The specific heat capacity of the produced brick. Is modern fireclay brick harmful? Specific heat capacity of fireclay bricks

The ability of a material to retain heat is measured by its specific heat, i.e. the amount of heat (in kJ) required to raise the temperature of one kilogram of material by one degree. For example, water has a specific heat capacity of 4.19 kJ/(kg*K). This means, for example, that it takes 4.19 kJ to raise the temperature of 1 kg of water by 1°K.

For water heating installations and liquid heating systems, it is best to use water as a heat storage material, and for air solar systems - pebbles, gravel, etc. It should be borne in mind that a pebble heat accumulator with the same energy intensity compared to a water heat accumulator has 3 times more volume and takes up 1.6 times large area. For example, a 1.5 m diameter, 1.4 m high water heat storage tank has a volume of 4.3 m 3 , while a cube-shaped pebble heat storage tank with a side of 2.4 m has a volume of 13.8 m 3 .

The heat storage density largely depends on the storage method and the type of heat storage material. It can be accumulated in chemical bound form in fuel. At the same time, the accumulation density corresponds to the calorific value, kWh/kg:

• oil - 11.3;
• coal (equivalent fuel) - 8.1;
• hydrogen - 33.6;
• wood - 4.2.

During thermochemical storage of heat in zeolite (adsorption-desorption processes), 286 Wh/kg of heat can be accumulated at a temperature difference of 55°C. The density of heat accumulation in solid materials (rock, pebbles, granite, concrete, brick) at a temperature difference of 60°C is 1417 W*h/kg, and in water - 70 W*h/kg. At phase transitions substances (melting - solidification), the accumulation density is much higher, W * h / kg:

• ice (melting) - 93;
• paraffin - 47;
• hydrates of salts of inorganic acids - 40130.

Unfortunately, the best of those given in Table 2 building materials- concrete, the specific heat capacity of which is 1.1 kJ / (kg * K), retains only ¼ of the amount of heat stored by water of the same weight. However, the density of concrete (kg / m 3) significantly exceeds the density of water. The second column of Table 2 shows the densities of these materials. Multiplying the specific heat capacity by the density of the material, we obtain the heat capacity by cubic meter. These values ​​are given in the third column of table 2. It should be noted that water, despite the fact that it has the lowest density of all the materials given, has a heat capacity 1 m 3 higher (2328.8 kJ / m 3) than the rest of the table materials, due to its much higher specific heat capacity. The low specific heat capacity of concrete is largely offset by its large mass, due to which it holds significant amount heat (1415.9 kJ / m 3).

The creation of an optimal microclimate and the consumption of thermal energy for heating a private house in the cold season largely depends on the thermal insulation properties of the building materials from which this building was built. One of these characteristics is heat capacity. This value must be taken into account when choosing building materials for constructing a private house. Therefore, the heat capacity of some building materials will be considered further.

Definition and formula of heat capacity

Each substance, to one degree or another, is capable of absorbing, storing and retaining thermal energy. To describe this process, the concept of heat capacity is introduced, which is the property of a material to absorb thermal energy when the surrounding air is heated.

To heat any material of mass m from temperature t initial to temperature t final, it will be necessary to spend a certain amount of thermal energy Q, which will be proportional to the mass and temperature difference ΔT (t end -t start). Therefore, the heat capacity formula will look like this: Q \u003d c * m * ΔТ, where c is the heat capacity coefficient (specific value). It can be calculated by the formula: c \u003d Q / (m * ΔT) (kcal / (kg * ° C)).

Conditionally assuming that the mass of the substance is 1 kg, and ΔТ = 1°C, we can obtain that c = Q (kcal). This means that the specific heat capacity is equal to the amount of thermal energy that is spent on heating a 1 kg material by 1°C.

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The use of heat capacity in practice

Building materials with high heat capacity are used for the construction of heat-resistant structures. This is very important for private houses in which people live permanently. The fact is that such structures allow you to store (accumulate) heat, thanks to which the house is supported comfortable temperature for quite a long time. First heater heats the air and the walls, after which the walls themselves warm the air. This saves cash on heating and make your stay more comfortable. For a house in which people live periodically (for example, on weekends), the large heat capacity of building materials will have the opposite effect: such a building will be quite difficult to heat quickly.

