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Creation of a constant flow requires a constant driving force and a constant pressure coefficient or loss coefficient. An almost constant driving force can be obtained by using a very large driving head with small variations due to level fluctuations in the stock tanks. A more practical approach is to use a float valve to regulate the chemical level in a small tank. The constant fluid level can then be used to develop a constant flow. Recent advances in small low cost chemical resistant float valves have made it possible to use float valves even with corrosive chlorine solutions.
Laminar flow constraint
Head loss constraint
The minimum theoretical diameter that could be used is the maximum of the previous two equations.
The design diameter of the tubing is obtained by selecting the minimum diameter of available tubing that is larger than the minimum theoretical diameter.
Minimum diameter of tubing to produce the desired head loss at the maximum flow using the minimum feasible length of tubing. Based on the Hagen-Poiseuille equation.
Application
flow control module design webpage
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