Selecting the most appropriate flowmeter is an important step in maximising the efficiency and productivity of the production process. Contributed by Burkert.
Fluid flow measurement technology is designed to improve productivity and provide crucial information for manufacturing processes. Within the food and beverage industry it is also required to meet the exacting standards relating to hygiene, purity and accuracy that fulfil regulatory requirements.
Many of the processes within this industry are required to operate within carefully defined spaces and therefore minimising the lengths of pipe runs is also important in maximising the production area.
Selecting the most appropriate flowmeter is an important step in maximising the efficiency and productivity of the production process. Each process has individual challenges and the market contains a variety of devices that are designed to accommodate different fluidic conditions.
All of these flowmeters have limitations leading to designers having to make a compromise in many cases. The need to improve this situation has led to the development of an existing surface acoustic wave technology to provide a solution to meet the requirements of the highly demanding food and beverage industry.
Flow measurement devices, from the most basic paddle wheel to an advanced Coriolis flowmeter, all have one or more constraints that can limit the applications in which they can be used. Many employ moving parts that are in contact with the fluid, which can cause a flow restriction as well as reducing the efficacy of the hygienic cleaning process.
The demand for more advanced, non-contact measurement technology has seen the rise in ultrasonic and Coriolistechnology and each of these have their place.
However, even these devices have limitations including measuring non-conducting liquids or those containing bubbles or debris. Ultimately it may be the location, space or orientation that may determine the most suitable design for a particular application.
Ultrasonic devices use either the Doppler Effect or transit time measurements to determine the flow of gasses and liquids. However, despite the high initial cost of these designs, the Doppler Effect versions cannot be used with pure fluids since they require the particulate material or bubbles to reflect the signal; conversely, the transit time devices can only be used with pure fluids.
It is possible to use combination units that assess the fluid conditions and then select the measurement operation as required, however, there is an additional cost implication with this selection. Furthermore, the accuracy of ultrasonic flowmeters can decrease in low flow situations.
The principle of operation of magnetic flowmeters is based on Faraday’s Law of Electromagnetic Induction, where the voltage measured is proportional to the velocity of the flow.
This can lead to reduced accuracy with reduced flow velocity. Magnetic flowmeters rely on the fluid having conductive properties to a greater or lesser degree depending on the individual design; however, applications involving hydrocarbons or de-ionised water are not viable.
An added complication is that the installation of magmeters normally requires the pipe to be grounded using specific procedures, which can increase the complexity of the installation. Failing to complete this properly can result in fluctuating signals. Furthermore, magnetic flowmeters also rely on the fluid being free of any entrained bubbles in order to provide reliable and consistent readings.
Coriolis flowmeters are regarded as the top specification flowmeter due to their versatile capabilities for both fluids and gases. However, the initial cost of such devices can be very high and they do have some constraints.
The design of the Coriolis flowmeter causes a pressure loss across the flowmeter and this can affect the upper limit of the measurement range. The pressure loss increases with flowrate and the corresponding velocity through the meter.
Additionally, the size and weight of the Coriolis flowmeter requires it to be carefully supported within the process pipework. The space required for Coriolis flowmeters is greater than that required for the designs discussed so far with additional pipe supports and installation time required.
In terms of liquid flow measurement, there is a clear opening for a device which can deliver a compact, non-contact measurement which is accurate irrespective of media characteristics, flow direction and flow conditions.
New Technology Explained
Surface Acoustic Waves (SAW) were first discovered in 1885 and their properties have been examined for many years, with a great deal of modern technology using the principle.
Part of that research has led to the development of a fluid flow measuring sensor by Bürkert Fluid Control Systems, which aims to deliver every requirement of a hygienic, accurate and reliable flowmeter, without the constraints that affect traditional flowmeters, including cost.
The main principle of this flow measurement system is based on wave propagation forms similar to seismic waves, which start from an initial point of excitation and spread along the surface of a solid material. Interdigital transducers, which are located on the outside of the measuring tube, are used as both senders and receivers of the waves.
The physical design of this revolutionary flow measurement system means that the sensor part is not in direct contact with the fluid, the first of many advantages.
The absolute time for the wave to travel from the sender to the receiver depends mainly on the tube diameter and the type of liquid. The difference between the time of propagation in the forward and backward direction is proportional to the flow.
