In thermodynamics, a throttling process, also called a Joule-Thomson process, is a type of isenthalpic process where a liquid or gas is cooled as it passes from a higher pressure state to a lower pressure state.

This process is especially very important in field of refrigration where refrigrant passes from higher pressure to lower pressure along with the corresponding decrease in temperature.The slope of an isenthalpic curve is called the joule thomson coefficient

In other words:

A throttlillg process is defined as a process in which there is no change in enthalpy from state one to state two, h_I = h₂: No work is done, W= 0: and the process is adiabatic: Q = O. To better understand the theory of  ideal throttling process let's compare what we can observe with the above theoretical asumptions. An example of throttling process is an ideal gas flowing through a valve in mid position.

From experience we can observe that: P_in> P_out and vel._in < Vel._out (where P = pressure and vel = velocity). These observations confirm the theory that h_in = h_out. Remember: h = u + Pv (v = specific volume), so if pressure decreases then specific volume must increase if enthalpy is to remain constant (assuming u is constat). Because mass flow is constant, the change in specific volume is observed as an increase in gas velocity, and this is verified by our observations.

The theory also states W=0. Our observations again confirm this to be  true as clearly no "work" has been done by the throttling process.Finally,the theory states that an ideal throttling process is adiabatic. This cannot clearly  be proven by observation since a "real" throttling process is not ideal and will have some heat transfer.

Dear student,

A throttling process is defined as a process in which there is no change in enthalpy from state one to state two, h1 = h2; no work is done, W = 0; and the process is adiabatic, Q = 0. To better understand the theory of the ideal throttling process let’s compare what we can observe with the above theoretical assumptions. An example of a throttling process is an ideal gas flowing through a valve in mid position.

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Askiitians Expert

Sagar Singh

B.Tech, IIT Delhi

give the practical example of throttling

fine