On Wednesday, November 20, 2019 at 4:16:41 PM UTC-6, Thomas Koenig wrote:   
   > Hi,   
   >   
   > It is a well-known effect that when an "insulating" liquid (electric   
   > conductivity of less than 50 * 10^(-12) S/m) flows through a metal,   
   > grounded pipe, charge separation can occur, and the liquid at the   
   > outlet of the pipe then carries an electrostatic charge.   
   >   
   > This can be quite relevant because such liquids are also often   
   > flammable, and their vapors can form explosive mixtures with air,   
   > which can be ignited by the electrostatic charge, with literally   
   > catastrophic results.   
   >   
   > I have found a qualitative explanation of the effect of charge   
   > accumulation in the book "Static Electricity" by Lüttgens et al.   
   > (which you can find with Google books if you're interested)   
   > in chapter 2.5, but the authors do not cite any sources, and no   
   > quantitative relationships for charging of the liquid depending   
   > on material parameters, flow characteristics and so on.   
   >   
   > Has quantitative work been done on this?  Given the large   
   > significance of the problem, I would expect something, but so   
   > far I have not been able to find a lot.   
      
   I am far from an expert on this subject, but perhaps this graph, and the   
   source data for it, is a lead to the quantitative data you are looking   
   for:   
      
   https://en.wikipedia.org/wiki/Triboelectric_effect#/media/File:T   
   iboelectric_charge_density.jpg   
      
   Rich L   
      
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