Thing I made: 3-D Printed Liquid Piston Stirling Engine Demonstrator v2
The Internet Archive has a 40 year-old book, Liquid piston Stirling engines by C.D. West. It's a lovely book and buried in it is a design for a small Stirling engine demonstrator made from Acrylic and powered by a wirewound resistor.
Today I successfully reproduced this design in a 3D-printed model. It's not fantastic, as I managed to gloop adhesive everywhere when installing the cover, but it works!
The cover is acrylic secured to the base with Liquid Nails clear-seal all purpose sealant. The model is printed in Hatchbox PETG and the resistor is a TT ELECTRONICS / WELWYN WHS3-22RJA1 22 ohm 3W from Newark.com (https://www.newark.com/tt-electronics-welwyn/whs3-22rja1/res-wirewound-22r-5-3w-axial/dp/48W3730) It maintained steady-state operation for ~ 5 minutes at an input power of ~17.7 v and .79 amps. The power draw varied as I played with the inputs, and the exact values were not recorded over time.
This is my second attempt at reproducing this. I didn't publish any details of the first attempt. It used the same geometry and components with two significant changes. This first attempt used white silicone caulk. The other difference was where the leads for the resistor penetrated the case. In that design the leads exited very close to the resistor and the seal failed when the heat on the leads caused the sealant to fail. In v2 I relocated the leads as far down into the working fluid (water) as possible to cool them before penetrating the plastic.
Ideas for future work:
I want to refactor the cover mount. Adhering it with sealant is expeditious, but not workable. With my hand tremors it's impossible to apply effectively without obscuring the cover. I'd like to try a TPU gasket and mechanical fasteners instead.
The resistor is operating well above (~400%) of its rated power capacity. It survives because its liquid cooled, but it will self-destruct if the water boils away or I get the water levels wrong. Need better component selection.
I need a better solution for feeding power to the resistor/heater block to prevent self-destructing when overheated.
The model has sharp corners that introduce turbulence. A "rounder" design should waste less energy.
A proper Stirling engine should have a regenerator.
The fluid level in the working chamber and output column should be made adjustable. Currently it requires tipping and shaking the model, and that's not conducive to experimentation.
I need to think about how to instrument this for experiments. The other experiments I've seen focus on input power and the frequency and magnitude of the change in the output column.
Use a tripod. :|
Mr. West, if you happen to read this, thank you very much for writing this book. I'm just a couple of hours west of you and I'd love to drive over and meet you if you're accepting visitors. My email is firstname.lastname@example.org. Thanks!
The model is on my GitHub, but I don't recommend printing it. This is very much a work in progress.
MakerProjects/CD West Liquid Piston Stirling Engine/20230525 v2 at main · ElizabethGreene/MakerProjects · GitHub