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Inducing Oscillation Movement of Alternating Heat Sink Fins to Disrupt Thermal Boundary Layers for Enhanced Cooling Disclosure Number: IPCOM000241408D
Publication Date: 2015-Apr-23
Document File: 3 page(s) / 54K

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Described is the use of e present vibration and fin motion via a piezoelectric device to improve the heat dissipation capacity of a plate-finned heat sink.

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Inducing Oscillation Movement of Alternating Heat Sink Fins to Disrupt Thermal Boundary Layers for Enhanced Cooling

Fin efficiency is one of the parameters which makes a higher thermal conductivity material important. A fin of a heat sink may be considered to be a flat plate with heat flowing in one end and being dissipated into the surrounding fluid as it travels to the other. As heat flows through the fin, the combination of the thermal resistance of the heat sink impeding the flow and the heat lost due to convection, the temperature of the fin and, therefore, the heat transfer to the fluid, will decrease from the base to the end of the fin. This factor is called the fin efficiency and is defined as the actual heat transferred by the fin, divided by the heat transferred. Another parameter that concerns the thermal conductivity of the heat sink material is spreading resistance. Spreading resistance occurs when thermal energy is transferred from a small area to a larger area in a substance with finite thermal conductivity. In a heat sink, this means that heat does not distribute uniformly through the heat sink base. The spreading resistance phenomenon is shown by how the heat travels from the heat source location and causes a large temperature gradient between the heat source and the edges of the heat sink. This means that some fins are at a lower temperature than if the heat source were uniform across the base of the heat sink. This nonuniformity increases the heat sink's effective thermal resistance.

    It is also known that a boundary layer of relatively static fluid usually forms on the surface of a solid object (fin) when a stream of fluid flows over that object. Where the fluid is air, the relatively static boundary layer acts as a layer of thermal insulation which forms a barrier to the transfer of heat from the solid object into the flowing fluid stream. A boundary layer may be laminar or turbulent. In general, the boundary layer is thickest when the rate of fluid flow over the object is lowest. Figure 1 depicts the typical velocity profiles for laminar and turbulent boundary layers. As a consequence of intense mixing, a turbulent boundary layer has a steep gradient of velocity at the wall and, therefore, a large shear stress. Thus, the greater turbulence the flow, the longer the surface area in the length in the direction of the airflow can maintain a smaller boundary layer thickness.

    In general, the larger the surface exposed to airflow vectors which are turbulent substantially disrupts a stagnant surface boundary layer and increase the heat transfer efficiency.

Figure 1


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    However, the primary con of sustaining a high enough velocity to maintain turbulent airflow over the entire length of the fin channel cost in terms of quadric rise in pressure drop. For relative longer distances, "T" or "L" from Figure 1, the turbulent airflow will quickly transition back into the less desired laminar airflow. The heat trans...