A FloEFD simulation of two high school students’ water-saving automotive heat exchanger. (Image courtesy of Tucker Sawyer.)

Eighteen-year-old Tucker Sawyer of Hays County, TX, had a flash of inspiration while sitting in his high school chemistry class. Reflecting on the perennial issue of droughts in his home state, Sawyer realized that a lot of water is wasted as a by-product of combustion vehicles. If he could somehow collect and condense the water vapor released in combustion, he would be able to reclaim hundreds of millions of gallons of water per week.

“I thought, wait a minute, we're wasting hundreds of millions of gallons of water vapor all the time when we drive. Why don't we do anything with that? And it took off from there,” Sawyer recounted.

Sawyer’s idea was to affix a heat exchanger onto a vehicle’s exhaust system to collect the wasted water vapor. Little did he know, he was about to embark on a gruelling—but rewarding—engineering journey.

Curiosity in Chemistry

Sawyer isn’t the type of person to have an idea and leave it at that. Ever since his tenth-grade chemistry class, he’s had a curiosity for science and the drive to apply his knowledge. That year, he built a mini laboratory in his garage to put his chemistry lessons to use (on the fourth of July, for example, Sawyer and his friends made celebratory smoke bombs). Without even realizing it, Sawyer had kicked in the door to the world of engineering.

“I hadn't really heard of engineering. I heard the title, but I didn't know what it was,” he admitted. “Applying science is already something that I enjoyed doing, and when I took up this project it definitely opened up my eyes to what engineering really is.”

To make his heat exchanger a reality, Sawyer was about to learn one of the first lessons of engineering: having an idea is one thing, but executing it is another. He quickly realized that to have any shot at success, he would need help. He bounced his idea off his teacher and mentor Jad Jadeja, who put Sawyer in contact with a teammate: sixteen-year-old Alfredo Salazar. While Sawyer planned to concentrate on the mechanical design of the heat exchanger, Salazar would focus on data collection and analysis. Jason Massey, the students’ auto tech teacher, also came on board to advise the students on exhaust systems and safety.

From left to right: Alfredo Salazar, Tucker Sawyer, Jason Massey and Jad Jadeja.

Even with his crack team assembled, Sawyer knew he lacked the necessary skills and knowledge to tackle the project.

“If I approached this [project] like a professionally trained engineer, I would have needed lots of calculus, four years of a mechanical engineering degree, things I don't have yet,” he acknowledged. “I'd never had to deal with a budget, I'd never had to deal with designing an official prototype, putting together a bill of materials. So, this project really put me in that position.”

Despite his admitted unpreparedness, Sawyer was committed to finding an approach that would enable him to succeed. To do that, he was going to need to learn on the fly. He already had some familiarity with Siemens Solid Edge, which he had used for mechanical design since Grade 10. But he would need to extend his skillset to Siemens FloEFD, an integrated computational fluid dynamics (CFD) solver, for simulations of the heat exchanger.

“I had heard about computational fluid dynamics before. I had no idea what it was,” Sawyer said. “So, it was really fun learning how to use [FloEFD], learning what inputs do we put here, what output should we expect, what data is normal when it's running the program.”

Designing the Heat Exchanger

Before they could run any FloEFD simulations, and before they could even begin their design, Sawyer and Salazar first needed to collect data. With an old Ford F-150 pickup truck as a test subject, the pair used anemometers, thermal probes and a thermal camera to determine exactly how to achieve their specification of 40 percent water vapor collection.

A thermal camera image of an exhaust pipe. (Image courtesy of Tucker Sawyer.)

The measurements revealed to Sawyer and Salazar the parameters their heat exchanger needed to achieve. During the design phase, Sawyer would sketch out a prototype idea in Solid Edge, pass it off to Salazar to embody an assembly, and then the pair would simulate the design in FloEFD. The students had quickly grasped the CFD software and were readily using it to explore the design envelope.

A flow analysis of the first design in FloEFD. (Image courtesy of Tucker Sawyer.)

“Those [FloEFD] results would tell us that this needs to change or we need to split these pipes up even more or we need to make these longer,” Sawyer explained. “It would give us direction for what our prototype should be doing to satisfy the requirements.”

The Prototype Loop

Once Sawyer and Salazar had simulated the heat exchanger to their satisfaction, they could move on to the next step: building a prototype. As most engineers will be able to sympathize with, Sawyer and Salazar were constrained by their limited construction capabilities. Not only did this make building the prototype difficult, but it also forced the pair to pick materials that, in retrospect, were suboptimal.

“We chose to use copper and steel, and on their own they're not terrible, but when you try to put them together it is an absolute nightmare. We selected bad materials based on our prototyping capabilities,” Sawyer explained.

Unsurprisingly, the initial prototype failed.

“Our first prototype had a lot of construction and embodiment issues, just based on the prototyping capabilities we had and the materials we chose to use,” Sawyer said. “We can't CNC machine steel here, and copper and steel don't ever want to connect. We had to use a lot of power tools to cut the steel plates out. And that ended up causing a lot of inconsistencies with our design. There's only so much accuracy you can get with an angle grinder and a welding torch.”

The first prototype heat exchanger and its complete test setup. (Image courtesy of Tucker Sawyer.)

Sawyer and Salazar were forced back to the drawing board. They decided to swap out copper for aluminum, sacrificing a slight amount of thermal performance in exchange for stronger welds and easier machining.

Flow analysis of the second design with aluminum in place of copper. (Image courtesy of Tucker Sawyer.)

Today, the heat exchanger remains in the prototype loop. Sawyer lists four requirements he wants to meet before finalizing the design: make it watertight, recover 40 percent water vapor, add a storage tank, and add a particulate filter. He also envisions a future design that is integrated within a vehicle’s exhaust system. But for now, as Sawyer prepares to study nuclear physics at the University of Texas at Austin this fall, the project has taken a back seat.

“It's definitely something I plan to finish,” he said. “But I'm putting it on hold for a little bit. When I'm going to college, I really want to focus on just absorbing everything and honing in on certain interests. But it's definitely a project I intend to finish at some point in the next couple of years.”

A Book’s Worth of Lessons

Pursuing such an ambitious project gave Sawyer ample insight into what it takes to be an engineer. “I could write a book about the things that I learned,” he proclaimed.

He crystallized those lessons into three big takeaways. The first was the importance of setting a goal, and narrowing your scope to achieve a specific target. The second was the importance of proper coordination, with both his teammate Salazar and their advisers Jadeja and Massey. The third and biggest takeaway was one Sawyer says he’ll remember for life: the importance of mindset.

“I need to pick my mindset very carefully based on what I'm up against and the tools I have,” he said. Instead of chasing a deep understanding about every aspect of his project, Sawyer learned to recognize his shortcomings and work around them. Rather than starting from first principles, he looked to the heat exchanger industry to see the common techniques and use them as a starting point; instead of deriving analytical solutions for material properties, he could simply measure them. In other words, he learned to adopt a flexible—and practical—engineering mindset.

These are lessons which will serve Sawyer well, especially as he works towards his ultimate career goal.

“I want to own a scientific research and engineering company,” he said. “From where I stand right now, I see that as an opportunity that will give me the flexibility to attack different projects and try to solve different issues at the same time. But the path to get there—that’s still in the works.”

To learn more about FloEFD, visit the Siemens website.