Abstract
In this study, the classical problems natural convection from vertical isothermal plate arrays is re-examined numerically. The dissertation is composed of three parts. In the first part, the effect of different computation domains on two-dimensional single channel is investigated. The results show that setting the inlet boundary at the entrance of the channel would ignore the recirculation flow formed near the entrance corner and the associated flow resistance; while setting the outlet boundary at the exit of the channel would miss the additional buoyancy provided by the hot plume above the channel. In the second part, the flow field and thermal performance of two-dimensional multi-channel fin arrays are analyzed. Multiple channels present higher average heat transfer coefficients (h) than a single channel, with h being highest at the central channel and decreasing to the lowest at the edge channel. The differences in h between the central and the edge channel increase with increasing number of channels. This phenomenon can be attributed to the greater hot plume regions which provide more additional buoyancy. The third part discusses the characteristics of three-dimensional natural convection from isothermal vertical plate arrays with a finite width under fixed height and spacing. The results of single-channel calculations demonstrate high h at the plate edge due to the effect of side flow. The value of h decreases inwardly but rebounds near the center of the plate as a result of higher additional plume buoyancy therein. As the plate width increases, the stronger plume buoyancy promotes the average h, which approaches the 2-D value when the plate is sufficiently wide. It is also found that the correction factors q (≡ Q3D /Q2D) used by Elanbaas [1] to correct his 3-D data into 2-D ones are considerably over-estimated for plate spacing b > 5 mm. The reason is that, with the presence of side flow, the 3-D plume region reduces and provides less buoyancy than the 2-D situation. The 3-D multi-channel conditions with finite plate width are also analyzed for their flow fields and the thermal performances with the configurations and effects of the 3-D plume regions discussed.