The process of transferring energy from a hotter part of the body to a less heated one is called thermal conduction. The numerical value of such a process reflects the thermal conductivity of the material. This concept is very important in the construction and repair of buildings. Properly selected materials allow you to create a favorable microclimate in the room and save a significant amount on heating.
The concept of thermal conductivity
Thermal conductivity is the process of thermal energy exchange, which occurs due to the collision of the smallest particles of the body. Moreover, this process will not stop until the moment of temperature equilibrium comes. This takes a certain amount of time. The more time spent on heat exchange, the lower the thermal conductivity.
This indicator is expressed as a coefficient of thermal conductivitymaterials. The table contains already measured values for most materials. The calculation is made according to the amount of thermal energy that has passed through a given surface area of the material. The larger the calculated value, the faster the object will give up all its heat.
Factors affecting thermal conductivity
The thermal conductivity of a material depends on several factors:
Material density. With an increase in this indicator, the interaction of the particles of the material becomes stronger. Accordingly, they will transfer the temperature faster. This means that with an increase in the density of the material, heat transfer improves
The porosity of a substance. Porous materials are heterogeneous in their structure. There is a lot of air inside them. And this means that it will be difficult for molecules and other particles to move thermal energy. Accordingly, the thermal conductivity increases
Humidity also affects thermal conductivity. Wet material surfaces allow more heat to pass through. Some tables even indicate the calculated coefficient of thermal conductivity of the material in three states: dry, medium (normal) and wet
When choosing a material for room insulation, it is also important to consider the conditions in which it will be used.
The concept of thermal conductivity in practice
Thermal conductivity is taken into account at the stage of building design. This takes into account the ability of materials to retain heat. Thanks to their correct selection, residents inside the premises will always be comfortable. During operation, money for heating will be significantly saved.
Insulation at the design stage is the best, but not the only solution. It is not difficult to insulate an already finished building by carrying out internal or external work. The thickness of the insulation layer will depend on the materials chosen. Some of them (for example, wood, foam concrete) can in some cases be used without an additional layer of thermal insulation. The main thing is that their thickness exceeds 50 centimeters.
Particular attention should be paid to the insulation of the roof, window and door openings, floors. Most of the heat escapes through these elements. Visually, this can be seen in the photo at the beginning of the article.
Construction materials and their indicators
For the construction of buildings, materials with a low coefficient of thermal conductivity are used. The most popular are:
- Concrete. Its thermal conductivity is within 1.29-1.52W/mK. The exact value depends on the consistency of the solution. This indicator is also affected by the density of the source material, which is 500-2500 kg/m3. This material is used in the form of a mortar for foundations, in the form of blocks - for the construction of walls and foundations.
- Reinforced concrete whose thermal conductivity value is 1.68W/mK. The density of the material reaches 2400-2500 kg/m3.
- Wood that has been used as a building material since ancient times. Its density and thermal conductivity, depending on the rock, are 150-2100 kg/m3 and 0.2-0.23W/mK, respectively.
Another popular building material is brick. Depending on the composition, it has the following indicators:
adobe (made from clay): 0.1-0.4 W/mK;
ceramic (fired): 0.35-0.81W/mK;
silicate (from sand with lime): 0.82-0.88 W/mK
Concrete materials with the addition of porous aggregates
The thermal conductivity of the material allows you to use the latter for the construction of garages, sheds, summer houses, baths and other structures. This group includes:
- Foam concrete. Produced with the addition of foaming agents, due to which it is characterized by a porous structure with a density of 500-1000 kg/m3. At the same time, the ability to transfer heat is determined by the value 0.1-0.37W/mK.
Expanded concrete, the performance of which depends on its type. Solid blocks do not have voids and holes. Hollow blocks are made with voids inside, which are less durable than the first option. In the second case, the thermal conductivity will be lower. If we consider the general figures, then the density of expanded clay concrete is 500-1800 kg / m3. Its indicator is in the range of 0.14-0.65W/mK
Aerated concrete, inside which pores of 1-3 are formedmillimeter. This structure determines the density of the material (300-800kg/m3). Due to this, the coefficient reaches 0.1-0.3 W/mK.
Indicators of thermal insulation materials
Coefficient of thermal conductivity of thermal insulation materials, the most popular in our time:
- foam, which has a density of 15-50kg/m3, with thermal conductivity of 0.031-0.033W/mK;
expanded polystyrene, the density of which is the same as that of the previous material. But at the same time, the heat transfer coefficient is at the level of 0.029-0.036W/mK;
glass wool. It is characterized by a coefficient equal to 0.038-0.045W/mK;
stone wool 0.035-0.042W/mK
Scoreboard
For the convenience of work, the coefficient of thermal conductivity of the material is usually entered in the table. In addition to the coefficient itself, such indicators as the degree of humidity, density, and others can be reflected in it. Materials with a high coefficient of thermal conductivity are combined in the table with indicators of low thermal conductivity. An example of this table is shown below:
Using the thermal conductivity of the material will allow you to build the desired building. The main thing: to choose a product that meets all the necessary requirements. Then the building will be comfortable for living; it will maintain a favorable microclimate.
Correctly selected insulating materialwill reduce heat loss, due to which it will no longer be necessary to “heat the street”. Thanks to this, financial costs for heating will be significantly reduced. Such savings will soon return all the money that will be spent on the purchase of a heat insulator.
