Thermal insulation materialIt refers to the material that can block heat flow transmission, also called thermal insulation material.Traditional thermal insulation materials, such asglass fibre、asbestos、Rock wool、silicateNew thermal insulation materials, such asAerogel felt, vacuum plate, etc.They are used for building envelope or thermal equipment, materials or material complexes that resist heat flow transmission, including both thermal insulation materials and cold insulation materials.On the one hand, thermal insulation materials meet the thermal environment of building space or thermal equipment, on the other hand, they also save energy.Therefore, some countries regard thermal insulation materials as the followingnatural gasThe "fifth largest energy" after nuclear energy.
Chinese name
Thermal insulation material
Foreign name
thermal insulation material
Category
Material Science
Include
Thermal insulation materials and cold insulation materials
Category
porous material , thermal reflective material and vacuum material
Thermal insulation materials are divided intoporous material , thermal reflective materials and vacuum materials.The former uses theporeInsulation because of air orinert gasOfthermal conductivityVery low, such as foam materialfibreMaterials, etc;Heat reflective materials have highreflection coefficient, can reflect heat, such asgold、silver、nickel、aluminum foilOr metallizedpolyester、Polyimide filmEtc.vacuumThermal insulation materialIt uses the internal vacuum of the material to block convection for heat insulation.Aerospace industryWeight andvolumeThe requirements are more stringent, and they often require bothsound insulation、Damping, corrosion resistance, etc.variousAerocraftThe need for insulation materials varies.aircraftcockpitandcockpitCommonly used internallyFoam plastic、Ultra fine glass woolHigh silicon oxygen cotton and vacuum insulation board are used for heat insulation.MissileThe thermal insulation material used for the head wasphenolic foam , with good temperature resistancePolyurethane foamIn addition, the single thermal insulation material is developed into sandwich structure.The thermal insulation method of the missile instrument cabin is to apply a layer of several millimeters thick foam coating on the outer skin of the cabin as anti-corrosion at room temperaturecoatingWhen the pneumatic heating reaches above 200 ° C, it will foam evenly and play the role of heat insulation.Artificial earth satelliteIt is used to move in the alternating environment of high temperature and low temperature. It is necessary to use multi-layer heat insulation materials with high reflective performance, generally consisting of dozens of layersmetalized film , aluminized polyester film, aluminized polyimide film.In addition, the surfaceInsulating tileThe successful development ofspace shuttleOfheat insulationAt the same time, it also marks a higher level of development of thermal insulation materials.[1]
principle
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There are three ways of heat transfer in building heat exchange: heat conduction+convection heat<25%, radiant heat>75%.
After the temperature of the tile roof rises in summer, a large amount of radiant heat enters the room, causing the temperature to rise continuously, and the working and living environment is extremely uncomfortable.
DikeSolar radiation absorption coefficient(Normal total radiation radiation rate) 0.07, radiating very little heat.It is widely used for heat insulation of roof and wall.
heat energyTransmission route (without heat insulation film): sun - infrared magnetic wave - heat energy hits tile to raise temperature - tile becomes heat source and radiates heat energy - heat energy hits cast-in-place roof to raise temperature - cast-in-place roof becomes heat source and radiates heat energy - indoor ambient temperature continues to rise
Heat energy transmission route (with thermal insulation film): sun - infrared magnetic wave - heat energy hits tile to raise temperature - tile becomes heat source and radiates heat energy - heat energy hits aluminum foilsurface temperature Increase - the emission rate of aluminum foil is extremely low, emitting a small amount of heat energy - maintain a comfortable ambient temperature indoors.
classification
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Thermal insulation materials are generally lightweight, loose and porous fibrous materials.[2]
component
According to their different compositions, they can be divided into organic materials and inorganic materials.
Thermal equipment and pipeline insulation materials are mostly inorganic insulation materials.Such materials have the characteristics of non decay, non combustion and high temperature resistance, such as asbestos, diatomite, perliteAerogel felt, glass fiber, foam concrete, calcium silicate, etc.
Organic thermal insulation materials are commonly used in low temperature insulation engineering.Such materials have the characteristics of low apparent density, low thermal conductivity, wide sources of raw materials, high temperature resistance, and perishability when hygroscopic, such as cork, polystyrene foam, polyurethane, cattle felt, wool felt, etc.
Service temperature
According to the use temperature limit of thermal insulation materials, they can be divided into three types: high temperature insulation materials, medium temperature insulation materials and low temperature insulation materials.
Heat insulation material for high temperature, the operating temperature can be above 700 ℃.This kindFibrous materialAluminum silicate fiber and silicon fiber;Porous materials include diatomite, vermiculite, asbestos and heat-resistant adhesives.
Thermal insulation material is used for medium temperature, and the operating temperature is between 100~700 ℃.Fiber materials for medium temperature includeAerogel felt, asbestos, slag wool, glass fiber, etc;Porous materials include calcium silicate, expanded perlite, vermiculite and foam concrete.
