An adiabatic process is a thermodynamic process in which the system does not exchange heat with its surroundings. An adiabatic process may also be isentropic, which means that the process may be reversible.
A process that does not involve the transfer of heat or matter inside or outside a system, so that Q = 0, is called the adiabatic process, and said system is said to be adiabatically isolated. The assumption that a process is adiabatic is a simplifying assumption that is made frequently. For example, it is assumed that the compression of a gas inside a cylinder of a heat engine occurs so rapidly that, in the time scale of the compression process, a small part of the energy of the system can be transferred as heat to the surroundings. Although the cylinders of the thermal engines are not insulated and are quite conductive, that process is idealized to be adiabatic. The same can be said to be true for the process of expanding said system.
The adiabatic insulation assumption of a system is useful, and often combined with others to make possible the calculation of system behavior. Such assumptions are idealizations, they approximate, but they are not real. The behavior of real machines deviates from these idealizations, but the assumption of such perfect behavior provides a useful first approximation of how the real world works.
In the study of thermodynamics, it is usual to simplify the system in order to calculate approximately the behavior of the system.
Adiabatic heating and cooling
The adiabatic compression of a gas causes an increase in the temperature of the gas. Adiabatic expansion against pressure, or a spring, causes a drop in temperature. On the contrary, free expansion is an isothermal process for an ideal gas.
Such temperature changes can be quantified using the ideal gas law or the hydrostatic equation for atmospheric processes.
In practice, no process is truly an adiabatic process. Many processes depend on a large difference in time scales of the process of interest and the dissipation rate of thermal energy through a system boundary, and â € <â €
Adiabatic heating occurs when the pressure of a gas increases because of the work done on it by its environment. An example of adiabatic heating is that of a piston of a heat engine that compresses a gas contained within a cylinder. The compression of the gas leads to the elevation of the temperature. In many practical situations the conduction of heat through the walls can be slow compared to the compression time that is considered null.
This feature has a practical application in diesel thermal engines that depend on the lack of heat dissipation during the compression stroke to raise the temperature of the fuel vapor enough to ignite it.
Adiabatic cooling occurs when pressure on an adiabatically isolated system decreases, allowing it to expand. This expansion makes it work in your environment. When the pressure applied on an air pack is reduced, the air in the pack is allowed to expand; as the volume increases, the temperature decreases as its internal energy decreases.
Adiabatic cooling occurs in the Earth's atmosphere with orographic uplift and leeward waves, and this can form pileus or lenticular clouds.
Adiabatic cooling does not have to involve a fluid. A technique used to reach very low temperatures (thousandths and even millionths of a degree above absolute zero) is through adiabatic demagnetization. In adiabatic demagnetization the change in the magnetic field of a magnetic material is used to provide adiabatic cooling. In addition, the content of an expanding universe can be described (of the first order) as an adiabatic cooling fluid. (See death by heat of the universe).
Last review: March 19, 2018