Availability Efficiency⚠ unverified
Physics / Thermodynamics · Compute the second-law (exergetic) efficiency
Parameters
| Input | Symbol | Unit | Default | Description |
|---|---|---|---|---|
| W_actual | Wactual | J | 1.0 | Actual work produced |
| W_rev | Wrev | J | 1.0 | Reversible (maximum available) work |
| Output | Symbol | Unit | Description |
|---|---|---|---|
| result | ηII | — | Second-law efficiency (dimensionless). Returns 0.0 if ``W_rev`` is not positive |
The science & history
Understanding the Parameters
- $W_{\mathrm{actual}}$ — measured or first-law work of the real device.
-
$W_{\mathrm{rev}}$ — from exergy balance / reversible limit between the same states (or Carnot- limited heat input). Must use a consistent sign convention (both positive magnitudes for engines).
-
$\eta_{II}$ — $\le 1$ for engines when $W_{\mathrm{rev}}$ is the maximum producible work; for work-consuming devices the ratio is often inverted in textbooks — check your definition.
Derivation (Approaching a Proof)
Exergy destroyed is $W_{\mathrm{rev}} - W_{\mathrm{actual}}$ (engine). The fraction of reversible work actually obtained is
$$\eta_{II} = \frac{W_{\mathrm{actual}}}{W_{\mathrm{rev}}}.$$
This is definitional once both works are defined; it incorporates second-law losses that first-law Thermal Efficiency can miss.
History
Second-law efficiency became standard in modern energy-systems analysis to rank processes that look similar on a first-law basis but destroy different amounts of exergy.
Related Concepts: Exergy, Exergy Destruction, Availability Change, Carnot Efficiency, Thermal Efficiency
Notes: Registry calculator availability-efficiency (unverified). Simple ratio form; device-
specific $\eta_{II}$ definitions may differ.