Thermal insulation materials for low temperature shall be used in cold insulation projects with temperature below 100 ℃.
shape
It can be divided into loose powder, fibrous, granular, tile andbrickAnd other materials.
Construction method
According to different construction methods, it can be divided into wet plastered insulation materials, filled insulation materials, binding insulation materials, wrapped and wound insulation materials and poured insulation materials.
Wet plastering type: add water to heat preservation materials such as asbestos, asbestos diatomite, etc., and mix them into cement to coat on the external surface of thermal equipment and pipes.
Filling type: the cover is made on the outside of the equipment or pipeline, and the inside is filled with thermal insulation materials, such as slag wool, glass wool, etc.
Binding type: place some prefabricated insulation boards or pipe shells outside the equipment or pipes, bind them with iron wires, and then apply protective layer materials outside.Materials in this category include asbestos products, expanded perlite products, expanded vermiculite products and calcium silicate products.
Wrapping and winding: the insulation material is made into felt or rope shape and directly wrapped or wound on the insulated object.Materials in this category include slag wool felt, glass wool felt, asbestos rope and straw rope.
Pouring type: the foaming material is poured into the mold shell of the insulated pipeline and equipment at the site, and then foamed into the insulation (cold) layer structure at the site.It is also directly sprayed on the outer wall of pipes and equipment to form an insulation (cold) layer by instant foaming.
Protective layer material
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The thermal insulation structure is composed of thermal insulation layer and protective layer.The thermal insulation material is filled in the thermal insulation layer, and the external protective layer uses different materials due to different construction methods.
The coated protective layer is made of asphalt mortar and asbestos cement mortar;
The metal protective layer is made of black iron sheet, galvanized iron sheet, PVC steel sheet and stainless steel sheet;[3]
Key points for selection
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Common application types and design selection of thermal insulation materials in buildings shall comply with GB/T 17369-1998 Application Types and Basic Requirements of Thermal Insulation Materials in Buildings.
In addition to the thermal conductivity of the material (the thermal conductivity shall not be greater than 0.175W/(m · K)), the water absorption, combustion performance, strength and other indicators of the material shall also be considered.See the corresponding classification guide for the performance characteristics of different thermal insulation materials.
Performance advantages and disadvantages
Thermal insulation performance is mainly reflected by thermal conductivity: thermal conductivity λ=W/(m · k)
The thermal conductivity represents the thermal conductivity of the material under the condition of stable heat transfer.The smaller the thermal conductivity, the better.
The λ value of 0.20w/(m.k) is used as the boundary value between thermal insulation materials and non thermal insulation materials.λ> 0.20w/(m.k) material shall not be used as thermal insulation material generally.
Thermal conductivity value
Aerogel felt - 0.018w/(m.k)
Still air - 0.026w/(m.k)
Water - 0.552 w/(m.k)
Ice - 2.2 w/(m.k)
Iron - 350 w/(m.k)
Ultra fine glass wool - 0.041 w/(m.k)
Polyethylene foam plastic - 0.038 w/(m.k)
Aerogel felt——The applicable range is - 200 ℃~650 ℃. It is absolutely hydrophobic. The thermal conductivity λ increases most slowly with temperature.
As the service life of thermal insulation material increases, its thermal conductivity λ value also increases, because any kind of thermal insulation material will absorb moisture under the normal service environment.The thermal conductivity of water is far higher than the initial thermal conductivity of the insulation material, so moisture absorption in the insulation material body into the water vapor (or water) is bound to increase the thermal conductivity of the material and eventually lose its thermal insulation function.
Moisture permeability coefficient
The service life of insulation materials is determined by the moisture permeability coefficient δ g/(m.s. pa) and the moisture resistance factor u.
U =D/δ
μ - humidity resistance factor of the product;
D -- unit: g/(m.s. pa);
δ - unit: g/(m.s. pa)
Water vapor diffusion coefficient in air D=0.01988/P
P -- local atmospheric pressure, Pa. The water vapor diffusion coefficient D in the air is related to the local atmospheric pressure P,
The larger the μ value, the stronger the resistance to water vapor penetration of the material, and the longer the service life of the material.
The μ value of common fiber materials is 3-5
The μ value of foamed polyethylene plastic is about - 1000
The μ value of expanded polystyrene plastic is about - 100
The μ value of B2 rubber plastic foaming material is about - 3000
Grade B1 rubber plastic foaming material μ value is 3500-8000
The μ value of metal aluminum plate and aluminum foil is ∞.
Industry development trend
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In 2012, the main product types of China's thermal insulation industry changed significantly: the supply and demand of foamed plastic thermal insulation materials grew rapidly, and the share of mineral fiber thermal insulation materials remained basically stable;The proportion of hard thermal insulation products is declining year by year.
