At the core of almost any heat engine is a thermodynamic phenomenon, as the work done by the gas during the expansion or compression.It is worth remembering that in physics at work meant a quantitative measure characterizing the effect of a certain strength to the body.In accordance with the work of the gas, a necessary condition for the fulfillment of which is a change in its volume, there is nothing but the product of the pressure of this change in volume.
Working gas when changing its volume can be both isobaric and isothermal character.In addition, the expansion process itself can wear and arbitrary.Gas work, which is performed when the isobaric expansion, can be found on the following formula:
A = pΔV,
where p - quantitative characteristic of the gas pressure, and ΔV - the difference between the initial and final volume.
process arbitrary expansion of the gas in physics is usually presented as a series of separate isobaric and isochoric processes.The latter are characterized by the fact that the work of the gas, as well as its quantitative indicators, equal to zero, because the movement of the piston in the cylinder occurs.Under such circumstances, it turns out that the work gas at an arbitrary process will vary in direct proportion to the increase in the volume of the vessel, in which the movement of the piston.
If you compare the work done by the gas during the expansion and compression, it may be noted that the expansion direction of the vector movement of the piston coincides with the vector of the pressure forces the gas itself, so the calculation of the scalar operation gas is positive, but external forces - negative.When compressed gas under the general direction of movement of the cylinder coincides already vector of external forces, so their work is positive and negative work gas.
Consideration of the concept of "work done by the gas" would be incomplete if you do not also affect the adiabatic process.Under such a phenomenon in thermodynamics is the process when there is no heat exchange with any external bodies.It is possible, for example, in the case where a vessel with a working piston is provided with good thermal insulation.Moreover, the processes of compression or expansion of the gas can be equated to adiabatic if the time changes in the volume of gas is much less than the time interval during which thermal equilibrium occurs between the bodies and the surrounding gas.
most frequently encountered in everyday life adiabatic process can be regarded 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 internal energy of the gas is quantitatively equal to the forces directed from the outside.This work is in its positive direction, and therefore the internal energy of the gas will increase, and the temperature of its rise.Against this baseline, it is clear that the adiabatic expansion work of the gas will come from the reduction of its internal energy, respectively, the temperature in this process will be reduced.
