Abstract
In several situationss the control of a surface temperature is ensured by convective exchange; for examples for steel metallurgy or electronic components. And among the three types of convective exchanges, forced convection is often used because of its efficiency. A contrario natural convection has the advantage to be free in terms of energy expense but generates low heat transfer coefficient. Thus it will be interesting to improve free convection heat transfer in order to substitute for the expensive forced convection. Laminar free convection problem on a vertical wall has been plentifully investigated considering a wall heat flux density constant [1–3] or varying sinusoidally [4]. But only two studies deal with the influence of the different parameters of the problem. Thereby Yang et al. [4] evaluated the influence of the amplitude and of the frequencies of the sinusoid whereas the Vargas and Bejan [5] study is based on the optimisation of heat transfer. This last investigation considers a fluid (water) initially at rest before being suddenly put in motion thanks to a periodical heat flux density applied to the wall. Scale analysis, numerical and experimental studies have been carried out and show that the heat transfer is optimised when the heating and cooling (wall adiabatic) periods are equal. In this paper the wall is subjected to a uniform heat flux density until the steady states (thermal and dynamical) are reached. Then a periodical heat flux density which varies from qw to 0 (adiabatic wall) is applied to the surface in order to improve the free convection heat transfer. A parametric study is then carried out in order to optimise the heat transfer. 2. Modelling
Published Version
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