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Introduction
The AguaClara team is making changes in the arrangement of the Rapid Mix system. revising a design for smaller flow rates. This page will document and describe the current changes in the Rapid Mix system and the algorithm for preparing an AutoCADD drawing of the Rapid Mix system.
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In the current design, we have two circular orifices on the same pipe segment. Originally, the micro-mixing orifice was after the first pipe bend. However we have decided to change that to allow facility of removal when cleaning is required. The micro-mixing orifice is two pipe diameters below the macro-mixing orifice. This ensures adequate mixing time for macro-mixing to take effect. The orifices for both equations are sized using the equations of minor loss coefficient for a submerged orifice.
Where:
K.e.orifice: Minor loss coefficientCoefficient
K.vc: Vena contracta coefficientContracta Coefficient
d.pipe: Pipe Inner Diameter
d.orifice: Orifice Diameter of orifice
Figure 1: Design Layout of Rapid Mix System
Research has estimated that for a macro-mixing orifice, we should have a minor loss coefficient of 1.3. This is what we are using for our design. In the case of a macro-mixing orifice, each pipe diameter allows for one orifice size. An increase in flow-rates will give the macro-mixing orifice a significant head loss. In the algorithm, if there is significant head loss (2 cm or above), then the piping is upgraded to the next size. The reason for having a minimum flow-rate for macro-mixing is that we plan to use the macro-mixing orifice as a flow-measurement device which can handle 20-50 cm maximum head loss at maximum flow-rate. The micro-mixing orifice is sized for a minor loss coefficient that allows for this type of flow and head loss.
The equation for head loss is shown below:
Where:
h: Head Loss
K: Minor Loss Coefficient
V: Velocity of Fluid
G: Gravitational Constant
The equation for minor loss coefficients for a submerged orifice shown above is used to find the orifice diameter needed.
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For a flow rate of 1 L/s with 50 cm maximum head loss, we obtained an inner pipe diameter of 1.89 in and macro-mixing and micro-mixing orifice diameters of 1.64 in and 0.94 in respectively. For the case of 2 L/s with 50-cm maximum head loss, we obtained an inner pipe diameter of 2.80 in and macro-mixing and micro-mixing diameters of 2.42 in and 1.33 in respectively. There will be changes made to make this algorithm more robust and they are in process. In the cases of higher flow-rates, it is better to transition to the waterfall rapid mix design that the research team came up with before.