Boosting learning by putting theory into practice

For engineers, little can be more satisfying than turning your ideas into working objects you can see and touch. That's exactly what two groups from EPFL's chemistry and chemical engineering section recently got to experience. After six months of hard work on the DLL Molecular - Chemical Engineering program, the dozen or so Master's students got to unveil their creations: a self-heating food box and a self-cooling vaccine container.

It all started with the Chemical Engineering Product Design class in the fall semester. Interested students were given the option of signing up for the Chemical Engineering Lab & Project in the spring semester, giving them a chance to build a prototype of their initial blueprints. "The class has a dual purpose: working through the design process from start to finish, and rethinking everyday products to make them more sustainable," says Prof. Jeremy Luterbacher, who heads EPFL's Laboratory of Sustainable and Catalytic Processing (LPDC). The approach is about giving students the freedom to unleash their creativity, forge a sense of belonging to the School and their group, and develop cutting-edge engineering skills.

Students who signed up for the class chose from a predefined list of projects and started by developing a technical blueprint. The participants who showed the highest levels of motivation and interest were then selected to build a prototype. While EPFL has offered the desk-based class for many years, this was the first time students were given an opportunity to prototype their designs. The process inevitably threw up unexpected challenges but proved to be a valuable learning experience - one that produced compelling findings.

"The groups not only built something that works, but also performed a vast array of calculations and methods - it was an elegant exercise in chemical engineering," explains Luterbacher, who was impressed with how the students applied themselves. Their hard work is embodied in the prototypes they built, each of which has a special feature. The self-heating food box, made from 3D-printed resin, is stylishly designed and decorated, while the self-cooling vaccine container - dubbed Frigivax - has its own logo, carefully engraved on the lid.

A hotbed of ideas

The students were challenged to come up with designs that used neither microwaves nor electricity. The group behind the self-heating food box opted for a block filled with calcium oxyde - better known as slaked lime. It's used widely in the construction industry and reacts with water to form calcium hydroxyde and release heat. The students dropped the block into the box, added a generous dose of water, placed the food on top, and then closed the lid. After 10 minutes, the food was heated through and ready to eat, with tests showing that the temperature inside the box could reach as much as 100°C. What's more, the block's contents can be recycled and reused - a fact that further bolsters the project's environmental credentials.

Getting to this point wasn't easy, however. For the four students in the group, developing the food-heating system meant exercising their gray matter. "We spent at least two months doing nothing but brainstorming," says Jana Lukic. According to fellow student Lorenzo Mazzoli, the group "put around a hundred ideas on the table." Group member Ting-Wei Weng adds: "We considered every possible avenue, narrowing the field down to five or six realistic options." Maxime Brunisholz says the students "even explored crazy-sounding options like whacking the food to generate heat."

One challenge the students faced stemmed from the properties of calcium hydroxide, which can cause chemical burns when it comes into contact with skin. They ultimately bypassed this problem by adding citric acid.

The oral exam was a unique experience: I ended up tasting the end product

Hands-on building

The group behind the self-cooling vaccine container faced a dual challenge. In order to maintain a temperature of between 2°C and 10°C for several days on end, they had to come up with a way to both absorb heat and keep the box insulated.

For the first challenge, the students drew on a property that's common to most materials. Compounds in a solid state generate cold when they melt; those in a liquid state generate heat when they freeze. The group combed through research by NASA into the physical properties of cooling materials, looking for those that operated within their target temperature range. In the end, they opted for tetradecane, which they fashioned into ice packs to sit at the bottom of the container.

Tetradecane is a hydrocarbon that melts at around 6°C, keeping the temperature inside the box constant at around the same level. "If it's 40°C outside, the system will last twice as long as if it's 25°C, even with the same amount of tetradecane," says Raphaël Finizola. "We can customize the containers by adding more or less of the material as required."

To keep the box insulated, the group initially wrapped it in insulating foam. But that wasn't enough, so they also added vacuum insulation panels. "Combining tetradecane with the insulating materials produced the result we were looking for: the temperature inside the container rose from 2°C to 6°C in just four days," says Lise Boitard-Crépeau. "Self-cooling systems like these already existed, but ours is the first one that works for so long." Although the Frigivax container is designed to carry vaccines, it could also be used to transport food, or potentially organs. What's more, all the components can be recycled and reused.

"It was an interesting experience," says Simon Baillet. "As self-reliant engineers, we had to do everything ourselves: design the system and choose the materials - while keeping within our assigned budget. We really learned a lot in the process. And it was good to do some hands-on building in what's otherwise a very science-focused program."