The values ​​of the heat capacity of building materials are given in SNiP II-3-79. Below is a table of the main building materials and the values ​​\u200b\u200bof their specific heat capacity.

Table 1

Brick has a high heat capacity, so it is ideal for building houses and building stoves.

Speaking of heat capacity, it should be noted that heating furnaces it is recommended to build from brick, since the value of its heat capacity is quite high. This allows you to use the oven as a kind of heat accumulator. Heat accumulators in heating systems(especially in water heating systems) are used more and more every year. Such devices are convenient in that it is enough to heat them well once with an intensive firebox. solid fuel boiler, after which they will heat your home for a whole day and even more. This will significantly save your budget.

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Heat capacity of building materials

What should be the walls of a private house in order to comply with building codes? The answer to this question has several nuances. To deal with them, an example will be given of the heat capacity of the 2 most popular building materials: concrete and wood. has a value of 0.84 kJ / (kg * ° C), and a tree - 2.3 kJ / (kg * ° C).

At first glance, one might think that wood is a more heat-intensive material than concrete. This is true, because wood contains almost 3 times more thermal energy than concrete. To heat 1 kg of wood, you need to spend 2.3 kJ of thermal energy, but when it cools, it will also release 2.3 kJ into space. At the same time, 1 kg concrete structure is able to accumulate and, accordingly, give only 0.84 kJ.

But do not rush to conclusions. For example, you need to find out what heat capacity 1 m 2 of concrete and wooden wall 30 cm thick. To do this, you first need to calculate the weight of such structures. 1 m 2 of this concrete wall will weigh: 2300 kg / m 3 * 0.3 m 3 \u003d 690 kg. 1 m 2 of a wooden wall will weigh: 500 kg / m 3 * 0.3 m 3 \u003d 150 kg.

• for a concrete wall: 0.84*690*22 = 12751 kJ;
• for wooden structure: 2.3 * 150 * 22 \u003d 7590 kJ.

From the result obtained, we can conclude that 1 m 3 of wood will accumulate heat almost 2 times less than concrete. An intermediate material in terms of heat capacity between concrete and wood is brickwork, in the unit volume of which, under the same conditions, 9199 kJ of thermal energy will be contained. At the same time, aerated concrete, as a building material, will contain only 3326 kJ, which will be much less than wood. However, in practice, the thickness of a wooden structure can be 15-20 cm, when aerated concrete can be laid in several rows, significantly increasing the specific heat of the wall.

From thermal insulation properties material depends on the temperature inside the room, which is why the heat capacity of a brick is an important indicator that shows its ability to accumulate heat. The specific heat capacity is determined during laboratory research, according to which, the most warm material is solid brick. It should be noted that the indicator depends on the type of brick material.

What it is?

The physical characteristic of heat capacity is inherent in any substance. It refers to the amount of heat absorbed physical body when heated by 1 degree Celsius or Kelvin. mistakenly identify general concept with specific, since the latter implies the temperature required to heat one kilogram of a substance. It is possible to accurately determine its number only in laboratory conditions. The indicator is necessary to determine the heat resistance of the walls of the building and in the case when construction work is carried out at sub-zero temperatures. For the construction of private and multi-storey residential buildings and premises, materials with high thermal conductivity are used, since they accumulate heat and maintain the temperature in the room.

The advantage of brick buildings is that they save on heating bills.

What determines the heat capacity of bricks?

The heat capacity coefficient is primarily affected by the temperature of the substance and the state of aggregation, since the heat capacity of the same substance in the liquid and solid state differs in favor of the liquid. In addition, the volumes of the material and the density of its structure are important. The more voids in it, the less it is able to retain heat inside itself.

Types of bricks and their indicators

Ceramic material used in the oven business.

More than 10 varieties are produced, differing in manufacturing technology. But more often silicate, ceramic, facing, refractory and warm are used. Standard ceramic bricks are made from red clay with impurities and fired. Its heat index is 700-900 J / (kg deg). It is considered quite resistant to high and low temperatures. Sometimes used for laying out furnace heating. Its porosity and density varies and affects the heat capacity coefficient. Sand-lime brick consists of a mixture of sand, clay and additives. It is full and hollow, different sizes and, consequently, its specific heat is equal to values ​​from 754 to 837 J / (kg deg). The advantage of silicate brickwork - good sound insulation even when laying out the wall in one layer.

