In the past week or so, I have had several people walk into my office and ask a question that has been popular for as long as I can remember - - "What is the ratio of cross section to depth that defines the cleanability of a blind hole?" As is so often the case in cleaning world (and others too), the simple answer is, "It all depends!" I used to think that there must be a number that defines the problem and have probably told a couple of thousand people that it's in the 1:4 to 1:6 range (that would be cross section vs. depth). And then, silly me, I started thinking more about it and came to conclusion that there is a lot more to it! For the purpose of our discussion here, let's define a "blind hole" as any cavity that has only one open end. Holes drilled into solid blocks and closed-end glass tubes will serve as good examples for our purposes. Secondly, let's assume that in order to effectively clean inside the confined space of a blind hole there must be a means to introduce and remove air and liquid(s) from that confined space. For an "exchange" to take place, one media must be entering the blind hole through the single available access simultaneously with another escaping through the same access. Buoyancy, fluid dynamics and surface tension all come into play. In most cases, blind holes are filled with air as they enter the cleaning process. The initial challenge is to remove the air from within the blind hole and replace it with liquid as the first step in cleaning. It's not rocket science that if the open end of the blind hole is facing down, the buoyancy of the air will prevent its escape from the hole much like an inverted drinking glass or a diving bell. This can be easily demonstrated using a test tube suspended in water.
- FJF -