Question

What is the throttling process in thermodynamics?

Answer 1

Hint: The throttling process is associated with the pressure changes in fluids (gas or liquids) when they are made to pass through restricted passages. The process can be defined using a certain set of conditions or thermodynamic properties that remain constant throughout.

Complete answer:
The flow of a gas or a liquid through a valve brings certain changes to it. These changes are the part of a thermodynamic process called the throttling process.
Each thermodynamic process is carried out under certain conditions of temperature, pressure, enthalpy or heat. The changes associated with a system under observation are measured by keeping certain state variables constant.
Mechanical work done on a system brings a change in its pressure or volume. If work is not done by the system or the surrounding then the changes can be done at the expense of the enthalpy associated with the system. But a process that affects the pressure of the system without changing enthalpy or work is known as a throttling process.
When a fluid passes through a valve, it faces certain restrictions that lead to a significant prop in pressure without any appreciable change in the kinetic or potential energy. Thus the throttling process involves no change in enthalpy, work or heat. The conditions associated with a throttling process are as follows:
 $ \Delta H = 0 $
 $ w = 0 $
 $ q = 0 $
For ideal gases the throttling process brings no change in temperature as enthalpy is a function of only temperature for ideal gases.
For real gases, a temperature drop parallel to the decrease in pressure is observed.
Hence, a throttling process is the process of suddenly decreasing the pressure without changing the enthalpy (isenthalpic process) or utilizing work or heat.

Note:
State variables or state functions are those thermodynamic properties that are path independent in nature. This means that when a system undergoes a change in state then the value of the state function depends upon the difference between the initial and final state (irrespective of the path through which the change was carried out.)