calculate amount of liquid left in a 55 gallon drum

I'm trying to determine how much material remains as a residual film on the inside of a 55-gallon drum after empyting it of its liquid
content. I assume the amount that remains will vary by viscosity, temperature and time the drum was upside-down and also by composition of the drum (steel, plastic, urethane-coated etc). Does anyone have data on this (either models or empirical data) or any references to the literature? One rule of thumb I've seen is 1 to 4% of the original volume remains but I can't find anything to support this. Any help is appreciated.
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pa snipped-for-privacy@hotmail.com (Paul Nkui) wrote in message

It should be rather easy to calculate the internal surface area of the drum with a small correction for the ripples in the wall. Then take a small sample of identical drum material with a known surface area (the largest you can weigh easily, or the whole drum if you have the capability) and dip it into your liquid. Record the weight before and after and you now have the weight of liquid per square inch which can easily be converted into a volume if you know the density. Remember this value will be for a given temperature and then you can ratio the volume to the size of your drum. Finding this value experimentally is your best bet, as to model this would require significant data on viscosity, rheology, wetting behavior, solution vs. suspension, combined with experimental data to get this right.
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