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Encyclopedia > Thermal insulation
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Thermal insulation on the Huygens probe
Thermal insulation on the Huygens probe
Rockwool Insulation, 1600 dpi scan against the grain
Rockwool Insulation, 1600 dpi scan against the grain
Rockwool Insulation, 1600 dpi scan with the grain
Rockwool Insulation, 1600 dpi scan with the grain

The term thermal insulation can refer to materials used to reduce the rate of heat transfer, or the methods and processes used to reduce heat transfer. Image File history File links Download high resolution version (2245x1518, 915 KB)Original caption:KENNEDY SPACE CENTER, FLA. -- An employee in the Payload Hazardous Servicing Facility (PHSF) sews thermal insulation material on the back cover and heat shield of the Huygens probe during prelaunch processing, testing and integration in that... Image File history File links Download high resolution version (2245x1518, 915 KB)Original caption:KENNEDY SPACE CENTER, FLA. -- An employee in the Payload Hazardous Servicing Facility (PHSF) sews thermal insulation material on the back cover and heat shield of the Huygens probe during prelaunch processing, testing and integration in that... The Huygens probe, supplied by the European Space Agency (ESA) and named after the Dutch 17th century astronomer Christiaan Huygens, is an atmospheric entry probe carried to Saturns moon Titan as part of the Cassini-Huygens mission. ... Image File history File links Size of this preview: 800 × 428 pixelsFull resolution‎ (5,904 × 3,159 pixels, file size: 2. ... Image File history File links Size of this preview: 800 × 428 pixelsFull resolution‎ (5,904 × 3,159 pixels, file size: 2. ... Mineral wool, means fibres made from minerals or metal oxides, be they synthetic or natural. ... Mineral wool, also known as mineral cotton, silicate cotton, stone wool, slag wool, rockwool, and rock wool, is an inorganic substance used for insulation and filtering. ... In thermal physics, heat transfer is the passage of thermal energy from a hot to a colder body. ...


Heat energy can be transferred by conduction, convection, radiation or when undergoing a phase change. For the purposes of this discussion only the first three mechanisms need to be considered. For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ... Conduction has several meanings. ... Convection in the most general terms refers to the movement of currents within fluids (i. ... For other uses, see Radiation (disambiguation). ... In its most common usage, the term phase change indicates that a substance has changed among the three classical phases of matter: solid, liquid and gas. ...


The flow of heat can be delayed by addressing one or more of these mechanisms and is dependent on the physical properties of the material employed to do this.

Contents

Thermal radiation and radiant barriers

Thermal radiation is comprised of the infra-red wavelength of the electromagnetic spectrum. As with all electromagnetic radiation, it requires no medium in which to travel. The amount of energy radiated by an object is proportional its surface temperature and its emissivity. Any object above Absolute Zero radiates thermal radiation. As all objects radiate energy towards one another, the important consideration is the net direction of energy flow. Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... Although some radiations are marked as N for no in the diagram, some waves do in fact penetrate the atmosphere, although extremely minimally compared to the other radiations The electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. ... The emissivity of a material (usually written ) is the ratio of energy radiated by the material to energy radiated by a black body at the same temperature. ... For other uses, see Absolute Zero (disambiguation). ...


Thermal radiant barriers possess the characteristics of low emissivity, low absorptivity and high reflectivity in the infra-red spectrum. They may also exhibit this for other wavelengths including visible light but this is not necessary to function as thermal barrier. Only a small fraction of radiant energy is absorbed by such a material (most being reflected back away) and therefore only a small fraction is re-emitted. Highly polished metals are one example. Conversely, dark materials with low reflectivity will absorb a large fraction of energy, and similarly emit a large fraction. (see Black Body, Grey Body) The emissivity of a material (usually written ) is the ratio of energy radiated by the material to energy radiated by a black body at the same temperature. ... In analytical chemistry, the molar absorptivity or extinction coefficient ε of a chemical species at a given wavelength is a measure of how strongly the species absorbs light at that wavelength. ... In optics, reflectivity is the reflectance (the ratio of reflected power to incident power, generally expressed in decibels or percentage) at the surface of a material so thick that the reflectance does not change with increasing thickness; , the intrinsic reflectance of the surface, irrespective of other parameters such as the... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ...


