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Wednesday 21 June 2006
NUMERICAL ANALYSIS OF TRANSIENT NATURAL CONVECTION IN AIR IN CONVERGENT CHANNELS WITH UNIFORMLY HEATED PLATES
L. Langellotto
Referee: T. Coppola
Paper presented to: XXIV Congresso nazionale UIT sulla Trasmissione del Calore
Napoli, 21-23 June 2006
A numerical investigation on natural convection in convergent vertical channel is accomplished in order to carried out the thermal and fluid dynamics behaviours of the transient regime in this configuration. The convergent channel has the two principal flat plates at uniform heat flux and the numerical analysis is carried out in two dimensional laminar regime. The computational domain is extended to simulate the free-stream condition and allows to account the diffusive effects.
Results in terms of wall temperature profiles as a function of the time for some inclination angle, between 0° and 10°, aspect ratios, in the range from 10 to 58, and channel Rayleigh numbers, from 5.0 to 3.8x103, are presented. Wall temperature profiles have a stronger dependence on the convergence angle than the aspect ratio and channel Rayleigh number and maximum wall dimensionless temperature as a function of the dimensionless time changes in a very small range at small values of dimensionless time. Overshoots and undershoots along maximum and average dimensionless wall temperatures as well as for dimensionless mass flow rate are detected. The Nusselt number, referred to the minimum channel spacing, in all considered cases decreases strongly between the initial time and 0.2. According to previous results for steady state investigations, the channel with a convergence angle equal to 2° is the best configuration in terms of maximum wall temperature and heat transfer coefficient. Stream function and dimensionless air temperature fields allow to analyze fluid dynamics and thermal behaviours for different times.
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