The role of convection in the transient hot wire method

Overview & Synopsis

We study experimentally the transition between two heat transfer regimes in a liquid around a long vertical wire heated by a constant electric power q from an initial time t = 0. In the first regime (short times) the heat transfer along the horizontal is purely diffusive. The second regime appears after a characteristic time tc and can be related to a vertical component of the thermal gradient. This vertical gradient plays a destabilizing effect on the conductive boundary layer which develops during the first regime. The study of this transition indicates that tc can be defined by means of a Rayleigh number. A relation between the time tc, the power q and the properties of the fluid is given here.