Viscosity-pressure dependence — Barus & Roelands (reference case)
Barus and Roelands piezoviscosity ratios η/η₀ for one worked reference lubricant (η₀=60 mPa·s, pressure-viscosity coefficient α=20×10⁻⁹ 1/Pa, at p=100 MPa). The original site never ships the Barus/Roelands equations client-side — only this login-gated worked example.
Viscosity ratio, Barus, η/η₀7.39
Viscosity ratio, Roelands, η/η₀6.19
There is no Barus/Roelands equation in this source to generalize. This module reproduces the gate exactly: change any input away from the reference case and both outputs are undefined (NaN), matching the original blanking the fields.
Method & references
- Barus equation — accurate up to about 0.1 GPa.
- Roelands equation — more accurate at higher pressure.
- The legacy client-side source contains no piezoviscosity formula — only a login gate around two hardcoded results for one reference case. This port is faithful to that: it is not a general viscosity-pressure calculator.
The computation is a literal port of the original client-side JavaScript from /calculators/barus_roelands.htm. Results are verified equal to the original by an automated golden-master test. No formula has been re-derived or “improved”.