Forced convective heat transfer enhancement of 90° bend plate-fin heat sink with grid generated turbulence

This study numerically investigates the effects of grid-bars cross-sectional geometry and grid-fins arrangement to reshape the windward flow in promoting 90° bend plate-fin heat sink forced convection at Reynolds number 60.6 × 10³. Three grid-bars cross-sections are proposed, namely: (i) reverse classic triangle (A), (ii) reverse flat-bottomed Reuleaux triangle (B), and (iii) reverse aerofoil (C), with regular grid of rectangular cross-section (G) as the control. The grid-fins configurations are structured as: (i) Inline-arranged regular grid (1), (ii) inline-arranged parallel grid (PG) (2), and (iii) staggered PG-fins (3). Results show that albeit the mild-decay in local-Nu_fin,L along the 90° bend, B₂-grid gives the highest 57% overall system performance (a balance between Nu_fin and pressure coefficient) compared to the control without grid, interestingly, the G₁ is −60%. Such achievement is attributed to the gradual curvature development along each bar that suppresses aerodynamic stall flow separation. The induced flow dynamic enables predominant channelling of air into fin separations. Most importantly, the vortex generation between the grid and fin strengthens the turbulence proximate to fin surface, hence enhances heat transfer. Overall, this study may shed light on the utilisation of B₂-grid induced turbulence to promote an energy sustainable HVAC's 90° bend finned-tube heat exchanger forced convection.