KEVOS® MAKEOS · Power Transmission
Gearbox or Hydraulic Unit Heat Balance and Cooling
How hot will this gearbox or hydraulic power unit run, and does it need a cooler?
Thermal balance of an enclosed gearbox or hydraulic power unit: heat generated from the power and efficiency, equilibrium oil temperature from the housing or tank surface area and a heat transfer coefficient (natural or fan-cooled), the thermal power limit for the maximum oil temperature, and the cooler duty and oil flow needed when the surface alone is not enough.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Unit | choice | Gearbox or hydraulic power unit (affects wording only). |
| Input power | kW | Power going into the unit. |
| Efficiency (gearbox) or overall system efficiency (hydraulics) | % | Share of input power delivered usefully; the rest becomes heat (worm gears can be 50–90%, spur and helical about 95–98% per stage; hydraulic systems often 60–80%). |
| Heat-dissipating surface area | m² | External surface area of the housing or reservoir that sheds heat (exclude the base on a foundation). |
| Heat transfer coefficient | W/m²·K | Heat transfer coefficient: about 10–15 W/m²·K in still air, 20–40 with a shaft fan or good air flow. |
| Ambient temperature | °C | Surrounding air temperature. |
| Maximum oil temperature | °C | Highest oil temperature you accept (from the lubricant and seals). |
| Oil temperature drop across the cooler | K | Temperature drop of the oil through the cooler. |
| Oil specific heat | kJ/kg·K | Specific heat of the oil. |
| Oil density | kg/m³ | Density of the oil. |
Method and formulas
- Heat generated = P (1 − η).
- Equilibrium oil temperature = T_amb + heat ÷ (h A).
- Thermal power limit = h A (T_max − T_amb) ÷ (1 − η).
- Cooler duty = heat − h A (T_max − T_amb); oil flow = duty ÷ (ρ c_p ΔT).
- Example: 15 kW at 92% efficiency on 2 m² settles at about 70 °C.
Limitations
- Steady state with uniform surface temperature; churning and fan effects are in the coefficient.
- Gear makers publish thermal ratings that supersede this estimate.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check whether a worm gearbox will overheat at full power
- Size an oil cooler for a hydraulic power unit
- Compare natural and fan cooling
Who it is for
- Design engineers
- Mechanical engineers
- Maintenance engineers
What you get
- Heat generated and equilibrium temperature
- Thermal power limit
- Cooler duty and oil flow
Interpreting the result
- If the thermal limit is below the mechanical rating, the thermal limit governs (as the handbook notes for worm gearing).
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3339–3340, 2430–2436. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Gearbox or Hydraulic Unit Heat Balance and Cooling calculator
