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 .
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
The full cool down curve of the tank and a fitted curve ()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).