Facing brick used for building facades has quite high density and heat capacity within 880 J/(kg deg). Refractory brick, ideal for laying the furnace, because it can withstand temperatures up to 1500 degrees Celsius. Fireclay, carborundum, magnesite and others belong to this subspecies. And the heat capacity coefficient (J/kg) is different:

picking up suitable material to carry out some kind of construction works, Special attention should refer to it specifications. This also applies to the specific heat capacity of bricks, on which the need for a house for subsequent thermal insulation and additional wall decoration largely depends.

Characteristics of a brick that affect its use:

• Specific heat. A quantity that determines the amount of thermal energy required to heat 1 kg by 1 degree.
• Thermal conductivity. A very important characteristic for brick products, which allows you to determine the amount of heat transferred from the room to the street.
• To the level of heat transfer brick wall the characteristics of the material used for its construction directly affect. In cases where it is multilayer masonry, it will be necessary to take into account the coefficient of thermal conductivity of each layer separately.

Ceramic

Useful information:

Based on the production technology, the brick is classified into ceramic and silicate groups. Moreover, both types have significant material, specific heat capacity and thermal conductivity. Raw materials for manufacturing ceramic brick, also called red, is clay, to which a number of components are added. Formed raw blanks are fired in special furnaces. The specific heat index can vary within 0.7-0.9 kJ/(kg·K). As for the average density, it is usually at the level of 1400 kg/m3.

Among strengths ceramic bricks can be distinguished:

1. Smooth surface. This enhances its external aesthetics and ease of installation.
2. Resistance to frost and moisture. Under normal conditions, the walls do not need additional moisture and thermal insulation.
3. Ability to endure high temperatures. This allows you to use ceramic bricks for the construction of stoves, barbecues, heat-resistant partitions.
4. Density 700-2100 kg/m3. This characteristic is directly affected by the presence of internal pores. As the porosity of the material increases, its density decreases and the thermal insulation characteristics increase.

Silicate

As for silicate brick, it can be full-bodied, hollow and porous. Based on the size, single, one-and-a-half and double bricks are distinguished. On average, silicate brick has a density of 1600 kg / m3. The noise-absorbing characteristics of silicate masonry are especially appreciated: even if we are talking about a wall of small thickness, the level of its sound insulation will be an order of magnitude higher than in the case of using other types of masonry material.

Facing

Separately, it is worth mentioning the facing brick, which with equal success resists both water and temperature rise. The specific heat index of this material is at the level of 0.88 kJ/(kg·K), at a density of up to 2700 kg/m3. On sale facing bricks are presented in a wide variety of shades. They are suitable for both cladding and laying.

Refractory

Represented by dinas, carborundum, magnesite and fireclay bricks. The mass of one brick is quite large, due to the significant density (2700 kg / m3). The lowest heat capacity index when heated is carborundum brick 0.779 kJ / (kg K) for a temperature of +1000 degrees. The heating rate of the furnace, laid from this brick, significantly exceeds the heating of fireclay masonry, however, cooling occurs faster.

Furnaces are equipped from refractory bricks, providing for heating up to +1500 degrees. For specific heat capacity this material big influence provides heating temperature. For example, the same fireclay brick at +100 degrees has a heat capacity of 0.83 kJ / (kg K). However, if it is heated to +1500 degrees, this will provoke an increase in heat capacity up to 1.25 kJ / (kg K).

Dependence on the temperature of use

The technical performance of bricks is greatly influenced by temperature regime:

