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3ОСНОВНЫЕ ТРЕБОВАНИЯ К СОВРЕМЕННЫМ ТЕПЛОИЗОЛЯЦИОННЫМ
СТРОИТЕЛЬНЫМ МАТЕРИАЛАМ
В данной статье разъясняются понятия современных теплоизоляционных материалов и требования к таким строительным материалам. Рассмотрены основные и дополнительные требования к теплоизоляционным материалам.
Ключевые слова: теплопроводность, термическое сопротивление, изоляция, свойства материала, толщина.
BASIC REQUIREMENTS FOR MODERN HEAT-INSULATING BUILDING MATERIALS
This article explains the concepts of modern thermal insulation materials and the requirements for such building materials. The main and additional requirements of heat insulating materials are discussed.
Key words: thermal conductivity, thermal resistance, insulation, material properties, thickness.
Nowadays, the demand for modern energy-efficient buildings is increasing. This, in turn, increases the demand for the production of new heat-insulating materials in the production of the construction industry. New heat-insulating materials also need to be modern and have their own technical characteristics. Thermal insulation materials are designed to protect against the penetration of heat or cold. These are usually very porous materials with a density of no more than 600 kg / m3 and a low thermal conductivity of no more than 0.18 W / (m • K). Thermal conductivity is the property of a material to transfer heat from one surface to another. X air = 0.023 W/(m-K) less solid. The main requirements for modern heat-insulating materials:
1. Mechanical strength, ensuring the reliability of materials during installation and operation.
2. High biostability, excluding rotting and damage by rodents.
3. Chemical resistance.
4. The dry material must be non-hygroscopic.
The technical characteristics of the material and the dimensions of the thickness have a great influence on the thermal conductivity of the material. The material tends to create small closed pores in order to reduce the amount of heat transferred by convection and radiation. In practice, it is convenient to judge the thermal conductivity of a material by its density. For some groups of materials, a certain relationship has been established between thermal conductivity and relative density p according to the Nekrasov formula
where p is the density of the material, g/cm3.
Thermal conductivity X (W / (m • K)) is characterized by the amount of heat (J) passing through a material 1 m thick, 1 m2 in area for 1 s, with a temperature difference of 1 °C on opposite surfaces of the material. The thermal conductivity coefficient X depends on the chemical composition and structure, the degree and nature of porosity, humidity and temperature at which the heat transfer process occurs (Fig. 1, a - f). Materials of a layered or fibrous structure have different thermal conductivity depending on the direction of the heat flow with respect to the fibers.
Феруза Кодирова Хакимов Содикжон Тургунбаева Мадина
Наманганский инженерно-строительный институт
Fig. 1 Dependence of thermal conductivity of materials on: a - density; b - porosity; c, d -
humidity; e, f - temperatures For example, in wood, the thermal conductivity along the fibers is twice that across the fibers. A material with a crystalline structure is more thermally conductive than a material of the same composition but with an amorphous structure.
The thermal conductivity of materials is taken into account in thermal engineering calculations of the thickness of walls and floors of heated buildings, as well as in determining the required thickness of thermal insulation of hot surfaces and refrigerators. It is related to the thermal resistance of the material layer R (m2 • K/W), which is determined by the formula:
R = 5 / X ,
where R is thermal resistance, m2 • K/W; 5 is the thickness of the material layer, m; X is the thermal conductivity of the material layer, W/(m • K).
The thickness of the outer walls and the fuel consumption for heating buildings depend on the thermal resistance R. Let us give examples of the values of the thermal conductivity coefficients X of some building materials in an air-dry state, W / (m • K) Steel Granite
Heavy concrete Ceramic brick (solid) Limestone Water
Lightweight concrete
58
2.9...3.3 1.55...1.85 0.81.0.93 0.52.0.98 0.59
0.35.0.8
Cellular structural and heat-insulating concretes on porous aggregates 0.23... 0.46 Foam concrete 0.12.0.15
Fibrolite 0.09.0.17
Wood fiber boards 0.08
Mineral wool 0.06.0.09
The heat-insulating ability of a material depends not only on the number, but also on the nature of the pores, their distribution, size, whether they are open or closed. The porosity of heat-insulating materials is from 50 to 98%. The highest thermal insulation properties are possessed by materials containing, all other things being equal, a large number of small and closed pores filled with air. The main methods for the formation of a highly porous structure of materials:
- a method of creating a fibrous frame based on the mechanical interlacing of fibers (asbestos, mineral wool and glass wool fibers);
- use of natural porosity of natural material (diatomite, tripoli);
- introduction of porous and fibrous aggregates (mineral wool products on a synthetic binder, lightweight refractory heat-insulating concretes);
- introduction of an increased amount of water into the molding mass (used in the production of lime-siliceous, perlite-cement products);
- introduction of burnable additives (ceramic heat-insulating products);
- use of foam (foam concrete);
- introduction of air-entraining additives (perlite-ceramic products);
- introduction of gas-forming additives (aerated concrete, gas silicate, foam glass, foam plastics);
- a method of recrystallization of chemical salts (sovelite);
- swelling when heated (expanded clay, expanded perlite, vermiculite).
When characterizing the thermal insulation properties of materials used in the form of backfills, grain size is of great importance. With a decrease in grain size, the heat-shielding properties of materials improve.
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