Hi, Jerson

Halas, this measuring principle has to be used only with gases, as the heather power must be somewhat reasonnable:

Water would need 700+ times more power than air ... @ same temp rise.

Ultrasonic measurements also could be made ... but it needs meters between sensors !

I believe the best @ this scale, is to use an axial floweter ( with a small propeller inside ).
I got one years ago for gasoline, from a JAEGER brand car onboard computer ( Years 75-76 , when oil began to cost a lot ... )

it sure must still exist somewhere ( probably Water flowmeters for camping cars ... )

http://dx.com/p/hs05-high-precision-...r-white-227090

The real advantage here is there are no flow change ( and no false measure ) when the sub makes a sharp turn ...
as pitot tube needs to be close to flow direction ...

Alain