Human Physiological Model Helps Evaluate NASA's Liquid Cooling Garments

Advanced Automotive Manikin
(ADAM) human physiological model
National Renewable Energy Laboratory
Golden, CO

Although space is mostly a cold environment, space suits traditionally have been designed like a Thermos bottle to prevent rapid cooling or high heat influx from the Sun and infrared sources. For an astronaut, this means that a cooling or ventilation system is needed within a spacesuit. Starting with the Gemini program, through the International Space Station (ISS) program, a liquid cooling garment (LCG) has been used to cool astronauts by removing heat from the skin directly to the garment’s water tubes.

To evaluate its LCGs, NASA used an Advanced Automotive Manikin (ADAM) controlled by a finite-element physiological model that approximates human thermoregulatory responses to external thermal stimuli. The 40,000-element model predicts bone, muscle, fat, and skin temperatures, as well as heat transfer through the circulatory system. Vasoconstriction, vasodilation, and heat loss through breathing are modeled. As a result, ADAM has human-like responses to thermal environments. The human thermal comfort empirical model is based on the results of 109 human subject tests under various non-uniform, transient thermal environments. It determines how a person would feel thermally by determining local thermal sensations, which are used to predict local and global thermal comfort.

In experiments, ADAM’s thermal response to a baseline LCG was measured, and the thermal sensation and comfort followed the expected trends as the LCG inlet fluid temperature was changed. The overall thermal comfort showed less variation than expected when testing points off the NASA comfort curve. The results also can be applied to other personal protective clothing, including HAZMAT suits, nuclear, biological, chemical, or fire protection suits.

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