Liquid Cooling and Ventilation Garment
Encyclopedia
Form-fitting garment
A form-fitting garment is an article of clothing that tightly follows the contours of the part of the body being covered. There are numerous types of clothing which typically are or which can be made form-fitting. For example, stockings, leggings, tights and socks are usually form-fitting...
that is used to remove body heat
Body heat
Body Heat is a 1981 film by Lawrence Kasdan.Body Heat may also refer to:*Body heat or thermoregulation, the ability of an organism to keep its body temperature within certain boundaries*Body Heat...
from the wearer in environments where evaporative cooling from sweating
Sweating
Perspiration is the production of a fluid consisting primarily of water as well as various dissolved solids , that is excreted by the sweat glands in the skin of mammals...
and open air convection cooling does not work, or the wearer has a biological problem that hinders self-regulation of body temperature.
A Liquid Cooling and Ventilation Garment (LCVG) has additional crush-resistant ventilation ducts, which draw moist air from the wearer's extremities, keeping the wearer dry. In a fully enclosing suit where exhaled breathing air can enter the suit, the exhaled air is moist and can lead to an uncomfortable feeling of dampness or wetness.
While this technology is most commonly associated with space suit
Space suit
A space suit is a garment worn to keep an astronaut alive in the harsh environment of outer space. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, and are necessary for extra-vehicular activity , work done outside spacecraft...
s, it is also used in a wide range of Earth-bound applications where open-air cooling is difficult or impossible to achieve, such as fire fighting
Fire fighting
Firefighting is the act of extinguishing fires. A firefighter fights fires to prevent loss of life, and/or destruction of property and the environment...
or working in a steel mill
Steel mill
A steel mill or steelworks is an industrial plant for the manufacture of steel.Steel is an alloy of iron and carbon. It is produced in a two-stage process. First, iron ore is reduced or smelted with coke and limestone in a blast furnace, producing molten iron which is either cast into pig iron or...
.
Technology
There are typically two parts to a liquid cooling garment:- the heat collection garment and tubing
- a heat exchanger for removal of heat from the circulated fluid
Garment and tubing
The garment is typically a close-fitting non-stretching fabric or a tight-fitting elastic fabric, with flexible tubing sewn onto the fabric. A single-layer of fabric may be used, with the tubing either on the inside directly contacting the wearer's skin, or on the outside separated by the fabric. If two layers of fabric are used, stitched channels can be formed which enclose the tubing between the two fabric layers. Where flame resistance is needed, the garment may be constructed out of materials such as nomexNomex
Nomex is a registered trademark for flame resistant meta-aramid material developed in the early 1960s by DuPont and first marketed in 1967.- Properties:...
.
The tubing is typically a few millimeters in diameter, and may be made out of any number of flexible plastics such as polyvinyl chloride
Polyvinyl chloride
Polyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...
(PVC) or silicone
Silicone
Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....
. Smaller diameter tubing permits a higher degree of garment flexibility, but at a cost of lower heat absorption capacity, and increased pressure needed to push liquid through the tubing.
When a large area needs to be cooled or the external environment also heats the tubing, a single long tube may not be enough because the liquid becomes saturated with heat and can not cool any further. Making the liquid much colder is not an option since it leads to uncomfortable coldness where the liquid enters the tubes. Instead, multiple parallel tubes are used to increase the volume of liquid available to absorb heat.
Skin coverage and tubing density can vary depending on the application. The garment may simply be a short-sleeved shirt, or it may be a full-body suit covering the arms and legs. Where the heat removal requirement is low, the tubing may be spaced several centimeters apart across the garment surface. Where there is a very large amount of heat to remove, the tubing can be arranged in a dense grid with no gaps between the tubes.
Heat exchanger
For portable earth bound applications, the heat exchanger for cooling the liquid can be very low-tech, consisting simply of a container for holding ice, and an electric pump to circulate water from the container through the tubing. The return water is cooled by the melting ice, and again pumped through the tubes. Regulation of flow is done by varying pump speed or using an adjustable flow valve. Ice storage can be achieved using a belt-pack, a backpack, or a duffel bag, depending on the length of time needed for the cooling system to operate between refilling the ice storage.In situations where the wearer must stay in place inside a vehicle, heavy but long-term-operation heat exchangers can be used, such as a refrigration system to cool the liquid.
When the user's movement is partially hindered through the use of a life-support umbilical, cooling liquid can also be supplied via the umbilical.
Space applications
Astronauts commonly wear a Liquid Cooling and Ventilation Garment in order to maintain a comfortable core body temperature during extra-vehicular activityExtra-vehicular activity
Extra-vehicular activity is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth , but also applies to an EVA made on the surface of the Moon...
(EVA). The LCVG accomplishes this task by circulating cool water through a network of flexible tubes in direct contact with the astronaut's skin. The water draws heat away from the body, resulting in a lower core temperature. The water then returns to the Primary Life Support System
Primary Life Support System
A Primary Life Support System , is a device connected to an astronaut's or cosmonaut's spacesuit, which allows extra-vehicular activity with maximum freedom, independent of a spacecraft's life support system. The PLSS is generally worn like a backpack...
(PLSS), where it is cooled in a heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
before being recirculated. In an independent space suit, the heat is ultimately transferred to a thin sheet of ice (formed by a separate feed water source). Due to the extremely low pressure in space, the heated ice sublimates directly to water vapor, which is then vented away from the suit. In a dependent space suit (such as the ones used in the Gemini program or within lunar orbit on the Apollo program), the heat is carried back to a host spacecraft through an umbilical
Umbilical cable
An umbilical cable or umbilical is a cable which supplies required consumables to an apparatus. It is named by analogy with an umbilical cord...
connection, where it is ultimately radiated or sublimated via the spacecraft's own thermal control system.
Because the space environment
Space environment
Space environment is a branch of astronautics, aerospace engineering and space physics that seeks to understand and address conditions existing in space that affect the operation of spacecraft...
is essentially a vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
, heat cannot be lost through heat convection, and can only be directly dissipated through thermal radiation
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
, a much slower process. Thus, even though the environment of space can be extremely cold, excessive heat build-up is inevitable. Without an LCVG, there would be no means by which to expel this heat, and it would affect not only EVA performance, but the health of the suit occupant as well. The LCVG used with the Apollo/Skylab A7L
Apollo/Skylab A7L
The A7L Apollo & Skylab spacesuit is the primary pressure suit worn by NASA astronauts for Project Apollo, the three manned Skylab flights, and the Apollo-Soyuz Test Project between 1968 and the termination of the Apollo program in 1975. The "A7L" designation is used by NASA as the seventh Apollo...
suit could remove heat at a rate of approximately 2000 Btu/h (600 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s).
The LCVG used with NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Extravehicular Mobility Unit
Extravehicular Mobility Unit
The Space Shuttle/International Space Station Extravehicular Mobility Unit is an independent anthropomorphic system that provides environmental protection, mobility, life support, and communications for a Space Shuttle or International Space Station crew member to perform extra-vehicular activity...
is primarily constructed of spandex
Spandex
Spandex or elastane is a synthetic fibre known for its exceptional elasticity. It is strong, but less durable than natural Latex, its major non-synthetic competitor. It is a polyurethane-polyurea copolymer that was co-invented in 1959 by chemists C. L. Sandquist and Joseph Shivers at DuPont's...
, with a nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
tricot liner. The tubes are made of polyvinyl chloride
Polyvinyl chloride
Polyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...
.
