Note: this link has been obsoleted by the GunnsFluidDistributedIf link. We recommend using that link instead.

In general, splitting a fluid circulation loop (such as a coolant or ventilation loop) across 2 GUNNS networks makes for a very unstable interface, particularly for liquid loops. This link allows such a split to be stable. Use this link on the pump/fan-side of the interface in lieu of 2 GunnsFluidExternalSupply links. The external section can also be connected to other EqConductors, allowing multiple pumps access to the same section (although only one such interface can be open at a time).

This class represents a portion of an external network as a single conductor within the local network. Historical perspective: this is the same concept as the sub-network from legacy SSTF's PFN. This is intended to allow fluid loops to be split across two networks, with the pump/fan in the local network and a portion of the loop path in the external network. This link interfaces with two GunnsFluidExternalDemand links in the external network, which are at the end points of the represented loop section. This link acts like the two GunnsFluidExternalSupply links that the Demand links would normally interface with. This link supplies pressure and fluid properties of the local nodes to the ExternalDemands, and receives demanded flux from them.

This creates the same flow and pressure drop across this link that the resulting external network section would experience if it were in place of this link. The external section can be either gas or liquid (but not both), can leak out, and can change the fluid temperature. The external section can contain any number of nodes and a mix of parallel and series flow paths. Pressure & flow can go in either direction. This link assumes that any difference between inlet & outlet flux demands are due to leaks from the external section. An equal leak mass is removed from the local network, as if it were leaking out through the external section.

This picture shows how to hook up the GunnsFluidEqConductor in the local network and the GunnsFluidExternalDemand links in the external network and the simbus interfaces between the networks:

Port Connection Rules (These are limitations on the port connection to nodes that the link enforces in run-time):

• Ports 0 and 1 cannot connect to the same non-Ground node.

Other Rules (These are extra rules you should always try to follow):

• Do not mix fluid phases across the link. That is, both nodes should contain the same phase (gas or liquid), and not different phases.
• The external section must have no active capacitance, potential sources, or flow sources.
• The external section must not change the fluid mixture.
• The external section must not have flow enter into it from other links besides the two demand links.
• If the external section can be connected to multiple EqConductors, it must only be open to one set of demand links at a time. Valves, jumpers, etc can be used to control which set of demand links is connected.
• The external section must reside entirely within one network, in other words the 2 external demand links can't be in separate networks.
• This link does not support demanded mass flow (kg/s), so the external demand links must send demanded flux as kg*mol/s.
• The external network must have the same fluid constituents as the local network and in the same order. Unlike the GunnsFluidExternalSupply link, this link cannot deal with differing or re-ordered fluid constituents.
• The external network must update at the same frequency as the local network.

Configuration Data Parameters:

• useNetworkCapacitance (default = false): Setting this true may help improve the stability of the interface with the external demand links in some cases. Setting this true causes this link to output its 2 port node network capacitances to the external demand links for use in their supply capacitance filters (see the GunnsFluidExternalDemand help page on how to make use of this). Use simbus to send this link's mPort0SupplyCapacitance and mPort1SupplyCapacitance simbus output terms to the external demand links' mSupplyCapacitance simbus input terms. Setting this term false causes the node network capacitances to not be calculated and the external demands will not use their mSupplyCapacitance values. NOTE: setting the term true and using this capability causes the GUNNS solver to use a small amount of extra CPU each pass when solving this network, so this capability should be used sparingly.

Input Data Parameters:

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• Pressure/flow oscillations: The most common problem will be an oscillation in the node pressures and flow rates.
  • First, make sure all of the limitations detailed above in the Background section are met.
  • Tune the external flow path such that it creates the correct flow rate for the correct delta-pressure across it. This is very important - if the effective conductivity of the external flow path is unrealistically high, it can exacerbate the instability. By creating a bottle-neck somewhere in the external network, this raises the delta-pressure required across the section to create the same flow, and this is easier for the EqConductor to handle.
  • Rule out that the oscillation is coming from the local network. The EqConductor's mEffectiveConductivity term will be oscillating. Find the approximate mid-point of the oscillating mEffectiveConductivity. Using the user port commands in the links, temporarily replace the EqConductor with a spare regular GunnsFluidConductor (or add a new one in the drawing - but it helps to keep spare conductors in the network for things like this) and set its mMaxConductivity to the recorded mEffectiveConductivity from the EqConductor. You've now replaced the EqConductor with a regular conductor with approximately the same conductivity. If the pressure & flow through this conductor are still oscillating, then there is something else in your network causing the problem.
  • Turn on this EqConductor link's useNetworkCapacitance flag and hook up the supply capacitance terms to the external demands as shown. See the GunnsFluidExternalDemand help page for more info.
  • As a last resort, reduce the conductivity of the external flow path further by introducing a blockage of some kind, or tuning the flow bottle-neck to a smaller conductivity. Depending on your accuracy requirements, you may be able to live with a higher delta-pressure across the section in order to get stable flow.

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