Thermodynamics ER 1050 Overview

System and Surroundings

• A system is a defined quantity of matter or a region in space selected for study.
• Surroundings refer to everything outside the system.
• A boundary separates the system from its surroundings; it can be fixed, movable, and has no thickness.

Types of Systems

• Closed Systems

  • Known as control mass; contains a fixed amount of mass.
  • Mass cannot cross the boundary, but energy (heat or work) can.

• Open Systems

  • Also known as control volume; both mass and energy can cross boundaries.
  • Common in devices involving mass flow like compressors and turbines.
  • Control surface can be real or imaginary, and may vary in size and shape.

• Isolated Systems

  • A special type of closed system where neither energy nor matter can be exchanged with surroundings.

Properties of a System

• Properties include pressure (P), temperature (T), volume (V), and mass (m), among others.
• Properties can be categorized as:
  • Intensive properties: Independent of mass (e.g., temperature, pressure).
  • Extensive properties: Dependent on size or extent (e.g., total mass, total volume).
  • Specific properties: Extensive properties per unit mass (e.g., specific volume, specific total energy).

Continuum Concept

• The continuum assumption treats matter as continuous and homogeneous, ignoring molecular structure.
• Applicable when the system size is large compared to molecular spacing.

State and Equilibrium

• A state is defined by a set of properties that describe a system's condition; changes in one property alter the state.
• An equilibrium state refers to no unbalanced potentials within the system.
• Types of equilibrium include thermal, mechanical, phase, and chemical.

The State Postulate

• A simple compressible system’s state is identified by two independent intensive properties.
• For single-phase systems, temperature and specific volume can determine the state, while for multiphase systems, they may be dependent.

Processes and Cycles

• A process is a transition from one equilibrium state to another, with a sequence of states representing its path.
• Types of thermodynamic processes include:
  • Adiabatic: No heat transfer.
  • Isothermal: Constant temperature.
  • Isobaric: Constant pressure.
  • Isochoric: Constant volume.
  • Isentropic: Constant entropy.
  • Isenthalpic: Constant enthalpy.

Steady-Flow Process

• In a steady-flow process, fluid properties can vary from point to point within the control volume but remain constant at any fixed point.
• Ideal for continuous operation devices like turbines and pumps, while some cyclic devices can still be analyzed under steady-flow conditions with averaged properties.

Modes of Energy Transfer

• Heat: Energy transferred due to temperature differences.
• Work: Energy transferred through interactions other than heat.
• Both heat and work are recognized only during boundary crossing, are path-dependent, and represent energy interaction during processes rather than states.

Heat Transfer Modes

• Different methods of heat transfer include:
  • Conduction
  • Convection
  • Radiation