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Changes in entropy and enthalpy after throttling and expansion

Changes in entropy and enthalpy after throttling and expansion
Sep 05, 2025
Author: DEAR AST

Throttling and expansion are two commonly used methods for generating cooling capacity. The throttling process generally involves a sudden decrease in the flow area of gas through the throttle valve, causing a pressure drop due to gas disturbance. Due to the short time, there is no heat exchange with the outside world, and the enthalpy value of the gas remains unchanged. The throttling process is irreversible, resulting in an increase in entropy. Expansion is the work done by the gas, and the enthalpy of the gas decreases. Ideally, this is a reversible process, so the entropy value of the expansion process remains unchanged.

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