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Heat 'scavenging' could reduce vehicle weight for little outlay

02 November 2012

US Army researchers are scavenging heat dissipated by weapon system engines or tailpipes and turning it into electrical power. The work could lead to smaller, lighter ground and air vehicles.

M1A2 Abrams main battle tank at Fort Benning, Ga. (US Army photo)
M1A2 Abrams main battle tank at Fort Benning, Ga. (US Army photo)

In one of its latest research projects, the US Army Research Laboratory (ARL) is investigating thermoelectric properties of materials on the Shadow Tactical Unmanned Aerial System (UAS), and techniques that could convert heat into energy. The Shadow UAS is used by the Army and Marine Corps for reconnaissance, surveillance, target acquisition and battle damage assessment.

The team is studying the possibilities of 'thermoelectric power generation' - taking advantage of the electric power producing potential between hot and cold surfaces, like the difference between engine exhaust gases and the cold air at altitude. This is wasted energy that ARL researchers are looking to harness, package and shrink, with the hope that it could one day lead to soldier-worn power sources converted from body heat and cool ambient air, or reduce the size of a vehicle alternator.

Earlier this year, ARL teamed with Research Triangle Institute (RTI) International, General Dynamics Land Systems and Creare, Inc., to demonstrate a prototype robust energy harvesting system that converts residual thermal energy from an M1 Abrams tank exhaust into useable electric power. The waste heat recovery system captures heat from the exhaust of the turbine engine, converts this heat into electrical power with a thermoelectric generator, and dissipates the heat through a heat-rejection system.

A report of that effort revealed that the prototype waste heat recovery system, once scaled up, could be retrofitted to existing tanks without requiring any modification to the engine or powertrain. A small-scale demonstration of more than 80W of power from the exhaust heat of an M1 Abrams tank set the stage for developing a full-scale system to recover waste heat from the vehicle.

ARL's unmanned aerial vehicle (UAV) study began as a first principles analysis that looked at the total energy available in the fuel, and made certain assumptions about how much was used in generating power and how much was lost as waste heat. Researchers then applied that waste heat to a model thermoelectric device and showed that this work, at a minimum, is promising and there is perhaps some region of overlap between the operating conditions of the UAV and the operating range of the thermoelectric device that will be useful to the military.

ARL developed novel techniques to miniaturise and manufacture custom thermoelectric devices to increase the scope of applicable missions. For example, miniature autonomous microsystems that have curved exhaust ducting that generate heated surfaces from air swirling inside the duct, could offer could offer new potential areas for applying new thermoelectric devices.

Researchers say developing thermoelectric technology is a worthy pursuit, because it has no moving parts, low weight, modularity, covert and silent, high power density, low amortised cost and long service life with no required maintenance.

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