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Visual Water Designer

Frequently Asked Questions

Listed below are the most current frequently asked questions in relation to use of the Visual Water Designer software.  The questions are broken down into the three main sections of the software - pumping/hydraulics, standard treatment units, and advanced treatment units. Questions are updated as they are received.  If you have a question that is not covered below, please contact us immediately.

 

Pumping/Hydraulics Frequently Asked Questions

When analyzing the hydraulics of a pipe, three methods for determining the friction loss are supplied – Darcy-Weisbach, Manning’s Equation, and the Hazen-Williams equation.  Which is the most accurate, and is there a better time to use one equation over another?

In theory, the most accurate equation is the Darcy-Weisbach equation since it is the only equation that relates its roughness value (f) to the diameter of the pipe, and also accounts for the varying regimes of flow.  This is mostly a non-issue, however, since almost all pipes encountered during a hydraulic analysis exhibit fully turbulent behavior.  The Hazen-Williams equation is still the most popular equation used in practice today because of its relative simplicity and accurate results.  The Manning equation is typically reserved more for open channel flow but is also acceptable for full flow pipe analysis.

In consulting a few of my engineering reference manuals, I’ve noticed that there can be some considerable variation in the K values reported for different pipe fittings.  How was the K value list used in Visual Water Designer compiled?

This is a perfect example of the fact that hydraulics is never an exact science.  Many fittings have universal K values, such as standard bends and valves, but many fitting K values can vary from source to source.  Visual Water Designer's K value database was compiled from the comparison of numerous popular hydraulic sources.  Visual Water Designer was programmed with a built-in working K value database that allows you to change K values for fittings and add fittings that may not exist in the standard database.  This allows you to tailor the K value database to your needs.

When performing a pumping analysis, there are check boxes provided for specifying primary sludge or secondary/digested sludge.  If a sludge pumping analysis is being performed, how does Visual Water Designer account for this?

Visual Water Designer will account for the additional friction loss from pumping sludge by assigning the friction loss a multiplying factor.  This factor is based on the type of sludge being pumped and the percent solids in the sludge.

Can negative suction and/or discharge heads be specified when performing a pump analysis?

Yes, Visual Water Designer will allow the entry of negative suction and discharge heads.

 

How does the specific gravity of the fluid being pumped affect the pump evaluation?

The fluid specific gravity is taken into consideration when calculating the maximum vapor pressure at the pump, which is part of the net positive suction head (NPSH) calculation.  Additionally, the liquid specific gravity affects the discharge pressure of the pump.

 

How does Visual Water Designer analyze a sewer if the sewer is flowing full for part of its length?

Visual Water Designer uses the open channel standard step method to start downstream and work upstream in analyzing a sewer depth.  If during the analysis a full flow depth is reached before the total length of the sewer is analyzed, the remaining portion that is flowing full is analyzed as a full flow pipe.

 

During a culvert analysis, the tailwater depth may be specified as critical depth.  Why is this?

If the flow exiting the culvert will experience no effect from any downstream control, such as a drop at the end of the culvert, the depth coming out of the culvert will be at minimum energy, which is critical depth.

 

Standard Treatment Units Frequently Asked Questions

 

For the BOD reduction analysis in a trickling filter, two methodologies are available, the NRC equations and the Velz-Schultz methodology.  Which should be used and is more accurate?

The Velz-Schultz equations were developed for more modern media, which is plastic media.  The NRC equations are more widely used and generally accepted for BOD reduction analysis, but the Velz-Schultz equations more accurately take into consideration the type of media and media characteristics than the NRC equations.  Simply put, for plastic (vertical or crossflow) media, the Velz-Schultz equations are more accurate, whereas the NRC equations apply more to other types of media (rock, stone, wood, etc).

 

For disinfection, it was noticed that equations exist for the calculation of the CT product for chlorine, yet equations are not used for the CT product for ozone and chlorine dioxide.  How are these CT values calculated?

This is correct, equations have been developed for the calculation of the CT value for chlorine.  Although various complex equations have been developed for the calculation of CT values for chlorine dioxide and ozone, tables of CT values are used to simplify the calculation.  These tables are based on the temperature of the water and the log inactivation desired.  These tables are provided in the theory section of the user manual.

 

For rotating biological contactors, how does the software consider multiple stages for BOD reduction?

For BOD reduction in rotating biological contactors, the effluent BOD is based on the influent BOD coming into the RBC.  If multiple stage RBCs are being analyzed, the effluent BOD from the first stage is then used as the influent BOD to the next stage.  This procedure is followed until all BOD stages are analyzed.

 

Advanced Treatment Units Frequently Asked Questions

 

When evaluating the fluid flux for a reverse osmosis system, if a solute other than salt is being considered, how does the analysis differ?

The osmotic pressure is affected directly by the molecular weight of the solute, therefore the molecular weight of the solute must be known.  The osmotic pressure in turn affects the fluid flux through the membrane.

 

For a UV evaluation, how does the theoretical UV dose differ from the required UV dose?

The theoretical UV dose is the dose applied to the liquid under perfect conditions.  The required UV dose takes into account other factors that will affect the dose delivered to the liquid.  The factors considered in this calculation are the lamp fouling factor and lamp aging factor, which can significantly reduce the dose applied by the UV system.

 

Other Frequently Asked Questions

 

If an assumption is changed during an analysis, does this assumption get saved if the file is saved?

Yes.  If an assumption is changed for a particular analysis or calculation and that file is saved, the updated assumption will also be saved.

 

On the assumptions form, there is an option to “Restore defaults”.  What happens if the default assumptions are restored? 

The Visual Water Designer software is shipped with a variety of assumptions that are used in various calculations throughout the software.  The user may change any of these assumptions at any time.  If it is desired to revert back to the original assumption values shipped with the software, this option will allow the user to restore those values.  Note that once this is done, any changes that were saved in the assumptions database will be lost.

 

I notice there is a “Specialties” tab but it never seems to be active.  What is this tab used for?

The Specialties tab was put in the place for the pumping analysis option.  It provides additional calculations for pump power requirements, affinity laws, and pump operational costs.  This tab will only become active when analyzing a pumping system.

 

If the “Clear” option at the bottom of the design form is selected, it clears all of the active data from the form.  Does it remove the data from a file with other active calculations?

No.  If more than one parameter for a particular feature is analyzed, the clear option will only remove the data for the active parameter being analyzed.

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