Linear headloss in Watergems/Hammer?

Question

Hello! 
 In order to study a reverse osmosis plant, I need to represent linear headlosses (the flow in the membrane cartridge is laminar). 
 How to do so in WaterGems and Hammer ?

Scott Kampa · Answer

Hello Khalid, 
 A general purpose valve may work for what you are trying to model. This allows you to include a headloss curve where you can enter a table of flow and headloss, which allows you to control the headloss at the valve. 
 For information on how valves operate in HAMMER, please see this link: Model Reference - Valves . You can include an operating rule to change how the valve operates, but the valve headloss is assumed to be held at the value calculated during the initial conditions calculation. 
 Regards, 
 Scott

WPsquared · Answer

Khalid, 
 If you put in a GPV valve in the location where the headloss occurs you can use this wiki to represent a constant headloss .

Jesse Dringoli · Answer

In WaterGEMS (or with a steady state or EPS in HAMMER initial conditions), you can model a specific rating table of flow vs. headloss with the GPV element, but if you want a constant headloss for all flows, use a PBV (pressure breaker valve). 
 Note though that these will not work the same during a transient simulation in HAMMER. HAMMER always uses the pair of initial flow and initial headloss through each valve element, to calculate a discharge coefficient which it uses during the transient simulation. This means that even if you use a PBV for the initial conditions, the headloss will vary during the transient simulation. 
 See: Modeling a Constant Headloss

Scott Kampa · Answer

Hello Khalid, 
 A sensitivity analysis would allow you to see how much of an impact the valve settings will have. Reviewing the Modeling Reference related to valves is also recommended. In HAMMER, the initial conditions calculation will calculated a Darcy-Weisbach friction factor. This value is used throughout the transient run. 
 If the valve is initially partially closed, you can also review this link , which has some details how to model this in HAMMER. 
 Regards, 
 Scott