News

November 1, 2013

Magnetically stimulated flow patterns offer strategy for heat transfer issues

WATCHING PATTERNS FORM — Jim Martin (1114) peers between specially built magnets as he watches patterns form in a fluid inside a 3 cm glass container. Jim and doctoral researcher Kyle Solis have discovered how to harness magnetic fields to create vigorous, organized fluid flows in particle suspensions. (Photo by Randy Montoya)

by Sue Major Holmes

Jim Martin and Kyle Solis have what Jim calls "a devil of a problem."

They’ve discovered how to harness magnetic fields to create vigorous, organized fluid flows in particle suspensions. The magnetically stimulated flows offer an alternative for when heat transfer is difficult because they overcome natural convection limits. Jim and Kyle even demonstrated a potential application: cooling overheated computers with a heat transfer valve they created.

But Jim and Kyle (both 1114) aren’t sure how and why the magnetically stimulated flow patterns occur, although clearly it’s a complex physical behavior stemming from fundamental phenomenon.

"Just because an effect is easy to generate doesn’t mean that it’s going to be easy to understand," Jim says. It’s also a tough problem to simulate because of the huge scale of the flow patterns compared to the tiny particle size, he says.

He and Kyle, a Student Intern Program doctoral researcher, have been generating flow patterns in magnetic platelet suspensions for about three years. They published a paper in 2010 in the American Institute of Physics’ Applied Physics Letters and another paper, which the editor selected as a research highlight, in February 2012 in the Royal Society of Chemistry’s journal Soft Matter, outlining flow patterns and how they created them. Jim has been invited to lead a topical review, called "Driving self-assembly and emergent dynamics in colloidal suspensions by time-dependent magnetic fields," for the international journal Reports on Progress in Physics in November.

The research, funded by the DOE’s Office of Science, is concentrating on extending fundamental understanding of novel heat transport in liquids, evaluating the effectiveness of various flows, and exploring what happens when researchers modify parameters of various experiments.

Jim and Kyle found the patterns occur only for magnetic particles shaped like plates, essentially magnetic confetti. Spherical and rod-like particles don’t produce the effects.

Making fluid flow like convection

The goal is making fluid flow on its own, as in thermal convection. Convection is familiar to everyone who boils water or marvels at birds and gliders riding on thermals. However, it doesn’t work in outer space where there’s no gravity or in a liquid that’s beneath rather than above a hot object. The modern world forces convection by using pumps and fans with associated seals and valves in contact with the particular fluid, but sooner or later those moving parts corrode and break down.

Jim and Kyle make fluids move by adding a small amount of magnetic platelets to a liquid and applying modest, uniform AC magnetic fields. The phenomenon, which they’ve termed isothermal magnetic advection, has shown very good results for noncontact heat transfer and would be useful for cooling microsystems or cooling in microgravity or for transferring heat in circumstances that prevent convection, they say.

"We don’t have a lot of understanding of why these things occur, but we can determine what the effects are and how well it works," Jim says. Ongoing experiments, coupled with modeling, are advancing the understanding of the phenomena.

Because a uniform magnetic field can be easily scaled to any size, Jim says, the technology could be practical for problems ranging from microfluidics to reactor cooling.

The researchers discovered various flow patterns they call advection lattices. "The patterns are pretty remarkable because it’s not easy to understand why the fluid should flow in the first place because a uniform magnetic field does not exert a force on a particle, just a torque," Jim says.

He compares the flow lattices to the patterns, or murmurations, of flying, wheeling flocks of birds, with "every bird obeying some simple rules like avoiding crashing into neighboring birds. There’s no leader. These patterns just spontaneously emerge from these simple rules. That’s more or less the same thing here. Each particle is obeying simple rules but collectively there’s this emergent behavior that’s quite surprising."

Specially built magnet generates uniform field

It’s not necessary to use very strong magnetic fields for the fluid flows. The researchers generate a uniform multiaxial AC magnetic field with a specially constructed magnet consisting of three nested pairs of coils arranged to create three mutually perpendicular magnetic fields. Imagine a rectangular box with a wire coil glued flat to each of the six faces. Coils on opposite sides are wired together and produce a field directed along their cylindrical axis. The arrangement enables researchers to create magnetic fields with independent frequencies along the north-south, east-west, and up-down directions simultaneously.

The net effect is a magnetic field whose direction and magnitude vary wildly and rapidly with time.

Normally a magnetic field is a constant DC field, which results in stationary magnetic field lines like those of the Earth. Jim and Kyle, on the other hand, use alternating magnetic fields ranging from about 50 Hz to 1,000 Hz. Only two field components are needed to create flow fields, but three can create especially vigorous flows.

