Calculator
Example data table
A ready-to-test blend using volume fractions and kinematic viscosity. Use “Load example” to copy these values into the form.
| Component | Volume fraction | ν (cSt) | ρ (kg/m³) |
|---|---|---|---|
| Oil A | 0.50 | 46 | 870 |
| Oil B | 0.30 | 100 | 890 |
| Oil C | 0.20 | 10 | 820 |
Formula used
How to use this calculator
- Select the number of components and your fraction basis.
- Choose a mixing model that matches your workflow.
- Enter each component’s fraction and viscosity at one temperature.
- Add densities if using mass fractions or dynamic viscosity units.
- Click Calculate to see results above the form.
- Use the download buttons to export CSV or PDF summaries.
For critical applications, validate blends with lab measurements and standards.
Mixing-rule estimates in early design
In blending operations, the calculator estimates a mixture viscosity before running lab tests. Engineers use the mixed value to size pumps, predict pressure drop, and check laminar or turbulent flow. For many mineral oils and solvents, a reasonable screening target is within about 10–20% of measured data. When components differ by decades in viscosity, selecting an appropriate mixing rule becomes essential for credible early design decisions. Aids routine screening and reporting.
Fraction basis, density, and units
Fraction basis matters because most viscosity rules weight by volume. If you start from mass fractions, the tool converts using densities so that the same blend gives consistent results. Enter densities in kg/m³ or g/cm³; common lubricant values sit near 800–950 kg/m³. Kinematic viscosity can be entered in cSt or mm²/s, then dynamic viscosity is derived as μ=mPa·s when ρ is available. Inputs are normalized automatically. to reduce rounding surprises.
How model choice shifts the estimate
Model selection influences the estimate, especially for wide viscosity spreads. The logarithmic rule gives a geometric-type mean and is a reliable baseline for many Newtonian liquids. The cubic Kendall–Monroe form can better match some hydrocarbon cuts but may drift high at extremes. Refutas converts ν to VBN and often performs well for lubricants from roughly 2 to 1000 cSt at one temperature. Grunberg–Nissan adds interaction term G12 for blends.
Input checks and sensitivity practices
Built‑in checks help prevent common input errors. Fractions should sum to 1.0, but the calculator will normalize and report the adjusted values. Always keep all component viscosities at the same temperature, because viscosity changes sharply with temperature. If you need extrapolation, document the method separately; ASTM D341 is frequently used in industry. Sensitivity testing is useful: a small fraction of a very viscous component can shift ln‑based blends noticeably.
Documentation with CSV and PDF exports
Export features make the estimate traceable in reviews and audits. The CSV download captures component names, units, normalized fractions, and all model outputs in a single row set. The PDF summary is suited to design packages, change requests, or supplier discussions, and it prints cleanly. For batch work, keep consistent component naming and note any assumed densities. Final qualification should include a measured viscosity and, when needed, shear‑rate validation at temperature.
FAQs
1) Which mixing rule should I choose?
Start with the logarithmic rule for general screening. Use Refutas when blending lubricants and reporting in cSt. Try the cubic rule for hydrocarbon cuts. If you have blend data, tune Grunberg–Nissan using G12 to improve fit.
2) Why does the calculator ask for density?
Density is needed to convert mass fractions to volume weighting and to convert kinematic viscosity to dynamic viscosity. Without density, the tool can still compute kinematic results for volume-based rules.
3) Can I enter fractions as percentages?
Yes. If any fraction is greater than 1, the tool treats entries as percent and divides by 100, then normalizes the set.
4) Is this valid for non‑Newtonian fluids?
The rules assume Newtonian behavior at a single temperature. For shear‑thinning or thickening fluids, apparent viscosity depends on shear rate, so lab measurements and a rheology model are required.
5) Why do the models give different answers?
Each rule embeds a different assumption about molecular interactions and how viscosity scales with composition. Differences grow when component viscosities are far apart. Comparing multiple models helps you bracket an expected range before testing.
6) What temperature should the inputs represent?
Use viscosities measured at the same stated temperature, such as 40°C or 100°C for lubricants. Mixing rules do not correct temperature. If you must translate between temperatures, do it first and document the method.