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Double Tube Rotating Machine Coolers

Increased safety and availability of cooling for generators and large electric motors

Double tube electrical machine coolers are a specific type of closed air circuit water-cooled (CACW) cooler. While removing excess heat generated by large electric motors and generators it exhibits, based on a specific design feature, increased availability for situation where it is critical to have equipment operational.

Key benefits

  • Compact – Marginally less efficient than a standard single tube CACW the double tube option is still a very compact arrangement.

  • Robust – Materials are selected to suit the coolant in use. Coolant can vary between inhibited fresh water to varying qualities of sea water.

  • Equipment availability – In addition to a level of in-built redundancy, the cooler is configured to allow continued operation for a limited period in the face of inner tube failure. This allows contingency plans to be put in place.

  • Marine approvals – The arrangement can be configured to meet third-party requirements for marine applications both for ships and offshore facilities.


How it works

All electrical motors and generators need a clean airstream to cool the internal components including the rotor and stator. Small electric motors simply have cooling fins on the outside of the motor frame. Larger machines generate much more heat, and direct cooling of the individual components is required.

Direct (primary) cooling is provided by passing air through passages within the machine air circuit. A fan on the machine shaft is used for air circulation in the majority of applications. A separate cooling fan is installed when necessary to establish a consistent airflow. Air alone is a poor heat transfer medium. A CACW cooler installed to facilitate the secondary cooling of the airstream enhances the heat transfer rate, significantly increases the cooling system efficiency.

If the tube is in contact with the water fail, the double tube feature ensures the leaking water is directed outside the cooler enclosure to a leak detection system. This gives the operator the opportunity to plan an intervention without immediately shutting down the machine or process.

Every installation is different. Some design considerations are given below:

  • Generator construction –double (safety) tube.
  • Redundancy requirements for series and / or parallel operating arrangements.
  • Restrictions to the available air side pressure drop.
  • Specifications for marine cooling equipment generally require double (safety) tube construction to ensure that a tube failure does not lead to the immediate shutdown of the generator or motor.
  • Limitations on the cooling water flow or permitted temperature rise of the water stream (Local Regulations can limit the increase allowed on water before discharging back to the sea or to an inland watercourse).


Our flexible optimising heat exchanger software offers a number of design options to suit all applications and restraints. We can call upon a wide range of options to meet your thermal and mechanical specifications for the overall equipment requirement.

Sterling Thermal Technology can address the most stringent requirements with our design capability, quality system and production facility. We can design and build in accordance with ABS, Lloyds, DNV and a range of other marine regulations.


If you feel you need another type of heat exchanger, visit our products and services page or contact us.

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We have used Double (safety) tube CACW Coolers for a number of different generator installations, mainly relating to marine applications. The service from Sterling Thermal Technology has been excellent and their products have always met our expectations.

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