thermal conductivity of stone. Thermal conductivity of building materials. Comparative data of building materials with the same thermal conductivity

People also have different thermal conductivity, some warm like fluff, while others take heat like iron.

Yuri Serezhkin

The word "also" in the above statement shows that the concept of "thermal conductivity" is applied to people only conditionally. Although…

Did you know: a fur coat does not heat, it only retains the heat that the human body produces.

It means that human body has the ability to conduct heat in a literal, and not just figurative sense. This is all poetry, in fact, we will compare heaters in terms of thermal conductivity.

You know better, because you yourself typed in the search engine "thermal conductivity of heaters." What exactly did you want to know? And if without jokes, then it is important to know about this concept, because different materials behave very differently when used. important, although not key point when choosing is precisely the ability of the material to conduct thermal energy. If you choose wrong thermal insulation material simply will not perform its function, namely to keep the heat in the room.

Step 2: Theory concept

From school course Physicists will most likely remember that there are three types of heat transfer:

• Convection;
• Radiation;
• Thermal conductivity.

So thermal conductivity is a type of heat transfer or movement of thermal energy. It has to do with the internal structure of the bodies. One molecule transfers energy to another. Now would you like a little test?

Which type of substance transmits (transfers) the most energy?

• Solid bodies?
• Liquids?
• Gases?

That's right, the crystal lattice transfers energy most of all solids. Their molecules are closer to each other and therefore can interact more effectively. Gases have the lowest thermal conductivity. Their molecules are at the greatest distance from each other.

Step 3: What can be a heater

We continue our conversation about the thermal conductivity of heaters. All bodies that are nearby tend to equalize the temperature among themselves. A house or apartment, as an object, seeks to equalize the temperature with the street. Are all building materials capable of being insulators? No. For example, concrete allows the heat flow from your house to the street too quickly, so the heating equipment will not have time to maintain the desired temperature regime in room. The thermal conductivity coefficient for insulation is calculated by the formula:

Where W is our heat flux, and m2 is the area of ​​\u200b\u200binsulation with a temperature difference of one Kelvin (It is equal to one degree Celsius). For our concrete, this coefficient is 1.5. This means that conditionally, one square meter concrete with a temperature difference of one degree Celsius is able to pass 1.5 watts of thermal energy per second. But, there are materials with a coefficient of 0.023. It is clear that such materials are much better suited for the role of heaters. Does thickness matter, you ask? Plays. But, here you still can not forget about the heat transfer coefficient. To achieve the same results, you will need a concrete wall 3.2 m thick or a sheet of foam plastic 0.1 m thick. It is clear that although concrete can technically be a heater, it is not economically feasible. That's why:

Insulation can be called a material that conducts through itself least amount thermal energy, preventing it from leaving the premises and at the same time costing as little as possible.

The best heat insulator is air. Therefore, the task of any insulation is the creation of a fixed air gap without convection (movement) of air inside it. That is why, for example, foam plastic is 98% air. The most common insulating materials are:

• Styrofoam;
• extruded polystyrene foam;
• mineral wool;
• Penofol;
• Penoizol;
• Foam glass;
• Polyurethane foam (PPU);
• Ecowool (cellulose);

The thermal insulation properties of all the materials listed above lie close to these limits. It is also worth considering: the higher the density of the material, the more it conducts energy through itself. Remember from theory? The closer the molecules are, the more efficiently heat is conducted.

Step 4: Compare. Table of thermal conductivity of heaters

The table shows a comparison of heaters in terms of thermal conductivity declared by manufacturers and corresponding to GOSTs:

Comparative table of thermal conductivity building materials, which are not considered to be heaters:

The heat transfer rate only indicates the rate of heat transfer from one molecule to another. For real life this indicator is not so important. But you can’t do without a thermal calculation of the wall. Heat transfer resistance is the reciprocal of thermal conductivity. We are talking about the ability of the material (insulation) to retain heat flow. To calculate the resistance to heat transfer, you need to divide the thickness by the coefficient of thermal conductivity. The example below shows the calculation of the thermal resistance of a wall made of a 180 mm thick beam.

