Free expansion means resisting vacuum expansion, W=0. Adiabatic process Q=0. Therefore, according to the first law of thermodynamics, Δ u of gas = 0.
No matter whether the gas is an ideal gas or a real gas, the above conclusion is true.
If the gas is an ideal gas, the thermodynamic energy is only related to the temperature, and the temperature of the gas remains unchanged.
If it is a real gas, it needs some discussion.
This problem is translated into a mathematical language, that is, how does T change with the increase of V when U is constant?
Immediately ask:
Next, it is necessary to substitute the specific gas state equation. Because the actual gases are different and satisfy different equations of state, the sign of the above expression is uncertain.
Extended data:
Principle of vacuum expansion:
Vacuum expansion is the basic standard of vacuum measurement, which is mainly used to calibrate vacuum sub-standards such as capacitance film vacuum gauge and magnetic suspension rotor vacuum gauge.
At the same time, it can also be used to calibrate ionization vacuum gauge, resistance vacuum gauge and heat conduction vacuum gauge.
Its primary expansion method and secondary expansion method provide technical support for ensuring the accuracy and uniformity of vacuum value.
It uses Boyle-Edm Edme Mariotte's law to measure vacuum gauge by expansion method or direct comparison calibration method with time gauge, and its uncertainty analysis conforms to JJF 1050- 1996 Calibration Specification for Thermal Conductivity Vacuum Gauges for Work and JJF 1062- 1999.
Reference source: Baidu Encyclopedia-free expansion
Reference source: Baidu Encyclopedia-Vacuum Expansion