Military

May 2002 Excerpt

Thermal Management for the Next Generation Navy

By Mark Zerby

PHILADELPHIA—Warships of the future will have electrically powered propulsion systems, auxiliary systems, launchers, sensors, countermeasures, and high power weapons. These, coupled with low self-signatures, will permit detection and engagement of the enemy far outside the envelope for counterattack.

Future warship and combat vehicle machinery systems will provide warfighters the capability to make mission-based tactical allocations of total installed power among weapons, sensors, propulsion, and mission loads. Breakthroughs in propulsion, power generation, power distribution, and power conversion will provide the critical concepts, architectures, and systems to enable this revolutionary warfighting advantage.

This technology has distinct advantages … and penalties—a marked increase in the amount of waste heat generated. This heat is generated due to changes in circuit topology. Circuit topology is an arrangement of electrical components such as switches, inductors, capacitors, and resistors to perform an electrical function. Circuit topology objectives for the enabling advanced power electronics are to:

• Improve power fidelity (as a result of increased switching frequency).
• Reduce power electronics size.
• Increase power capability (longer switch transition times, higher on-state voltage, and current).

The implementation of the design features to achieve these objectives for the next generation of power electronics results in the generation of additional waste heat. Thermal issues are key in electronic product development at all levels of the electronic product hierarchy, from components such as the chip to the transfer of heat through ship systems and out to sea. Shrinking component sizes are resulting in increasing volumetric heat generation rates and surface heat fluxes in many devices. The rate of heat flux is expected to eventually top 1000 watts per square centimeter due to material advances, smaller electronics components, and faster switching speeds. The addition of advanced power electronics, advanced radar, dynamic armor, and weapons systems such as the EM Railgun and the Free Electron Laser in future Naval combatants, will result in heat loads eventually requiring a 700% increase in cooling capacity.

Because of the importance of cooling to the success of the electric ship, NSWCCD Code 825 was tasked to conduct an investigation during FY 01 of next generation cooling of power electronics for future Naval ship application. The task was funded by the Office of Naval Research (ONR), under the direction of the ONR Code 334 Program Manager Dominic Troiano and the ONR Code 334 Program Officer Terry Ericsen. The program determined the thermal management impacts due to implementation of power electronic components, advanced weapons systems and the strategy needed to provide cooling to these additional loads in future naval combatants.

Code 82 has been involved in researching innovative thermal management solutions to the increased heat loads anticipated for the Next Generation Navy. Michael Kuszewski (825) is the leader of the Next Generation Navy Thermal Management (NGNTM) team. Mark Zerby (825) has recently delivered a report to ONR titled “Next Generation Navy Thermal Management.” This report documents the thermal management impacts due to the addition of power electronic components, the implementation of advanced weapons systems, and the strategy needed to provide cooling to these additional loads in future naval combatants. Zerby worked with Code 81 to become familiar with the design and operation of future power electronics and to define the power electronics heat loads for the future Navy. Instrumental in this effort were Stephen Smith (813), Dr. Laura Stubbs (812), and Joseph Sullivan (813).

The study’s conclusions highlight the fact that heat rejection and heat transfer are critical to the electric warship. The increases in switching frequency enabling higher power quality in future power electronics and the sheer magnitude of the heat loads located in increasingly smaller enclosures will have exacerbated an already growing heat transfer situation.

Thermal management has been identified by Code 82 as an enabler of the electric warship. Advanced power electronics require an evolution in cooling technology to be operational in the electric warship. Several new cooling technologies have been studied and identified as candidates to provide cooling aboard the electric warship. Technologies such as heat pipes, magnetic refrigeration, thermoacoustics, and thermoelectrics have been identified for risk reduction and/or demonstration models.

In addition to cooling technology, advanced power electronics also require a systems approach to enable the extremely high heat fluxes to be rejected to the sea. To determine the impacts of inserting a particular advanced thermal management technology, an integrated systems approach is needed. A new technology may or may not be effective within existing system architecture. New system architectures may be necessary to fully implement these technologies. Also, there may be instances where the new technology is the new system architecture. Using an integrated systems approach will account for interactions and resulting benefits/adverse effects. A number of thermal management architectural concepts have been identified for future development and demonstration.

High power sensors and weapons require a systems approach based on the documented emerging cooling requirements to enable effective thermal management on next generation naval vessels. The concepts proposed in this report address a number of alternative cooling technologies and a number of alternative architecture approaches to explore as these new capabilities are defined. Current team emphasis is on developing modeling and simulation tools to support implementation of these technologies and concepts.

Greg Anderson (825) is developing thermal models as part of a technology evaluation exercise for the Integrated Power Systems (IPS) program and for use inside the Virtual Test Bed (VTB), which is being developed by the University of South Carolina. The VTB presently includes electrical power models developed under the program. He plans to introduce a thermal model into the VTB under the Electromagnetic Aircraft Launch (EMALS) program.

Denis Colahan (824) has worked with Thermacore to develop a next Generation bleed air cooler concept. This concept will decrease maintenance problems due to heat exchanger scaling caused by the excessive temperatures of the bleed air using Thermacore heat pipes to cool the air and greatly reduce the amount of scaling. He is also working with Thermacore heat pipe technology in the development of “thermal bus” solutions for cooling electronic cabinets.

Kevin King (822) is presently working with Penn State University in the development of the “Triton,” which is a 3-ton thermoacoustic chiller now being prepared for testing. He is also active with industry and academia in the development of cooling technologies such as magnetic refrigeration and thermoelectrics. Currently, King has an active CRADA in place with Astronautics to explore Navy applications of magnetic refrigeration.

Zerby has worked for the last three years defining thermal management requirements for the Next Generation Navy, and identifying and evaluating emerging thermal management technologies for application to future naval vessels under the sponsorship of ONR and PMS 510.