Flow control is indispensable in biological, chemical, food and other manufacturing processes, or for analytical purposes. In these processes, it seems obviously necessary to supply fluids (gases, liquids, or vapors) in a controllable manner. Essentially, this is the definition of flow control. Accurate flow control will improve final product quality and process understanding by investigating varying process flows. It may also speed up process steps. Ultimately, flow control will improve process economics. To this end, flow control devices, known as flow controllers, are useful.
Flow controllers add one or more chemical compounds in gaseous, vapor, or liquid form to a process by controlling the compound’s flow rate. This can be a mass flow rate, for example, grams of compound per minute. Or, it can instead be a volumetric flow rate, such as liters per hour.
A flow controller is a flow meter combined with a control valve and control firmware. The flow meter measures the flow rate of the compound that is supplied to the process. In flow measurement, the setpoint value is the necessary flow rate of the compound that a user adds to a process. Then, if the actual flow value deviates from the setpoint value, the control valve will open or close to compensate for the discrepancy. Through this action, the actual (measurement) flow rate will eventually reach the necessary setpoint value.
To explain how a flow controller operates, let’s look at the main components of an EL-FLOW Prestige mass flow controller, from Bronkhorst. The laminar flow element inside the body guides part of the fluid flow to the sensor that measures the flow rate. Then, the control valve, positioned in series with this flow measurement part of the device, will vary the size of the flow passage by opening or closing to match actual flow value to setpoint value. Accordingly, the pc-board inside the enclosure houses the control and feedback software between the flow meter and the valve.
Control valves can be an integral part of the overall flow controller device. It is a separate component that’s used in combination with a flow meter. As a result, control values with direct coupling and electromagnetic operation are fast, low cost, and use very little power to control flow. Furthermore, to handle higher pressures and flows, larger direct valves or indirect control valve configurations are available.
The sensor type largely determines the kinds of flow controllers that are available.
Flow controllers that operate according to the thermal principle employ the heat capacity of gases or liquids to control their mass flow rate. Bronkhorst has several of these thermal mass flow controllers available, each with their own sensor technique.
Coriolis flow controllers that use the Coriolis principle rely on a direct relationship between fluid mass flow rate and mass inertia. They operate fluid independently, which means that they can be used for varying and unknown mixtures. Moreover, with these Coriolis-based flow controllers, there is no need for conversion when the device is used for other liquids. We offer a variety of Coriolis based flow meters and controllers:
Flow meters with ultrasonic sensors measure the flow velocity across the tube cross-section inside the device. As a result, volumetric liquid flow rates are measured. Our flow meters that use the ultrasound technique include:
According to the positive displacement principle, gear pumps are a type of volumetric flow controller. In gear pumps, a motor first causes gears to rotate. There, the space between the teeth of two interlocking rotating gears determines the stroke volume. Accordingly, successive strokes will generate a continuous fluid flow.
In summary, some flow controllers are particularly suitable for gases, and some specifically for liquids. Moreover, there are flow controllers available that are independent of fluid properties. Therefore, they can control the flow rate of both gases and liquids. For more information on which flow meter would be best for your process, check out our article: How to Choose the Right Flow Meter.
Flow controllers contribute to the accurate control of liquid flows for dosing liquid additives in continuous pharmaceutical manufacturing applications. For a leading company in this industry, we provided a complete, custom liquid dosing skid solution. This particular dosing system combines a mini CORI-FLOW mass flow meter, a gear pump, and a pressure sensor from the IN-PRESS Series. As a result, the process occurs faster, more reliably, and more flexibly for the customer.
To investigate the storage of hydrogen in metal hydride containers, the German Aerospace Center needs to control the introduction of hydrogen gas into a container. For example, devices from the IN-FLOW flow meter series, in combination with Vary-P valves, can achieve this with ease.
For ice cream production, the aeration process is essential. Here, air blends into a liquid mixture of various food ingredients. For the right final product consistency and structure, the ice cream must contain the correct amount of air bubbles. To this end, aeration mixer manufacturers use EL-FLOW Select mass flow controllers to dose an exact amount of air into the cooled mixer. You can read more about this in our article: Flow Meters in the Food Industry.
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