Non-invasive fluid flow sensing based on injected heat tracers and indirect temperature monitoring

A method of monitoring flow in a fluid-bearing passageway comprising steps of:

• introducing propagating heat fluctuations into a flow of liquid through said passageway, said propagating heat fluctuations being introduced at a first position along said passageway;
• measuring temperature-dependent changes in resistivity of said liquid along a first interrogation region of said passageway, including monitoring said resistivity over a period of time sufficiently great to enable at least one said propagating heat fluctuation to propagate into said first interrogation region;
• and
• determining a flow rate of said liquid based upon said monitoring of said resistivity to determine times for said propagating heat fluctuations to travel from said first position to said interrogation region.

A method of monitoring flow in a fluid-bearing passageway comprising steps of:

• introducing heat fluctuations into a flow of liquid through said passageway, said heat fluctuations being introduced at a first position along said passageway;
• directing a beam from a light source into said liquid at a first interrogation region of said passageway;
• detecting light energy from said beam following interaction of said light energy with said liquid, including monitoring refractive index of said liquid over a period of time;
• and
• determining a flow rate of said liquid based upon said monitoring of said refraction index and upon determining times required for said heat fluctuations to travel from said first position to said first interrogation region, including detecting entrances of said heat fluctuations into said first interrogation region by correlating changes in said refractive index with said entrances of said heat fluctuations.