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Nik

Sat Oct 17 2015, 01:15AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

Cool whiskers! I always check our old equipment in the plan for them but I have yet to find any.

Nik

Tue May 24 2016, 03:02AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

Double post but it has been a few months...

I saw some shock diamonds at work this week! Compressed air was being used to clean equipment while the air dryer was turned off, as the air left a rounded over (converging) nozzle the water vapor condensed and made these shock diamonds visible. I plan on making a small nozzle for home use so I can get some better photos.

klugesmith

Tue May 24 2016, 10:20PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Nik wrote ...
I saw some shock diamonds at work this week!

Nicely photographed, Nik. Did you add blue illumination?

When I became interested in shock diamonds without combustion, some 10 years ago, a co-worker told me of a similar experience. I learned that they form more often than not, in air jets driven by at least a few bar (enough for supersonic flow) from anything that passes for a nozzle but fails to "properly" expand the flow. For example, typical compressed-air blowguns and Dust-off cans.
The tiny, transparent diamonds can be visualized by schlieren or shadowgraph methods, e.g. shadows cast by sunlight, or sunlight reflected from a convex mirror, or an undiffused and unlensed LED or LD or flashlight bulb. Or just seeing distortion of a background scene that has high contrast and sharp edges.

This little video is a shadowgraph using flashlight bulb and un-lensed webcam sensor.

I'm looking forward to seeing water condensation diamond pictures from Nik. Diamonds visible from a safe distance without optical trickery.

Nik

Wed May 25 2016, 05:14AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

The blue is from my phone camera and the LED work light I was using.

Great photo and video, I never knew they were so common. I'll have to try out my canned air as well.

I'm going to start with a pipe cap and making 2 countersunk holes meet up. If that doesn't work I'll fill the cap with solder and "mill" a more conventional CD nozzle into the solder. I'm thinking of using a bare laser LED to cast a "schliren" shadow onto a screen or maybe onto a camera sensor if I cant get enough water vapor into my compressor (because that's not really the greatest thing for it).

klugesmith

Thu May 26 2016, 02:10AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Could a compressed air dryer be loaded up with enough water to become a humidifier?

CO2 gas from a bulk cylinder might make a different pattern than humid air. I bet the heat and volume changes from partial condensation, if there's time for that to happen, would make larger deviations from ideal-gas isentropic expansion.

They say great minds think alike. I started by making some CD nozzles from thin brass tubing on the order of 4 mm in diameter, plugged with solder, then drilled from both ends. At least one end was done with a small center drill, to get a 60 degree cone and untapered throat section. With inlet pressures on the order of 100 psi, they would have been "way" overexpanding. But I sort of dropped the ball after discovering that plain cylindrical nozzles make shock diamonds. I'm cleaning my workshop & will watch out for the little converging-diverging ones.

There's a ton of literature about over-, ideal, and under-expanded supersonic flows, because many real propulsion nozzles have to work in a wide range of atmospheric pressures.

[soapbox] Many people don't know the difference between schlieren photographs and shadowgraphs, which superficially look about the same. For any given very-slightly-refracting transparent object, the resulting image bright and dark areas are very different. In the schlieren case, they also depend on the orientation of the knife edge. Prof. Andrew Davidhazy tells it right:

The word schlieren is an ordinary noun (meaning streaks), not the name of some inventor. So in English it should not be capitalized, except in titles or beginnings of sentences. [/soapbox]

Nik

Thu May 26 2016, 08:49PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

"Great minds think alike" indeed, you just described my original plan exactly, I was going to make 2 wedges to "drill" tapers into a plug of solder. I ended up finding 1/4" threaded steel pipe plugs and drilling into those but the results are about what I was looking for.

To make it more visible I was thinking of using a venturi pick up but for the sake of cheapness I put a pipe T before the nozzle with a short length of capped pipe, I'll fill the capped pipe with water and tip it just enough to get some vapour in the stream. I did wonder if I could feed extra humid air into my compressor but that's really not the best of it :/

Thanks for the link, I did some Googling prior to this but didn't see that page. Interesting about schlieren, I must have Googled it 100 times before and never noticed that it wasn't a proper noun. If it's has anything to do with optics and has a German sounding name I just assumed it was the name of the guy who discovered it >_<

Weston

Thu Jun 09 2016, 01:19PM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

Visited the electronics market in Shenzhen yesterday and I found the (a?) IGBT booth! Sadly I did not have time to see their full selection / ask about prices.

1465478365 1316 FT6000 Img 20160608 123752

klugesmith

Sat Oct 22 2016, 10:32AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

At last, a reasonably successful picture of the glow from my first spinthariscope.

I got some translucent plastic sheets with ZnS(Ag) fluorescent coating on one side.

Took a smoke detector board & removed the upper ionization chamber electrode. That lets us see the alpha particle source -- less than 1 microcurie of americium-232. Re-covered the source with one of the fluorescent screens.

Turned off the lights & waited for my eyes to become dark-adapted. After about 5 minutes, I began to see a very faint, fuzzy, luminous spot on the screen. On close examination with a small convex lens, the spot was all sparkly! Imagine how Prof. Crookes felt, as the first human to see the phenomenon.

Next challenge was to get a picture of it. Here with lights on:

and with lights off, except for a flashlight directed away from the subject for a few seconds:

Camera details to follow. Those are screen capture snips from original jpg's -- no image manipulation.

Hazmatt_(The Underdog)

Fri Nov 04 2016, 08:51PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

My Fluke meters are showing their age, they are hand-me-downs I received as a result of another engineer passing away, and they have
been useful, but it is time for an upgrade.

I am looking to upgrade the power supplies too, but that is something in-process. For now the meters are all I can afford.

SAD BENCH

HAPPY BENCH

Nik

Tue Dec 06 2016, 11:39PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

First hover from my Paul Ion Trap. I have to find a reliable way to get particles in without getting my fingers too close. The rails are at ~3kv.

Animated gif:

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