modelFlowWork

Information

Process used to account for the flow work w_flow = p*v, which represents the difference between the specific enthalpy h and the specific internal energy u: h = u + p*v, where p denotes the pressure and v the specific volume.

This process is required to properly account for work when switching between an open-cycle and a closed-cycle perspective, and vice versa. See, for example, Examples.TurboChargedEngine.Cycle.

The flow work rate P = -m_flow * w_flow is required where fluid enters the closed-cycle system, and the flow work rate P = m_flow * w_flow is required where fluid leaves the closed-cycle system. Most processes already account for the flow work if they are formulated using inlet and outlet specific enthalpy h_in and h_out rather than initial and final specific internal energy u1 and u2.

The sign of the flow work can be derived from the conservation of energy. For a closed system, the change in specific internal energy between the initial and final state is u2 - u1 = q + w_cycle, where q is the specific heat transfer and w_cycle is the specific work of the cycle process.
When switching to an open-system formulation, the energy balance is written in terms of specific enthalpy: h2 - h1 = q + w_open, where w_open denotes the specific work of the open process. Alternatively one could write 0 = q + w_open + h_in - h_out and identify h_in = h1 and h_out = h2.
Combining both formulations yields w_open = w_cycle + (pv)2 - (pv)1. Consequently, at the outlet (2) a positive flow work contribution w_flow2 = (pv)2 must be considered, whereas at the inlet (1) a negative flow work contribution -w_flow1 = -(pv)1 must be taken into account.

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Revisions

• 2026-08, by Silvan Keim (silvan.keim@dlr.de):
  Improved icon.
• 2026, by Raphael Gebhart (raphael.gebhart@dlr.de):
  Initial version.