KEVOS® MAKEOS · Engineering
Journal Bearing Friction (Petroff) and Sommerfeld Number
What friction torque, power loss and Sommerfeld number does this lightly loaded journal bearing have?
Unit load, Petroff friction torque, coefficient of friction and power loss of a hydrodynamic journal bearing, with the Sommerfeld number for use with design charts.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Journal diameter | mm | Journal (shaft) diameter. |
| Bearing length | mm | Bearing length. |
| Radial clearance | mm | Radial clearance = (bore − journal) ÷ 2. |
| Oil viscosity at operating temperature | mPa·s (cP) | Dynamic viscosity at the film temperature (centistokes × density in g/cm³ gives mPa·s; see the oil viscosity tool). |
| Speed | rpm | Shaft speed. |
| Radial load | N | Radial load on the bearing. |
Method and formulas
- Unit load P = W ÷ (d L).
- Petroff torque T = 4π² r³ L μ N ÷ c (N in rev/s); friction coefficient f = 2π² (μN/P)(r/c).
- Sommerfeld number S = (r/c)² μN ÷ P; power loss = 2πN T.
- Example: the default bearing has S = 0.12207, f = 0.0038553 and loses 75.699 W.
Limitations
- Petroff’s equation assumes a concentric journal (light load); at higher loads use the Sommerfeld number with design charts.
- Viscosity must be taken at the actual film temperature.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Estimate friction and heat in sleeve bearings
- Calculate the Sommerfeld number for Raimondi–Boyd charts
- Compare clearances and oils
Who it is for
- Design engineers
- Tribology and lubrication engineers
- Maintenance engineers
What you get
- Unit load
- Petroff friction torque and coefficient
- Power loss
- Sommerfeld number
Interpreting the result
- A larger Sommerfeld number means a thicker film; very small values risk boundary contact.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2326–2337. Topic reference; no source tables or recommended settings are reproduced.
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Open the Journal Bearing Friction (Petroff) and Sommerfeld Number calculator