The analysis of all the signals and comparisons based on different criteria such as amplitude, frequency and time of flights, allows evaluation of the quality of the measurement as well as the kind of liquid and its Properties.
The angle with which the waves couple out of the liquid is dependent on the velocity of the wave on the tube surface and the velocity of the wave in the liquid. An ‘acoustic fingerprint’ of the medium is created by combining this with the reception signal characteristics, which depend on whether the signals have passed through the medium singly or multiply.
From this, the volume flow rate, density and temperature and so mass flow rate can be determined, as well as additional information about the medium itself. Since the technology requires no elements within the pipe, the diameter and therefore the flow resistance remain unchanged.
SAW Flow Measurement Advantages
In common with several other designs, SAW based inline flowmeters have no direct contact with the fluid, which means there is no pressure drop and no restriction in flow, but the measurement principles of SAW allow it to overcome the shortcomings of other, similar, flowmeters.
The principles behind this design enable the flowmeter to work with a stagnant liquid and so reliable flow figures are available even for the smallest flow volumes. The technology also enables it to recognise quick flow changes reliably, which makes it suitable for fast filling processes as well.
The technology does not depend on the conductivity of the fluid, allowing it to perform accurately on a wider range of fluids compared to magmeters. Neither is it affected by entrained bubbles or debris, allowing it to deliver consistent, repeatable readings, which may not be the case when using other, more traditional measurement devices.
FLOWave is designed to offer a modular device that can be specified to deliver the exact requirements of a particular process with excellent flexibility to allow future expansion.
Due to the wide range of applications that are suitable for FLOWave measurement, and the simplicity of its design, there is considerably less effort required in specifying the correct device for a particular application.
The actual installation process is significantly less complicated when using a FLOWave device as it can be mounted in any orientation and it requires a great deal less space that similar devices using more traditional measurement techniques.
The FLOWave can also be specified with or without a display module that can be positioned to suit the final orientation in the process of pipework.
Furthermore, once installed, the FLOWave range offers ongoing benefits including a device status indicator which provides diagnostic status information to the operator, as outlined by NAMUR NE107.
In addition, this technology requires considerably less energy to operate; approximately one third of that required by a standard Coriolis flowmeter. In situations where choosing between minimising contamination and maximising accuracy is not acceptable, selecting the latest innovation in liquid flow measurement may be the best method of gaining the benefits of both criteria.
Benefits To The Food & Beverage Industry
For an industry that uses batch production techniques it is important to maintain the highest hygiene standards so as to avoid any cross contamination. This industry also uses a wide range of fluids which have a variety of properties and, in terms of production efficiency, it may be more beneficial to have the ability to use the same production line for a number of different products.
The foremost asset of FLOWave is the internal surface of the tube where there is no direct contact of any sensor components with the fluid.
Furthermore, it can be manufactured to the same surface finish as the rest of the pipeline, meaning that, in terms of hygiene, cleaning and flow conditions, there is no difference to any other piece of straight pipe.
The non-contact nature of the design brings the hygiene benefits that are seen in high specification flowmeters, except without the additional cost premium.
Food and beverage production invariably involves liquids of varying purity and often include entrained bubbles or solids which may predetermine the type of flowmeter to be used on a particular line.
However, this may restrict the number of products that can be manufactured on one line. The use of FLOWave technology is designed to remove these restrictions and improve the versatility of the production line while maintaining high levels of precision and hygiene.
In addition, the compact design of the FLOWave range simplifies the installation process with inlet and outlet sections that are a lot shorter in installation length than Coriolis flowmeters.
These characteristics provide a significant space saving benefit for designers and installers that are working to a restricted footprint for an application.
The design also delivers significant weight savings compared to traditional flowmeters, which further simplifies the installation and removes the need for additional pipe supports. This also translates into reduced transportation and handling issues.
Flow measurement in a variety of fluid conditions can improve overall product quality, consistency and process efficiency as well as reducing waste of expensive ingredients.
The more advanced, non-contact, flow measurement technologies, such as ultrasonic, electro-magnetic and Coriolis sensors, still have limitations.
The flow characteristics, media purity and space constraints of most current flowmeters can be determining factors in deciding which design is best suited to a particular application.
Bürkert has looked to address all of these issues in the creation of a new flowmeter technology and design.
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