Flumes and weirs work wonders for flow rate measurement in a variety of industries, including the mining industry. It’s important to remember, however, that the mining industry can be particularly tough on infrastructure considering how much debris and corrosion there can be throughout the process. In addition, there are regulations on water use throughout the process, along with requirements regarding the status of any wastewater produced. To ensure that you’re remaining compliant, you’ll need a proper flow rate measurement device.
With the harsh environments of mines and quarries, flow rate measurement devices from meters to flumes and weirs need to be built for longevity and be resistant to abrasions and corrosion. Fortunately, fiberglass construction may offer the solution you need, allowing you to keep track of water use and wastewater to remain compliant with regulations while also getting the job done properly. Here’s how you can find the right flume for use in the mining industry.
Important Material Considerations
The most important factor to keep in mind when working in the mining industry is that your device needs to be protected against harsh conditions. Debris and solids will inevitably enter your flow, so you’ll need to opt for materials that can withstand that kind of punishment throughout their operation.
Stainless steel is often used in mining applications because of its long life span. It’s important to note, however, that this is entirely dependent on the flow conditions it has to deal with. When used on particularly hazardous flows, such as what you might find in the mining industry, the material will eventually degrade over time. When this happens, the material’s longevity is essentially rendered useless. In addition, considering the cost of stainless steel, it’s not financially responsible to use it for applications that aren’t so corrosive because other appropriate materials can be cheaper.
Galvanized steel is much like stainless steel, but it’s significantly cheaper. This eliminates the overkill problem that stainless steel creates when used in normal flows, but galvanized steel has its own unique set of problems to contend with. Galvanized steel is constructed with a zinc coating that protects it from wear, which only really occurs from water impurities. Because of this, it’s one of the best options for freshwater flows. If the flow is particularly corrosive or hard, however, the zinc coating will degrade quickly and your flume’s dimensions will be compromised.
Considering the problems with various steel materials, fiberglass is likely your best bet when it comes to flow rate measurements in the mining industry. The corrosiveness of the flow still plays a role in the material’s life span, of course, but fiberglass can typically last more than a decade in most applications. The outer gel coat protects the fiberglass laminate inside, and it’s just as effective at protecting from debris in a flow as it is at protecting against UV radiation from the sun. Because of this, it’s often the go-to material for outdoor flumes.
Finding the Right Flume
The key to finding the right flume is understanding the different styles and how they work in certain applications. While mining applications can vary quite a bit, there are two types of flumes you’ll likely encounter.
Arguably the most iconic flume in the world is the Parshall flume thanks to more than a century of research and a proven history of providing accurate measurements. While it’s not applicable in every situation, there are enough equations for compensation to make it one of the most versatile flumes on the market.
The Parshall flume sports an hourglass shape and consists of inlet, throat, and discharge sections. Like all other flumes, it works by accelerating a subcritical flow as it passes through, allowing for a singular point of measurement under normal conditions. The inlet and discharge walls flare out, though the outlet is narrower than the inlet.
A cutthroat flume is essentially a Parshall flume without the throat section, which is where the name comes from. It still sports the hourglass shape, but the throat section is functionally a point in between the inlet and discharge sections. One important factor, however, is that the discharge section is exactly twice the length of the inlet section.
One of the key differences between a cutthroat and a Parshall is how the floor of the flume functions. With a Parshall, the inlet is flat, while the throat has the floor drop toward the discharge section. Meanwhile, a cutthroat flume is flat-bottomed throughout its entire length. That’s what makes cutthroat flumes so invaluable for channels in which you cannot account for the necessary floor drop.
Flumes for the Mining Industry
When it comes to the mining industry, you’ll mostly be dealing with either Parshall flumes or cutthroat flumes due to their shape and convenient mounting/end connection capabilities. Both inlet and outlet adapters are readily available for these kinds of flumes, so they can be integrated seamlessly into piping systems. With the addition of wing walls, transitioning flow into these flumes is easy too.
Pipe Slope Considerations
Implementing a flume into a mining operation more often than not requires you to fit a flume into a piped system. Pipes are necessary for operations, as they keep potentially hazardous substances from spilling out over the site or being exposed to the open air. When you’re working with a piped system, though, you’ll need to consider the pipe slope.
Flume equations are generally easy to understand, especially if you’re using a style as well-researched as the Parshall or the cutthroat. Adding pipe slope into the mix does add some extra steps, but if you do it all right, you’ll find it easy to integrate a flume into a piped system and still get the accurate flow rate measurements you’ve come to expect.