As you can see, the thermal resistance of such a wall will be 1.5. Enough? It depends on the region. The example shows the calculation for Krasnoyarsk. For this region, the required coefficient of resistance of enclosing structures is set at 3.62. The answer is clear. Even for Kyiv, which is much further south, this figure is 2.04.

Thermal resistance is the reciprocal of thermal conductivity.

This means that abilities wooden house resisting heat loss is not enough. Warming is necessary, and already, with what material - calculate according to the formula.

Step 5: Mounting Rules

It is worth saying that all the above indicators are given for DRY materials. If the material gets wet, it will lose its properties by at least half, or even turn into a “rag”. Therefore, it is necessary to protect thermal insulation. Styrofoam is most often insulated under wet facade in which the insulation is protected by a layer of plaster. Superimposed on the mineral wool waterproofing membrane to keep moisture out.

Another point that deserves attention is wind protection. Heaters have different porosity. For example, let's compare expanded polystyrene boards and mineral wool. If the first one looks solid, the second one clearly shows pores or fibers. Therefore, if you are installing fibrous thermal insulation, such as mineral wool or ecowool, on a wind-blown fence, be sure to take care of the wind protection. Otherwise, the good thermal performance of the insulation will not be useful.

conclusions

So, we discussed that the thermal conductivity of heaters is their ability to transfer thermal energy. The heat insulator must not release the heat generated heating system at home. The primary task of any material is to keep air inside. It is the gas that has the lowest thermal conductivity. It is also necessary to calculate the thermal resistance of the wall in order to find out the correct coefficient of thermal insulation of the building. If you have any questions about this topic, please leave them in the comments.

Three interesting facts about thermal insulation

• The snow serves as a heat insulator for the bear in the den.
• Clothing is also a heat insulator. We are not very comfortable when our body tries to equalize temperature with temperature. environment, which can be -30 degrees, instead of the usual 36.6.
• The blanket is a thermal insulator. It does not allow the heat of the human body to escape.

Bonus

As a bonus for the curious who have read to the end interesting experiment with thermal conductivity:

It is better to start the construction of each object with the planning of the project and careful calculation of thermal parameters. Accurate data will allow you to get a table of thermal conductivity of building materials. Proper construction of buildings contributes to optimal climatic parameters in the room. And the table will help you choose the right raw materials that will be used for construction.

The thermal conductivity of materials affects the thickness of the walls

Thermal conductivity is a measure of the transfer of thermal energy from heated objects in a room to objects with a lower temperature. The heat exchange process is carried out until the temperature indicators are equalized. To designate thermal energy, a special coefficient of thermal conductivity of building materials is used. The table will help you see all the required values. The parameter indicates how much heat energy is passed through a unit area per unit time. The larger this designation, the better the heat transfer will be. When erecting buildings, it is necessary to use a material with a minimum value of thermal conductivity.

The thermal conductivity coefficient is a value that is equal to the amount of heat passing through a meter of material thickness per hour. The use of such a characteristic is mandatory to create better thermal insulation. Thermal conductivity should be taken into account when selecting additional insulating structures.

What affects the thermal conductivity?

Thermal conductivity is determined by such factors:

• porosity determines the heterogeneity of the structure. When heat is passed through such materials, the cooling process is negligible;
• an increased density value affects the close contact of the particles, which contributes to faster heat transfer;
• high humidity increases this indicator.

Use of thermal conductivity values ​​in practice

Materials are represented by structural and heat-insulating varieties. The first type has high thermal conductivity. They are used for the construction of ceilings, fences and walls.

With the help of the table, the possibilities of their heat transfer are determined. In order for this indicator to be low enough for a normal indoor microclimate, walls made of some materials must be especially thick. To avoid this, it is recommended to use additional heat-insulating components.

Thermal conductivity indicators for finished buildings. Types of insulation

When creating a project, all methods of heat leakage must be taken into account. It can exit through walls and roofs, as well as through floors and doors. If you do the design calculations incorrectly, you will have to be content with only the thermal energy received from the heating devices. Buildings built from standard raw materials: stone, brick or concrete need to be additionally insulated.

Additional thermal insulation is carried out in frame buildings. Wherein wooden frame gives rigidity to the structure, and the insulating material is laid in the space between the uprights. In buildings made of bricks and cinder blocks, insulation is carried out outside the structure.

