MS Thesis Presentation by Timothy C. Ernst
Friday, February 11, 2005
(Dr. Srinivas Garimella, Chair)
" Design, Fabrication and Testing of a Wearable Cooling System"
A wearable cooling system was developed in this study for use in elevated temperature environments by military, fire-fighting, chemical-response, and other hazardous duty personnel. Such a system is expected to reduce heat-related stresses, increasing productivity and allowable mission duration, reduce fatigue, and lead to a safer working environment. The cooling system consists of an engine-driven vapor-compression system assembled in a backpack configuration, coupled with a cooling garment containing refrigerant lines worn in close proximity to the skin. A 2 L racing engine fuel tank in the back pack powers a small-scale engine that runs a compressor modified from the original air compression application to the refrigerant compression application here. A centrifugal clutch and reduction gear train system was designed and fabricated to couple the engine output to the refrigerant compressor and heat rejection fan. The overall cooling system, including the wearable evaporator, had a total mass of 5.31 kg (11.7 lb) and measured 0.318 × 0.273 × 0.152 m (12.5 × 10.75 × 6 inches).
Testing was conducted in a controlled environment to determine system performance over a wide range of expected ambient temperatures (37.7-47.5°C), evaporator refrigerant temperatures (22.2-26.1°C), and engine speeds (10,500-13,300 RPM). Heat removal rates of up to 300 W, which is the cooling rate established in the literature as being required for maintaining comfort at an activity level comparable to calisthenics or moderate exercise, were demonstrated at a nominal ambient temperature of 43.3°C (110°F). Modeling the fuel as 88 percent methanol (LHV ~ 1.992×107 J/kg) and 12 percent oil, the system consumed 1750 W at an average fuel mass flow rate of 0.316 kg/hr to provide a nominal cooling rate of 178 W for 5.7 hrs between refueling.