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Cooling garments (sometimes called "microclimate air-conditioning") permit the wearer to operate in thermal environments that would otherwise be debilitating. They have applications in construction, industry, the military, entertainment (costμmed characters at theme parks), sports, recreation (sportsmen), and medicine (patients incapable of controlling core body temperature, heat-stroke victims). Certain technologies maintain a specific temperature, whether by cooling or heating.
The garments variously operate with air, cooled water, evaporation, or phase-change (of water or hydrocarbon gel).
Basal (resting) metabolism, oft-quoted 2000 Calories per day, which works out to 90 watts. Physical exertion can increase that by 10 or 15 times, with corresponding increase in waste heat to be rejected. (Although the brain uses 20% of the body's blood supply/energy, and it increases with effort, not as much.) The hμman body pμmps heat through blood from the muscles to the skin, evaporative cooling by perspiration -- latent heat of water. (Effective because hμmans are largely hairless. Various other mammals, such as cats and dogs, do not perspire, and reject heat through the lungs, by panting. Also, those long noses contain a heat exchanger for the brain.)
Such devices manufactured as vests, but also chaps (for the legs), headgear (helmet liners, headbands, cowls), and neck (the large blood vessels in the neck make it a good place for heat exchange). Typically a washable fabric carrier with pockets for individual PCM packs, or a removable water bladder. Some also use an outer evaporative layer, which must be separately moistened. Vests typically effective for 2-4 hours, weight 5-10 lbs, and cost $200. Some can be adapted to heat (by charging with hot water instead of cool), and inherent PCM properties maintain heat in reverse -- if temp drops *below*, material freezes, releasing heat.
Phase-change materials (PCMs) exploit the thermodynamic property called "latent heat". Physical phase, meaning solid liquid gas. With "sensible heat", a liquid or solid material absorbs heat input, so long as it stays in that phase, a certain nμmber of joules per gram of material, its "specific heat". The heat needed to change phase, solid to liquid ("heat of fusion"), is much greater per gram; moreover, the material remains at a constant temperature. (Freezing water and melting ice are *always* at 0°C). Water ice (contained in flexible plastic packs), but since the transition at 0°C, multiple disadvantages: it's painful to hμman skin, so an intervening insulation layer is needed. It causes surface vasoconstriction, reducing the body's ability to pipe heat to the surface. It's below the dew point, condenses moisture from the air, stealing cooling capacity. It's necessarily recharged at freezing, impractical if an electrical freezer is not available. Long-chain hydrocarbons (ie, paraffins) have a melting temperature of 50-70°F, which avoids these problems. Can be rapidly recharged in a refrigerator or ice water, or less so by burying in sand (markedly cooler than surface layers), or allowing to radiate to night air.
The PAC Diffuse Air Vest ("personal air conditioner") by ITW Vortec of (1961 US/OH/Cincinatti) uses compressed air cooled via a "vortex tubes". Effective to 130°F alone, or 200°F with protective outer clothing. www.itwvortec.com/personal_air.php
(The "vortex tube" is an ingenious device with no moving parts, in which warm air enters a tube at an angle, forms an outer helical vortex, hot air escapes from an escape valve, reflects, inner cool vortex, forming an immaterial heat-exchanger; temperature can be adjusted by the escape valve.)
The Eliminator™ Thermal Comfort System vest, invented by Donny Jenkins and manufactured by Jenkins Comfort Systems LLC, contains a serpentine vinyl water bladder which is charged (with either hot or cold water, as necessary) from an external electric pμmp. An overvest for evaporative cooling, which must be separately moistened (by spritzing, or immersion-then-wringing). www.jenkinscomfort.com
The STACool Vest™ by ??? uses water(?) PCM packs, with an outer shell of Dupont Cordura® nylon and 3M Thinsulate™ insulation. www.stacoolvest.com
The HeatShield™ by ClimaTech/PCM Thermal Solutions of US/IL/Naperville uses PCM. The vest itself condenses body moisture, then wicks it out through channels between a surface layer of IR reflectors. The CoolMan™ uses a set of eutectic gel packs with differential cooling: 60°F on one side, 72°F on the other. Effective to 120°F for 4h. www.pcm-solutions.com/coolingvests.html
The CoolVest by CoolSport (US/CA/Torrance) uses PCM at 65°F, good at 100°F for 2.5h, which recharges in ice water in 20m or a fridge in 35m. (The difference: ice water permits more effective conductive heat loss.) Shell of poly cotton twill, or Supplex® and fire-retardant Banox F-R3®. The CoolVest Classic contains 4 Cool Packs and weights 4.8lbs. www.coolsport.net/index2.html, www.texascoolvest.com/index2.html
ThermalWear® vests (aka Chill-Its®) by Ergodyne® of (1983, US/MN/St.Paul) use a PCM 55°F, in a carrier of cotton fabric treated with Banox FR3. The company also sells a variety of evaporative cooling garments: headband, hat, neck shade, hard had liner, sweatbands. www.ergodyne.com/prod_bigframes.htm
Triangle Research & Development Corp (TR°C) developed encapsulated paraffin PCMs, used by its product group, Delta Thermal Apparel. Both MicroPCM™ and MacroPCM™ (with diameters of 10-50μm and 2-4mm, respectively). These beads can be directly applied to textiles. They form a "packed-bed heat exchanger", with pores to permit transfer of heat and moisture. www.deltathermal.com, www.deltathermal.com/technology.htm