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Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Mates wrote ...
Even if I would be irradiating only one dish (which is a bit impractical due the variations between doses) the size of the "middle" dish is 10cm in diameter. I need 100-90% photon intensity distribution within this area. It practically means to keep the x-ray tube at least 40cm (rather more) away.
I remember that some time ago in my old lab we wanted to buy a new X-ray device which would be table based construction (all standing on the table). The irradiation surface was just for one 10cm dish which was rotating. The irradiation time for 10Gy was over 20minutes! The time was unacceptable because of the type of research we are doing (studies on the early response to DNA damage) so we had to give up that product. There is no way for me how to avoid the necessity for a big generator - unfortunately.
Ok that more clearly explains the parameters of the experiment!
Well then you have a fun job, pumping all that oil out then! I`m pretty sure that when you come to refill it, you will have to attach a vacuum pump to it, to outgas the oil,and ensure that it soaks into the windings displacing any air. Wiring some form of control panel shouldnt be too difficult at all. Cooling the tube could be a PITA. Are they rotating anode tubes? Do you have a photo?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Even if I would be irradiating only one dish (which is a bit impractical due the variations between doses) the size of the "middle" dish is 10cm in diameter. I need 100-90% photon intensity distribution within this area. It practically means to keep the x-ray tube at least 40cm (rather more) away
I wonder if you could have some sort of arrangement for moving the sample during irradiation. This could average the exposure area to allow you to tolerate a less uniform beam, which then might let you cut down the distance and so increase the flux density. I saw this type of arrangement in a food gamma irradiator, which swapped the food between the shelves of a carosel to even out the dose, it might be possible to extend the principle to your dishes? It might be a very cheap way to halve your exposure time?
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
plazmatron wrote ...
I`m pretty sure that when you come to refill it, you will have to attach a vacuum pump to it, to outgas the oil,and ensure that it soaks into the windings displacing any air. Wiring some form of control panel shouldnt be too difficult at all. Cooling the tube could be a PITA. Are they rotating anode tubes? Do you have a photo?
Leslie
I'll post other pictures of all the components tomorrow. The cooling is not a problem - the tubes are water cooled and I have the original holder for the tubes which has standard hose connections.
Regarding the oil refilling - that's a good point... There is no chance to apply vacuum on that box... I pumped 1/3 of the oil out at the moment and the transformers are still under oil. Maybe I could put the whole device aslope now and suck the oil from the lowest bottom corner to get the water out? What do you think? Some persisting water leftovers could be much smaller problem than air in the windings - I guess
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
[quote]
wrote ...
Regarding the oil refilling - that's a good point... There is no chance to apply vacuum on that box... I pumped 1/3 of the oil out at the moment and the transformers are still under oil. Maybe I could put the whole device aslope now and suck the oil from the lowest bottom corner to get the water out? What do you think? Some persisting water leftovers could be much smaller problem than air in the windings - I guess
Yes I would be inclined to tip the transformer, to suck out the remaining water.
If you want to get shut of any drops, and there will inevitably be some left in there, you could try this:
And yes, that would probably be much less laborious than emptying, refilling etc. but..........
There is always the possibility that some water may have penetrated the windings, and thats a worry.
From the look of the transformer, making a small panel with a barb in it for vacuum connection, shouldnt be too difficult. We arent talking extreme negative pressures, maybe pump down to 100mbar or so. If you have a cold trap between the pump and the tx,if there is any water left it, should show up in there.
The other possibility is heating the oil itself, which should drive out any remaining moisture. The two options for that are direct heating, with some form of submersible heater perhaps, or just run the tx at a low input voltage for a few days?
Thanks for your help guys... Btw: Does anyone know what's inside the water absorbing sock? Silkagel, NaOH or something simillar? I can get any type of chemicals relatively easily...
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
plazmatron wrote ...
The other possibility is heating the oil itself, which should drive out any remaining moisture. The two options for that are direct heating, with some form of submersible heater perhaps, or just run the tx at a low input voltage for a few days?
Short the output and drive the primary through a ballast (capacitive is OK), possibly at the rated VA, to heat it up.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Mates wrote ...
Thanks for your help guys... Btw: Does anyone know what's inside the water absorbing sock? Silkagel, NaOH or something simillar? I can get any type of chemicals relatively easily...
Probably Silica Gel and CaCl2. NaOH is probably not used since it would likely react with the oil.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Drying of transformer insulation using zeolite Fofana, I.; Wasserberg, V.; Borsi, H.; Gockenbach, E. Electrical Insulation Magazine, IEEE Volume 20, Issue 1, Jan.-Feb. 2004 Page(s): 20 - 30 Summary: Power and distribution transformers are some of the most important components in the power network. The presence of moisture in a transformer deteriorates the transformer insulation by decreasing both the electrical and mechanical strength of the solid insulation. It is of great importance to pay attention to the moisture content of composite insulation systems in order to maintain low dielectric loss, high dielectric breakdown strength and low rates of degradation of the insulating system in HV equipment. In this paper, an approach to the said problem is presented. With the application of a synthetic hygroscopic mineral (molecular sieve zeolites) - a revolutionary, environment friendly, multipurpose mineral - a continuous drying process of the transformer oil during operation without the need for service interruption is achieved. A study of the effects of zeolite on the electrical and dielectric behaviour of the insulating liquid of the transformer is included in this paper.
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Industrial X-ray machine - will it work?
