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 Sat Aug 27 17:42:40 2016, awade, Summary, TempCtrl, Heat load of vacuum can held above room temperature. Mon Aug 29 19:09:19 2016, awade, Summary, TempCtrl, Heat load of vacuum can held above room temperature. Wed Aug 31 12:41:30 2016, awade, Summary, TempCtrl, Heat load of vacuum can held above room temperature. Thu Sep 29 17:57:32 2016, awade, Summary, TempCtrl, Heat load of vacuum can held above room temperature.
Message ID: 1728     Entry time: Thu Sep 29 17:57:32 2016     In reply to: 1712
 Author: awade Type: Summary Category: TempCtrl Subject: Heat load of vacuum can held above room temperature.

The previous cool down test was repeated over a longer time period.  The tank was heated overnight with a 30 V (18 W) (as stated in previous post) and its settling temperature was 44.36±0.05 C. This gives us some idea of the expected DC heat load that the tank will require to maintain an elevated temperature of ~45 C.

The supply was turned off and a cool down curve was recorded over the next day. Plot is below.  Fitted values were

a = 19.4291±0.0005 C, b=13980±730 s, c=20.75216 ± 0.00003 C

for the fitted equation $T(t) = a*\exp(t/b)+c$.

With this test (with a longer cool down tail), the time constant for the insulated tank to come to room temperature was 3.88 h

Quote:

The full cool down curve of the tank and a fitted curve ($T = A\exp(-t/\tau)+C$)are attached below.

Least squares fitted values are

a=23.4145±-0.0005 C, tau=7596±170 s, c=21.00947±0.00004

The variance on the time constant is very large, I think this might be due to a poor fit owing to the fact that the temperature was still rising (rather than steady) when I turned the heating off. We want the whole system to be at equalibrium at the start of the test and we also want a decent tail on the decay. I have therefore repeated the measurment this time heating overnight with 30 V (18 W) which settled on 44.36 C.  I have now left the vac can to cool for the rest of the day (starting about 9.30 am).

## Either way it looks like the characteitic 1/e decay time is on the order of 2.1 hours.

 Attachment 1: 20160830_plot_TankHeatUpAndStepDowntoRoom_30VConst.eps  218 kB
 Attachment 2: 20160830_VacTankHeatUpAndStepDown45CtoRoom20C_SecondTest.zip  1.099 MB
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