Calculating number of cooling fins on a waveguide load
Calculating number of cooling fins on a waveguide load
(OP)
I need some help in ways of calculating the number and size of fins required to disperse heat generated by a load element inside a piece of wave guide.
The load element is silicon carbide absorbing 200W of power in copper or aluminium WR75 waveguide.
Any pointers would be very much appreciated
The load element is silicon carbide absorbing 200W of power in copper or aluminium WR75 waveguide.
Any pointers would be very much appreciated





RE: Calculating number of cooling fins on a waveguide load
1) Please confirm that the heatsink is on the outside of the waveguide?
2) Is the heatsink force convection cooled (fan blown) or natural convection cooled (or dipped in water!)
3) How hot is the base of the heatsink allowed to get?
Let's do some simple sums. If the load dissipates 200W and you want a temperature rise on the load of not more than say 50 degC then you need a heatsink better than 50degC/200W= 0.25degC/watt. You can look in a distributer's catalog at 4degC/watt heatsinks and see how big they are. You may not find one as big as a 0.25degC/watt. This is a BIG heatsink and without fan cooling it may not be workable.
RE: Calculating number of cooling fins on a waveguide load
2. Is natural convection cooled
3. Say about 60 degC
I was thinking of using a set of individual fins mounted in the same plane as a flange would be, about 100mm by 100mm by 2mm, spaced along the guide at regular intervals.
The finished load would look something like this one .
Many thanks for your help
RE: Calculating number of cooling fins on a waveguide load
Obviously, a higher HTC would yield different results.
TTFN
RE: Calculating number of cooling fins on a waveguide load
In otherwords, the higher you are willing to allow the waveguide wall temperature to rise, the less heatsink area you need.
RE: Calculating number of cooling fins on a waveguide load
That will give you a rough starting point. Another way is to look up the specifications of commercially available heatsinks of roughly similar fin size and spacing, and do a little reverse engineering.
For 200W, and a fin size of 100 x 100mm, I would start thinking about having at least a minimum of twelve to fifteen fins, spaced widely enough apart not to restrict free convective airflow.
Build up a prototype, and use a simple resistance heating element and a dc power supply to test with, and get some exact temperature rise figures. Then you will have a pretty good idea where to go from there.
RE: Calculating number of cooling fins on a waveguide load
http://www.milpi.com/582main.html
RE: Calculating number of cooling fins on a waveguide load
"Natural convection can be as low 4 W/m2ºC."
Is that from your experience or can I find that in a (thermodynamics) book sowmewhere?
Thanks,
Z
RE: Calculating number of cooling fins on a waveguide load
ht
http://www.mhtl.uwaterloo.ca/cgi-bin/rect_hs
Caveat on the supposed conditions in the calculator.
TTFN