Project Title: "HOT AND COLD WIRE: Theoretical concepts and applications"

Author: Esteban Crespo, Universidad de Costa Rica, Costa Rica.

Host Supervisor: Prof. Bernard Desmet, Université de Valenciennes et du Hainaut Cambrésis, France

A methodology for simultaneous measurements of local and instantaneous flow velocities and temperatures has been developed. The technique uses at the same time a hot wire to measure velocity and a cold wire to measure temperature. The hot wire will measure the heat transfer that occurs in the form of convection between the flow and the probe. When temperature is constant, it is possible to use an already existing equation (King’s Law) to relate the voltage that travels through the probe with the velocity of the flow. On the other hand, the principle on which is based the cold wire is to have a resistance that varies strongly with temperature. A low electric current remains constant, and since the resistance varies linearly with temperature, it is possible to associate a certain voltage to its corresponding temperature. A complete characterization of the cold wire response was formulated using a simulation on Matlab.

The problem is that King’s Law will not be efficient if there is a variation in temperature because now the heat transfer will depend on the velocity and temperature fluctuations of the flows. So it is essential to examine how this Law will be affected if there is a deviation in temperature. For this purpose the cold wire signal is used to correct the velocity given by the hot wire. A modified King’s Law has been deducted theoretically. Finally this equation, in parallel with the cold wire response, will be used to correct the velocity given by the hot wire.