Technical thermodynamics: basic concepts. What technical thermodynamics studies

Investigating the relationship between energy and entropy is what technical thermodynamics studies. It encompasses a whole set of theories that compare macroscopic properties that can be measured (temperature, pressure and volume) with energy and its ability to do work.

Introduction

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 part, this is one of the great theories on which the current understanding of matter is based. A thermodynamic system is defined as the amount of matter of a fixed mass and identity. Everything external to it is the environment from which it is separated by borders. The use of technical thermodynamics includes such structures as:

• air conditioners and refrigerators;
• turbochargers and superchargers in automobile engines;
• steam turbines in power plants;
• jet engines in airplanes.

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 complicated. In classical technical thermodynamics, the definition of absolute body temperature was given. It led to the creation of the Kelvin scale. The minimum temperature for all bodies is Kelvin zero (-273.15 ° C). This is an absolute zero, the concept of which first appeared in 1702 thanks to the French physicist Guillaume Amonton.

Heat is harder to determine. Technical thermodynamics interprets it as a random transfer of energy from a system to the external environment. It corresponds to the kinetic energy of molecules moving and subjected to random impacts (Brownian motion). The transmitted energy is called random at the microscopic level, in contrast to ordered, performed through work at the macroscopic level.

State of substance

The 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;
• plasma;
• superfluid (the rarest).

Many substances can pass between the gas, liquid and solid phases. Plasma is a special state of matter, such as lightning.

Thermal capacity

The heat capacity (C) is the ratio of the change in heat (ΔQ, where the Greek symbol Delta indicates the amount) to the change in temperature (ΔT):

C = Δ Q / Δ T.

It shows the ease with which a substance heats up. A good thermal conductor has a low capacity indicator. A strong heat insulator has a high heat capacity.

Terminology

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

1. Heat transfer is the mutual exchange of temperatures between two substances.
2. The microscopic approach is 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 substance or region in space selected for research.
5. The environment is all external systems.
6. Conduction - Heat is transferred through a heated solid.
7. Convection - heated particles return heat to another substance.
8. Radiation - heating is transmitted through electromagnetic waves, for example, from the sun.
9. Entropy - in thermodynamics, is a physical quantity used to characterize an isothermal process.

More about science

The interpretation of thermodynamics as a separate discipline of physics is not entirely true. It affects almost all areas. Without the ability of the system to use internal energy to do the 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. It is associated with the assessment of energy transfer in the working substance of the machine.
2. Cryophysics (cryogenics) is the science of low temperatures. Investigates the physical properties of substances under conditions experienced even in the coldest region of the Earth. An example of this is the study of superfluid substances.
3. Hydrodynamics - the study of the physical properties of liquids.
4. High pressure physics. Investigates the physical properties of substances in extremely high pressure systems associated with fluid dynamics.
5. Meteorology is a scientific study of the atmosphere that focuses on weather processes and forecasting.
6. Plasma physics - the study of a substance in a plasma state.

Zero law

The subject and method of technical thermodynamics are experimental observations recorded in the form of laws. The zero law of thermodynamics states: when two bodies have an equal temperature with a third, they in turn have an equal temperature with each other. For example: one block of copper is brought into contact with a thermometer until it reaches a temperature equality. Then deleted. The second block of copper is brought into contact with the same thermometer. If at the same time there is no change in the level of mercury, then we can say that both units are in thermal equilibrium with a thermometer.

First law

This law says: since the 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 change in energy of a system is always equal to the net energy that crosses the boundary of the system. The latter may be internal, kinetic, or potential.

Second law

It is used to determine the direction in which a particular thermal process can occur. This law of thermodynamics states: it is impossible to create a device that works in a cycle and does not produce any effect, except for the transfer of heat from a body with a low temperature to a hotter body. It is sometimes called the law of entropy, because it introduces this important property. Entropy can be seen as a measure of how close the system is to equilibrium or disorder.

Thermal process

A 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 that have special properties:

• adiabatic - without heat transfer in the system;
• isochoric - without changing the volume;
• isobaric - no change in pressure;
• isothermal - no change in temperature.

Reversibility

A process is considered reversible, which, after it has taken place, can be canceled. It leaves no changes in the system or the environment. To be reversible, the system must be in equilibrium. There are factors that make the process irreversible. For example, friction and rampant expansion.

Application

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 may use a gas or diesel engine, but the law remains the same.
2. Air and gas compressors, blowers, fans operate on a different thermodynamic cycle.
3. Heat transfer is used in evaporators, condensers, radiators, coolers, heaters.
4. Refrigerators, freezers, industrial refrigeration systems, all types of air conditioning systems and heat pumps work thanks 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.