Thermal and Fluid Dynamic Behavior of Symmetrically Heated Vertical Channels with Auxiliary Plate

Air natural convection in vertical channel configurations is strongly attractive in thermal design and control of devices. This is mainly due to its simplicity, no maintenance costs and reliability. This paper examines air natural convection in vertical channels with an auxiliary plate along the centerline. The channel is symmetrically heated and the walls are at uniform heat flux, whereas the auxiliary plate is either adiabatic or heated at uniform heat flux. The analysis is obtained for a two-dimensional steady state and laminar regime, and the fully elliptic equations are solved numerically by the control volume method on a finite I-shaped computational domain. Results in terms of stream function and temperature fields, velocity and temperature profiles inside the channel and pressure profiles along the centerline are given either for insulated auxiliary plate or for heated auxiliary plate. The adiabatic auxiliary plate along the centerline of the channel produces a chimney effect reduction of the channel while the heated auxiliary plate, at higher Ra values (105-106), provides an increase in the mass flow rate in the channel. Finally, two correlations between average channel Nusselt number, channel Rayleigh number, Ra* and dimensionless auxiliary plate height, h/L, are proposed. One correlation is for the channel with heated auxiliary plate and another is for the channel with unheated auxiliary plate. The channel Rayleigh number range is 102-105 and the dimensionless auxiliary plate height, h/L, is in the range [0,1]