the fluid which is being measured for flow rate according to the present invention is a corrosive fluid the interior wall 10 a of the conduit c may be coated with a suitable corrosion resistant material such as a fluorinated hydrocarbon or other corrosion resistant synthetic resin film coating a first heat detector or thermocouple 12 or other suitable heat sensing device capable of forming an electrical indication of sensed temperature is attached by suitable techniques to the inlet section 10 the thermocouple 12 senses ambient or reference temperature of the tube inlet section 10 and the incoming fluid to be measured in the system s a heat transfer section 14 is formed in the conduit c in the downstream direction of fluid flow from a transition area 16 of the inlet section 10 in the transition area 16 the conduit c changes from a cylindrical or tubular cross section to one better adapted for heat transfers as will be set forth a power applicator electrical contact 18 is formed on the heat transfer section 14 of the conduit c for connection through an electrical connector 20 to an electronic control circuit e fig1 and 3 of the system s with the present invention the reference temperature sensing thermocouple 12 is located outside of and upstream of the heat transfer section 14.