Insulation Heat

(or thermal insulation), protection of buildings, thermal industrial installations or their components, refrigeration chambers, pipelines, and the like against unwanted heat exchange with the environment. For example, heat insulation is essential in construction and heat engineering to reduce heat losses to the environment; in refrigeration and cryogenics it is needed to protect equipment against the influx of heat from without.

Heat insulation is achieved by installing special barriers made of insulating materials in the form of casings or coatings, which obstruct heat transfer; these means of protection from heat themselves are also called heat insulation. Where convective heat exchange predominates, barriers containing layers of airtight material are used; in the case of radiant heat exchange, insulation made of materials that reflect radiant heat, such as foil and metallized lavsan (the Soviet equivalent of Dacron) film, are used. In the case of heat conduction, which is the primary mechanism of heat transfer, materials with extensive porous structures are used.

Where heat is transferred by conduction, the effectiveness of heat insulation is defined by the thermal resistance R of the insulating material. For a single-layer element, R = δ/λ, where δ is the thickness of the layer of insulating material and λ is the material’s thermal conductivity. The effectiveness of heat insulation is increased by using highly porous materials and multilayer insulating elements with air interlayers.

The purpose of insulating buildings is to reduce heat losses during the cold part of the year and maintain a relatively constant temperature inside over the course of the day in spite of fluctuations in the outside air temperature. The use of efficient heat insulating materials makes possible a significant reduction in the thickness and weight of the enclosing members, thus reducing the expenditure of basic building materials (brick, cement, steel, and so on) and increasing the permissible dimensions of prefabricated elements.

In thermal industrial installations, such as industrial furnaces, boilers, and autoclaves, heat insulation provides significant fuel savings and helps increase the capacity and efficiency of heating units, intensify production processes, and reduce consumption of basic materials. The economic efficiency of heat insulation in industry is often estimated by the coefficient of heat preservation η = (Q₁ – Q₂)/Q₁ where Q₁ is in the installation’s heat loss without insulation and Q₂ is the loss with insulation. Heat insulation of industrial installations that operate at high temperatures also helps provide normal working conditions in high-temperature shops and reduces industrial accidents. Heat insulation is very important in refrigeration engineering, since the cooling of refrigeration units and machines involves significant energy consumption.

Heat insulation is an essential component of such means of transportation as ships and railroad cars. The part played by heat insulation is determined by the purpose of the vehicle. Thus, for passenger transportation, insulation is required to maintain a comfortable microclimate in passenger areas; for freight transportation, such as ships, refrigerator cars, and trucks for shipping perishable foods, insulation ensures a specific temperature with minimum energy expenditure. The requirements for heat insulation effectiveness in transportation are more stringent because of constraints on the weight and volume of the enclosing members of vehicles.