Technical thermodynamics: basic concepts. What does technical thermodynamics study?

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Technical thermodynamics: basic concepts. What does technical thermodynamics study?
Technical thermodynamics: basic concepts. What does technical thermodynamics study?

The study of the relationship between energy and entropy is what technical thermodynamics studies. It encompasses a whole set of theories that relate measurable macroscopic properties (temperature, pressure, and volume) to energy and its ability to do work.


The concepts of heat and temperature are the most fundamental for technical thermodynamics. It can be called the science of all phenomena that depend on temperature and its changes. In statistical physics, of which it is now a part, it is one of the great theories on which the current understanding of matter is based. A thermodynamic system is defined as a quantity of matter of a fixed mass and identity. Everything external to it is the environment from which it is separated by boundaries. Applications of technical thermodynamics include constructions such as:

  • air conditioners and refrigerators;
  • turbochargers and superchargers in automotive engines;
  • steam turbines in power plants;
  • reactiveaircraft engines.
Generated energy

Heat and temperature

Every person has an intuitive knowledge of the concept of temperature. The body is hot or cold, depending on whether its temperature is more or less high. But the exact definition is more difficult. In classical technical thermodynamics, the absolute temperature of a body was defined. It led to the creation of the Kelvin scale. The minimum temperature for all bodies is zero Kelvin (-273, 15°C). This is absolute zero, the concept of which first appeared in 1702 thanks to the French physicist Guillaume Amonton.

Heat is harder to define. Technical thermodynamics interprets it as a random transfer of energy from the system to the external environment. It corresponds to the kinetic energy of molecules moving and being subjected to random impacts (Brownian motion). The transmitted energy is called disordered at the microscopic level, as opposed to orderly, done through work at the macroscopic level.

Fluid thermodynamics

State of matter

A state of matter is a description of the type of physical structure that a substance exhibits. It has properties that describe how a material maintains its structure. There are five states of matter:

  • gas;
  • liquid;
  • solid body;
  • plasma;
  • superfluid (the rarest).

Many substances can move between gas, liquid and solid phases. Plasma is a special state of matterlike lightning.

Heat capacity

Heat capacity (C) is the ratio of change in heat (ΔQ, where the Greek character Delta stands for quantity) to change in temperature (ΔT):

C=Δ Q / Δ T.

She shows the ease with which the substance is heated. A good thermal conductor has a low capacitance rating. Strong heat insulator with high heat capacity.

Gas thermodynamics


Each science has its own unique vocabulary. The basic concepts of technical thermodynamics include:

  1. Heat transfer is the mutual exchange of temperatures between two substances.
  2. Microscopic approach - the study of the behavior of each atom and molecule (quantum mechanics).
  3. Macroscopic approach - observation of the general behavior of many particles.
  4. Thermodynamic system - the amount of matter or area in space chosen for research.
  5. Environment - all external systems.
  6. Conduction - heat is transferred through a heated solid body.
  7. Convection - heated particles return heat to another substance.
  8. Radiation - heat is transmitted through electromagnetic waves, such as from the sun.
  9. Entropy - in thermodynamics is a physical quantity used to characterize an isothermal process.
Uneven heat transfer

More about science

The interpretation of thermodynamics as a separate discipline of physics is not entirely correct. It affects almost everythingareas. Without the system's ability to use internal energy to do work, physicists would have nothing to study. There are also some very useful areas of thermodynamics:

  1. Heat engineering. It studies two possibilities of energy transfer: work and heat. Associated with the assessment of energy transfer in the working substance of the machine.
  2. Cryophysics (cryogenics) - the science of low temperatures. Explores the physical properties of substances under conditions experienced even in the coldest region of the Earth. An example of this is the study of superfluids.
  3. Hydrodynamics is the study of the physical properties of liquids.
  4. Physics of high pressures. Explores the physical properties of substances in extremely high pressure systems related to fluid dynamics.
  5. Meteorology is the scientific study of the atmosphere that focuses on weather processes and forecasting.
  6. Plasma Physics - the study of matter in the plasma state.
solar heat dissipation

Zero Law

The subject and method of technical thermodynamics are experimental observations written in the form of laws. The zeroth law of thermodynamics states that when two bodies have the same temperature as a third, they in turn have the same temperature with each other. For example: one block of copper is brought into contact with a thermometer until the temperature is equal. Then it is removed. The second block of copper is brought into contact with the same thermometer. If this does not change the level of mercury, then we can say that both blocks are inthermal equilibrium with a thermometer.

First Law

This law states that as a system undergoes a state change, energy can cross the boundary either as heat or as work. Each of them can be positive or negative. The net energy change of a system is always equal to the net energy that crosses the boundary of the system. The latter can be internal, kinetic or potential.

Applications of thermodynamics

Second Law

It is used to determine the direction in which a particular thermal process can take place. This law of thermodynamics states that it is impossible to create a device that works in a cycle and does not produce any effect other than transferring heat from a body with a lower temperature to a hotter body. It is sometimes called the law of entropy because it introduces this important property. Entropy can be thought of as a measure of how close a system is to equilibrium or disorder.

Thermal process

The system undergoes a thermodynamic process when some kind of energy change occurs in it, usually associated with the transformation of pressure, volume, temperature. There are several specific types with special properties:

  • adiabatic - no heat exchange in the system;
  • isochoric - no change in volume;
  • isobaric - no change in pressure;
  • isothermal - no change in temperature.


A reversible process is one that, after it has taken place, can becanceled. It does not leave any changes either in the system or in the environment. To be reversible, the system must be in equilibrium. There are factors that make the process irreversible. For example, friction and runaway expansion.

Thermodynamics of solids


Many aspects of the life of modern mankind are built on the foundations of heat engineering. These include:

  1. All vehicles (cars, motorcycles, carts, ships, planes, etc.) operate on the basis of the second law of thermodynamics and the Carnot cycle. They can use a gasoline or diesel engine, but the law remains the same.
  2. Air and gas compressors, blowers, fans operate on different thermodynamic cycles.
  3. Heat exchange is used in evaporators, condensers, radiators, coolers, heaters.
  4. Refrigerators, freezers, industrial refrigeration systems, all types of air conditioning systems and heat pumps work due to the second law.

Technical thermodynamics also includes the study of various types of power plants: thermal, nuclear, hydroelectric, based on renewable energy sources (such as solar, wind, geothermal), tides, waves and others.

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