What are the types of boundaries in thermodynamics?

In thermodynamics the types of boundaries are fixed, movable, real and imaginary.

• A boundary in thermodynamics is the surface (real or imaginary) that separates a system from its surroundings.
• The four types of boundaries:
  • Fixed boundary: boundary does not change shape, size or position (e.g., a rigid container).
  • Movable boundary: boundary can move or change shape (e.g., piston in a cylinder).
  • Real boundary: an actual physical barrier in the system (e.g., walls of a vessel).

  • Imaginary boundary: a conceptual surface without physical material, used for analysis (e.g., control volume boundary drawn in open-system analysis).