Enthelpy in Throttle Process (Joule–Thomson expansion)

In summary, the Joule-Thompson effect involves converting from one pressure to another with no heat loss. This results in a constant enthalpy due to conservation of energy, as expressed by the "flow work" equation. This may seem confusing in the context of enthalpy being traditionally associated with systems at constant pressure, but the pressure in the Joule-Thompson effect is changing. The flow work equation is used instead of the integral form due to the fluid's work on itself. This is all derived from the open-system version of the first law of thermodynamics.
  • #1
MisterX
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Why is it written that enthalpy (##H##) is constant for Joule-Thompson expansion? It seems the essence of this process is to convert from one pressure to another with no heat loss. How does that connect with enthalpy being constant? When I learned about enthalpy it seemed to be most relevant to systems at constant pressure. However in the Joule-Thompson effect the pressure is surely changing. Sources mention that the "flow work" is ## P_2V_2 - P_1V_1##. This leads to constant ##H## by conservation of energy. I guess I don't understand why the flow work is ##\Delta(PV)## and not ## \int P dV##. Maybe it also seems strange for me to think of a fluid doing work on itself or something. Anyway, I feel confused about this.
 
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  • #2
Are you familiar with the derivation of the open-system (control volume) version of the first law of thermodynamics?
 

1. What is enthalpy in the throttle process?

Enthalpy in the throttle process, also known as Joule-Thomson expansion, is a thermodynamic concept that describes the change in enthalpy (total energy of a system) when a gas undergoes a sudden decrease in pressure without any change in temperature.

2. How is enthalpy related to the throttle process?

Enthalpy is directly related to the throttle process, as it is a measure of the energy of a system. In the throttle process, the sudden decrease in pressure causes a decrease in the enthalpy of the gas, resulting in a decrease in temperature.

3. What is the significance of enthalpy in the throttle process?

The significance of enthalpy in the throttle process lies in its ability to describe the change in energy and temperature of a gas when it undergoes a sudden decrease in pressure. This is important in various industrial processes, such as refrigeration and natural gas production.

4. How is the Joule-Thomson coefficient related to enthalpy in the throttle process?

The Joule-Thomson coefficient is a measure of the change in temperature with respect to pressure during the throttle process. It is directly related to enthalpy, as it is a measure of the change in energy of the system.

5. How does enthalpy change during the throttle process?

In the throttle process, the enthalpy of a gas decreases as the gas expands due to the decrease in pressure. This decrease in enthalpy leads to a decrease in temperature as well. However, the change in enthalpy is dependent on the initial temperature and pressure of the gas.

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