Heat Transfer & Cooling Capacity

[Tone L]

TL;DR

Trying to figure out how to compute the size of a heat sink or TEC to dissipate the heat from an electronics module.

Hi, zero education on heat transfer here, need some help.

I have an electronics module that generates 15 W of electrical power over a 70mm x 20mm x 15mm heat load volume (aluminum). The ambient temperature is 25° C, the maximum temperature the heat sink can be is 40° C (ΔT = 15° C).

Does anyone know how to compute what size / type of heat sink I need? Laird Thermal Systems and Wakefield are two vendors I was looking at.

Thanks!

Aluminum characteristics: Density 2710 kg/m^3 & Specific heat: 921 J/kg*K

 

[berkeman]

The datasheets for their heatsinks should give "thermal resistance" numbers in units of degrees C per Watt for different airflow situations. Can you attach their heatsinks firmly to your (metal?) module using Heat Sink Grease to ensure good thermal coupling? Will you be using a fan or fans to generate some airflow rate? Are you sure that your ambient temperature will be 25C, or is this module (and the fan(s)) in an enclosure?

 

[Tone L]

The datasheets for their heatsinks should give "thermal resistance" numbers in units of degrees C per Watt for different airflow situations. Can you attach their heatsinks firmly to your (metal?) module using Heat Sink Grease to ensure good thermal coupling? Will you be using a fan or fans to generate some airflow rate? Are you sure that your ambient temperature will be 25C, or is this module (and the fan(s)) in an enclosure?

My thermal resistance is 15C/15W = 1C/W I presume, so I need to find a heatsink that is greater than this value?

The joint between the heat load and the heat sink will be coupled well, thermal paste will be used as an interference between the two as well. It will be in a lab setting where the room will be between 21 - 25C.I hadn't yet looked at fans yet, I was curious of the capabilities of a heat sink using fins.

 

[berkeman]

My thermal resistance is 15C/15W = 1C/W I presume, so I need to find a heatsink that is greater than this value?

That's pretty aggressive, but should be do-able with forced air. Did you recheck the heatsink datasheets?

I hadn't yet looked at fans yet, I was curious of the capabilities of a heat sink using fins.

I'd have to look at the numbers for your enclosure and the heatsinks, but 1C/W is pretty aggressive for convective non-forced air cooling even in a vertical enclosure with lots of venting.

 

[berkeman]

This looks like a good design resource. You should be able to find similar resources at the heatsink manufacturer websites...

https://www.digikey.com/Site/Global/Layouts/DownloadPdf.ashx?pdfUrl=F51974C9A6D544F1A7D8F119514B67FF

Edit/Add -- Maybe this plot from the paper is instructive:

 

[berkeman]

My thermal resistance is 15C/15W = 1C/W I presume, so I need to find a heatsink that is greater than this value?

You mean "better" than that value of 1C/W, not "greater". So you need less than or equal to 1C/W.

That is pretty hard to achieve without forced airflow. What does your enclosure look like?

 

[Tom.G]

The catalog @berkeman referenced would be available from the manufacturer at:
https://wakefieldthermal.com/

That, any many more documents, were found with:
https://www.google.com/search?q=wakefield+heatsink+catalog

Their general catalog is:
https://wakefieldthermal.com/content/catalogs/2019_Catalog.pdf
It has 149 pages -- but they are 11x17 inch pages!

Wakefield is one of the major heatsink manufacturers, if they don't show you how to determine size, geometry, technology, and already make one you can use, it probably doesn't exist.

Cheers,
Tom