3D printing & Heat Exchangers

Author: Russell Muren

Although the summer was packed with business development efforts associated with the Cleantech Open, over in the Rebound labs we did indeed find time to get some tech development done! I thought it would be a great time to give an update and share some results.

A significant chunk of the summer and fall were spent developing a piece of process equipment called the INCIF (extra credit: try to figure out what that stands for). The INCIF is a special heat exchanger that increases the ice efficiency of the cycle. The tricky part about the INCIF is its very large surface area and geometry makes it difficult to manufacture. We know this because we built the first one by hand with nothing more then a Dremel, a blowtorch, and an excess of expletives.

Once manufacturing was completed we thought we were on easy street but, as always, unavoidable complications caused a delay. The membrane that completed the prototype cycle was lost by the shipper for a month and eventually arrived, internally damaged beyond repair. Dark days. Fortunately we had plenty of other work to keep us busy including thinking through the next generation INCIF design. Using traditional manufacturing techniques, the INCIF is extremely expensive because it has thousands of parts, an untenable geometry, and many manufacturing steps. We needed a better manufacturing method.

Additive manufacturing, also called 3D printing, is a way to make very complicated plastic parts in one printing step with only one additionally cleaning step. A 3D printed INCIF could be manufactured in 2 steps instead of thousands (and at a 30X reduction in material cost to boot).

If you know anything about heat exchangers right now you are thinking, “wait, a plastic heat exchanger? That isn’t right.” And in most cases you would be correct, but the INCIF is special. It isn’t your every day heat exchanger and we have solved literally millions of equations that tell us that metal or plastic, the performance will be the same.

The question was not whether a plastic INCIF would perform, but if it could be made in the first place. To help us answer this question we teamed up with Dr. Shanon Reckinger and her student Yenny Rua at Fairfield University. Over the summer and fall we printed roughly 50 heat exchanger coupons and tested them under flow conditions similar to and more aggressive than the INCIF. The results were fairly startling: we were able to print heat exchanger walls down to 0.032mm (about 1/7th the thickness of a sheet of paper) and test them under flow with no leaks. This was more than 10X thinner than our goal of 0.5mm.

Building on this work, we are continuing our project with Dr. Reckinger to print out scaled, but fully integrated INCIF designs. At the same time, back in our own labs, we’re finally wrapping up testing on the original copper INCIF. As always, testing has exposed the errors in our initial design, but it has also demonstrated the INCIF’s overall utility. Trials with the INCIF have roughly twice the ice efficiency than trials without.

Without a doubt there is still much work to be done. And with SunChill spinning up, the workload will only increase from here. But in the Rebound labs we will keep chipping away on the technical problems faced by both IcePoint and SunChill. This initial validation of the INCIF concept is certainly a step in the right direction.