Summary This device allows you to make functional heat exchangers by welding together layers of plastic garbage bags! This may be counter intuitive, but our latest theoretical and early experimental results show that this type of heat exchanger can be very efficient as well as absurdly cheap. A project by the [Michigan Tech's Open Sustainability Technology Research Group]( http://www.mse.mtu.edu/MOST). For similar see the Open-Source Lab How to Build Your Own Hardware and Reduce Research Costs Instructions First a special thanks to Peter for the providing the designs for his laser cutter. http://www.thingiverse.com/thing:11653 Please start there for understanding the basics of the mechanical setup. The variations we made included the following: We mounted the whole system in a double drawer file cabinet that we hollowed out, put on a safety switch for the laser, and new drawers with magnetic closers. A hole was drilled through the top for the wires and the fiber laser to pass through. We extended the legs past a square bottom to allow for the cabinet rails to remain intact as seen in the photo. We added a second substrate layer that slides in consisting of a metal (Al) substrate and a lower iron glass cover plate (again see details in photo). We added new 3-D printed parts to couple a fiber laser to the rig. In our case it is hanging down just over the glass with a lens positioned so that the focal point is just under the glass. For full instructions go here: http://www.appropedia.org/Open-source_laser_system_for_polymeric_welding For full operations go here: http://www.appropedia.org/Laser_welding_protocol:_MOST For firmware, open-source software, and a template go here: https://sourceforge.net/projects/lasersystemforp/ If you are interested in what we are using it for (polymer-based expanded microchannel heat exchangers) check out our latest paper here: http://www.appropedia.org/Expanded_microchannel_heat_exchanger Open access to the full text: http://mtu.academia.edu/JoshuaPearce/Papers/1671667/Expanded_microchannel_heat_exchanger_design_fabrication_and_preliminary_experimental_test These heat exchangers can be used for all kinds of energy efficiency applications including our work to make solar powered water pasteurization systems. If we can get a system that works it will represent an extremely inexpensive method of pasteurizing water at the family or household scale. Thanks to Rodrigo, Nick, Thad and Ravi for work on the system.