Thermal water barrier
This contraption was used in photochemistry work to block thermal radiation from high-intensity light sources by passing a slow water current through it.
The .STL files provided will fit standard size microscope slides on both faces (two each for the large one) although the size can be edited in the .SCAD source code.
It goes without saying that the glass slides should be attached securely (and checked for leaks) to the device before placing it over or near electrically powered light sources. High infill values (or solid infill) are probably a good idea to minimize any leaks through pores or gaps in the plastic walls.
The initial design called for single microscope slides to be compressed between two frames on both faces of the device (as seen in the .STL of the small/shallow device). I wasn't able to find a correctly sized O-ring to fit the device so ended up just gluing the glass slides to both sides. If you find a rubber seal of the correct size, a groove for this is part of the design (and its size can be modified slightly in the source code).