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PoultryTech

Volume 17 | Number 2 | Summer 2005 | Environmental Issue

page 1
Researchers Use High-speed Cameras to Better Understand Fluid Flow in Taylor Vortex-based UV Disinfection System

page 2
Survey Studies Industry Pretreatment Use and SPN Handling Options

page 3
Industrial Storm Water: A Look at Georgia’s Proposed New Permit
By Jim Walsh & John Starkey

page 4
Water Reuse and Recycling News

page 5
Georgia Tech Researchers Partner with Industry to Study Alternative Uses for Eggshell Waste

page 6
WASHINGTON UPDATE:
Thousands of Animal Feeding Operations Sign EPA’s Air Compliance Agreement

page 7
Visit Poultry World at the 2005 Georgia National Fair

 

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Researchers Use High-speed Cameras to Better Understand Fluid Flow in Taylor Vortex-based UV Disinfection System

Taylor vortex-based ultraviolet disinfection system

Georgia Tech researchers John Pierson (right) and Aklilu Giorges adjust a high-speed camera to conduct flow visualization studies for the Taylor vortex-based ultraviolet disinfection system.
Photo by Gary Meek

Over the past year, Georgia Tech’s innovative Taylor vortex-based advanced UV (ultraviolet) disinfection system has proven its effectiveness at pathogen control in turbid liquid streams. Using aerobic plate counts (APC), researchers have shown a 5-log removal of pathogens in sample streams. The high level of inactivation occurs even with juices and beverages that are opaque to germicidal UV light as well as other liquids that contain suspended solids and turbidity (cloudiness). Even though this is a significant accomplishment, the research team is now focused on further improving the system to gain higher flow throughput and disinfection for liquid streams containing significant turbidity. To do this, however, researchers realized they needed a better analytical tool to more fully understand fluid flow in the stream. Because APC does not tell the researchers exactly how each pathogen in the fluid is moving, they turned to a different technology altogether, high-speed cameras.

“Understanding the flow field of the reactor’s disinfection column is crucial to grasping how disinfection is taking place,” says Aklilu Giorges, a research engineer spearheading the flow visualization study supported by the high-speed cameras.

Taylor vortex-based ultraviolet disinfection system

Taylor vortex-based ultraviolet disinfection system

Images recorded during the flow visualization study show the flow field of the Taylor column at 17 rpm (top) and 170 rpm (bottom). The slower speed shows several counter-rotating vortexes are formed within the Taylor column, whereas the higher speed shows a decrease in counter-rotating vortexes and a chaotic flow.

The term flow field describes the location of a particle in fluid. To ensure the Taylor vortex design maximizes inactivation, researchers would like to know the location of pathogens as they move through the reactor, especially their proximity to the UV lamps. As a particle (or pathogen) moves about in a fluid, its speed changes from point to point. Rather than trying to follow the history of each individual particle, it is more convenient to describe the flow field in terms of velocity, pressure, density, etc., at every point of space relative to time. Predictions can then be made relative to how effectively the lamps will be in inactivating pathogens in a particular part of the flow field. High-speed cameras are helpful in that thousands of images can be captured each second and then analyzed with regard to particle movement.

The flow visualization study used Photron© computer-based high-speed imaging technology. To enhance the visibility of the flow field, rheoscopic fluid was used. Rheoscopic fluid, a water-based suspension of microscopic crystals, is commonly used in flow visualization experiments. The microscopic crystals reflect light so the high-speed camera can track crystal movement throughout the fluid.

The flow field was recorded with a camera frame rate of 1,000 frames per second, explains Giorges. These images were then replayed at slower speeds that allowed a qualitative assessment of the flow field.

“When the images were played at the slower speed, it was obvious that several pairs of counter-rotating vortexes were formed within the Taylor column. An entrance effect was observed that was limited to the bottom of the column. In addition, the entire flow field was observed pulsating because of the pump feed,” explains Giorges. There was, however, no indication that the counter-rotating flow pattern was disrupted because of these pulsations, adds Giorges.

When the rotor speed was increased, the number of counter-rotating vortexes decreased and the flow became chaotic. Giorges says the optimal operating conditions observed in previous APC experiments correlated well with the higher number of vortex rings and laminar (ordered) flow generated during the imaging study.

According to Giorges, the flow path visualization process clearly shows that the vortex rings are effectively moving the fluid into and out of the region where effective UV penetration is achieved even with turbid fluids.

Such visualization techniques provide researchers with improved tools not only for assessing current performance but also for gaining a better understanding of the impact design changes can have on providing even greater performance enhancements.

How It Works:
The Taylor Vortex-based UV Disinfection System

Unlike conventional UV disinfection technology, the Georgia Tech system utilizes the Taylor vortex mixing principle to produce outward moving vortices. The device that achieves this is comprised of a solid rotating cylinder (rotor) that is turned within an open cylinder (stator). The gap between the rotor and inner stator wall is significantly smaller than the radius of the rotor. As a result, the fluid in the gap is moved uniformly toward the outer wall such that any bacteria in the fluid are moved outward as well. The system’s UV lamps, which are placed around a transparent quartz stator, ensure that UV exposure is maximized. In a nutshell, the Taylor vortex design continuously pushes the liquid to the quartz stator surface where it exposes any bacteria present to a uniform dosage of radiation, thus providing much greater inactivation efficiency.

For more information, follow the link below to read the online version of an article that originally appeared in the Summer 2004 Environmental issue of PoultryTech, http://atrp.gatech.edu/pt16-2/16-2_p1.html.



Taylor vortex-based ultraviolet disinfection system

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Taylor vortex-based ultraviolet disinfection system

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Taylor vortex-based ultraviolet disinfection system

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193 KB | JPEG

 

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PoultryTech is published by the Agricultural Technology Resarch Program (ATRP), Food Processing Technology Division (FPTD) of the Georgia Tech Research Institute. ATRP is conducted in cooperation with the Georgia Poutry Federation with funding from the Georgia Legislature.