Keeping Cool Under Pressure

09/01/2023
By Edwin L. Aquirre

Conflicts can break out in any part of the world, and keeping the soldiers who are engaged in those conflicts cool and comfortable in the field can be a challenge, especially in harsh jungle or desert environments.

A team of researchers from the Harnessing Emerging Research Opportunities to Empower Soldiers (HEROES) initiative at UMass Lowell and the Army DEVCOM Soldier Center in Natick, Massachusetts, is working to alleviate the situation with an improved microclimate cooling system. The lightweight cooling vest is designed to be worn by military personnel—from helicopter pilots to bomb-disposal technicians—over their undershirt to increase comfort and allow them to work effectively in hot, humid environments for extended periods of time.

While cooling vests have been around for years, the team’s innovations could lead to significant enhancements to them.

“Our goal was to build upon prior research efforts to further improve the performance and efficiency of the soldiers’ cooling system,” says Mechanical Engineering Assoc. Prof. Hunter Mack, the project’s principal investigator.

“Our goal was to build upon prior research efforts to further improve the performance and efficiency of the soldiers’ cooling system.” -Assoc. Prof. Hunter Mack

He says the team’s approach was to focus on the materials used in the vest, rather than developing a dramatically different cooling system.

“This was a deliberate decision on our part, to shorten the timeline between lab research and prototyping to actual deployment in the field,” Mack says. “If we are able to borrow components from existing cooling vests and leverage approaches that have already been proven in the field, it increases the likelihood of success.”

The project is supported by a grant totaling $450,000 from the Army. Mack’s co-PIs are Profs. Meg Sobkowicz-Kline and Stephen Johnston of the Department of Plastics Engineering.

Military and Civilian Applications

The team’s active microclimate cooling system consists of heat-absorbing flexible tubes stitched onto a vest that covers only the chest and back so it does not hinder the soldier’s motion and mobility. A small, battery-powered pump circulates water through the closed-loop system; the water goes to a heat exchanger to dissipate excess heat away from the body before flowing back into the vest. The fully loaded vest weighs approximately seven pounds.

The heat output of a human body can reach as high as 600 watts per square meter, which corresponds to the body’s output during a constant, strenuous paced run, says Mack. If not addressed, this can lead to heat stress, a serious condition in which the body cannot get rid of excess heat.

According to Mack, one of the main innovations of the project was the successful fabrication of the cooling tubes using special formulations of polymeric materials. By using custom composites rather than commercial resins, they were able to produce tubing with significantly higher thermal conductivity, he says.

“This resulted in a 10% increase in the system’s cooling performance, compared to previous benchmarks,” says Mack.

The researchers were able to construct prototypes of the vests and test them using an in-house testing chamber in Mack’s lab. They also evaluated the system performance through a combination of computational modeling and eventual testing using sensor-laden manikins.

Mack says the technological advances that the team has demonstrated have applications beyond the military, including civilian high-heat jobs such as farm workers, firefighters, construction laborers, roofers, road pavers, welders and foundry workers.

“In fact, one of our collaborators, Rini Technologies, has developed systems that are in use by professional race car drivers. Additionally, there may be medical applications related to body-temperature regulation that could benefit from using materials with different thermal properties,” he says.

Seven undergraduate and graduate students worked with the team on the lab research. UMass Lowell’s Fashion Makerspace at the Fabric Discovery Center also collaborated on the project.

“Diana Coluntino, director of the Fashion Makerspace, was instrumental in constructing our prototype vests,” Mack says. “Modern Dispersions Inc. in Leominster, Massachusetts, also provided thermally conductive materials for use in our cooling tubes.”

A Great Opportunity for Collaboration

“This project helps improve the next generation of high-performance cooling garments,” says Michael R. Zielinski of the Soldier Effectiveness Directorate’s Advanced Soldier and Small Unit Equipment Team at the U.S. Army DEVCOM Soldier Center.

“The development of new thermally conductive polymer blends will help our efforts to improve overall cooling system performance and efficiency, and subsequently help reduce logistical burdens on our soldiers for portable cooling system applications,” he says.

Zielinski says the HEROES initiative is a great opportunity to work with academia and expand the Soldier Center’s research and development efforts to a wider support network.

“The faculty and student researchers are excellent. I really enjoyed working with everyone and I learned a lot from them,” he says.