Properties of materials. Specific heat

The study of thermal phenomena required from physicistsintroduction of the concept of specific heat. Despite its volatility and dependence on many factors, this value makes it easier to carry out calculations not only during experiments, but also in the process of practical production activities.

The physical meaning of the specific heat, which inThe SI system is measured in joules per kilogram-kelvin, consisting in the amount of heat (heat energy) required for a substance with a mass of one kilogram to change its temperature by one kelvin (degree).

On the value of specific heat rendersinfluence real temperature of substance. Water heated to 20 ° C and up to 60 ° C has different values ​​of this characterizing index. For the basic substances in the course of experimental studies, their specific heat was calculated. The formula was derived to determine the relationship between several quantities. A mathematical expression combines several physical quantities. The first is the specific heat, which, for the sake of simplicity, is taken as a constant value under standard conditions. Sometimes it is calculated for individual conditions, for example, for water vapor (heated water to a temperature of 373 Kelvin or 100 ° C). Then follows the value that determines the amount of heat received (released) by the substance when heated (cooled), the mass of the substance being heated (cooled), the temperature difference before and after the end of the process.

Specific heat capacity is of great importance forthe choice of a certain substance as a building material, for use in a variety of refrigeration systems or heating systems. It has long been noted that materials having the same mass for heating use a different amount of thermal energy. Aluminum coatings, for example, receiving the same heat input from natural solar radiation, heat up faster and faster than the same woodwork or conventional plaster.

Considering concrete with a specific heat capacity of 1000J / kg-K, it can be concluded that heating one kilogram of this material per one kelvin will require an amount of energy of 1000 J. Wood produces the same effect twice as much heat as the same mass of aerated concrete. This affects not only the microclimatic comfort of the premises, but also the various parameters of the thermal elongation of the structures.

Particular interest in the implementationheat exchange processes cause normal water. On her example, you can clearly see that the index of "specific heat" of each substance is greatly influenced by its aggregate state. Continuing the example of water, an interesting pattern is revealed. At 0 ° C in the liquid state, it has a specific heat capacity of 4.218, and with an increase in temperature to 40 ° C, it is already 4.178 kJ / (kg * K). But for the ice on the temperature step 0 ° C the specific heat drops to the level of 2.11 kJ / (kg * K).

Water is the liquid with the highestspecific heat factor. For the next jump by one degree, it absorbs or gives away a large amount of heat than any other substance. It is water used in cases of necessity to provide artificial heat exchange.

For convenience of calculations the table of specificheat capacity except for the graph with the calculated indices per one kilogram of mass, has an additional column with the expressions of this characteristic per one liter (or dm3) of the substance. Using the data in the table, engineers and designers make the selection of the most optimal materials for the implementation of their ideas and ideas. With the advent of new materials with unique properties, the range for choice has expanded considerably, but even simple and accessible substances can sometimes make them worthy of competition.

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