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Cooling Water Silicone Tubing Preferred Values.

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Proud Mary

Wed Jul 29 2009, 04:38PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The water inlet and outlet ports of a cooled anode are presented as ridged nipples 6mm diameter.

Given the very close proximity of the 40kVp anode contacts, what would be the best Inner Diameter of silicone tubing to form a snug, totally watertight couping when the tube is shrugged up over the 6mm diameter nipple and secured with Jubilee clips?

I am guessing 4mm.

Are sealants such as RTV used in this type of (hopefully!) high-reliability connection?

The heat to be pumped away is equivalent to 40W, so I am not expecting the water in the coolant reservoir or in the 'hot' exit tube to be heated to any great degree. Pumping speed is 200l/hr.

Mathias

Wed Jul 29 2009, 06:03PM

Registered Member #1381 Joined: Fri Mar 07 2008, 05:24PM
Location: Hungary
Posts: 74

I would say a silicone tube with 5mm inner diameter will do. No need for sealant.

Then again why not just use plain gardening hose with Jubilee clips :P (that way there wasn't any spilling problems with a Turbomolecular pump that has similar cooling ports)

Proud Mary

Wed Jul 29 2009, 07:12PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thanks, Mathias, I was thinking 4mm was too small - that 5mm would be better.

Are you sure the clips will be enough without sealant? If the inlet tube blows off and water sprays all over the hot glass, there will be irrecoverable damage!

I don't know how long the plastic/polymer cooling tubes immediately around the anode will take to degrade and lose their elasticity due to photon damage, (Is this 'Photo-Fries Rearrangement' or just having your picture taken serving Big Macs the day after flunking your physics exam!

) but I should much rather use silicone than garden hose, which would be a false economy compared with the cost of a new tube.

In any case, I have set my heart on a blue tube for the cold water, and red for the exhaust, so that I can see what is going on at a glance.

I am also looking for a rate-of-flow or flow-failure sensor/transducer, so that if the input cooling fails, a master relay will shut down the whole machine in the correct sequence. At present I know nothing about these, but am sure an in-line type must exist. (As a back up I shall put a thermal sensor in the reservoir, but this will not be fast enough to cause shut down if the pump fails or if there is a catastrophic loss of pressure.)

Any suggestions welcome.

Mathias

Wed Jul 29 2009, 09:54PM

Registered Member #1381 Joined: Fri Mar 07 2008, 05:24PM
Location: Hungary
Posts: 74

Well i dont think you need to worry about the tube blowing off. Just guessing
from what you let me know about the pump (200L/h) "googling" a bit turned up pumps that produce 5bar max.
So if this is true than in the worst possible scenario by having the tube blocked by the inlet. Having the effective area of 19.625mm^2 (D=5mm) the force acting upon would be 9,8125N at best.

couldn't find the friction coefficient for silicone tube materials but from my experience it kinda sticks to cooper and most metals (We are using a alot of CuSO4 resistors with in the marx generator at the lab)

So I would say don't worry about this sort of thing happening , but to be sure just secure the tubes beetween 2 ridges.

Proud Mary

Wed Jul 29 2009, 10:57PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thanks Mathias, much appreciated. I have gone ahead and ordered the beautiful, glossy, red and blue 5mm ID silicone hoses, and stainless steel jubilee clips.

I hadn't thought about it before, but I suppose I shall have to use deionized water to stop calcium 'fur' building up inside the anode head.

It builds up in my kitchen kettle like billy-oh - I live in chalk country - so it is just as well I thought of it now. I couldn't bear it if some stupid oversight should harm Iron Man. (50kVp, 25W, Fe target, 2mm x 2mm anode spot, focusing grid - From Russia With Love! )

aonomus

Wed Jul 29 2009, 11:32PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

If you are really afraid perhaps you could drill a small hole the size of the OD of the tubing into some acrylic and use it as a shield so that even if the tubing pops off, it hits the plastic before the glass.

Proud Mary

Wed Jul 29 2009, 11:56PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

aonomus wrote ...

If you are really afraid perhaps you could drill a small hole the size of the OD of the tubing into some acrylic and use it as a shield so that even if the tubing pops off, it hits the plastic before the glass.

I respect Mathias opinion in this, as he kindly worked it through for me, but I had thought of something along the lines you suggest, though having chosen high quality silicone hoses and good clips, I think I should be able to put my confidence in them. I feel I should be better to invest some time in strain relievers, so that an unexpected shock load on the hoses couldn't add to the water pressure and so pull them off.

Making 50kV stay just where you want it without half of it trying to sneak off somewhere can be hard enough as it is, so you will understand my caution about adding water to the recipe!

It's very exciting though, because I'm learning a lot that I never knew before.

aonomus

Thu Jul 30 2009, 12:39AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

I'm thinking that adding any fungicides or other things to the water to prevent bacterial/fungal/mould growth would make it more conductive, especially when dealing with 50kV. Some of those chemicals are metal based (eg: copper).

But it also then questions: open or closed loop? If its closed loop there shouldn't be any food for stuff to grow... just another thought.

Electroholic

Thu Jul 30 2009, 03:11AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

you can actually find hose clamps that small? I usually just use zip ties for tubings under 3/4".

Proud Mary

Thu Jul 30 2009, 03:47AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Electroholic wrote ...

you can actually find hose clamps that small? I usually just use zip ties for tubings under 3/4".

Yes, it's Jubilee Size 000 (range 8mm - 12mm)

My hose has ID 5mm, and walls 2.5mm, and must stretch over a 6mm nipple - i.e. it will have a diameter of 11mm when stretched onto the cooling spigot. Hence Size 000 is the correct size, allowing 1mm slack for easy installation.

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