Thermal conduction and conductive barriers

Conduction occurs when heat travels through a medium. The rate at which this occurs is proportional to the thickness of the material, the cross-sectional area over which it travels, the temperature gradients between its surfaces and its thermal conductivity. K value redirects here. ...


Most gases including air are poor conductors. Conductive barriers often incorporate a layer or pockets of air to reduce heat transfer. Examples include styrofoam and double glazed windows. Conductive heat transfer is largely reduced by the presence of the air-filled spaces (which has low thermal conductivity) rather than by the material itself. Metals exhibit high thermal conductivity and allow heat conduction to occur readily.


The effectiveness of a radiant barrier is negated if it abuts any material with high thermal conductivity[citation needed]. For instance reflective foil needs to be provided an adequate air gap to function adequately[citation needed].


Convective transfer and convective barriers

Convective heat transfer occur between two objects separated by a moving interface of liquid or gas. Convective currents driven by heat energy occur between the objects. The physical properties of the fluid or gas and the velocity at which the molecules travel influence the rate of transfer. Convection can be reduced by dividing the convective medium into small compartments to prevent large currents from forming.


Combined barriers

Materials which are often used to reduce conduction also decrease convection. The small air spaces retard convective movement. There is an ideal density of the material which maximises both effects simultaneously.


Another example where different systems are combined are the reflective surfaces and vacuum in a vacuum flask, or Dewar vessel. Look up Vacuum in Wiktionary, the free dictionary. ... Lunchbox and vacuum bottle owned by Harry S. Truman A vacuum flask or Thermos flask is a bottle that reduces heat transfer from the inside to the outside and conversely to a minimum, and therefore keeps warm drinks warm and refrigerated drinks cold. ... Dewar can mean: Dewar flask James Dewar Rt. ...


Understanding heat transfer is important when planning how to insulate an object or a person from heat or cold, for example with correct choice of insulated clothing, or laying insulating materials beneath in-floor heat cables or pipes in order to direct as much heat as possible upwards into the floor surface and reduce heating of the ground beneath.


Factors that compromise insulation

Moisture

Damp materials may lose most of their insulating properties. The choice of insulation often depends on the means used to manage moisture and condensation on one side or the other of the thermal insulator. Clothing and building insulation depend on this aspect to function as expected.


Heat bridging

Comparatively more heat flows through a path of least resistance than through insulated paths. This is known as a thermal bridge, heat leak, or short-circuiting. Insulation around a bridge is of little help in preventing heat loss or gain due to thermal bridging; the bridging has to be rebuilt with smaller or more insulative materials. A common example of this is an insulated wall which has a layer of rigid insulating material between the studs and the finish layer. When a thermal bridge is desired, it can be a conductive material, a heat pipe, or a radiative path. A thermal bridge is created when materials that are poor insulators come in contact, allowing heat to flow through the path created. ... A heat sink (aluminium) with heat pipe (copper) A heat pipe is a heat transfer mechanism that can transport large quantities of heat with a very small difference in temperature between the hotter and colder interfaces. ...


Calculating requirements

Industry standards are often "rules of thumb" developed over many years, that offset many conflicting goals: what people will pay for, manufacturing cost, local climate, traditional building practices, and varying standards of comfort. Heat-transfer analysis can be performed in large industrial applications, but in household situations (appliances and building insulation), airtightness is the key in reducing heat transfer due to air leakage (forced or natural convection). Once airtightness is achieved, it has often been sufficient to choose the thickness of the insulative layer based on rules of thumb. Diminishing returns are achieved with each successive doubling of the insulative layer.


It can be shown that for some systems, there is a minimum insulation thickness required for an improvement to be realized.[1]


Applications

Clothing

Clothing is chosen to maintain the temperature of the human body.