In Jim’s lab, they demonstrate patterns, first with a fluid suspension containing a small percentage of magnetic platelets by volume and then with a much denser suspension. Platelets start out as disorganized sediment, but when the field is applied patterns emerge immediately, their structure dependent on the magnetic field used. Jim and Kyle describe various patterns, whose features are mere millimeters in size, as looking like worms slithering by each other, tadpoles swimming upstream, fishing nets, sand ripples, ridges, a lattice of rivers. One pattern wriggles as if tiny bugs moved underneath.

Jim points out not all the "rivers" in the lattice flow in the same direction: Cutting through the fluid would reveal a checkerboard pattern of flow columns, some going one way and adjacent columns flowing the opposite.

"It’s an enigmatic phenomenon," he says as he uses a tiny light to illuminate the 3 cm square glass container of fluid sitting in the middle of the magnets.

Patterns evolve as magnetic field changes

The demonstration starts with one coil pair running at 150 Hz, or 150 cycles per second, and a second set at 75 Hz. Kyle changes frequencies by computer, and at one point introduces a slight frequency change in one field component to continuously modulate the flow pattern.

"The sample will go through all these transformations," Jim says. "In any one moment it’s trying to become what the field is directing it to become, but now the field is continuously changing, causing the pattern to evolve. In other words, there are lots of patterns that are possible and we can select these by carefully adjusting the phase angle between field components."

One pattern is a vortex lattice of micro-tornadoes spinning in the opposite direction of their neighbors. Jim explains it this way: Suppose you had a checkerboard with a gear mounted on a shaft in the middle of each square. If you turn a gear clockwise in the lattice of mesh gears, its four neighbors turn counterclockwise, and each of their neighbors turns the opposite direction and so on.

"This is the same kind of thing but it’s all a fluid," he says.

Kyle changes the experiment’s parameters by diluting the fluid with more solvent, in this case isopropyl alcohol, or removing most of the solvent. He also dials the magnetic strength up and down. Some patterns move rapidly, even violently, and the solution can suddenly crawl up the sides and spill out. At one point, Kyle shuts off the field and the fluid shows a ghostly remnant of the previous pattern. The flow immediately resumes when the field is restarted.

Demonstrating  heat transfer valve

Jim and Kyle used the phenomenon to create a heat transfer valve they can control to transfer or block heat. They made flow cells a few inches long with blocks on the outside walls through which water flows to keep the blocks cold. The water blocks flank a chamber divided by a razor-blade-size heater made of plastic embedded with wire. To test thermal transfer properties, they run current through the heater and measure how hot it gets. Since the temperature depends on the heat transfer properties of the chamber’s magnetically structured fluid, they can control the temperature by controlling the flow created by platelets in the magnetic field.

Some fields freeze the fluid and cause the heater to become very hot, while others create strong flows so efficient in extracting heat that the heater rises only 0.3 degrees C higher than the water block temperature, Jim says.

Thus it acts like a valve because it can control the transfer of heat over a 1 cm gap by a hundredfold, he says. "Think of a water valve that can control water flow by a factor of 100 —perhaps a little leaky, but still better than no valve," he says. There’s room for improvement, he adds.

"Heat transfer can be controlled over any size volume, and the relative efficiency of heat transfer actually increases with scale," Jim says. "It’s easy to create heat transfer over a large volume because the coils that produce magnetic fields are equally efficient at any size."

Isothermal magnetic advection could help efficiently manage overheating in computers. A difficulty with modern supercomputers is drawing heat away from chips that run ever hotter and use more power, a technical challenge that’s limiting development, Jim says. And it’s not just large systems. "One of the limitations for cooling right now on personal electronics like laptops is just how fast people can run the fans inside of them before the noise becomes too obnoxious," Kyle says.

-- Sue Major Holmes

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Lean on me: Veterans confront combat stress in a different kind of support group

GOT YOUR BACK — From left, John Bailon (5627), John Boehm (5343), Steve Becker (2144), and Jason Shelton (2998) say they are proud to step forward and talk about how combat affects a person. "It’s part of who you are," Jason says. (Photo by Randy Montoya)

by Nancy Salem

There’s nothing normal about fighting in a war. "That says it all," says John Boehm (5343), an Iraq combat veteran.

"My first experience with an IED (improvised explosive device), I thought I was watching a movie," he says. "Until the truth hits you, it’s real, but it’s not."

