Dave Liquorice wrote:


I can't think
of any physics that would allow the measurement of the flow of a
homogeneous fluid without something actually in the that fluid. There
*might* be something, maybe based on doppler, but I don't think that would
work without something in the fluid for the waves to bounce off(*).

The heat meters attached to the wood boilers I used to service were some
sort of acoustic device to measure flow of hot water. I think they sent
sound between two transceivers and worked out the liquid velocity by the
difference in trip time either way. The Landis ones were not clip on but I
did see this after a google

http://www.dmsltd.com/Non_Invasive_H...-On_Heat_Meter

AJH