CHIMNEY-ENHANCED NATURAL CONVECTION IN HONEYCOMBS

The natural convective heat transfer performance of an aluminum hexagonal honeycomb is experimentally investigated. The concept of adding an adiabatic square chimney extension for heat transfer enhancement is proposed, and the effects of chimney shape (straight, convergent and divergent), height and diameter are quantified. Strong enhancement in heat transfer is found with adding an adiabatic chimney on the honeycomb. Given different installation angles of electronic devices, the effect of inclination angle is also investigated. Clockwise inclination leads to better heat transfer performance than anti-clockwise inclination, as the heated substrate of the heat sink in the former case is directly swept by fluid (air) driven by buoyancy force in the honeycomb cells. For clockwise inclination, an optimal inclination angle exists for maximum heat transfer. At a given chimney height, honeycombs with divergent chimneys perform better than those with convergent ones. For a fixed divergent angle, the Nuav number increases monotonically with increasing chimney height, In contrast, with the convergent angle fixed, there exists an optimal chimney height for maximum heat transfer.