Comparison of TISE and SITE heatsinks - A numerical study

A comparison of different flow orientations in fan heatsinks was performed. Two designs were considered, top inlet - Side exit (TISE) and side inlet - Top exit (SITE). A heatsink of fixed planar size, (X-Y) of 80 and 63mm, dimensions representative of current mainstream processors for desktops and workstations, was considered. The fan was approximated as an inlet with a uniform discontinuity in pressure. Total volume flow rate and pressure drop were related by fan curves from catalog data. Low, medium and high speed fans were modeled. Initially, a conjugate heat transfer model was considered. However, this led to a very slow convergence of the solution scheme. As the aluminum to air thermal conductivity ratio is around 8000, an isothermal boundary condition is justified and was therefore used. Fin spacing was varied from 1 to 4mm, and heatsink height from 20 to 35mm. In all cases the taller heatsinks and higher speed fans offered higher thermal conductance. In general, the TISE configuration out-performed SITE. Performance was quite sensitive to fin spacing, with optimum fin spacing generally close to 1.5mm.