...
The last proposed design was to use install a PVC cap at the base of a small piece of tubing attached to the alum-doser exit orifice. A small orifice would also be drilled into this PVC cap as another exit orifice. Given the head loss that the tubing and orifice combination would provide, we again needed to determine if the resulting alum flow would be slow enough to dose the water appropriately. We looked at the range of flow based on the given allowable 20-percent error and discovered that the resulting flow of alum from this design was too large for our purposes as well.
Calculations
Download the PVC Cap Orifice Design MathCAD file here. These calculations are extremely similar to those found in the "Series of Orifices" design as both files require the determination of the resulting range in flow of alum.
Calculations
Download the PVC Cap Orifice Design MathCAD file here.
The head loss in the tube was determined using the equations for major and minor losses. The equations used in these calculations were found in online AguaClara notes and in Frank M. White's Fluid Mechanics (6th Edition).
...
Then, head loss through this system is calculated given the user-inputted value for the wall thickness of the desired PVC cap. These calculations utilize the fluids functions found at the top of this page. This head loss is composed of major losses, and hence shear losses, only. It should be noted that the head loss through the system did not include the head loss through the attached tubing. The diameter of the tube was relatively large and the length was generally short; therefore, we concluded that the head loss experienced through the tube would be negligible compared to that through the PVC cap orifice.
Using this information, the necessary flow of alum from the doser based on dimensions given above is determined. Using a required dose concentration of 1.5 mg/L in the untreated water, the necessary stock concentration located in the alum doser can be calculated.
...