Throttling effect cooling capacity is due to the pressure reduction, volume expansion, molecular interaction potential energy increases, resulting in the kinetic energy of molecular motion decreases, causing the gas temperature to decrease, so that the gas has a certain ability to absorb heat.
In air separation equipment, the throttling process usually occurs at the throttle valve, but the throttling effect cooling capacity is not generated only by the part of the gas that passes through the throttle valve. In air separation equipment, the throttle effect cooling capacity is closely related to the compression process. In the compressor, the air is compressed and the pressure rises, the temperature also rises. The compressed gas has high pressure energy and internal energy. After throttling the low temperature, low pressure gas flow through the heat exchanger, can be higher from the temperature of the gas heat absorption, will be the latter cooled, and the former heat absorption after the temperature is restored to the temperature before throttling. In this process, the low-temperature gas has the ability to absorb heat, that is, for its throttling effect cooling capacity.
The size of the throttling effect cooling capacity can be determined by calculating the enthalpy difference before and after throttling. Since the throttling process is an isenthalpic process (i.e., the enthalpy of the gas before and after throttling remains unchanged), the refrigeration capacity is equal to the difference between the enthalpy of the gas after throttling and the enthalpy of the gas before throttling. This difference is actually equal to the value of enthalpy reduction in isothermal compression, i.e., the refrigeration capacity of the throttling effect is already present in isothermal compression, and is manifested in the last two processes (throttling and heat absorption).
