Blind Holes – Surprises?

One thing I should have learned over the years is to not speculate on the outcome of experimentation.  In the previous blog, I advanced some theories on how liquid and air exchange might be enhanced in cleaning blind holes by using a carefully directed jet of water.  Then it was off the fish tank to verify what I thought was right was really right.  Oh well!  I got some surprises.

First, I used a 1/8″ I.D. by 1″ long glass tube with one end fused shut to establish a base line.  Previous videos had shown that without some induced mechanical interaction, there would not be an exchange of liquid within the 1″ long tube.  Using a stream of water directed at the open end of the tube, achieving an exchange of liquid was quite easy as shown in the video below.

 Water Stream Directed at Short Tube

 So far, so good!  Next I tried a much longer tube.  In this case, the stream of water was about 3/8″ in diameter so when water source and the tube were lined up, there was pretty much an even distribution of pressure on the mouth of the glass tube.  Here’s what that looked like.

Water Stream Directed at Longer Tube

Again, pretty much what I expected.  Although I tried, I could not see a result of offsetting the water stream as suggested in the preceding blog.

Next, I used a needle tip to direct the water stream into the longer tube.  At first, with the water stream directed at the end of the tube.  When that didn’t show much result, I inserted the needle tip about 1″ into the tube.  See that result below.

Needle Directed at and Inserted In the Longer Tube

Surprise!  Even with the needle snuggled against the side of the tube (to create an inward and outward flow) the exchange of liquid only penetrated about 2″ beyond the end of the needle tip.  Time didn’t appear to be an issue – even after several minutes, the penetration progressed no further.

Now it was time to move on to a larger “blind hole,” this time simulated by a test tube with a much larger internal diameter than the tubes above but with approximately the same cross section to depth ratio.  To achieve maximum effect, this test was conducted with the needle which, I felt, would surely create turbulation and an exchange of liquids within the tube.  The video below shows the result.

Test Tube with Needle Stream

 This result was surprising too!  Even with the needle, the exchange was slow and, even after quite a long exposure, not complete.  Compare the result using a submerged spray to that if the tube is filled and drained as shown in this final video clip.

Test Tube Fill and Drain

In summary, this and the preceding blog demonstrate the difficulty of creating the exchange of liquid necessary to effectively displace air from a blind hole and then provide cleaning.  The challenge of removing liquid remaining in the hole from the cleaning is, in fact, similar.  Upcoming blogs will discuss blind holes and how they might be cleaned (and dried) in more detail.

–  FJF  –