Properties of materials. Specific heat

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

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

The value of the specific heat is influenced by the actual temperature of the 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 (supplied) 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 in the selection of a certain substance as a building material, for use in various refrigeration units 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 of 1000 J / 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.

Special interest in the implementation of heat exchange processes is caused by ordinary 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 when the temperature is raised to 40 ° C, it is already 4.178 kJ / (kg * K). But for ice at the 0 ° C temperature step, the heat capacity drops to the level of 2.11 kJ / (kg * K).

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

For convenience of calculations, the specific heat table, in addition to the graph with the calculated indices per one kilogram of mass, has an additional column with 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.