When choosing heaters, it is necessary to pay attention to such factors as the level of humidity, the effect of elevated temperatures and the type of structure. Consider certain parameters of insulating structures:

• the thermal conductivity index affects the quality of the heat-insulating process;
• moisture absorption has great importance when insulating external elements;
• thickness affects the reliability of insulation. Thin insulation helps to keep usable area premises;
• flammability is important. High-quality raw materials have the ability to self-extinguish;
• thermal stability reflects the ability to withstand temperature changes;
• environmental friendliness and safety;
• soundproofing protects against noise.

The following types are used as heaters:

• mineral wool fire resistant and environmentally friendly. Important characteristics include low thermal conductivity;

• Styrofoam is a lightweight material with good insulating properties. It is easy to install and is moisture resistant. Recommended for use in non-residential buildings;
• basalt wool, unlike mineral wool, is different best performance resistance to moisture;
• penoplex is resistant to moisture, elevated temperatures and fire. It has excellent thermal conductivity, easy to install and durable;

• polyurethane foam is known for such qualities as incombustibility, good water-repellent properties and high fire resistance;
• extruded polystyrene foam undergoes additional processing during production. Has a uniform structure;

• penofol is a multilayer insulating layer. Contains polyethylene foam. The surface of the plate is covered with foil to provide reflection.

Bulk types of raw materials can be used for thermal insulation. These are paper granules or perlite. They are resistant to moisture and fire. And from organic varieties, you can consider fiber from wood, flax or cork. When choosing, Special attention pay attention to indicators such as environmental friendliness and fire safety.

Note! When designing thermal insulation, it is important to consider the installation of a waterproofing layer. This will avoid high humidity and increase resistance to heat transfer.

Table of thermal conductivity of building materials: features of indicators

The table of thermal conductivity of building materials contains indicators various kinds raw materials used in construction. Using this information, you can easily calculate the thickness of the walls and the amount of insulation.

How to use the table of thermal conductivity of materials and heaters?

The heat transfer resistance table of materials shows the most popular materials. When choosing a particular option for thermal insulation, it is important to consider not only physical properties, but also such characteristics as durability, price and ease of installation.

Did you know that the easiest way is to install penooizol and polyurethane foam. They are distributed over the surface in the form of foam. Such materials easily fill the cavities of structures. When comparing solid and foam options, it should be noted that the foam does not form joints.

Values ​​of heat transfer coefficients of materials in the table

When making calculations, you should know the coefficient of resistance to heat transfer. This value is the ratio of temperatures on both sides to the amount heat flow. In order to find the thermal resistance of certain walls, a thermal conductivity table is used.

You can do all the calculations yourself. For this, the thickness of the heat insulator layer is divided by the thermal conductivity coefficient. This value is often indicated on the packaging if it is insulation. Household materials are self-measured. This applies to thickness, and the coefficients can be found in special tables.

The drag coefficient helps to choose certain type thermal insulation and material layer thickness. Information on vapor permeability and density can be found in the table.

At correct use tabular data you can choose quality material for creating favorable microclimate in room.

Thermal conductivity of building materials (video)

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One of the most important characteristics concrete, of course, is its thermal conductivity. This indicator changes different types material can be within significant limits. DependsPmost of all, fromkindfiller used in it. The lighter the material, the better the insulator from the cold it is.

What is thermal conductivity: definition

In the construction of buildings and structures, different materials can be used. Residential and industrial buildings in the Russian climate are usually insulated. That is, during their construction, special insulators are used, the main purpose of which is to maintain a comfortable temperature inside the premises. When calculating required amount mineral wool or polystyrene foam, the thermal conductivity of the base material used for the construction of the enclosing structures is necessarily taken into account.

Very often, buildings and structures in our country are built from different types of concrete. Also for this purpose, useYutsya brickand tree.Actually, thermal conductivity itself is the ability of a substance to transfer energy in its thickness due to the movement of molecules. A similar process can take place both in the solid parts of the material and in its pores. In the first case, it is called conduction, in the second - convection.The cooling of the material is much faster in its solid parts. The air filling the pores retains heat, of course, better.

What does the index depend on?

The following conclusions can be drawn from the above. depends tthermal conductivity of concrete,wood and brick, as well as any other material,fromthem:

• density;
• porosity;
• humidity.

