Rate of water/foam level lowering in the cells
As known, the core of the 1992 F&P paper (1) is page 16, where an excess heat of 144.5 W was calculated, which allowed the authors to conclude: "We note that excess rate of energy production is about four times that of the enthalpy input even for this highly inefficient system".
This calculation is based on the central assumption that the last half of the electrolyte (ie 2.5 moles of heavy water) has vaporized in 600 seconds (10 minutes). This estimate was based on the video recorded during the test: "As it is possible to repeatedly reverse and run forward the video recordings at any stage of operation, it also becomes possible to make reasonably accurate estimates of the cell contents. We have chosen to time the evaporation/boiling of the last half of the D2O in cells of this type and this allows us to make particularly simple thermal balances for the operation in the region of the boiling point."
In 2009, a video titled "1992 Four-Cell Boil-Off" was published by Krivit on YouTube (2). This is a demonstration video showing some preliminary information on the F&P experiment started on April 11, 1992, such as the details of a cell. The main part of this video contains the video clips supposedly showing the last evaporation phase of the 4 cells. The temporal localization of these clips has been shown in a previous jpeg (3).
For each cell, the lowering of the apparent level is highlighted with a blue arrow that moves downwards. The first and last appearance of the arrow are accompanied by its time. The following jpeg collects some video frames that show all the positions of the blue arrow.
By estimating the vertical position of the arrows with respect to the ruler shown on the right, where it is assumed that the normal water level is 18 cm above the KEL-F support, it is possible to deduce the 4 curves shown in the graph, which describe the lowering of the arrow height in each cell. This graph shows that the upper arrow is usually positioned around 11.5 cm, while the lower one appears at a height of about 4 cm, so that the total decrease in the water level indicated by the arrows is 7.5 cm ca. The lowering time varies from 20 to 35 minutes.
Therefore, the resulting rate of level lowering indicated by the 4 curves is very different from the estimate made by F&P, ie 9 cm in 10 minutes, and which is drawn in red to the left of the graph.
Furthermore, the vertical ranges of the 4 curves are very different than expected. In fact, being referred to the last half of the D2O content, their lower ends should have been at 0 cm, not 4 cm above the support. This is evidently due to the fact that, at the end of the drying period, a thick layer of residual and persistent foam remained at the bottom of the cells. This interpretation is confirmed also by the extra lower arrow indicated at the end of the Cell 3 sequence, but which is taken from a clip filmed 4 days later, as already explained in a previous post (4).
In conclusion, the available videos of the 1992 four-cell experiment don't support the estimate made by F&P of a rapid vaporization in just 10 minutes of half the water content on which their calculation of an excess heat of 144.5 W was based. So, there is no way to figure out where the 10 minutes have come from, apart from a pure invention of the authors.