Reverse flow sensing hot wire anemometer

The technique described was developed to enable measurements of velocity to be made in essentially unidirectional pipe flow, under pulsating conditions where reversals of flow direction occurred. The technique uses an ordinary hot wire anemometer but with two additional fine resistance thermometer wires placed one on either side of the hot wire and at right angles to it. The resistance thermometers sense the heated wake of the hot wire and this signal is used to correct the 'rectifying' effect of the hot wire, upon the indicated velocity, under reverse flow conditions. The problem, like the standard hot wire probe, will, however, only quantify the components of velocity normal to the axis of the hot wire and so is unsuitable for use in cases where the flow angle varies appreciably from 0 or 180 degrees . During a study of pulsating air flow in a pipe, flow reversal over part of the pulsation cycle was encountered. A hot wire anemometer was used to record mean values of velocity and root mean square values of the a.c. component of velocity, but due to the inability of the anemometer to sense flow reversals, the measurements of the air velocities were subject to serious error.