With an increase, the degree of its thermal conductivity also increases. The more pores in the material, the better insulator from the cold it is.

Types of concrete

AT modern construction different types of this material can be used. However, all concretes existing on the market can be classified into two large groups:

• heavy;
• light foamy or with a porous filler.

Thermal conductivity of heavy concrete: indicators

Such materials are also divided into two main groups. Concrete can be used in construction:

• heavy;
• especially heavy.

In the production of the second type of material, fillers such as metal scrap, hematite, magnetite, barite are used. Especially heavy concretes are usually used only in the construction of facilities whose main purpose is protection from radiation. This group includes materials with a density of 2500 kg/m3.

Ordinary heavy concretes are made using such types of filler as granite, diabase or limestone, made on the basis of crushed stone. In the construction of buildings and structures, a similar 1600-2500 kg / m 3 is used.

What can be in this case thermal conductivity of concrete? Table,presented below shows indicators typical for different types heavy material.

Thermal conductivity of lightweight cellular concrete

Such material is also classified into two main varieties. Very often, concretes based on porous filler are used in construction. As the latter, expanded clay, tuff, slag, pumice are used. In the second group of lightweight concretes, a regular filler is used. But in the process of kneading, such material foams. As a result, after maturation, many pores remain in it.

Tthermal conductivity of concretelung is very low.But at the same time, in terms of strength characteristics, such a material is inferior to heavy. Lightweight concrete is used most often for the construction different kind residential and outbuildings that are not heavily loaded.

Classified not only by the method of manufacture, but also by purpose. In this regard, there are materials:

• heat-insulating (with density up to 800 kg/m3);
• structural and heat-insulating (up to 1400 kg/m3);
• structural (up to 1800 kg/m3).

Thermal conductivity of cellular concretelung of different types is representedin the table.

Thermal insulation materials

These are usually used for lining walls assembled from bricks or poured from cement mortar. As can be seen from the table,thermal conductivity concreteathis group can vary over a fairly large range.

Concrete of this variety is most often used as insulating materials. But sometimes all sorts of insignificant enclosing structures are erected from them.

Structural, heat-insulating and structural materials

Of this group, foam concrete, slag-pumice concrete, and slag concrete are most often used in construction. Some types of expanded clay concrete with a density over 0.29W/(m°C)may also be included in this species.

Very often thisconcrete with low thermal conductivity is used directly asbuilding material. But sometimes it is also used as an insulator that does not let the cold through.

How does thermal conductivity depend on humidity?

Everyone knows that almost any dry material insulates from the cold much better than wet. This is primarily due to the very low degree of thermal conductivity of water.Protect concrete walls, floors and ceilingsrooms from low outdoor temperatures , as we found out, mainly due to the presence of air-filled pores in the material. When wet, the latter is displaced by water. And, consequently, a significant increaseIn the cold season, water that has entered the pores of the material freezes.The result is thatthe heat-retaining qualities of walls, floors and ceilings are reduced even more.

The degree of moisture permeability for different types of concrete may vary. According to this indicator, the material is classified into several grades.

Wood as an insulator

Both "cold" heavy and light concrete, thermal conductivitytowhich is low,of course,verypopulareand sought-after looksbuildernyhmaterialov. In any case, the foundations of most buildings and structures are built precisely fromcement mortar mixed with crushed stone or rubble stone.

Applybconcrete mixture or blocks made from it and for the construction of enclosing structures. But quite often, other materials are used to assemble the floor, ceilings and walls, for example, wood. Timber and board differ, of course, much less strength than concrete. However, the degree of thermal conductivity of wood, of course, is much lower. For concrete, this indicator, as we found out, is 0.12-1.74W/(m°C).In a tree, the coefficient of thermal conductivity depends, among other things, on this particular species.

In other breeds, this figure may be different.It is believed that the average thermal conductivity of wood across the fibers is 0.14W/(m°C). The best way to insulate space from the cold is cedar. Its thermal conductivity is only 0.095 W / (m C).

Brick as an insulator

Next, for comparison, consider the characteristics in relation to thermal conductivity and this popular building material.In terms of strengthbricknot only is it not inferior to concrete, but often surpasses it.The same applies to the density of this building stone. All bricks used today in the construction of buildings and structurestoclassified into ceramic and silicate.

