KEVOS® MAKEOS · Power Transmission
Hydrodynamic Journal Bearing Design (Load, Friction, Heat and Oil)
Is this plain journal bearing within its unit load, how much heat does oil friction make, and how much oil must flow to carry it away?
First design of a full-film hydrodynamic journal bearing: unit load on the projected area, length-to-diameter ratio, surface speed, Sommerfeld number, Petroff friction torque, friction coefficient and power loss (as the Petroff tool), and the oil flow to carry the heat at an allowed temperature rise, with checks of unit load, L/D and Sommerfeld number against your limits.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Radial load | N | Radial load on the bearing. |
| Journal diameter | mm | Diameter of the journal. |
| Bearing length | mm | Length of the bearing. |
| Radial clearance | mm | Radial clearance (half the diametral clearance). |
| Speed | rpm | Shaft speed. |
| Oil viscosity at the film temperature | mPa·s (cP) | Dynamic viscosity of the oil at its working film temperature. |
| Allowed oil temperature rise | K | Temperature rise of the oil through the bearing. |
| Oil specific heat | kJ/kg·K | Specific heat of the oil. |
| Oil density | kg/m³ | Density of the oil. |
| Largest unit load | MPa | Largest unit load for the bearing material and duty (your value). |
| Smallest L/D | Smallest length-to-diameter ratio you design to. | |
| Largest L/D | Largest length-to-diameter ratio you design to. | |
| Smallest Sommerfeld number | Smallest Sommerfeld number you accept, so the film stays thick enough (your value). |
Method and formulas
- Unit load p = W ÷ (L d); surface speed V = π d n ÷ 60 000.
- Sommerfeld S = (r ÷ c)² μ N ÷ p, with N in rev/s.
- Petroff torque T = 4π² r³ L μ N ÷ c; f = 2π² (μ N ÷ p)(r ÷ c); power loss = 2π N T (as the Petroff tool).
- Oil flow = power loss ÷ (ρ c_p ΔT).
- Example: 5000 N on a 50 × 50 mm bearing gives 2 MPa, S = 0.12207, and 75.699 W of friction needing 0.27477 L/min of oil.
Limitations
- Petroff assumes a concentric, lightly loaded journal; at heavy load use the design charts for film thickness.
- Oil flow here carries heat only; the bearing’s own side leakage must also be supplied.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a plain bearing for a pump, fan or turbine shaft
- Estimate bearing heat and oil supply
- Compare clearances and oil grades
Who it is for
- Design engineers
- Maintenance engineers
- Power transmission engineers
What you get
- Unit load, L/D and surface speed
- Sommerfeld number and Petroff friction
- Power loss and oil flow
Interpreting the result
- A low Sommerfeld number means a thin film: raise viscosity or speed, or cut the clearance or unit load.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2326–2345. Topic reference; no source tables or recommended settings are reproduced.
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Open the Hydrodynamic Journal Bearing Design (Load, Friction, Heat and Oil) calculator
