C or 212°F).
• The Celsius scale is used in the SI unit system, while the Fahrenheit scale is used in the English unit system.
• The thermodynamic temperature scale is independent of the properties of any specific substance.
• The Kelvin scale (SI) and Rankine scale (E) are thermodynamic temperature scales.
• An ideal-gas temperature scale, closely related to the Kelvin scale, uses a constant-volume gas thermometer.

Pressure

• Pressure represents the normal force exerted by a fluid per unit area.
• Absolute pressure is the actual pressure at a point, measured relative to absolute vacuum.
• Gauge pressure represents the difference between the absolute pressure and the local atmospheric pressure.
• Vacuum pressures are below atmospheric pressure.
• Pascal's law states that pressure applied to a confined fluid increases the pressure throughout the fluid by the same amount.

Atmospheric Pressure

• A barometer is an instrument used to measure atmospheric pressure (often called barometric pressure).

Test your knowledge on the principles of thermodynamics, including the first and second laws, and the significance of dimensions and units in physical quantities. The quiz also covers the concepts of systems and control volumes in the study of energy. Dive into the essential aspects of energy transformation and conservation.