rate of heat transfer varies with the type of fluid, but it also tends to vary as the square kept of the velocity at which the fluid flows past the wire. the the wire is constant, the change in If current in signal resistance due to the cooling will yield a voltage cause the diameter of the wire element can be made very small, the device can be made very sensitive and responsive to high-frequency changes in the flow rate. One ot its chief uses is in aerodynamic research.