Wearable Air Conditioners Will Keep GIs Cool

By Roland Piquepaille

Modern soldiers are equipped with heavy suits which can protect them from chemical and biological weapons. But in case of extreme heat, they can be quickly incapacitated. The same is true for firemen. Now, researchers at Pacific Northwest National Laboratory are showing lightweight and man-portable cooling technology, leading to truly wearable air conditioners. As says this news release, "Hot, new microtechnology keeps GI's cool."

Researchers at Pacific Northwest National Laboratory are in the process of developing and demonstrating heat-actuated lightweight and compact cooling technology capable of sustaining manageable temperatures within the protective garb for several hours at a time.

The principles of microtechnology and the very high rates of heat and mass transfer at this miniature scale -- about the thickness of the human hair -- have enabled man-portable cooling systems now foreseen to weigh in at about three to four pounds. The system can chill water which flows through a vest worn by a solider capable of providing relief for up to six hours. Instead of using electricity to power a mechanical compressor, heat from burning fuel is used to power the cooling, thereby replacing bulky, heavy batteries with much lighter fuels. The key for making this portable is microtechnology, which can reduce the size and weight of a system based on traditional technology by five to 10 times.

Of course, this technology will be deployed for civilians as well.

"This same heat-actuated cooling technology will soon be used to benefit both military and commercial applications," said Ward TeGrotenhuis, chemical engineer at the Department of Energy's Pacific Northwest National Laboratory. "From troops operating in desert environments to astronauts or hazmat [hazardous materials] teams working in extreme conditions, the same principles apply."

In "Powerful machines are coming in small packages," the American Association for the Advancement of Science (AAAS) adds more details.

While conventional refrigeration systems in the United States require huge amounts of electricity, the one designed by Ward TeGrotenhuis and his colleagues at Pacific Northwest National Laboratory could run off burning fuel, carried in lightweight, portable canisters. They have demonstrated that miniaturizing each of the components of such as system is possible and are now working on fitting all the pieces together.

The final product would consist of an absorption heat pump, which would fit in a small backpack, connected to a vest threaded with water-filled microchannels. The water would be cooled in the pump then recirculated through the channels to keep the person wearing the vest from overheating.

And this kind of research field already has its acronym: MECS.

TeGrotenhuis, Paul, and their colleagues call their field "MECS," for "Microtechnology-based Energy and Chemical Systems." They have taken their cue from the technology known as "MEMS" (Microelectromechanical Systems), which involves the flow of electricity rather than fluids through micromechanical structures.

TeGrotenhuis presented his research work, "Miniaturized Man-Portable Cooling Systems" at the AAAS Annual Meeting and Science Innovation Exposition in Seattle on Friday, February 13. You can find the abstract by following a link to the "Miniaturization of Chemical, Energy and Biological Systems for Security Applications" symposium. Please find it below for your convenience.

Security personnel performing labor intensive tasks are vulnerable to heat stress when donning nuclear, biological and chemical (NBC) protective clothing, especially in hot environments such as the Middle East. Supplemental cooling will improve the efficacy, productivity, and longevity of personnel under NBC conditions. Of course, such a system must be lightweight and compact enough to be carried, including both the cooling system and power source. When electricity intensive approaches are taken, such as the conventional vapor compression cycle, the compactness of the system is ultimately constrained by the power density of batteries. Alternatively, the electrical power demand can be radically reduced by using heat-actuated cooling, thereby replacing batteries with liquid fuel having much higher energy density. The absorption heat pump is one heat-actuated alternative where the compressor of a vapor compression cycle is replaced by a thermochemical compressor, consisting of an absorber, desorber, liquid pump and recuperative heat exchanger. Here refrigerant vapor is absorbed into a solution at low pressure while heat is rejected at ambient temperature. The vapor is then desorbed at high temperature and pressure in a desorber which is supplied with combustion heat, thereby accomplishing compression. Recuperation of heat from the hot solution to the cold solution improves energy efficiency. The critical issues in developing a miniaturized absorption heat pump are mass transfer in the absorber and desorber and effective heat exchange for rejecting waste heat. Microchannel technologies offer a unique approach for intensifying these transport processes by reducing the characteristic length-scale to approximately a hundred microns. Data are presented that demonstrate the principles and viability of the technology as well as results supporting eventual size and weight objectives. Progress toward the demonstration of an integrated breadboard demonstrated is reported.

Sources: Pacific Northwest National Laboratory news release, February 13, 2004; American Association for the Advancement of Science press release, February 13, 2004, via EurekAlert!