Halvreversibel

Halvreversibel is a term used in thermodynamics and related technical disciplines to describe a process that contains both reversible and irreversible components. The word derives from the roots meaning half or partial (halv/half) and reversible, reflecting a process that is not entirely ideal or reversible.

Conceptually, a halvreversibel process is one in which part of the transformation can, in principle, be reversed without net entropy production, while another part proceeds irreversibly and generates entropy. This combination is common in real systems where ideal, quasi-static steps are interspersed with dissipative effects such as friction, finite-rate heat transfer, chemical dissipation, or material hysteresis. The overall state change and work exchange depend on the balance between the reversible and irreversible portions.

In analysis, the total entropy change of a halvreversibel process can be viewed as the sum of an ideal, reversible contribution and a positive irreversibility term. If the irreversible portion approaches zero, the process becomes fully reversible; if the reversible portion is negligible, the process behaves like a fully irreversible one. The concept is useful for estimating efficiency losses, optimizing cycle design, and understanding the impact of rate limitations and dissipation in engines, heat pumps, and chemical reactors.

Usage and terminology vary by field; halvreversibel is most common in languages that explicitly distinguish partial reversibility. Related concepts include quasi-reversible or semi-reversible processes, which describe intermediate behavior between ideal reversibility and full irreversibility.