Gas liquefaction methods — the Claude process In cryogenic engineering, the Claude process for gas liquefaction is distinguished by the inclusion of which key step in addition to heat exchange?

Introduction / Context:
Liquefaction processes use combinations of compression, heat exchange, and expansion to lower a gas temperature below its saturation temperature. The Claude process is a foundational cycle in cryogenics.

Given Data / Assumptions:

• The question contrasts different cooling/expansion steps.
• We assume idealized descriptions of Linde vs Claude cycles.

Concept / Approach:
The Linde cycle relies primarily on isenthalpic (Joule–Thomson) throttling after regenerative precooling. The Claude cycle adds a work-producing, near-isentropic (adiabatic) expansion in an expander (piston or turbine). This additional adiabatic expansion yields larger temperature drops, improving liquefaction efficiency.

Step-by-Step Solution:
Identify the hallmark of Claude: expansion turbine/piston allowing external work.Recognize that mere compression above critical pressure is insufficient for liquefaction.Joule–Thomson only describes Linde-style throttling, not uniquely Claude.Thus, the correct distinguishing step is adiabatic expansion in an expander.

Verification / Alternative check:
Process schematics show the Claude expander branch delivering work and deeper cooling before JT valve, enhancing liquid yield.

Why Other Options Are Wrong:

• Merely compressing above critical pressure does not ensure liquefaction upon cooling.
• Joule–Thomson only: not unique to Claude; also less efficient at high temperatures.
• Heat exchange only: necessary but not the defining feature.

Common Pitfalls:

• Equating all liquefaction cycles; ignoring the role of isentropic expansion work.

Final Answer:
Adiabatic expansion against a piston or in an expansion turbine