One percent of Americans serve in the military. About half of them are sent into battle. "It’s a very unique subset of people who actually experience combat," says John Bailon (5627), also an Iraq veteran. "It’s impossible to explain what it’s like to someone who hasn’t been there. People who are familiar with those feelings in different stages of their lives should talk to each other."

Jason Shelton (2998), a veteran of the wars in Afghanistan and Iraq, says no one comes out of combat unchanged. "It’s part of who you are," he says. "You can’t erase it but you can minimize the impact it has on your life."

Boehm, Bailon, and Jason are in Sandia’s Wounded Warrior Career Development Program, which opens specific jobs at the Labs to military veterans injured in combat. They’re working with the Labs’ Military Support Committee (MSC) to establish the Veteran Combat Stress Support Group to give Sandia veterans and the surrounding Department of Defense community a friendly, non-judgmental place where emotions, feelings, and stories can be discussed.

"When the MSC was established a few years ago, one thing we wanted to do was address issues the military service members in our workforce might be faced with," says committee member Jody Thomas (2995).

One issue was combat stress. The MSC held an awareness day featuring a panel of Sandia veterans, staff from the US Department of Veterans Affairs, and community resource representatives. "We had some very emotional testimony. It was heart wrenching. That gave us the first clue," Jody says. "The need is there for a support group on Kirtland Air Force Base."

Earn veterans’ trust

Jason, Bailon, and Boehm helped launch the idea with support from city of Albuquerque veterans’ liaison Roger Newell and Tim Hale of the New Mexico Department of Veteran Services. "They’ve been running with it ever since," Jody says.

Jason says the group wants to earn the trust of the veteran community. "This is a different type of support group. It’s peer driven," he says. "There are no psychologists or doctors, no reporting, no attendance lists, no public knowledge, or emails. The meetings are in a neutral place. We make it as laid-back as possible. When people show up, if they want to talk, they can talk. If they want to sit and listen, they can do that, too."

Steve Becker (2144), a veteran of two combat tours in Afghanistan and one in Iraq, attended a meeting and had a long conversation with Jason. He hadn’t talked to anyone about his combat experiences in a year. "I’d forgotten the common things we shared," says Steve, who spent 30 years in the military. "Sometimes you feel you’re on your own and need to deal with it alone. I felt so much better when Jason and I talked, knowing there are others with the same perspective and feelings. Afterward, I was emotionally and physically drained — in a good way."

The group did not want to be branded with the post-traumatic stress disorder (PTSD) label. PTSD applies to a multitude of situations, Jason says. "Those four letters carry huge baggage. There is a stigma assigned to anybody who identifies as having PTSD," he says. "It doesn’t matter what you say or do. People will look at you and wonder if you’re going to freak out. It’s not right. That’s not me. PTSD can come from any number of upsetting situations, from a car accident to falling off a horse."  

Combat stress is specific to the experiences of military personnel who fight in wars. It affects different people different ways, Boehm says. "Some react right away. Some don’t realize they have it until later on," he says. "Everybody is different. Some go to groups. Some find their own way through. Some need activities to keep their mind off it."

Switching on and off

Jason says many soldiers face the demands of combat by pushing reality away. "It’s almost like you don’t feel anything — fear, horror, anger — right then because you have to do a job," he says. "If you get emotional and start thinking about what’s really going on, that can put you in worse trouble. It’s a stereotype, but you go into a mode of doing what you are trained to do. Switch emotions off and do what you need to do to keep our people safe and stop the bad guys."

Difficulties arise when the switch turns back on, he says. "I didn’t have an issue with combat stress until I got out of the military," he says. "I went back to a normal life, and all the stuff I had pushed to the back of my mind started catching up with me."

Boehm says combat is counterintuitive in every way. "The phrase I use is ‘crazy, insane, stupid.’ Any normal person would look at what you do in combat and say, ‘Are you nuts? You’re running into that? Why aren’t you running the other way?’" he says. "You lose objectivity. It has to be done, and you do it. When the adrenaline wears off, it sinks in."

Steve describes the experience as "pushing things to the back of the brain, storing it in drawers and file cabinets.

"While it’s happening you can’t deal with it right then and there. The brain protects you. But when there’s time outside of combat, the mind has to digest all those experiences."

Emotions that surface range from deep sadness at the loss of friends to revulsion to terror, all triggered by images, sounds, and smells. "Weird things will trigger a memory, something as innocent as going to a fireworks show," Jason says. "Those are the things you work on as you return to a civilian life, minimize the impact of those triggers in your life."

