Revisit on natural convection from vertical isothermal plate arrays--effects of extra plume buoyancy

- Natural convection from vertical isothermal 2-D parallel-plate arrays is studied numerically.
- In multi-channel arrays, h is highest in the central channel and lowest in the edge channel.
- Differences in h between the central and the edge channels increase with increasing number of channels.
- The overall ho in the plate arrays increases with increasing number of plate channels.
- These phenomena mainly results from the extra buoyancy from the hot plume above the array.

In this study, natural convection from vertical isothermal parallel-plate arrays is examined using 2-D steady-state numerical analysis. Extended computation domains encompassing the single- or multi-channel plate arrays are adopted. Also investigated are the consequences of using computation domains without the inlet extension or/and the outlet extension. The plate height is fixed at 100 mm, the plate spacing is 7 mm, and the plate thickness is 1 mm. The Elenbaas Rayleigh number Ra' is fixed at 62.8. The results show that setting the inlet boundary at the entrance of the channel would ignore the separation formed near the outer entrance corner and the associated flow resistance; while setting the outlet boundary at the exit of the channel would omit the extra buoyancy provided by the hot plume above the arrays. In multi-channel arrays, the average heat transfer coefficients in different individual channels (hs) are different from each other. The h is the highest in the central channel and the lowest in the edge channel. Except for the edge channels, the h values are higher than that of a single channel. The differences in h between the central and the edge channels increase with increasing number of channels. This phenomenon can be ascribed to (1) the stronger extra hot-plume buoyancy in the inner plume region and (2) the higher entrance-separation resistance in the outer channels. The overall convection heat transfer coefficients in the plate arrays increase with increasing number of plate channels. The conventional assumption that all the channels of a multi-plate array have similar heat transfer performance needs re-evaluation.