The discussion centers on the concept of enthalpy from a macroscopic thermodynamics perspective, particularly in relation to isentropic processes and heat transfer calculations. Participants explore the definition of enthalpy, its relationship to internal energy and flow work, and its application in flow systems.
Participants express differing views on the relationship between enthalpy and work in isentropic processes, with no consensus reached on the implications of enthalpy in this context. The discussion remains unresolved regarding the specific applications and interpretations of enthalpy in these scenarios.
There are limitations in the assumptions made regarding the nature of the systems being discussed, particularly in distinguishing between open and closed systems and the conditions under which enthalpy is applied.
This is incorrect. In a reversible Carnot cycle, which is an isentropic process, the change in enthalpy is zero, and the work is equal to the net heat transferred. Even for an isentropic reversible single-step change for a closed system, it is the internal energy which is equal to minus the work done on the surroundings, not the enthalpy.stockzahn said:Enthalpy H is the sum of the internal energy U and the flow work p⋅V.
H = U + p⋅V
In an isentropic process no heat is transferred, the enthalpy difference of the fluid corrisponds to the work performed by/on the fluid.
Yes, sorry I forgot to add that.Chestermiller said:Apoorv312: Are you asking about an open system operating at steady state when you ask "how do we use it to calculate the total heat transfer in isentropic processes?"
Thank you sir, that really helped.Chestermiller said:For a flow system like the one described, you first follow each little parcel of gas going through the system, and treat it as a closed system that is subjected to an adiabatic reversible expansion to the final pressure exiting your device. On this basis, you determine the temperature change for each of the parcels. This will determine the exit temperature from your flow system. The change in enthalpy per unit mass flowing through your system is then equal to Cp times the temperature change.
Chet