Both of these types of stone, in turn, can be:

• corpulent;
• with voids;
• slotted.

Of course, solid bricks retain heat worse than hollow and slotted ones.

Thermal conductivity of concrete and brick, tthus practically the same. Both silicate and isolate the premises from the cold rather weakly. Therefore, houses built from such material should be additionally insulated. As insulators for sheathing brick walls as well as those poured from ordinary heavy concrete, polystyrene foam or mineral wool are most often used. Porous blocks can also be used for this purpose.

How is the thermal conductivity calculated

This indicator is determined by different materials, including concrete, according to special formulas. In total, two methods can be used. The thermal conductivity of concrete is determined by the Kaufman formula. It looks like this:

0.0935x(m) 0.5x2.28m + 0.025, where m is the mass of the solution.

For wet (more than 3%) solutions, the Nekrasov formula is used:(0.196 + 0.22 m2) 0.5 - 0.14 .

Toexpanded clay concrete with a density of 1000 kg/m3 has a mass of 1 kg. Respectively,for example,according to Kaufman, in this case, the coefficient will be 0.238.The thermal conductivity of concrete is determined at a temperature of the mixture C. For cold and heated materials, its indicators may vary slightly.

So what is thermal conductivity? From the point of view of physics thermal conductivity- this is the molecular transfer of heat between directly contacting bodies or particles of the same body with different temperature, at which there is an exchange of energy of motion of structural particles (molecules, atoms, free electrons).

It's easier to say thermal conductivity is the ability of a material to conduct heat. If there is a temperature difference inside the body, then thermal energy passes from its hotter part to its colder one. Heat transfer occurs due to the transfer of energy during the collision of the molecules of a substance. This happens until the temperature inside the body becomes the same. Such a process can occur in solid, liquid and gaseous substances.

In practice, for example, in construction with thermal insulation of buildings, another aspect of thermal conductivity is considered, associated with the transfer of thermal energy. Let's take the "abstract house" as an example. In the "abstract house" there is a heater that maintains a constant temperature inside the house, say, 25 ° C. Outside, the temperature is also constant, for example, 0 °C. It is quite clear that if you turn off the heater, then after a while the house will also be 0 ° C. All the heat (thermal energy) through the walls will go outside.

To keep the temperature in the house at 25 ° C, the heater must be constantly on. The heater constantly creates heat, which constantly escapes through the walls to the street.

Coefficient of thermal conductivity.

The amount of heat that passes through the walls (and scientifically - the intensity of heat transfer due to thermal conductivity) depends on the temperature difference (in the house and on the street), on the area of ​​\u200b\u200bthe walls and the thermal conductivity of the material from which these walls are made.

For quantification thermal conductivity exists coefficient of thermal conductivity of materials. This coefficient reflects the property of a substance to conduct thermal energy. The higher the value of the thermal conductivity of a material, the better it conducts heat. If we are going to insulate the house, then we need to choose materials with a small value of this coefficient. The smaller it is, the better. Now, as materials for the insulation of buildings, heaters from, and various ones are most widely used. Gain popularity new material with improved thermal insulation qualities -.

The coefficient of thermal conductivity of materials is indicated by the letter ? (Greek lowercase letter lambda) and is expressed in W/(m2*K). This means that if we take a brick wall with a thermal conductivity of 0.67 W / (m2 * K), 1 meter thick and 1 m2 in area, then with a temperature difference of 1 degree, 0.67 watts of thermal energy will pass through the wall. energy. If the temperature difference is 10 degrees, then 6.7 watts will pass. And if, with such a temperature difference, the wall is made 10 cm, then the heat loss will already be 67 watts. For more information about the method of calculating the heat loss of buildings, see

It should be noted that the values ​​of the thermal conductivity coefficient of materials are indicated for a material thickness of 1 meter. To determine the thermal conductivity of a material for any other thickness, the thermal conductivity coefficient must be divided by desired thickness expressed in meters.

