look at the gray line (no correction for heat loss) in the graph and see that it is higher than the red line (output, corrected for heat loss, I assume) for the first 30 minutes of the 5 hour run. At one point in that first 30 minutes, the uncorrected value (gray line) is about 130 watts while the corrected value (red line) is 50 watts.
Ah, I see what you mean. The red line goes up at the same slope for a while, then it suddenly drops, then recovers. It looks like it drops around minute 20 and recovers to rejoin the red line about 10 minutes later.
I don't know what that could be. My guess is that ambient temperature changes caused it. Things like that cause the biggest problems at low power levels. Interference from something like rapidly changing temperatures might last for 10 minutes. I guess it has to be some factor in the spreadsheet not used to compute the "no correction" curve. I guess the perturbation is introduced by the adjustment for heat losses from the insulated box, which of course are not included in the gray line. I don't recall seeing a spreadsheet with "no correction" so I don't know what factors are included in it. For the red line, the equation for heat adjusted for losses from the box is:
Wout/W = (Wn)/(5.76 × exp(−(Kn)/1512) − 4.78 + 0.00314 × (Kn)) [Kn is the reactor body temperature]
The equation for the temperature is pretty complicated:
(Tout − Tin)/deg = ((In) + (Jn)) × 0.5 − (HN) − (−0.302 × exp (− (On)/1.829)) − 0.376+ (Mn)
Maybe there is a different version of the temperature calculation for the gray line?