Flumes work by accelerating flow from a subcritical state to a point of criticality. This can only happen if the flow is subcritical before it reaches the flume. This state can be tough to achieve if the flow is traveling through a pipe with a rather unforgiving slope. Under these conditions, the flow may already be supercritical before it reaches the flume. As the flume’s design accelerates the flow, as all flumes do, it will only become more supercritical rather than get closer to a point of criticality.
The Froude Number
The Froude number is how you determine the criticality of any flow. If the Froude number is 1, you have a critical flow. Anything greater than 1 is supercritical, while anything less than 1 is subcritical. Think of it as a version of the Mach number, which is used to measure velocity through the air.
It’s important to remember that having a technically subcritical flow is only the beginning. A flow with a Froude number of 0.9 is technically subcritical, but the velocity may still be great enough to create surface turbulence, which makes taking accurate measurements more difficult. It’s generally best for an approach channel to create a Froud number closer to 0.5 to allow for accurate measurements.
Pipe Slope Specifics
Pipe slope is going to make it tough to ensure that your approach channel has the proper Froude number to avoid reaching super criticality too early and producing surface turbulence. A good rule of thumb to remember is that the greater the pipe size and slope, the greater the Froude number is going to be. This can help you plan accordingly, and potentially write off potential flume sites entirely simply for having unusable approach conditions.
As with regular channels, you’ll want to keep the Froude number closer to 0.5 rather than just under 1. Surface turbulence can be particularly problematic when it’s coming from a sloped approach, which will throw off your measurements to an even greater extent. The best practice is to implement a flume in a piped system only when the pipe slope is no greater than 2.83%. Anything greater than that will lead to problems with measurements.
Implementing a Flume in a Piped System
When it comes time to install a flume into a piped mining system, you’ll need to take advantage of end adapters. The Parshall flume may have been initially designed for irrigation channels out in the open, but years of research have led to the creation of handy end adapters that can easily integrate a Parshall flume into a piped flow.
One of the essential differences between a Parshall flume and a piped system is its shape. Parshall flumes are rectangular, while pipes are round. Quality end adapters account for this difference by working to minimize transition turbulence to allow for accurate measurements. They do this by having the inlet adapter have the flow rise vertically into the flume at a 1:4 slope. Wing walls keep the flow moving forward through the flume smoothly and uniformly. Just keep in mind that they need to be radius wing walls rather than flat wing walls to avoid the wave-trough phenomenon.
Remember the Throat Size
Unlike a lot of other flume styles that are used in piped systems, Parshalls rarely have a throat size that matches the size of the pipe they’re being connected to. Instead, you’ll find that your flume’s throat is only half or a third of the size of the pipe itself. This works in stark contrast to other kinds of flume styles like the Palmer-Bowlus, which would have a throat size that’s the same as the size of the pipe.
Keep It Watertight
When working in the mining industry, it’s important to keep all your flows watertight. When dealing with connectors and adapters, this may require some extra effort. You may want to implement accessories into the setup like band clamps or flexible couplings. You can even opt for coupling shields in particularly dubious setups that require some extra strength. Think of a coupling shield as a metal cover, typically made of stainless steel, that is affixed outside of the flexible coupling itself.
Working Outside of Piped Flows
In some mining scenarios, the flow channel won’t be in a pipe at all, and that can warrant a different kind of approach to flow rate measurement altogether. While a Parshall or cutthroat flume could still get the job done, some of these channels warrant a flume that fits more neatly into an earthen channel. This is where the trapezoidal flume may be your best bet.
Trapezoidal flumes are flat-bottomed and naturally help debris pass through effortlessly as the walls extend outward at an angle. If anything gets wedged in the lower parts of the flume, the buildup behind the blockage will often simply dislodge the debris on its own. In that sense, the trapezoidal flume is largely self-cleaning, though you’ll still have to perform maintenance on it sometimes.
One of the most important aspects of trapezoidal flumes you’ll need to remember, though, is that they work best with low flow rates in terms of accuracy, though they can still handle large flows. They come in several different sizes as well, and they can deal with greater levels of submergence compared to the Parshall.
Flumes From Tracom
When it’s time to get a flume of your own for any mining application, Tracom has got you covered. We have a wide range of Parshall, cutthroat and trapezoidal flumes to choose from, but that’s only the beginning. You can work with our team to create a custom fiberglass design that’s uniquely suitable for your flow channel conditions whether it’s open to the air or within a piped system.
Because we craft our flow rate measurement devices from fiberglass, they’re dimensionally exact every time, even when you opt for a custom design. Our team can also provide you with additional help throughout the flume’s lifespan to ensure that you’re getting as much as possible out of your investment. We firmly believe that a good flume should last for years. Contact our team today to get started.