Heatsink Design and Selection

Design factors which influence the thermal performance of a heat sink

Fin efficiency

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. Fin efficiency is defined as the actual heat transferred by the fin, divided by the heat transfer were the fin to be isothermal (hypothetically the fin having infinite thermal conductivity).

Equations are applicable for straight fins.

fin efficiency equation 1 fin efficiency equation 2

Where:

  • hf is the convection coefficient of the fin
    • Air: 10 to 100 W/(m2K)
    • Water: 500 to 10,000 W/(m2K)
  • k is the thermal conductivity of the fin material
    • Aluminum: 120 to 240 W/(m•K)
  • Lf is the fin height (m)
  • tf is the fin thickness (m)