Journal Bearing Power Loss (Petroff Law) Calculator

Estimate viscous shear torque, mechanical friction power loss (kW / HP), and coefficient of friction in hydrodynamic sleeve bearings.

Bearing Geometry & Speed

Journal Diameter D (mm):

Bearing Length L (mm):

Radial Clearance c (μm):

Operating Speed N (RPM):

Oil Viscosity in Film μ (cP):

Eccentricity Ratio ε (0 = concentric):

Frictional Heat & Drag Torque

Friction Power Loss:

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Viscous Drag Torque (T):

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Journal Surface Speed (U):

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Petroff Friction Factor (f):

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Thermal Heat Dissipation Load:

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Frequently Asked Questions

What is Petroff’s law for journal bearing power loss?

Petroff’s law computes the viscous shear torque in a lightly loaded, concentric fluid-film bearing where shear stress τ = μ·(U/c). Integrating across the cylindrical journal area yields torque T = (2π·μ·ω·R³·L)/c.

How does shaft eccentricity affect frictional power loss?

As shaft eccentricity ratio ε increases, the oil film thins locally on the loaded side, increasing velocity gradients and viscous shear losses by a factor of 1 / √(1 - ε²).

Where does the frictional energy go in a journal bearing?

Virtually 100% of bearing mechanical friction is converted directly into thermal heat within the oil film, which must be carried away by continuous oil circulation to an external shell-and-tube or plate oil cooler.