AT building codes and calculations, the concept of “thermal resistance of the material” is often used. This is the reciprocal of thermal conductivity. If, for example, the thermal conductivity of a 10 cm thick foam plastic is 0.37 W / (m2 * K), then its thermal resistance will be 1 / 0.37 W / (m2 * K) \u003d 2.7 (m2 * K) / Tue

The table below shows the values ​​of the thermal conductivity coefficient for some materials used in construction.

The term "thermal conductivity" is applied to the properties of materials to transmit thermal energy from hot to cold areas. Thermal conductivity is based on the movement of particles inside substances and materials. The ability to transfer heat energy in quantitative terms is the coefficient of thermal conductivity. The cycle of thermal energy transfer, or heat exchange, can take place in any substances with unequal placement of different temperature sections, but the thermal conductivity depends on the pressure and temperature in the material itself, as well as on its state - gaseous, liquid or solid.

Physically, the thermal conductivity of materials is equal to the amount of heat that flows through a homogeneous object of established dimensions and area for a certain time period at a specified temperature difference (1 K). In the SI system, a single indicator that has a thermal conductivity coefficient is usually measured in W / (m K).

How to Calculate Thermal Conductivity Using Fourier's Law

In a given thermal regime, the flux density during heat transfer is directly proportional to the maximum temperature increase vector, the parameters of which change from one section to another, and modulo with the same temperature increase rate in the direction of the vector:

q → = − ϰ x grad x (T), where:

• q → - the direction of the density of the object that transfers heat, or the volume of heat flow that flows through the site for a given time unit through a certain area, perpendicular to all axes;
• ϰ is the specific coefficient of thermal conductivity of the material;
• T is the temperature of the material.

When applying the Fourier law, the inertia of the flow of thermal energy is not taken into account, which means that the instantaneous transfer of heat from any point to any distance is meant. Therefore, the formula cannot be used to calculate heat transfer during processes with a high repetition rate. This is ultrasonic radiation, the transfer of thermal energy by shock or impulse waves, etc. There is a Fourier law solution with a relaxation term:

τ x ∂ q / ∂ t = − (q + ϰ x ∇T) .

If the relaxation τ is instantaneous, then the formula turns into the Fourier law.

Approximate table of thermal conductivity of materials:

The given table of thermal conductivity takes into account heat transfer by thermal radiation and heat exchange of particles. Since vacuum does not transfer heat, it flows with the help of solar radiation or other type of heat generation. In a gas or liquid medium, layers with different temperatures are mixed artificially or naturally.

When calculating the thermal conductivity of a wall, it must be taken into account that heat transfer through wall surfaces varies from the fact that the temperature in the building and on the street is always different, and depends on the area of ​​\u200b\u200ball surfaces of the house and on the thermal conductivity of building materials.

To quantify the thermal conductivity, a value such as the coefficient of thermal conductivity of materials was introduced. It shows how a particular material is able to transfer heat. The higher this value, for example, the thermal conductivity of steel, the more efficiently the steel will conduct heat.

• When insulating a house made of wood, it is recommended to choose building materials with a low coefficient.
• If the wall is brick, then with a coefficient value of 0.67 W / (m2 K) and a wall thickness of 1 m, with an area of ​​\u200b\u200bit 1 m 2, with a difference between the outside and inside temperatures of 1 0 C, the brick will transmit 0.67 W of energy. With a temperature difference of 10 0 C, the brick will transmit 6.7 W, etc.

The standard value of the thermal conductivity coefficient of thermal insulation and other building materials is valid for a wall thickness of 1 m. To calculate the thermal conductivity of a surface of a different thickness, the coefficient should be divided by the selected wall thickness value (meters).

In SNiP and when carrying out calculations, the term "thermal resistance of the material" appears, it means reverse thermal conductivity. That is, with a thermal conductivity of a foam sheet of 10 cm and its thermal conductivity of 0.35 W / (m 2 K), the thermal resistance of the sheet is 1 / 0.35 W / (m 2 K) \u003d 2.85 (m 2 K) / W.

Below is a table of thermal conductivity for popular building materials and heat insulators:

In addition, it is necessary to take into account the thermal conductivity of heaters due to their jet heat flows. In a dense medium, it is possible to “transfer” quasiparticles from one heated building material to another, colder or warmer, through submicron pores, which helps to spread sound and heat, even if there is an absolute vacuum in these pores.