Question

In a throttling process ............. remains constant.

• A. Temperature
• B. Pressure
• C. Entropy
• D. Enthalpy

Hint:

Throttling is an irreversible, isenthalpic (constant enthalpy) process.
The change in temperature during throttling is governed by the Joule-Thomson coefficient, \(\mu_{JT} = \left(\frac{\partial T}{\partial P}\right)_h\).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
A throttling process occurs when a fluid flows through a restricted passage (such as a partially opened valve, orifice, or capillary tube) without exchanging heat or performing external work.

Step 2: Detailed Explanation:
Let us analyze the energy equation for a steady-flow throttling process:
\[ h_1 + \frac{V_1^2}{2} + g z_1 + q = h_2 + \frac{V_2^2}{2} + g z_2 + w \]
For standard throttling devices:
- The process is highly rapid and localized, making heat transfer negligible (\(q = 0\)).
- No mechanical shaft work is performed (\(w = 0\)).
- Changes in kinetic and potential energies across the restriction are negligible (\(\Delta KE \approx 0\), \(\Delta PE \approx 0\)).
Substituting these boundary conditions simplifies the steady flow energy equation to:
\[ h_1 = h_2 \]
This indicates that the enthalpy of the fluid remains constant during a throttling process.

Step 3: Final Answer:
During a throttling process, the enthalpy of the fluid remains constant.