OAK RIDGE, Tenn., – Staying cool under fire could take on a new meaning with a personal cooling system being developed at the Department of Energy’s Oak Ridge National Laboratory.
The system takes advantage of high thermal conductivity graphite foam, an ORNL material that boasts thermal conductivity five times greater than aluminum. As envisioned by James Klett of ORNL’s Metals and Ceramics Division, the system would provide chilled air to circulate within the suit and helmet of a fighter pilot.
"Our proposed system would enhance the performance of a person’s natural cooling mechanisms," said Klett, who led a team that developed the thermally conductive graphite foam. "Instead of simply cooling the skin through a uniform, our approach would remove heat from the body surface and provide cooled air to breathe."
While the initial use is expected to be for fighter pilots, developers envision the system being highly desirable for race car drivers, firefighters, hazardous materials workers and others who have to contend with protective clothing and hot working environments.
"In addition to these conditions being dangerous to these people, the heat can substantially degrade a person’s effectiveness," Klett said. "And we are working with the racing industry to develop a system geared toward drivers’ needs."
Researchers note that their system would not have the disadvantages of existing microclimate control technologies. Some circulate chilled air or chilled water throughout the suit while others use a phase-change material inside a specially designed suit.
"The main drawbacks of these systems are their large power requirements and poor thermal coupling to the user," Klett said. "Our system should overcome these difficulties."
One of the innovations is respiratory cooling, which Klett believe has great potential to supplement or replace other cooling methods. The lungs, Klett notes, have a very high surface area and a very effective heat transfer medium -- blood -- flowing between them and the rest of the body.
"It turns out that the lungs can reject a large fraction of the waste heat the body generates under duress," Klett said.
While the upper limit of respiratory heat rejection likely will be reduced by psychological effects and the reduced respiratory rates associated with more sedentary activities, a respiratory heat rejection system still should provide significant personal cooling under all conditions. It also should be most effective when a person is working the hardest.
Prototype personal cooling devices that provide respiratory cooling already have been developed by ORNL for NASCAR drivers.
"NASCAR drivers must function at peak performance for several hours at high ambient temperatures in heavy fire-resistant suits," Klett said. "While we haven’t performed detailed physiological measurements, we’ve worked with an outside contractor who told us the reaction from drivers has been very positive."
The proposed first effort will center on developing a system specifically designed to provide personal cooling for Navy pilots. Main tasks include refining a thermal battery system so it will be more efficient, lightweight and compact and integrating the system with the flight suit and helmet.
Similar systems could be incorporated easily into existing equipment and into future technologies to provide cooling for ground troops, firefighters and hazardous materials emergency responders.
Funding for work that led to the material was provided by ORNL’s Laboratory Directed Research and Development program, which is provided by DOE. ORNL is a Department of Energy multiprogram research facility managed by UT-Battelle.
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