Advanced man-mounted heat-pipe for portable cooling

Numerous military and civilian occupations expose workers to high thermal stress, impairing performance and increasing injury risk. This problem is exacerbated for workers using encapsulating clothing ensembles (e.g., chemical or fire protective clothing). This paper reports on an effort by the authors to develop a man-mounted air-based cooling system that permits sustained operations under thermal stress. A desiccant (zeolite)-based heat pipe is under development that utilizes water as the heat transfer medium that is adsorbed by a zeolite bed. The cooling system is designed to integrate with a ventilated garment to exploit the body's evaporative cooling capacity. Cooling efficiency is attained by blowing cool, relatively dry air over the user's body surface and evaporating sweat. The system is designed to provide 300 L/min ventilation with a sustained temperature change (ambient - cooler output) ≥ 10 degrees C at ambient conditions = 32.2 degrees C, 30% RH. Evaporative cooling greatly enhances a convective cooling capacity roughly = 60W, based on a change in enthalpy = -9.80 kJ/kg across the heat exchanger capacity, to approximately 365W (assuming maximal sweat evaporation). The system is sized (mass of zeolite and internal water, power supply) to operate up to 3 hours at full efficiency. Current total system weight is approximately 5.9 kg with a target weight ≤ 4.5 kg and is configured to fit on a U.S. Navy helicopter crewman vest. The prototype system has performed up to specifications during bench top testing (roughly 170 min at temperature change ≥ 10 degrees C).