How do I apply fan performance curves to a heat sink?
How do I apply fan performance curves to a heat sink?
(OP)
I have designed an air-cooled motor housing equipped with cooling fins. Due to the short time available from concept to prototype, I did very brief analysis before choosing the fin height, width, and length. I chose these to be quite conservative based on the amount of heat loss expected from the motor.
Our customer has recently asked us to evaluate the possibility of operating the motor at much higher load. This of course generates much more waste heat that I need to get rid of.
While shopping around for fans, I have found several that appear to meet the environmental and voltage requirements. The fan manufacturers publish performance curves and this is where I have my question:
The curves are Static Pressure on the y-axis and Volumetric Airflow on the x-axis.
I am not familiar with fan design, so I'm not sure exactly what I'm looking at here.
I plan to shroud the heat sink fins in a sheet-metal duct to help direct the airflow. I expect a certain amount of pressure loss across the fins. Can I use the graph to determine the expected airflow rate? (so I can estimate convection heat transfer coefficient at the fins).
I don't know how to use the performance curves with the heat sink geometry to see if its enough fan for the job.
Any ideas or suggestions are appreciated.
Our customer has recently asked us to evaluate the possibility of operating the motor at much higher load. This of course generates much more waste heat that I need to get rid of.
While shopping around for fans, I have found several that appear to meet the environmental and voltage requirements. The fan manufacturers publish performance curves and this is where I have my question:
The curves are Static Pressure on the y-axis and Volumetric Airflow on the x-axis.
I am not familiar with fan design, so I'm not sure exactly what I'm looking at here.
I plan to shroud the heat sink fins in a sheet-metal duct to help direct the airflow. I expect a certain amount of pressure loss across the fins. Can I use the graph to determine the expected airflow rate? (so I can estimate convection heat transfer coefficient at the fins).
I don't know how to use the performance curves with the heat sink geometry to see if its enough fan for the job.
Any ideas or suggestions are appreciated.
Beat to fit, paint to match.





RE: How do I apply fan performance curves to a heat sink?
In theory yes, if you know the expected pressure drop at the desired airflow across the fins and through your duct (remember than the drop will be a function of flow) then yes, just use that value on the pressure axis of the fan curve and check that the flow will be what you need.
But, the fan curves were developed using idealized fan inlet and exit configurations - nice long straight sections of duct. I suspect that your configuration will be less than ideal, so the fan performance will be derated.
RE: How do I apply fan performance curves to a heat sink?
RE: How do I apply fan performance curves to a heat sink?
Tobalcane
"If you avoid failure, you also avoid success."
"Luck is where preparation meets opportunity"
RE: How do I apply fan performance curves to a heat sink?
I don't have any measuring capability at the moment. I don't have the fan in-hand, and the prototype shroud I built is with the customer. I'll have to estimate through calculation.
I had a look through my fluid dynamics books and this is what I figure I'll need to calculate to get the cooling fin pressure-loss curve onto the fan performance curve:
Reynolds number (Re)
Friction coefficient (h)
Velocity range (from volumetric flow data)
From that I should be able to estimate a pressure drop curve.
Whew!
Beat to fit, paint to match.
RE: How do I apply fan performance curves to a heat sink?
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RE: How do I apply fan performance curves to a heat sink?
I am treating them as two sets of "straight" heat-sinks.
I plan on using two fans, one to cool each bank of fins through two wrap-around shrouds. The fans would be very close to the cut-ends of the fins.
However, I'll need to work with out customer to see where the ducting can come from and go to. I may have to mount the fans remote and duct in the cooling air, although I suspect this won't be necessary.
Beat to fit, paint to match.
RE: How do I apply fan performance curves to a heat sink?
Tobalcane
"If you avoid failure, you also avoid success."
"Luck is where preparation meets opportunity"
RE: How do I apply fan performance curves to a heat sink?
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RE: How do I apply fan performance curves to a heat sink?
Ione, I've been using the Novel Concepts website for some time. The results they produced have proven to close to the results we've received from third party CFD guys. HOWEVER, for this case the pressure drop value I get is 100x larger for the Novel results than for my hand calcs...
I'm trying to figure that one out right now.
Beat to fit, paint to match.
RE: How do I apply fan performance curves to a heat sink?
Beat to fit, paint to match.