Paradoxical in Results (Trace)

Question

Hi 
 In the model, as the photo shows, water come from J-4 (as source node) to J-151 during an EPS simulation. Trace result for J-151 was calculated. Average of trace between times 5 and 10 was calculated too (=99.56%). 
 Water Quality Batch Run for J-151 and with considering J-4 as Trace Source was calculated. Trace Average for J-151 between times 5 and 10 is 4.1%. 
 Why did not it equal to what Trace result shows? What is my mistake which resulted this unequal? 
 
 7024.New folder.rar 
 
 Sim

Scott Kampa · Accepted Answer

Hello Simbaa,

It is possible to use junctions for a trace analysis. However, it is more typical that the trace element is the source of flow, such as a reservoir or tank, and the trace function will be best suited to this type of analysis. In your model (which appears to just be a reworked version of Example5.wtg, though why you did that is a bit of a mystery; Example1.wtg already has water quality scenarios, including a Trace analysis scenario), the data from J-4 would be the same as the data from the reservoir, so it really makes no sense to use a trace analysis with a junction in the first place.

Because the junction is not as a good typical Trace element, this can give odd results in the Water Quality Batch Run. That said, when the junction is set as an inflow node, meaning there is a negative demand, the results in Water Quality Batch Run are good.

Regards,
Scott

Scott Kampa · Answer

Hello Simbaa, 
 
Is there a reason you are using a junction for the trace analysis? A more typical workflow has a trace source be a boundary element, such as a reservoir or tank. In your case, since the the flow from J-4 would be identical to the reservoir, it makes sense to just assume make the source for the Water Quality Batch Run be the reservoir. 
 
Regards, 
Scott