At the core of virtually any heatmachines is a thermodynamic phenomenon, as the work done by gas during expansion or contraction. Here it is worth remembering that in physics, work is understood as a quantitative measure characterizing the effect of a certain force on a body. In accordance with this, the work of a gas, the necessary condition for the commission of which is a change in its volume, is nothing but the product of the pressure on this change in volume.
The work of the gas when changing its volume can beboth isobaric and isothermal. In addition, the expansion process itself may be arbitrary. The gas work, which is performed during isobaric expansion, can be found by the following formula:
A = pΔV,
in which p is the quantitative characteristic of the gas pressure, and ΔV is the difference between the initial and final volume.
The process of arbitrary gas expansion in physicsusually represented as a sequence of individual isobaric and isochoric processes. The latter are characterized by the fact that the gas, as well as its quantitative indicators, is equal to zero, because the piston does not move in the cylinder. Under such conditions, it turns out that the gas in an arbitrary process will vary in direct proportion to the increase in the volume of the vessel in which the piston moves.
If we compare the work done by gas atexpansion and compression, it can be noted that when expanding, the direction of the piston displacement vector coincides with the vector of pressure force of this gas, therefore, in scalar terms, the gas operation is positive and the external forces are negative. When a gas is compressed with a general direction of movement of the cylinder, the vector of external forces coincides; therefore, their work is positive and the work of gas is negative.
Рассмотрение понятия «работа, совершаемая газом» will be incomplete if adiabatic processes are not affected. In thermodynamics, this phenomenon is understood as the process when there is no heat exchange with any external bodies.
Наиболее часто встречающимся в повседневной жизни Adiabatic process can be considered as the work of the piston in an internal combustion engine. The essence of this process is as follows: as is known from the first law of thermodynamics, the change in the internal energy of a gas will be in quantitative terms equal to the work of forces directed from outside. This work is positive in its direction; therefore, the internal energy of the gas will increase and the temperature of the gas itself will increase. Under such initial conditions, it is clear that with adiabatic expansion, the gas operation will occur due to a decrease in its internal energy, respectively, the temperature within this process will decrease.
