Thermal and fluid dynamic behavior of symmetrically heated vertical channels with auxiliary plate

Air natural convection in vertical channel configurations is strongly attra ctive in thermal design and control of devices. This is mainly due to its s implicity, no maintenance costs and reliability. This paper examines air na tural convection in vertical channels with an auxiliary plate along the cen terline. The channel is symmetrically heated and the walls are at uniform h eat flux, whereas the auxiliary plate is either adiabatic or heated at unif orm 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. Re sults in terms of stream function and temperature fields, velocity and temp erature profiles inside the channel and pressure profiles along the centerl ine are given either for insulated auxiliary plate or for heated auxiliary plate. The adiabatic auxiliary plate along the centerline of the channel pr oduces a chimney effect reduction of the channel while the heated auxiliary plate, at higher Ra values (10(5)-10(6)), provides an increase in the mass flow rate in the channel. Finally, two correlations between average channe l Nusselt number, channel Rayleigh number, Ra*, and dimensionless auxiliary plate height, h/L, are proposed. One correlation is for the channel with h eated auxiliary plate and another is for the channel with unheated auxiliar y plate. The channel Rayleigh number range is 10(2)-10(5) and the dimension less auxiliary plate height, h/L, is in the range [0, 1]. (C) 2001 Elsevier Science Inc. All rights reserved.