Technology / R&D
Computational Fluid Mixing (CFM)
CFM is a powerful tool that is used to mathematically model fluid flows of different agitator/impeller designs in mixing tanks. Other valuable analyses include the mixing and reaction rates of chemicals and heat transfer.
Mixing of single and multi-phase fluids in stirred tank reactors is a common operation in many industries. Understanding the fluid flow in these tanks is critical for equipment design, scale-up, process control and economic factors. CFM models allow you to see what is taking place in the mixing vessel. The results enable an engineer to select the best agitator design to obtain the desired process performance.
The flow patterns in stirred tanks are complex, which makes traditional CFM a time-consuming process. A CFM technician may need as long as three days to define all of the equations and run the program. However, we have applied a variety of proprietary techniques to expedite this process. Chemineer engineers can obtain a two-dimensional CFM analysis in as little as 10 minutes, and a 3-D analysis in 3 to 4 hours.
Our analytical capabilities are not limited to just cylindrical stirred tanks. Rectangular and side-entering agitated tanks as well as turbulent and laminar flow static mixers can all be successfully evaluated using our CFM technology.
Chemineer's CFM models receive extensive validation using advanced experimental techniques. Chemineer is the first in the industry to use laser based Particle Image Velocimetry (PIV) for mixing analysis. The unique data obtained with PIV further improves our modeling capabilities and provides you with the most accurate design for your agitation needs.
Digital Particle Image Velocimetry (DPIV)
DPIV helps our engineers to better understand the flow phenomena occurring in mixing tanks. An Argon-Ion laser light sheet illuminates fluorescent, neutrally buoyant particles. A CCD camera captures the images, then an advanced timing system and a computer with image board freezes and digitizes the images. The picture below shows the motion of fluorescent particles illuminated by a sheet of Argon-Ion laser light. The particles (60 micrometers) are small and neutrally buoyant, so they follow the liquid flow. The tank is equipped with a pitched-blade turbine. The particle motion is filmed with a CCD camera. The velocity field is then extracted from the digitized images using cross-correlation software. Armed with this information, our engineers can better design agitation equipment for your specific application.
DPIV technology has the capability of measuring the entire fluid velocity field in a tank almost instantaneously making it possible to study large-scale, time-dependent phenomena in the tank, which is responsible for much of the mixing process.
The image below shows the result of a series of full flow field measurements using DPIV. The color shows the local, time-averaged velocity. Fast-moving regions are colored red and slow-moving regions are colored blue. The pitched-blade turbine creates a mixed axial/radial flow pattern. The highest velocities are found at the impeller blade tip. The velocities at the liquid surface are an order of magnitude lower.
When used in conjunction with Computational Fluid Mixing (CFM), DPIV provides the most accurate application evaluation possible. Various mathematical models used by the CFM software must be validated to ensure the accuracy of the procedural results. DPIV analysis provides that validation with actual experimental data and, if necessary, DPIV test data can be used to further improve CFM models so the predictions have an even higher degree of accuracy.
Laser Doppler Anemometry (LDA)
Laser Doppler Anemometry (LDA) is widely recognized as the best method of non-intrusively determining mean velocity and turbulence data with pinpoint accuracy. Chemineer uses the Dantec FlowLite turnkey measurement system to determine velocities in stirred tanks and static mixers. The measurement technique relies on the physical fact that when two laser beams of the same wavelength cross, an interference pattern of bright and dark fringes is formed. As a single particle passes through the intersection of two such laser beams, it reflects light at certain frequencies which depends only on the velocity of the particle and the fringe spacing. Appropriate optical collection and data analysis enable highly accurate velocity measurements within extremely small volumes of fluid. Within minutes, thousands of particles may pass through the measurement volume, enabling an accurate determination of velocity at that point.
Chemineer uses these measurements to verify ChemScale and also to characterize specific impeller zones. This information may often be used with Computational Fluid Mixing to accurately determine the flow in the entire mixing vessel.
Laser Induced Fluorescence (LIF)
One of the most challenging problems in fundamental diagnostics is directly measuring mixedness. Limiting factors in traditional mixing systems include the intrusion of probes and the number of probes required to statistically determine mixedness. Laser Induced Fluorescence (LIF) is a measurement technique which enables the user to gain a fundamental understanding of mixing in a straightforward fashion. Materials such as rhodamine or uranine will fluoresce when struck by light of certain wavelengths. We use this property to track the path and diffusion of injectants in agitated vessels and static mixers. A laser beam is spread into a sheet of coherent light which is projected through a clear pipe or vessel. When fluorescent material is struck by the light, it scatters light at a higher wavelength than the laser wavelength. The scattered light may be captured on video or on a CCD camera directly linked to a computer. These digital images may be analyzed to determine uniformity.
One of the benefits of such an analysis is that both qualitative and quantitative assessment of mixing may be gained simultaneously. In static mixer systems, we have used this information to calculate a coefficient of variation while in stirred tanks, blend times have been measured. In either circumstance, the user also gains a general understanding of the mixing mechanisms.
Chemineer R & D Labs
The Chemineer R&D Laboratory is located in Dayton, Ohio about 200 meters from our manufacturing facility. Our laboratory functionality is broken down into two different areas: customer testing and R&D.
Customer Test Facility
Not every application in mixing has been studied and many applications are difficult to model computationally. As a result, it is sometimes necessary to scale down the problem and study it in the laboratory. Chemineer has set aside a particular room for customer testing in its R&D facility. This room contains an OSHA-compliant 144-square-foot hood. Various pieces of test equipment are designed to be rolled into the hood to handle the myriad of possible dynamic and static mixing applications.
Dynamic agitators are studied in a wide variety of different vessels. Most vessels are see-through, either glass or acrylic, as witnessing the flow patterns created are very important to the mixing process. Vessels used are generally from 1 foot through 3 foot in diameter with various types of bottom heads to model the customer's full scale vessel. Baffles can be easily removed to study off-center mounted or viscous mixing applications. Rectangular and square vessels are also available. A wide range of impeller styles, often in 1/4 inch diameter increments, can be assembled in short order. An assortment of spargers is available to study gas dispersion applications. Data on torque and speed is electronically taken without the need to correct for bearing or gear losses. Acid-base neutralizations with an indicator are an effective means of determining mixedness to within about 99% uniformity.
Static mixers can also be studied in our Customer Test Facility. Similar to dynamic mixers, we endeavor to study static mixing in glass or acrylic in order to witness the progress of mixing. Centrifugal and positive displacement pumps are available in order to pump fluids with varying degrees of viscosity for laminar, transitional and turbulent flow applications. Line sizes range from 2 to 3 inches. Pressure drop and mixedness are typically the most desired properties. Acid-base neutralizations with an indicator are an effective means of determining mixedness to within about 99% uniformity.
Research & Development
The process design technology that works its way into our expert design programs comes from our continued research and development in the fields of mixing and agitation. Chemineer maintains an active R&D program. New products start in R&D and we are continually searching for highly efficient and cost effective impellers, impeller systems, static mixers and static mixer systems. We use various tools to assist us in evaluating the individual possibilities. These include DPIV (Digital Particle Image Velocimetry) and LDA (Laser Doppler Anemometry) to evaluate both instantaneous and time averaged velocity vector fields, LIF (Laser Induced Fluorescence) for blending studies, CFM (Computational Fluid Mixing), full scale vessel with strained gaged shafting for studying impeller hydraulic loads and power characteristics, full scale tanks for adequacy of scale-up rules as well as for the testing of new drives, an apparatus which simultaneously provides a reading of torque and thrust, a wind tunnel for gas-gas blending, and other tools.