Which process describes a constant enthalpy condition?

Which process describes a constant enthalpy condition?

• A. Isenthalpic Process
• B. Isobaric Process
• C. Isoenthalpic Process
• D. Isothermal Process

Answer: (A)

Constant enthalpy means the enthalpy H stays unchanged as the system moves from one state to another. Since H = U + pV, a zero change in H (dH = 0) means the internal energy change and the pressure-volume work balance so the total energy content associated with the flow remains the same. This situation commonly occurs in throttling processes, where the flow is adiabatic and there’s no shaft work or heat transfer across the boundary, so the inlet and outlet enthalpies are equal. You can have a large drop in pressure while the enthalpy doesn’t change, though the temperature can vary depending on the fluid. The term describing this is isenthalpic (often also spelled isenthalpic). The other descriptors refer to different state properties: constant pressure isobaric, constant temperature isothermal, and the alternative spelling doesn’t change the concept. So the description that matches constant enthalpy is the isenthalpic process.

Constant enthalpy means the enthalpy H stays unchanged as the system moves from one state to another. Since H = U + pV, a zero change in H (dH = 0) means the internal energy change and the pressure-volume work balance so the total energy content associated with the flow remains the same. This situation commonly occurs in throttling processes, where the flow is adiabatic and there’s no shaft work or heat transfer across the boundary, so the inlet and outlet enthalpies are equal. You can have a large drop in pressure while the enthalpy doesn’t change, though the temperature can vary depending on the fluid.

The term describing this is isenthalpic (often also spelled isenthalpic). The other descriptors refer to different state properties: constant pressure isobaric, constant temperature isothermal, and the alternative spelling doesn’t change the concept. So the description that matches constant enthalpy is the isenthalpic process.