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# Heat Sinks

## Heat Sink Types, Benefits & Size Estimates

There are numerous heat sink choices from zipper pack fins to extruded fin stacks, each with their own cost and performance characteristics.  While the heat sink choice can markedly affect heat dissipation performance, the biggest performance boost for any type of heat exchanger comes with forced convection.

## Estimating Required Heat Sink Volume

When beginning a thermal design project, engineers typically want to estimate the required heat sink size to cool a given heat source. Available air flow is the single biggest variable affecting heat sink size/volume.

Fortunately, there is a well-established, although simple, equation for estimating heat sink volume during the early design phase: V = (Q*Rv)/Delta T

Here, V is the outer dimensions of the heat sink in cubic centimeters, Q is total power it watts, Rv is the volumetric thermal resistance (cm3-C/W), and delta-T is the difference between maximum Tcase and ambient temperatures (degrees Celsius).

We find, it generally estimates heat sink size to within +/- 15% of the final part, once you’ve got a bit of experience using it and understanding its limitation. All of the variables are very straight forward except the Rv input – the volumetric thermal resistance. Provided you have a rough idea of the available air flow, as seen in the chart below, it becomes a simple task to input Rv. Notice, however, that for each air flow there is a range of volumetric thermal resistances that can be chosen.

The guidelines for making a selection are as follows. For smaller heat sinks in the 100-200 cmrange, use an Rv at the bottom end of the range. For larger heat sinks in the 1,000  range, us an Rv at the top end of the range.

Volumetric Thermal Resistance Based on Air Flow

The image below shows the online calculator for determining heat sink volume during the early design phase.