Welcome to the New Thermo and Fluids Lab. Please take your seat.

It is the first day of practicum in the newly renovated Thermodynamics and Fluid Mechanics laboratory, and the eager sophomores are ready to tackle their first experiment. Quickly, they learn their first lesson: the world is not as perfect as it seems in textbooks.   

“When you step out into the real world, a small mistake can either lead to a surprising new discovery or cause you to completely rethink your steps,” says Marcus Hultmark, Assistant Professor of Mechanical & Aerospace Engineering (MAE). “The students begin to appreciate that there is uncertainty in everything they do. This troubleshooting is often the biggest challenge for them, but it is through that journey in which we see an engineering mind develop.”

Take a seat for MAE 221/224—an integrated science and engineering laboratory that serves as a gateway course to Princeton’s Department of Mechanical and Aerospace Engineering. The place where the equations they have neatly solved in their freshman physics and chemistry notebooks suddenly have to hold up against the realities of the physical world. From turbulent flows in pipelines and aerodynamic forces pushing up on an airplane wing, to converting chemical and thermal energy into mechanical work, such as an automobile or jet engine, real-world engineering typically comes with a great deal of uncertainty that needs to be well understood. 

“The course is like a tasting menu for mechanical engineering,” explains Professor Hultmark. “The students begin to test all the concepts they have learned about in other classes and apply them to real world problems—at the same time, they explore basic electronics and sensors commonly used in laboratories. For many, it is the first real glimpse of what it might feel like to actually work in the engineering field.”

Professor Hultmark and his colleague Dan Steingart, PhD, Assistant Professor of MAE, first began talking about the project five years ago. They had a vision for a modern design-your-own-experiment laboratory that would give students more ownership over their experience.

“Traditionally, one of the main challenges in integrating labs with lectures is that only a few students can conduct large experiments simultaneously so the concepts that are discussed in the classroom are out of order for some,” says Professor Hultmark. “Our new design creates a synergy between the lecture hall and the laboratory bench.”  

The renovated space is set up to mirror the accompanying lectures with an authentic experiment that students build themselves in the lab. Since engineering challenges typically involve multiple disciplines, the facility combines fluid mechanics and thermodynamics into one space. Located on the second floor of the Engineering Quadrangle, Professors Hultmark and Steingart, and lab instructor Michael Vocaturo, designed the new lab to have an open floor plan that encourages this multidisciplinary collaboration. The lab also houses junior and senior thesis and independent work.

For example, in fluid mechanics, say the students are studying a boundary layer—an important feature of flows close to solid objects. First, they assemble the instruments they need to use at their lab benches. This might include building and calibrating a velocimeter or programing a linear actuator. Next, they use their setups in one of the wind tunnels in the lab to observe and investigate the concept. In thermodynamics, the four laws are investigated using experiments such as a bomb calorimeter to find the energy content of foods and fuels, a steam pressure vessel to find the heat of vaporization of water, a fuel cell to demonstrate direct energy conversion, and a heat pump refrigerator to explore a typical thermodynamic cycle.

Since the students assemble some of these experiments there is some amount of trial and error involved. In others, the apparatuses already exist and the student must manipulate its parameters, measure quantities, and analyze the system. In either case students realize that unless they are fastidious about the data they take they may be forced to make unreasonable assumptions, and if you make unreasonable assumptions you will come up with unreasonable results, says Vocaturo. In the end, they will know more about both the system and the flow itself.

“It is sort of like an Ikea catalog,” explains Hultmark. “All the parts are on their desk and have a purpose, but the way they fit together might not be immediately obvious. We want students to put them together in different ways, make mistakes, retrace their steps, and maybe even break a few inexpensive things in the process.”

In one of the experiments, for example, students use a wind tunnel to study the forces of drag and lift on large objects. How does the shape of an airfoil affect its lift? What happens to the flow around a cylinder when it is placed in a wind tunnel? By using wireless micro-controllers, the students can communicate with one piece of equipment at the same time and analyze their results on several different computers.

“From day one, I start asking my students the questions that they should be asking themselves. If you do that enough times, you start to see them think critically and begin to ask the right questions on their own,” says Michael Vocaturo, head of the laboratory. “Asking students thought-provoking questions leads them to the correct answer rather than giving it away”.

Each semester culminates in a project that incorporates concepts they have studied in the previous labs. In the spring semester, for example, the students compete in small groups to see who can design the most efficient wind turbine which they manufacture using 3D printers.

“When students come in with completely crazy designs, I think to myself – ‘Yes! That is exactly what they should do!’ Sometimes they work, sometimes they do not, and their predictions are not necessarily what they end up seeing—but that is the nature of fluid mechanics and thermodynamics,” says Hultmark.

“By the end of the year we see the students develop an appreciation for this uncertainty. They learn when they can trust their results and when it is better not to. It is fun, they make a bit of a mess, and suddenly it is not enough to just read about engineering—instead, they are itching to test it.”

~Carolyn Sayre