To offset high ambient heat, clothing must enable sweat to evaporate (cooling by evaporation). When we anticipate high temperatures and physical exertion, the billowing of fabric during movement creates air currents that increase evaporation and cooling. A layer of fabric insulates slightly and keeps skin temperatures cooler than otherwise.


To combat cold, evacuating skin humidity is still essential while several layers may be necessary to simultaneously achieve this goal while matching one's internal heat production to heat losses due to wind, ambient temperature, and radiation of heat into space. Also, crucial for footwear, is insulation against conduction of heat into solid materials.


Buildings

Main article: Building insulation
Common insulation applications in apartment building in Mississauga, Ontario, Canada.
Common insulation applications in apartment building in Mississauga, Ontario, Canada.

Maintaining acceptable temperatures in buildings (by heating and cooling) uses a large proportion of total energy consumption worldwide. When well insulated, a building: Common insulation applications inside an apartment building in Mississauga, Ontario, Canada. ... Image File history File links Size of this preview: 800 × 583 pixelsFull resolution (4718 × 3440 pixel, file size: 1. ... Image File history File links Size of this preview: 800 × 583 pixelsFull resolution (4718 × 3440 pixel, file size: 1. ... This article is about the structure. ... Old Executive Office Building, Washington D.C. Bank of China Tower, Hong Kong, China In architecture, construction, engineering and real estate development the word building may refer to one of the following: Any man-made structure used or intended for supporting or sheltering any use or continuous occupancy, or An... Motto: Pride in our past, Faith in our future Area: 288. ... This article is about the Canadian province. ... Old Executive Office Building, Washington D.C. Bank of China Tower, Hong Kong, China In architecture, construction, engineering and real estate development the word building may refer to one of the following: Any man-made structure used or intended for supporting or sheltering any use or continuous occupancy, or An...

  • is energy-efficient, thus saving the owner money.
  • provides more uniform temperatures throughout the space. There is less temperature gradient both vertically (between ankle height and head height) and horizontally from exterior walls, ceilings and windows to the interior walls, thus producing a more comfortable occupant environment when outside temperatures are extremely cold or hot.
  • has minimal recurring expense. Unlike heating and cooling equipment, insulation is permanent and does not require maintenance, upkeep, or adjustment.

Many forms of thermal insulations also absorb noise and vibration, both coming from the outside and from other rooms inside the house, thus producing a more comfortable occupant environment.


Pipe insulation is also important in buildings for pipes that carry heated or cooled fluids.


See also weatherization and thermal mass; both describe important methods of saving energy and creating comfort. Weatherization (American English) or weatherproofing (British English) is the practice of protecting a building and its interior from the elements, particularly from sunlight, precipitation, and wind, and of modifying a building to reduce energy consumption and optimize energy efficiency. ... Thermal mass, in the most general sense, is any mass that absorbs and holds heat. ...


Industry

In industry, energy has to be expended to raise, lower, or maintain the temperature of objects or process fluids. If these are not insulated, this increases the heat energy requirements of a process, and therefore the cost and environmental impact.


Space travel

Spacecraft have very demanding insulation requirements. Lightweight insulators are a strong requirement, as extra mass on a vehicle to be launched into earth orbit or beyond is extremely expensive. In space, there is no atmosphere to attenuate the sun's radiated energy, so the surfaces of objects in space heat up very quickly. In space, heat cannot be given off by convective heat transfer, nor conducted to another object. Multi-layer insulation, the gold foil often seen covering satellites and space probes, is used to control thermal radiation, as are specialty paints. Closeup of Multi-layer insulation from a satellite. ...


Launch and re-entry place severe mechanical stresses on spacecraft, so the strength of an insulator is critically important (as seen by the failure of insulating foam on the Space Shuttle Columbia). Re-entry through the atmosphere generates very high temperatures, requiring insulators with excellent thermal properties, for example the reinforced carbon-carbon composite nose cone and silica fiber tiles of the Space Shuttle. Space Shuttle Columbia (NASA Orbiter Vehicle Designation: OV-102) was the first spaceworthy space shuttle in NASAs orbital fleet. ... For other uses, see Carbon (disambiguation). ... R-phrases R42 R43 R49 S-phrases S22 S36 S37 S45 S53 Flash point non-flammable Supplementary data page Structure and properties n, εr, etc. ... This article is about the space vehicle. ...


