Thermodynamic energy is the sum of kinetic energy of irregular motion of molecules in matter and potential energy generated by mutual attraction between molecules. In the process of oxygen production, there are many flow processes, such as compression, expansion, heating and cooling. These processes not only involve the change of thermodynamic energy, but also involve the transformation between the flow energy and the thermodynamic energy. Enthalpy is the sum of material thermodynamic energy and material flow, so it is more convenient to study these flow processes with enthalpy.