Pure-Liquid Viscosity Estimation Calculator

Content

Estimate the dynamic viscosity of a pure liquid from molar volume, normal boiling point, and absolute temperature. Use this approximate correlation only for early engineering screening.

Liquid properties

cm³/mol · benzene example

Stle

K

K · absolute temperature

Ready.

Estimated dynamic viscosity
—mPa·s
Pa·s—
Poise—
±30% screening band— mPa·s
Exponent, 3.8Tb/T—

How to use

  1. Confirm the fluid is a pure, Newtonian liquid and this single screening mode is suitable.
  2. Enter molar volume V in cm³/mol from a credible property source.
  3. Enter normal boiling point Tb and evaluation temperature T, both in kelvin.
  4. Select Calculate to update the mPa·s result, conversions, screening band, and temperature trend.
  5. Select Reset to restore the benzene example and recalculate.
  6. Read the central estimate first and treat the ±30% range as an approximate error band, not a confidence interval.
  7. Do not use this model for mixtures, long, slender molecules, non-Newtonian fluids, phase transitions, high-pressure prediction, safety-critical design, or when measurements are required.

Equations used

μ = (NAh/V) exp(3.8Tb/T)

E = 3.8Tb/T · μPa·s = μP/10 · μmPa·s = 100μP

μlow = 0.70μ · μhigh = 1.30μ

Symbols and units. μ is dynamic viscosity. The correlation first gives μP in poise: 1 P = 1 g/(cm·s) = 0.1 Pa·s = 100 mPa·s. NA = 6.02214076×10²³ mol⁻¹ is the exact Avogadro constant; h = 6.62607015×10⁻²⁷ erg·s = g·cm²/s is the exact Planck constant; V is molar volume in cm³/mol; Tb is normal boiling point in K; T is evaluation temperature in K; E and 3.8 are dimensionless; exp is the natural exponential. Temperatures are positive absolute quantities—there is no signed temperature difference.

FunctionalProduct

Assumptions and limits. The model assumes one pure Newtonian liquid in a single liquid phase, representative property inputs, and low-pressure screening. Reported errors as large as ±30% are common, so the bounds are not statistical confidence limits. Very long, slender molecules are outside the method’s scope. Prefer measured viscosity whenever available.

References. Bird, Stewart & Lightfoot, Transport Phenomena, 2nd ed., Chapter 1, p.31 (publisher); NIST/CODATA fundamental constants; equation background.

Viscosity IndexViscosity–Temperature Interpolation