References

  1. ^ Frank P. Incropera; David P. De Witt (1990). Fundamentals of Heat and Mass Transfer, 3rd Ed., John Wiley & Sons, 100 - 103. ISBN 0-471-51729-1. 
  • U.S. Environmental Protection Agency and the U.S. Department of Energy's Office of Building Technologies.
  • Loose-Fill Insulations, DOE/GO-10095-060, FS 140, Energy Efficiency and Renewable Energy Clearinghouse (EREC), May 1995.
  • Insulation Fact Sheet, U.S. Department of Energy, update to be published 1996. Also available from EREC.
  • Lowe, Allen. "Insulation Update," The Southface Journal, 1995, No. 3. Southface Energy Institute, Atlanta, GA.
  • ICAA Directory of Professional Insulation Contractors, 1996, and A Plan to Stop Fluffing and Cheating of Loose-Fill Insulation in Attics, Insulation Contractors Association of America, 1321 Duke St., #303, Alexandria, VA 22314, (703)739-0356.
  • US DOE Consumer Energy Information.
  • Insulation Information for Nebraska Homeowners, NF 91-40.
  • Article in Daily Freeman, Thursday, 8 September 2005, Kingston, NY.
  • TM 5-852-6 AFR 88-19, Volume 6 (Army Corp of Engineers publication).
  • CenterPoint Energy Customer Relations.
  • US DOE publication, Residential Insulation
  • US DOE publication, Energy Efficient Windows
  • US EPA publication on home sealing
  • DOE/CE 2002
  • University of North Carolina at Chapel Hill
  • Alaska Science Forum, May 7, 1981, Rigid Insulation, Article #484, by T. Neil Davis, provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community.
  • Guide raisonné de la construction écologique (Guide to products /fabricants of green building materials mainly in France but also surrounding countries), Batir-Sain 2007

John Wiley & Sons, Inc. ... is the 251st day of the year (252nd in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 127th day of the year (128th in leap years) in the Gregorian calendar. ... AUGUST 25 1981 US Marine Sean Vance is Born on the 25th of August {ear nav|1981}} Year 1981 (MCMLXXXI) was a common year starting on Thursday (link displays the 1981 Gregorian calendar). ...

See also

In thermal physics, heat transfer is the passage of thermal energy from a hot to a colder body. ... Common insulation applications inside an apartment building in Mississauga, Ontario, Canada. ... Construction on the North Bytown Bridge in Ottawa, Canada. ... A Dewar flask is a vessel designed to provide very good thermal insulation. ... Superinsulation is an approach to building design, construction and retrofitting. ... Weatherization (American English) or weatherproofing (British English) is the practice of protecting a building and its interior from the elements, particularly from sunlight, precipitation, and wind, and of modifying a building to reduce energy consumption and optimize energy efficiency. ... Thermal mass, in the most general sense, is any mass that absorbs and holds heat. ... Fireproofing, a passive fire protection measure, subject to bounding, refers to the act of making materials or structures more resistant to fire, or to those materials themselves. ... Firestop after fire exposure during fire test in Tulsa, Oklahoma. ... Mineral wool, means fibres made from minerals or metal oxides, be they synthetic or natural. ... For other uses, see Asbestos (disambiguation). ... For other uses, see Polystyrene (disambiguation). ... Calcium silicate, otherwise known as slag, has a low bulk density and high physical water absorption. ... Vermiculite is a natural, non toxic mineral that expands with the application of heat. ... Expanded Perlite Perlite is an amorphous volcanic glass that has a relatively high water content. ... Bundle of fiberglass Fiberglass (also called fibreglass and glass fibre) is material made from extremely fine fibers of glass. ... Thinsulate is a synthetic fibre used for thermal insulation in clothing. ... Insulated shipping containers are a type of packaging used to ship temperature sensitive products such as foods, pharmaceuticals, and chemicals. ...

External links


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