[Dsg-ft] Discussion about thermal insulation of MFC

[Marc McMullen]

Hi All,

As an update, we are expecting 10 bottles of premix around the 3 or 4th 
week of January. If it comes early, I'll notify the group email. We have 
also order another 20 bottles, which should bring the total premix to 30 
bottles (e.g. ~90 running days).

Marc


On 1/2/2018 8:34 PM, mdefurne wrote:
> Hi Bob, Hi Todd,
>
> First of all I wish you all the best for this new year 2018. And thank 
> you Todd for installing the CF4 bottle.
>
> Tomorrow I would like to discuss with you about the insulation of the 
> mixing system. For instance, the metallic plate of the MFCs is 
> directly in contact with the metallic wall of the system. Don  t you 
> think the metallic walls may act as a heat sink by conduction?
>
> Also I am wondering why we cannot close the entire system with wood 
> panels and put a heater inside that will warm the air inside. Keeping 
> the air at 70F would be a lot more smoother and efficient to keep the 
> MFCs at good temperature than turning off-on the heat tape on the 
> MFC-plate. I am not sure that heat tape is the most efficient way to 
> keep their temperature high enough and maybe most importantly stable. 
> Indeed the heat tape will be turned on and off depending on the 
> outdoors temperature at a more or less relatively high-rate (You can 
> hear the thermostat turning on and off the heat tape every 5 seconds 
> currently). Will it not prevent the MFC from performing smoothly? 
> Because we need also to have a stable mixture of gas. Changing the 
> isobutane fraction by 1% makes a significant difference in the 
> detector performances.
>
> Moreover, even mixed, the isobutane may condensate. It is of course 
> much more complicated to have it condensated than when it is pure 
> (colder temperature and no flow). But I am willing to bet that it has 
> condensated in the small tank of the barrel with some premix since the 
> temperature has been really really and unusually cold and we did not 
> draw gas for 10 days. We will wait for monday, when temperature will 
> be much higher to flush everything with Argon to make sure there is no 
> inhomogeneities of mixture due to this condensation episode. 
> Nevertheless, we should try to prevent the isobutane from condensating 
> anywhere for the detector safety. This complete enclosure thing would 
> also keep the small tanks warm enough. Moreover I think it is a 
> relatively cheap and sure solution.
>
> After discussing with Marc and Brian, we agreed that turning the 
> mixing system ON should be interlocked with all heating systems 
> related to keeping MFCs or isobutane warm enough. If a heat tape or 
> heater fails, we should not take the risk to break a MFC.
>
> Finally, even if we plan to have the MFC repaired, I think we should 
> buy a few MFCs (2 or 3) as extra-spares. Delivery time is long (4-6 
> weeks), and we have no guarantee that everything will work smoothly 
> when we turn the system back on. Not as MVT expert but more as 
> spokesperson of the next experiment, we must have the MVT working. The 
> SVT has been damaged as you know and is performing badly compared to 
> what was expected. For the central tracking, MVT is now absolutely 
> necessary. I would not recommend to try saving money on 2 or 3 extra 
> MFCs. It will still be way cheaper than running with premix bottles 
> for 4-6 weeks while we are still trying to debug the system.
>
> I have a meeting from 8:30 to 10:30 so I can come to the Hall around 
> 11am.
>
> Best regards,
>
> Maxime
>
>

-- 
Marc McMullen
Detector Support Group
757-269-7738