• trepelny. At temperatures from -20 to + 20, the density varies within 700-1300 kg/m3. The heat capacity index is at a stable level of 0.712 kJ/(kg·K).
• Silicate. A similar temperature regime of -20 - +20 degrees and a density of 1000 to 2200 kg / m3 provides for the possibility of different specific heat capacities of 0.754-0.837 kJ / (kg K).
• adobe. With the same temperature as the previous type, it demonstrates a stable heat capacity of 0.753 kJ / (kg K).
• Red. It can be applied at a temperature of 0-100 degrees. Its density can vary from 1600-2070 kg/m3, and its heat capacity from 0.849 to 0.872 kJ/(kg K).
• Yellow. Temperature fluctuations from -20 to +20 degrees and a stable density of 1817 kg / m3 gives the same stable heat capacity of 0.728 kJ / (kg K).
• Building. At a temperature of +20 degrees and a density of 800-1500 kg / m3, the heat capacity is at the level of 0.8 kJ / (kg K).
• Facing. The same temperature regime of +20, with a material density of 1800 kg/m3, determines the heat capacity of 0.88 kJ/(kg K).
• Dinas. Operation at elevated temperature from +20 to +1500 and density of 1500-1900 kg/m3 implies a consistent increase in heat capacity from 0.842 to 1.243 kJ/(kg·K).
• carborundum. As it is heated from +20 to +100 degrees, a material with a density of 1000-1300 kg / m3 gradually increases its heat capacity from 0.7 to 0.841 kJ / (kg K). However, if the heating of carborundum brick is continued further, then its heat capacity begins to decrease. At a temperature of +1000 degrees, it will be equal to 0.779 kJ / (kg K).
• Magnesite. A material with a density of 2700 kg/m3 with an increase in temperature from +100 to +1500 degrees gradually increases its heat capacity of 0.93-1.239 kJ/(kg·K).
• Chromite. Heating a product with a density of 3050 kg/m3 from +100 to +1000 degrees provokes a gradual increase in its heat capacity from 0.712 to 0.912 kJ/(kg K).
• fireclay. It has a density of 1850 kg/m3. When heated from +100 to +1500 degrees, the heat capacity of the material increases from 0.833 to 1.251 kJ / (kg K).

Choose the right bricks, depending on the tasks at the construction site.

Brick is a running building material in the construction of buildings and structures. Many distinguish only red and white brick, but its types are much more diverse. They differ both externally (shape, color, dimensions) and properties such as density and heat capacity.

Traditionally, ceramic and silicate bricks are distinguished, which have different technology manufacturing. It is important to know that the density of a brick, its specific heat capacity, and each type can vary significantly.

Ceramic bricks are made from various additives and fired. The specific heat capacity of ceramic bricks is 700…900 J/(kg deg). Average density ceramic brick has a value of 1400 kg / m 3. The advantages of this type are: smooth surface, frost and water resistance, as well as resistance to high temperatures. The density of ceramic bricks is determined by its porosity and can range from 700 to 2100 kg/m 3 . The higher the porosity, the lower the brick density.

Silicate brick has the following varieties: solid, hollow and porous, it has several sizes: single, one and a half and double. The average density of silicate brick is 1600 kg/m 3 . The advantages of silicate brick in excellent soundproofing. Even if a thin layer of such material is laid, the soundproofing properties will remain at the proper level. The specific heat capacity of silicate brick is in the range from 750 to 850 J/(kg deg).

Brick density values various kinds and its specific (mass) heat capacity at various temperatures are presented in the table:

It should be noted another popular type of brick - facing brick. He is not afraid of moisture or cold. The specific heat capacity of the facing brick is 880 J/(kg deg). Facing brick has shades from bright yellow to fiery red. Such material can be used for finishing and facing works. The density of this type of brick is 1800 kg/m 3 .

It is worth noting a separate class of bricks - refractory bricks. This class includes dinas, carborundum, magnesite and fireclay bricks. Refractory bricks are quite heavy - the density of bricks of this class can reach 2700 kg / m 3.

The lowest heat capacity at high temperatures carborundum brick possesses - it is 779 J / (kg deg) at a temperature of 1000 ° C. Masonry from such a brick warms up much faster than from fireclay, but it retains heat worse.

Refractory bricks are used in the construction of furnaces, with operating temperature up to 1500°С. The specific heat capacity of refractory bricks depends significantly on temperature. For example, the specific heat capacity fireclay bricks has a value of 833 J/(kg deg) at 100°C and 1251 J/(kg deg) at 1500°C.

Sources:

1. Franchuk A. U. Tables of thermal performance of building materials, M .: Research Institute of Structural Physics, 1969 - 142 p.
2. tables physical quantities. Directory. Ed. acad. I. K. Kikoina. M.: Atomizdat, 1976. - 1008 p. construction physics, 1969 - 142 p.