The basic operations of a flume are easy enough to understand, but if you have to integrate pipe slope into the equation, there are some extra steps you’ll have to consider. Fortunately, this is simple to grasp once you know the process. Learn how to use a flume with pipe slope, and ensure that you’re getting the accurate measurements you deserve.
The basic force at work is the acceleration of flow through the flume. This allows the flume to push the flow to a critical state from a subcritical state. Once this is achieved, there’s a point of measurement where you can determine the flow rate. This point is typically upstream of the throat, or the portion that accelerates the flow.
Because of the necessity of criticality in measurement, it’s important to make sure that the flow channel conditions are appropriate. This means the flow must be subcritical before reaching the flume and supercritical after exiting the flume, with the point of criticality occurring in the flume itself. If it’s already supercritical before reaching the flume, accelerating the flow will only make it more supercritical rather than critical. A supercritical approach can be a common problem with pipe slope systems.
When determining whether a flow has reached criticality, you’ll have to look at the Froude number. This number is similar to the Mach number when measuring air travel velocity, with a Froude number of 1 being critical. Anything less than 1 is subcritical, while anything greater than 1 is supercritical.
With the Froude number rules in mind, the approach flow to the flume should measure less than 1. Ideally, however, you’ll want it to be closer to 0.5. If the approach is too strong, even if it’s less than 1, you may find yourself dealing with surface waves and turbulence. This makes taking the measurement tough even if criticality is reached at the right moment.
When you have to deal with pipe slope in a flow channel, you’ll find the Froude number heavily affected. As slope and pipe size increase, the Froude number also increases, though it’s important to remember that the pipe size increase is dependent on the slope as well. As the pipe size increases, the maximum slope you can use for subcritical flow decreases.
Similar to flow channels that don’t involve pipes, you’ll want a Froude number of around 0.5 because something closer to the higher end of subcriticality can inadvertently become critical or supercritical before it needs to. Plus, surface turbulence can be present as well. In general, it’s best not to allow any pipe slope to exceed 2.83%.
Flumes From Tracom
With how to use a flume with pipe slope in mind, it’s time to get a flume for your own piped system. That’s where Tracom is happy to help. You’ll find a wide variety of options available, or you can work with our team to create a custom flume specifically fitted for your unique flow channel conditions. Contact us today to get started.