Thermal insulation

Thermal insulation

Overview



Thermal insulation is the reduction of the effects of the various processes of heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

 between objects in thermal contact or in range of radiative influence. Heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

 is the transfer of thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

 between objects of differing temperature. The means to stem heat flow may be especially engineered methods or processes, as well as suitable static objects and materials.

Heat flow is an inevitable consequence of contact between objects of differing temperature.
Discussion
Ask a question about 'Thermal insulation'
Start a new discussion about 'Thermal insulation'
Answer questions from other users
Full Discussion Forum
 
Unanswered Questions
Recent Discussions
Encyclopedia



Thermal insulation is the reduction of the effects of the various processes of heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

 between objects in thermal contact or in range of radiative influence. Heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

 is the transfer of thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

 between objects of differing temperature. The means to stem heat flow may be especially engineered methods or processes, as well as suitable static objects and materials.

Heat flow is an inevitable consequence of contact between objects of differing temperature. Thermal insulation provides a means to maintain a gradient of temperature, by providing a region of insulation in which heat flow is reduced or 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....

 is reflected rather than absorbed.

In building construction, insulating materials are assigned a quantitative measure of the insulating capability, called the R-value
R-value (insulation)
The R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux through it or R = \Delta T/\dot Q_A.The R-value being discussed is the unit thermal resistance...

.

In thermal engineering of insulating systems for ovens, reactors, and furgances, thermal conductivity (K), product density and specific heat (C) are the key product characteristics, which influence insulating efficiency, such as acolodet insulating.

Low thermal conductivity (K) is analogous to high insulating capability (R).

Aerogels, microporous silica and ceramic fiber insulation are three best performing insulators for applications between 200 Celsius and 2000 Celsius. Zirconia fibers have the lowest thermal conductivity of all ceramic fiber products and are used in applications up to 2000 Celsius.

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 humans 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 of materials with different properties are necessary to simultaneously achieve this goal while matching one's internal heat production to the heat losses that occur. The key is layering for different purposes, as heat loss occurs due to wind, radiation of heat into space and conductive bridging. The latter is most apparent in footwear where insulation against conductive heat loss is most important.

Buildings




Maintaining acceptable temperatures in buildings (by heating and cooling) uses a large proportion of global energy consumption. When well insulated, a building
Building
In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...

:
  • 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 insulation also reduce noise and vibration, both coming from the outside and from other rooms inside a building, thus producing a more comfortable environment.

Window insulation film
Window insulation film
Window insulation film is a plastic film which can be applied to glass windows to reduce heat transfer. There are two types in common use designed to reduce heat flow via radiation and convection respectively.- Solar control film :...

 can be applied in weatherization
Weatherization
Weatherization or weatherproofing 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.Weatherization is distinct from building...

 applications to reduce incoming thermal radiation in summer and loss in winter.

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 energy requirements of a process, and therefore the cost and environmental impact.

Mechanical systems


Space heating and cooling systems distribute heat throughout buildings by means of pipe or ductwork. Insulating these pipes using pipe insulation
Pipe insulation
Pipe Insulation is thermal or acoustic insulation used on pipework.-Condensation control:Where pipes operate at below-ambient temperatures, the potential exists for water vapour to condense on the pipe surface...

 reduces energy into unoccupied rooms and prevents condensation
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

 from occurring on cold and chilled pipework.

Pipe insulation
Pipe insulation
Pipe Insulation is thermal or acoustic insulation used on pipework.-Condensation control:Where pipes operate at below-ambient temperatures, the potential exists for water vapour to condense on the pipe surface...

 is also used on water supply pipework to help delay pipe freezing for an acceptable length time.

Spacecraft


Insulation for applications on spacecraft must be light-weight. In particular, spacecraft must be insulated against radiative heating from 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....

 as no means exist in space for convective cooling by the atmosphere. Outside the Earth's atmosphere, radiated energy from the Sun is greater than on Earth, and all surfaces exposed heat up quickly. Thermal radiation insulation often consists of multi-layer insulation
Multi-layer insulation
Multi-layer insulation, or MLI, is thermal insulation composed of multiple layers of thin sheets often used on spacecraft. It one of the main items of the spacecraft thermal design, mainly intended to reduce heat loss by thermal radiation. In its basic form, it does not appreciably insulate...

 using special paints, foams, and layers of metal.

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
Space Shuttle Columbia
Space Shuttle Columbia was the first spaceworthy Space Shuttle in NASA's orbital fleet. First launched on the STS-1 mission, the first of the Space Shuttle program, it completed 27 missions before being destroyed during re-entry on February 1, 2003 near the end of its 28th, STS-107. All seven crew...

). Re-entry through the atmosphere generates very high temperatures because of friction against air at high speeds. Insulators must meet demanding physical properties beyond their thermal transfer retardant properties. E.g. reinforced carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

-carbon composite nose cone and silica
Silicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

 fiber tiles of the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

. See also Insulative paint
Insulative paint
Insulative paint is commonly thought to be paint containing ceramic micro-spheres that have the same heat reflective properties as the tiles on the space shuttle. This is a misconception that has come about due to marketing by paint manufacturers...

.

Automotive


Internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

s produce a lot of heat during their combustion cycle. This can have a negative effect when it reaches various heat-sensitive components such as sensors, batteries and starter motors. As a result, thermal insulation is necessary to prevent the heat from the exhaust reaching these components.

High performance cars often use thermal insulation as a means to increase engine performance.

Factors influencing performance


Insulation performance is influenced by many factors the most prominent of which include:
  • Thermal conductivity
    Thermal conductivity
    In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

     ("k" or "λ" value)
  • Surface emissivity
    Emissivity
    The emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature...

     ("ε" value)
  • Insulation thickness
  • Density
    Density
    The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

  • Specific heat capacity
  • Thermal bridging


It is important to note that the factors influencing performance may vary over time as material ages or environmental conditions change.

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. Both heat transfer and layer analysis may be performed in large industrial applications, but in household situations (appliances and building insulation), air tightness is the key in reducing heat transfer due to air leakage (forced or natural convection). Once air tightness is achieved, it has often been sufficient to choose the thickness of the insulating layer based on rules of thumb. Diminishing returns are achieved with each successive doubling of the insulating layer.
It can be shown that for some systems, there is a minimum insulation thickness required for an improvement to be realized.