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Author Topic: OAV Question  (Read 763 times)

Offline Dabbler

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OAV Question
« on: November 24, 2017, 01:38:24 pm »
I have noticed lately that when I do an OAV treatment (homemade glow plug based unit) the OA forms a ?crust? not in contact with the heating pan. As  result, I need to remove the heating pan and knock the ?crust? back into the pan to finish vaporizing. OA obtained is about 2 years old.

Anyone else have this happen?
What is the cause (moisture in OA?)?
How can I prevent this?



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Offline little john

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Re: OAV Question
« Reply #1 on: November 25, 2017, 05:42:11 am »
Hi Dabbler

When I first started experimenting with the vapourisation of Oxalic Acid, crust-formation frequently occurred when trialling a small cross-sectional area pan, but not when using a larger pan.  I concluded that crust-formation was being caused by the material 'bubbling', such that the 'bubble skin' became suspended above the heat of the pan by it being attached and thus supported by the slightly cooler sides.  With the larger area pan, the sides were sufficiently far apart to not support a 'bubble' in this way, so that any formed simply collapsed back down to be further heated and thus vapourised.

With an existing applicator - assuming that it's satisfactory in every other way - what I would suggest is that you weigh the crust which is formed and left behind.  I'm fairly confident that this will be a small amount.  If so, then simply increase the first dose by that amount, then add the normal 'dose' (I use one gram per brood box) to each subsequent application, along with any crust remaining from the previous treatment.   Then, at the end of the day, simply dispose of that last remaining crust.

'best, LJ
« Last Edit: November 25, 2017, 10:13:40 am by little john »
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Offline Dabbler

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Re: OAV Question
« Reply #2 on: November 25, 2017, 10:36:55 am »
Hi Dabbler

When I first started experimenting with the vapourisation of Oxalic Acid, crust-formation frequently occurred when trialling a small cross-sectional area pan, but not when using a larger pan.  I concluded that crust-formation was being caused by the material 'bubbling', such that the 'bubble skin' became suspended above the heat of the pan by it being attached and thus supported by the slightly cooler sides.  With the larger area pan, the sides were sufficiently far apart to not support a 'bubble' in this way, so that any formed simply collapsed back down to be further heated and thus vapourised.

With an existing applicator - assuming that it's satisfactory in every other way - what I would suggest is that you weigh the crust which is formed and left behind.  I'm fairly confident that this will be a small amount.  If so, then simply increase the first dose by that amount, then add the normal 'dose' (I use one gram per brood box) to each subsequent application, along with any crust remaining from the previous treatment.   Then, at the end of the day, simply dispose of that last remaining crust.

'best, LJ
LJ
Thanks for your thoughts. The weigh residue and add extra is a good pragmatic approach.

The engineeer in me was intrigued by the route cause so I will investigate your pan area comments. I do not remember the bubble skin (sounds better than crust) forming when I first started using the unit. I was wondering if the OA might be bubbling more now do to absorbing humidity.
I need to experiment.
Thanks again


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Experience is a hard teacher because she gives the tests first, the lessons afterwards .
-Vernon Sanders Law