A reusable saturated salt humidifier (vis-a-vis Boveda) utilizing the humidification properties of a saturated salt solution in equilibrium.
** Important update 7/11/2019 ** - I believe I traced down the source of the leaking at what I had assumed was the bottle cap. Upon closer inspection I determined that the leak was coming from the very base of the thread where it attaches to the main body. To combat potential leaks in this area I've reinforced this area with a raised boss. While this change reduces the thread capacity, it still leaves plenty of room for a standard bottle cap.
However if absolute water tightness is required, I do advise the use of a 28mm "sealed for your protection" bottle-cap seals (as found on vitamin bottles). They should be pressed into the bottle cap first, then tightened where it will activate the adhesive. They are slightly oversized for the purpose, but this has been the best size to ensure a good seal.
After some long-term testing I have 2 points of caution:
please test each of your prints for at least a week, preferably 2. Out of the 13 test units I printed 4 of them developed slow to major leaks. 3 of them were non-obvious and would've passed a visual inspection, and the fourth a result of poor layer adhesion, while more continue to fail in long-term testing. While by its very nature non-toxic, you wouldn't want to spoil an expensive cigar(s) w/salt!
My poor results w/respect to water-tightness appears to be a result of under-extrusion and, perhaps, having left coasting on as a contributing factor. As always and particularly here YMMV, as I'm still relatively new to 3D printing and often run into my share of process-related issues.
I ultimately was able to salvage my leaking prints by coating the interior w/a slurry made from an off-the-shelf ABS fitting dissolved in acetone. You will not need an entire fitting - just a small piece from one. Swirl it around the interior of the print ensuring coverage over all walls, and let fully dry overnight. It'll dry to a hard ABS coating which in my testing has so-far proven to be watertight.
- even if you believe you do not need a water-tight seal at the cap, I'd still recommend the precautionary use of a bottle cap seal. 3 out of my 13 test units developed "salt-creep" during long-term testing, where salt climbs up the vessel and if unrestrained outside of it. This is a known and published phenomenon noticed by conservators who have used similar saturated salt solutions for humidification.
Features:
- maintains 75% RH across a wide range of temperatures
- uses only salt and water
- uses a standard bottle cap to service
- deep well below cap allows easy inspection for undissolved salt
- easy to gauge maximum water fill - proper water fill level maximizes surface area for responsive RH regulation
- Gore Tex fabric frame elevated to keep above surface of salt solution
- tested to be watertight when left upside-down overnight (keeping right side up recommended)
- designed to be printed with internal support that's easy to remove
To use, one only needs:
- water, approx. 30 ml
- table salt, minimum 12 grams (full saturation reached above 36% of the water weight in salt)
- a small patch of Gore Tex fabric (<3 sq. in. required; typically sells for $10/sq. yd. via online sources)
- a standard bottle cap
- Super Glue
To assemble:
- carefully cut a small patch of Gore Tex fabric to fit the bottom surface of the fitted frame/cap
- place a thin line of Super Glue on one end of frame and align with one end of the Gore Tex fabric, pressing in place
- run another thin line on the remaining three sides of frame and press the rest of the Gore Tex fabric - the frame/Gore Tex should be glued only along its perimeter; doing otherwise will reduce its effectiveness
- attach cover to main body - it should be a press fit, but one can alternatively super glue it as well
- please test for water tightness with cap & Gore Tex retention frame, though not absolutely necessary as these will both remain above the waterline if kept reasonably level
To use:
- remove cap and fill w/water to bottom rim of fill hole (exception: use less for humid climates)
- add salt through fill hole and totally dissolve; repeat until salt no longer can be dissolved. (gently tilt the fill hole down to settle any undissolved salt into the deep well directly below the fill hole)
- add additional salt to provide "a backup charge"; the added salt should settle to the bottom and be visible through the fill hole - for proper operation always maintain some amount of undissolved salt
- replace cap
To maintain:
- simply open cap and ensure there is both
- sufficient water (though no higher than the bottom rim of fill hole)
- undissolved salt in the salt well (the deep well directly below the cap)
- add either as needed to maintain water level and presence of undissolved salt, though other than loss through spillage you shouldn't need to add any additional salt beyond the initial charge when first setting up (unless you live in a humid climate where you'll also be removing water as the level reaches the fill line)
Table of RH w/various saturated salt solutions: - https://bio.groups.et.byu.net/EquilibriumSS.phtml
Bottle thread was based upon Vijit's 25_bolt.stl https://www.thingiverse.com/thing:3533967
cgfan
