Thermal insulation

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Thermal insulation is the reduction of heat transfer (ie transfer of heat energy between objects with different temperatures) between the objects in thermal contact or within the range of radiation effects. Thermal insulation can be achieved by a specially designed method or process, as well as with appropriate object shapes and materials.

Heat flow is an inevitable consequence of contact between different temperature objects. Thermal insulation provides an isolation area in which thermal conduction is reduced or thermal radiation is reflected rather than absorbed by the body of lower temperatures.

Material insulation capability is measured as the inverse of thermal conductivity (k). Low thermal conductivity is equivalent to high insulation ability (barrier value). In thermal engineering, other important properties of the insulating material are the density of the product (?) And the specific heat capacity (c).

Video Thermal insulation

Definisi

Konduktivitas termal k diukur dalam watt per-meter per kelvin (WÂ · m ^-1 Â · K ^-1 ). Ini karena perpindahan panas, yang diukur sebagai Daya, telah ditemukan (kira-kira) sebanding dengan

• perbedaan suhu ${\ displaystyle \ Delta T}  ÂÂ$ ;
• luas permukaan kontak termal ${\ displaystyle A}  ÂÂ$
• kebalikan dari tebal bahan ${\ displaystyle d}  ÂÂ$

Dari sini, dapat disimpulkan bahwa kekuatan kehilangan panas ${\ displaystyle P}  ÂÂ$ diberikan oleh ${\ displaystyle P = {\ frac {kA \, \ Delta T} {d}}}  ÂÂ$

The thermal conductivity depends on the material, and, for the liquid, its temperature and its pressure. For comparison purposes, conductivity under standard conditions (20 Â ° C at 1 atm) is usually used. For some materials, thermal conductivity may also depend on the direction of heat transfer.

The isolation action is carried out by wrapping the object with a low thermal conductivity material in high thickness. Reducing the open surface area can also decrease heat transfer, but this quantity is usually set by the geometry of the object to be isolated.

Multi-layer insulation is used when the radiation loss dominates, or when the user is limited by volume and weight of insulation (eg, Emergency Blanket, radiation barrier)

Cylinder isolation

For isolated cylinders, a critical radius should be contacted. Before a critical radius is reached, any additional insulation will increase heat transfer. Convective thermal resistance is inversely proportional to the surface area and therefore the radius of the cylinder, while the thermal resistance of the cylindrical shell (insulating layer) depends on the ratio between the outer and inner radius, not on the fingers themselves. If the outer radius of the cylinder is increased by applying insulation, a fixed amount of conductive resistance (equal to 2 * pi * k * L (Tin-Tout)/ln (Rout/Rin)) is added. However, at the same time, convective resistance is reduced. This means that adding isolation below a certain critical radius actually increases heat transfer. For isolated cylinders, the critical radius is given by the equation

${\ displaystyle {r_ {critical}} = {k \ over h}}$

This equation shows that the critical radius depends only on the heat transfer coefficient and the thermal conductivity of the insulation. If the isolated cylinder radius is smaller than the critical radius for insulation, increasing the amount of insulation will increase heat transfer.

Maps Thermal insulation

Apps

Clothes and isolation of natural animals in birds and mammals

Gases have poor thermal conduction properties compared to liquids and solids, and thus make good insulating materials if they can get stuck. To further increase the effectiveness of a gas (such as air) it can be disrupted into small cells that can not effectively transfer heat with natural convection. Convection involves a larger gas flow which is driven by buoyancy and temperature difference, and does not work well in small cells where there is little difference in density to move it.

To achieve the formation of gaseous cells in manmade thermal insulation, glass and polymeric materials can be used to trap air in structures such as foam. This principle is used by industry in building and insulating pipes such as (glass wool), cellulose, rock wool, polystyrene foam (styrofoam), urethane foam, vermiculite, perlite, and cork. Air traps are also a principle in all materials of highly isolated clothing such as wool, down feathers and fleece.

Air catcher properties are also an insulation principle used by home animals to stay warm, for example down feathers, and seal the hair like natural sheep's wool. In both cases the primary insulating material is air, and the polymer used to trap air is a natural keratin protein.

Building

Maintaining acceptable temperatures in buildings (by heating and cooling) uses most of the global energy consumption. The insulation building also typically uses the principle of trapped small air cells as described above, eg. fiberglass (especially glass wool), cellulose, rock wool, polystyrene foam, urethane foam, vermiculite, pearlite, cork, etc. For a period of time, Asbestos is also used, however, it causes health problems.

When it is well insulated, a building:

• energy-efficient, saving the owner money.
• provides a more uniform temperature across space. There is less vertical gradient temperature (between ankle height and head height) and horizontally from the outer walls, ceilings and windows to interior walls, resulting in a more comfortable occupant environment when outside temperatures are very cold or hot.
• has minimal recurring costs. Unlike heating and cooling, insulation is permanent and requires no maintenance, maintenance, or adjustment.
• lowers the building's carbon footprint.

Many forms of thermal insulation also reduce noise and vibration, either from outside or from other rooms within the building, resulting in a more comfortable environment.

Window insulation films can be applied in weather applications to reduce incoming thermal radiation in summer and loss in winter.

In industry, energy must be incurred to raise, lower, or maintain the temperature of the processor or liquid. If this is not isolated, it increases the energy requirements of a process, and therefore the cost and environmental impact.

Mechanical system

Heating chamber and cooling systems distribute heat to the entire building through pipes or require ducts. Isolation of these pipes using pipe insulation reduces energy into uninhabited spaces and prevents condensation in cold and cold pipes.

Pipe insulation is also used in water supply pipes to help delay pipe freezing for an acceptable time period.

Mechanical insulation is generally installed in industrial and commercial facilities.

Cooling

The refrigerator consists of a heat pump and a thermal compartment.

Spacecraft

The launch and re-entry place heavy mechanical stresses on the spacecraft, so the strength of an isolator is critical (as seen by the failure of tile insulation in the Space Shuttle Columbia, causing the shuttle body to overheat and crack during re-entry, killing the onboard astronauts). Reentering through the atmosphere produces very high temperatures due to compressed air at high speeds. Insulators must satisfy demanding physical properties beyond heat resistance. Examples of isolation used on spacecraft include a reinforced carbon-carbon composite nose cone and a silica fiber tile from Space Shuttle. See also Insulative paint.

Automotive

The internal combustion engine generates a lot of heat during its 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 required to prevent heat from exhaust reaching these components.

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

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Factors that affect performance

The performance of isolation is influenced by many factors, the most prominent of which include:

• Thermal conductivity ("k" or "?" value)
• Emissivity surface ("?" value)
• Insulation thickness
• Density
• Specific heat capacity
• Thermal shift

It is important to note that the factors that affect performance may vary over time as the material age or changes in environmental conditions.

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Calculate requirements

Industrial standards are often a rule of thumb, developed over the years, that offset many conflicting goals: what people will pay, production costs, local climate, traditional development practices, and various comfort standards. Both heat transfer and layer analysis can be performed in large industrial applications, but in domestic situations (equipment and building insulation), air tightness is key in reducing heat transfer due to air leaks (forced or natural convection). Once the air tightness is reached, it is often sufficient to select the thickness of the insulating layer based on the rule of thumb. The reduced return is achieved with each successive multiplication of the isolation layer. It can be shown that for some systems, there is a minimum insulation thickness required for the improvements to be realized.

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See also

• Thermal mass
• List of thermal conductivity
• Insulative paint

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References

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Further reading

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External links

• Thermal Performance: Understand how reflective insulation works

Source of the article : Wikipedia