Importance of Melt Flow Direction during Injection Molding on Polymer Heat Sinks’ Cooling Efficiency

Abstract

Polymers with highly conductive fillers could possibly replace standardly used materials, such as aluminum and copper alloys, for passive cooling purposes. The main problem of the composite polymer-based heat sinks is that their high thermal conductivity is uneven. The orientation of this anisotropy is set according to the position of the highly thermally conductive filler. Its orientation is influenced by the melt flow during the polymer heat sink molding process. This article shows that change of the melt flow inside the mold cavity can improve the overall cooling efficiency of a polymer heat sink, which leads to lower temperatures on the heat source used. Two polymer heat sinks of identical geometries were produced. Their high thermal conductivity was given by the use of graphite flakes as the filler. The only difference between the heat sinks was in the position of the fan gate during their production. Different temperatures of the heat source between the two heat sinks were observed for the same measurement conditions. The measurements were conducted at Heatlab, BUT/Brno.

Influence of Ambient Temperature on Radiative and Convective Heat Dissipation Ratio in Polymer Heat Sinks

“…To prove this change in heat transfer means from the heat sinks to the ambient the same approach to the efficiency comparison as in [ 12 ] was used. The equations used in this approach are to be found in [ 17 ] and it analyses the amount of dissipated heat via heat sink’s fins.…”

“…It has also been proven that the importance of the melt entry point during the production for the overall heat sink efficiency as shown in [ 12 ] slowly loses its importance in case of higher ambient temperatures. This is because the heat dissipation via convection diminishes and the heat dissipation via radiation rises.…”

“…The positions were named ‘default’ and ‘upside-down’. This led to change of the filler orientation in relation to gravity and therefore buoyancy in case of the polymer heat sink with the melt entry point parallel to the fins, which as was shown in [ 12 ] led to different cooling efficiencies. Change of the melt flow direction in regard to gravity is shown in Figure 6 .…”

“…Both measured polymer heat sinks were measured in two positions as in [ 12 ]. The positions were named ‘default’ and ‘upside-down’.…”

“…Behavior of polymer heat sinks enriched with graphite flakes used in ambient with room temperature was studied in [ 12 ]. These results showed especially the importance of the choice of melt entry during their fabrication but did not delve deeper into the heat sinks’ efficiency if conditions would be any different from the room temperature and if natural convection would be limited due to use in enclosed space as is often the case in real applications.…”