loss coefficient not beeing calculated correctly

[EPrade]

Problem:
The loss coefficient parameter in the components heat exchanger and pressure control cannot be used without a diameter and the diameter is not an input parameter at the moment.

Possible solutions:

For pressure Control:

Remove loss coefficient for pressure control, since the pressure is set within that component anyway.

For heat exchangers:

Replace the loss coefficient with an input parameter for a fixed pressure loss e.g. "fixed pressure loss[bar]", so that the user can directly input the pressure loss the heat exchanger should induce.

[kava-matrix]

A relationship to V² is needed to implement the loss coefficient in a familiar way.

Ideally this would be able to be entered as a factor K (zeta in image above) and the diameter (or average diameter) of the upstream pipes connected to from_junction could be used to calculate V.

Alternatively, the deprecated parameter diameter_m could be undepricated and used. I think this is the better solution. It allows the user to enter a hydraulic diameter, which is useful.

[SimonRubenDrauz]

In pandapipes the equations are solved for the mass flow going through the heat exchanger, therefore we do not solve for the velocity. I do not understand how the diameter of the upstream pipes helps us to determine the velocity within the heat exchanger. How does this relate to the diameter of a connected heat exchanger?

The idea of the pressure drop is due to the problem that there is no information about the pipe inside the heat exchanger. Therefore, the Darcy-Weisbach-equation is not solvable. Any ideas on that?

[kava-matrix]

The loss coefficient is typically derived from experimental data. The diameter would typically be specified as the inlet diameter for example, but someone could also enter the hydraulic diameter. Really, it doesn't matter what diameter you enter as long as it is understandable / predictable. Here is what I would do:

• Specify the diameter of the inlets to my heat exchanger D
• V is calculated from D as V = vol_flow_rate / area = 4 * mass_flow_rate / (pi * density * D²)
• Based on V, specify a loss coefficient K_L as 2 * dP / (density * V²) where dP is a known pressure drop for an experimental inlet velocity V.

But really we could also define an alternative loss coefficient which produces a pressure drop proportional to mdot². It would be a non-standard way of defining the loss coefficient, which isn't ideal.