Promises kept

Jason, Boehm, and Bailon hope the Combat Stress Support Group will help. They set up a website and presence on Facebook and Twitter, and plan two meetings a month, the first and third Tuesdays at the Kirtland Air Force Base chapel, one featuring a theme and speaker to spur discussion.

Bailon says he got involved to keep a promise he made to the Marine Corps. "The Corps’ values are honor, courage, and commitment. Commitment doesn’t end after four years," Bailon says. "Seeing guys in action, doing really brave things, if I can help them in some way I’m continuing my commitment."

Steve says he also fulfilled a promise when he stepped forward. "I do this publicly because, at a bad point in my life, I made a commitment to God that if I could get back to normal, I would do what I could to help others," he says.

Boehm says his activism stems from the fact that many combat veterans commit suicide. "Live another day," he says. "That’s enough for me."

-- Nancy Salem

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Sandian Randy McKee named Professional of the Year by AISES

Randy McKee (1657) says he enjoys guiding students to advanced technical degrees. "It’s great to see young minds grow into mature scientists," he says. (Photo by Randy Montoya)

by Nancy Salem

Randy McKee’s passion is engineering excellence. "I’m a process guy," he says. "I always put that first in anything I do."

Close behind is a desire to help young people become professional engineers. Randy (1657) has spent countless hours mentoring in minority recruitment, graduate, and undergraduate programs at Sandia.  "Connecting back to the community through young people who want to get into science fields is important to me," he says.

In recognition of his technical excellence and community service, Randy was named 2014 Professional of the Year by the American Indian Science and Engineering Society (AISES). He is being honored at the organization’s national conference in Denver this week.

Since 1977, AISES has worked to increase American Indian and Alaska Native representation in science, technology, engineering, and math (STEM) fields as students, professionals, mentors, and leaders. The group supports and provides STEM educational services at all levels through graduate school. It also offers professional development, mentoring, networking, community service, and awards programs.

"It was very humbling to be recognized. I’m honored," says Randy, a member of the Cherokee Nation. "The competition is steep, and Sandia gave me the advantage. I’ve had great mentors and peers who have helped me along the way. Reaching up for help is as important as reaching back and giving help. I wouldn’t be here without guidance and mentorship from Keith Matzen (director of Nuclear Weapons Science & Technology Programs Center 1200) and John Porter (manager of Laser Operations & Engineering Dept. 1682)."

Robotics at Sandia and LANL

Randy’s family moved from Oklahoma to Albuquerque, where Randy earned a bachelor’s degree in mechanical engineering and a master’s in business administration from the University of New Mexico. He joined Sandia in 1991 as a contractor in the robotics center and was hired in 1995 as a principal member of Laboratory staff. He worked with Los Alamos National Laboratory in nuclear materials handling using robotics.

In 2000, Randy left Sandia to start the manufacturing division of Ktech Corp., a high-tech engineering firm in the Sandia Science & Technology Park. "Ktech is closely tied to Sandia, and I did contracting back into the Labs," Randy says.

He returned to Sandia in 2003 as a pulsed power manufacturing engineer and was promoted within six months to manager of Pulsed Power Engineering Dept. 1657. "Sandia offers lots of opportunities to succeed and be really challenged," Randy says. "It’s very difficult work with great rewards and significant impact on the weapons and energy sectors. The Z machine is a fantastic place to be with its significant engineering, manufacturing, and operations challenges. Engineering excellence is required with all we do here."

Randy says one-on-one mentoring can make the difference in a young person’s career. "I spend a lot of time really helping them find their way into advanced technical degrees," he says. "It’s great to see young minds grow into mature scientists over a period of three to five years. They come in as freshmen, doe-eyed and looking at a world of science they can’t comprehend. By the time they leave they can function in a technical environment."

Much of his effort has been directed to student interns from minority-focused colleges such as North Carolina A&T State University, working with recruiter Ken Holley (35553). "We create an environment at Sandia that keeps them focused on STEM and advanced degrees," Randy says. "Most of them go on to master’s degrees and PhDs. Some come back to Sandia and others go out and work at other places. They have been very successful, and that’s the important thing.

"I tell them that if they want a challenging and rewarding career, STEM will always provide that."

AISES is the only professional society established by and for American Indian and Alaska Natives that specifically emphasizes lifelong learning and education achievement using cultural aspects with STEM. More than 200 tribal nations are represented within AISES.

Randy says mentoring is critical to building staff in STEM fields. "We need new people coming in so we can sustain the national position Sandia holds," he says. "Young people are very important. Developing a pipeline of diverse talent is key to our success."

-- Nancy Salem

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