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The adiabatic compression of a gas causes a rise in temperature of the gas. Adiabatic expansion against pressure, or a spring, causes a drop in temperature. In contrast, free expansion is an isothermal process for an ideal gas.
The adiabatic (no heat exchanged) expansion of a gas may be carried out in a number of ways. The change in temperature experienced by the gas during expansion depends not only on the initial and final pressure, but also on the manner in which the expansion is carried out.
Under other conditions, free-energy change is not equal to work; for instance, for a reversible adiabatic expansion of an ideal gas, =. Importantly, for a heat engine, including the Carnot cycle , the free-energy change after a full cycle is zero, Δ cyc A = 0 {\displaystyle \Delta _{\text{cyc}}A=0} , while the engine produces nonzero work.
Consider a gas in cylinder with a free floating piston resting on top of a volume of gas V 1 at a temperature T 1. If the gas is heated so that the temperature of the gas goes up to T 2 while the piston is allowed to rise to V 2 as in Figure 1, then the pressure is kept the same in this process due to the free floating piston being allowed to ...
We assume the expansion occurs without exchange of heat (adiabatic expansion). Doing this work, air inside the cylinder will cool to below the target temperature. To return to the target temperature (still with a free piston), the air must be heated, but is no longer under constant volume, since the piston is free to move as the gas is reheated.
If the calorically perfect gas approximation is used, then the ideal gas law may also be expressed as follows = where is the number density of the gas (number of atoms/molecules per unit volume), = / is the (constant) adiabatic index (ratio of specific heats), = is the internal energy per unit mass (the "specific internal energy"), is the ...
The four points in the graph indicate the crank angle in degrees. [7] The adiabatic Stirling cycle is similar to the idealized Stirling cycle; however, the four thermodynamic processes are slightly different (see graph above): 180° to 270°, pseudo-isothermal expansion. The expansion space is heated externally, and the gas undergoes near ...
In thermodynamics, a temperature–entropy (T–s) diagram is a thermodynamic diagram used to visualize changes to temperature (T ) and specific entropy (s) during a thermodynamic process or cycle as the graph of a curve. It is a useful and common tool, particularly because it helps to visualize the heat transfer during a process.