Basically, the “boundary” is simply an imaginary dotted line drawn around the volume of a something in which there is going to be a change in the internal energy of that something. Anything that passes across the boundary that effects a change in the internal energy of that something needs to be accounted for in the energy balance equation. That “something” can be the volumetric region surrounding a single atom resonating energy, such as Max Planck defined in 1900, it can be a body of steam or air in a steam engine, such as Sadi Carnot defined in 1824, or it can be the body of a tropical cyclone, such as Kerry Emanuel theorized in 1986 in the field of atmospheric thermodynamics, or it can be a single nuclide, i.e. a system of quarks, as some are theorizing presently in quantum thermodynamics.
For an engine, a fixed boundary means the piston is locked at its position; as such, a constant volume process occurs. In that same engine, a moveable boundary allows the piston to move in and out. For closed systems, boundaries are real while for open system boundaries are often imaginary.
Molecular-level thermodynamic switch controls chemical equilibrium in sequence-specific hydrophobic interaction of 35 dipeptide pairs
Feb 01, 2003; ABSTRACT Applying the Planck-Benzinger methodology, the sequence-specific hydrophobic interactions of 35 dipeptide pairs were...
Extension of the implicit curve-fitting method for fast calculation of thermodynamic properties of subcooled refrigerants.(Report)
Sep 01, 2009; INTRODUCTION To enhance the energy efficiency of refrigeration systems, the design method needs to be improved. When designing...