Baffle and Reservoir Considerations
The expanded gas distal to the needle valve moves at a high speed. This jet of gas could agitate the collected liquid and propel it back out of the collecting reservoir. One needs a method to slow down the gas stream so the collected liquid is left undisturbed. The solution is a baffle.
The baffle can have a number of configurations, but the effect is the same. The baffle slows the throttle’s exiting gas to a speed that does not disturb the liquid below. A small copper stem attaches to the output end of the throttle. A small piece of a copper scrubbing sponge, obtained at a supermarket, covers the end of the stem. The fine mesh-work obstructs the stream and disperses it over the surface area of the sponge. The copper sponge also obtains a cold enough temperature to recollect and condense the gas in the bottle. The copper is thin, so its mass does significantly impede the cooling of the surrounding gas.
The bottle itself should have a narrow neck. This limits the area where cold gas can escape. Trapped gas has the opportunity to re-condense; however, if the gas can easily escape it does no good once it gets into the regeneration tubing. There are formulas for the ratio of the bottle length to the mouth orifice. One can find suitable stainless steel vacuum bottles on Ebay and Amazon. The one I used I found on the latter site. A 4L Dewar bottle has an ideal shape with a large body and small neck. Unfortunately, the compressor used for this project did not have a high enough flow output to handle such a large reservoir. I could have used the 4L Dewar, and it would have nicely held onto the condensed liquid, but the cool-down time would have been four times longer.
In summary, one needs a narrow-neck collecting vacuum bottle. The bottle needs to have a size compatible with the compressor’s output if one wishes to have a reasonable cool-down period. One needs to slow the expanding gas jet so it does not expel the collected liquid out of the bottle. A metal baffle slows the gas jet sufficiently to accomplish this purpose.