h1. Entrance Tank Design Program
The purpose of this program is to design the dimensions of the entrance tank based on the flow rate of the plant and the flow rate required for rapid mixing. The Entrance Tank is constructed as a separate channel before the flocculator, and includes a grit chamber to help with aeration issues.
!Et1.PNG!!Et2.PNG!
h2. Entrance Tank Design Program Algorithm
[Entrance Tank Program Inputs|Entrance Tank Design Program Inputs]
[Entrance Tank Program Outputs|Entrance Tank Design Program Outputs]
[Entrance Tank AutoCAD Drawing Program| AutoCAD Entrance Tank Program]
h3. Algorithm
The entrance tank is designed to be an extra channel before the flocculator, and the same size as a single floc channel. This program therefore calls variables defined in the [Flocculation|GTheta Flocculation Design Program] design program. Variables are also called from the [Rapid Mix|Rapid Mix Chamber Design Program] program to meet requirements for rapid mix to occur in the entrance tank.
The area of the entrance tank is calculated based on the flow rate through the plant and the required up-velocity through the entrance tank (found in [Design Assumptions|Design Assumptions Design Program]).
{include: A.Et}
The water level in the entrance tank is designed to meet requirements for rapid mix, as well as head loss due to flow from the entrance tank to the flocculator. These variables can be found in the [Rapid Mix|Rapid Mix Chamber Design Program], [Flocculation|GTheta Flocculation Design Program], [Sedimentation Inlet Slopes|Sedimentation Inlet Slopes Design Program], and [User Inputs|User Inputs Design Program] design programs.
{latex}
\large
$$
HW_{EtTotal} = HW_{EtMax} + HL_{FlocEntryOrifice} + HL_{Floc} + HW_{Sed} + HW_{EtWaterFall} + HW_{EtChannel}
$$
{latex}
The height of the entrance channel is based on the required water depth, and the plant freeboard defined in [User Inputs|User Inputs Design Program].
{latex}
\large
$$
H_{Et} = HW_{EtTotal} + H_{PlantFreeboard}
$$
{latex}
The length of the entrance tank (L.Et) includes the length of the grit chamber, and equals the length of the sedimentation tank (which is also the length of a single floc channel). The width of the entrance tank is chosen so that it meets the geometry requirements, as well as the width required for rapid mix. In the [Rapid Mix|Rapid Mix Chamber Design Program], the width of the entrance channel needs to be at least the the spacing between the floc baffles in the first channel (S.FlocBaffle0).
{latex}
\large
$$
W_{Et} = \max \left( {{{A_{Et} } \over {L_{Et} }},W_{EtChannel} } \right)
$$
{latex}
h5. Rapid Mixer
The rapid mix system is centered in the middle of the entrance tank (RM.origin) and consists of a pipes with interfaces that produce head losses through changes in diameter. The desired total head loss throughout the entire plant (HL.PlantTotal) is 40 cm and the head loss for the rapid mix system (h.totalRM) is determined by subtracting the head losses throughout the plant from this value. The head loss for the macro-mixing orifice is constrained at 5 cm (MacroMHConstraint), so the micromixing orifice size and number accounts for the head loss discrepancies that need to be met. The elevation of the rapid mix system is determined from the height of the weir at the end of the sedimentation tank, so when there is no flow through the plant, the water level will remain constant. The bottom of the rapid mix system is at a height the thickness of the plant concrete, and the size of an elbow above the bottom of the plant origin. The length of the pipe is determined in the Rapid Mixer design program. The nominal diameter of the pipes and elbows that are part of the rapid mix system is determined from the required head loss desired throughout the plant and the rapid mix system.
Since the entrance tank is situated next to the chemical storage tanks, the system must be connected to the flocculator with addition pipes than just the pipe that runs vertically in the entrance tank. The pipe must span the walkway between the flocculator and the entrance tank and if there is an odd number of flocculation tanks, the pipe must run the entire length of the tank to the side opposite the entrance tank. This total length -- that is, the length of the pipe in the tank, and the length of the pipe joins this pipe (via elbows) to the flocculation tank is the length that is used in the head loss considerations that calculate the nominal diameter of the pipe system as well as the diameter of the macromixing orifice and the size and diameter of the micromixing orifice.
The macromixing orifice is a cap that sits atop the pipe in the entrance tank and has a hole in it of the size of the macromix orifice diameter. The micromixing interface is located where the pipe in the entrance tank hits the floor of the entrance tank. This interface is achieved via a couple.
h5. Grit Chamber
The grit chamber is contained within the entrance tank. A concrete barrier will be built to give the grit chamber a length that satisfies the upward velocity constraint previously mentioned.
{include: L.Grit}
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