WHAT ARE THE BASIC PROPERTIES OF HEAT INSULATING MATERIALS?

In architecture, the material that prevents the outflow of indoor heat is commonly called an adiabater. On the other hand, the material which prevents the flow of external heat is called insulator. These two are collectively called insulating materials.

Such materials are mainly used for walls, ceilings, thermal equipment and thermal pipelines. It is sometimes used to preserve heat in winter construction. In general, it can also be used to refrigerate rooms and appliances.


It is known that heat current flows from higher temperature to lower temperature. To keep the room warm in winter, a continuous indoor heat supply must be provided to compensate for heat loss due to temperature difference. This problem can be partially addressed by using heat-insulating materials. For example, a four-unit six-story residential building in Beijing, China, uses a frame structure of mineral cotton composite plate, and it reduces heat loss by 40% compared to a masonry-concrete structure.

According to statistics, a good insulation building can reduce fuel consumption by 25% 50%, And to achieve this, one must consider the following questions:

  • What kind of structure is easier to lose heat, and vice versa;
  • how the composition of the material is related to its heat-insulating property;
  • what are the factors affecting the heat-insulating property of the material, and
  • How to choose the right material.

Exterior protected construction is made of various building materials, the thermal conductivity and specific heat, which are important parameters for wall, roof, floor designation and heat engineering calculations. The material with low thermal conductivity and high specific heat can improve the heat-insulating property of the outdoor protected construction and keep the indoor temperature constant.


The basic requirement for selecting a heat-insulating material is that the thermal conductivity is well below 0.23 W/(m*K), the apparent density is less than 600kg/m3, and compressive strength above 0.3MPa. In addition, the material’s hygroscopicity, temperature stability and corrosion resistance should all be taken into account according to the characteristics of the project.

The following is an introduction to the basic properties of heat-insulating materials.


1. thermal conductivity

Thermal conductivity is a measure of the heat transfer capacity of a material. It is affected by physical composition, porosity, ambient temperature and the direction of the heat current.

physical constitution

Thermal conductivity can be affected by the chemical composition and molecular structure of the material. Materials with simple chemical composition and molecular structure have higher thermal conductivity than compound.

porosity

The thermal conductivity of solids is higher than that of air. Therefore, the greater the porosity, the lower the thermal conductivity. In this aspect, not only the porosity matters, but also the size, distribution, shape and connectivity of the pores.

Moisture

The material has high thermal conductivity under moist conditions. What should be noted is that if water freezes, its thermal conductivity will become higher. This is because the thermal conductivity of water is 20 is many times greater than that of air whereas ice is 80 Many times more than air. Therefore, special attention should be paid to protecting the heat insulating material from moisture.

Temperature

If the temperature becomes higher, the thermal conductivity increases accordingly. As the temperature increases, the thermal motion of the molecular solid becomes more active; The heat conduction of air in the pores is promoted, and the radiation effect of the pore wall is strong.

direction of heat current

In the case of the material being anisotropic (fibrous material like wood), when the heat current flows parallel to the fibers, there will be no strong resistance; However, when the heat current flows against the fibers, there will be strong resistance.

2. temperature stability

Temperature stability is the ability of a material to retain its original property when exposed to heat. This is usually expressed by the ultimate temperature, the point at which the material will lose its heat-insulating function.

3. Strength

A heat insulating material is usually measured by its compressive strength and flexural strength. Since the material is highly porous, its strength is weak. Thus it is better not to allow the insulating material to bear much of the load.

Er. Mukesh Kumar

Photo of author
Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.