Algodoo

What is "V(m/s)"? I'm guessing velocity in meters per second, but that doesn't seem right. Please explain.

Q: What is "V(m/s)"?
A: V(m/s) is air velocity which is used to calculate the convection coefficient which determines how fast the object responds to room air temperature changes.

Seems logical. Thanks.

One more question: Is it common to mix imperial and metric units for this type of calculation (V in m/s and T in degrees Fahrenheit)? Just curious.

Q: Is it common to mix imperial and metric units for this type of calculation.
A: No, normally you would use consistent units, but I used Watts for energy generation since I have a better physical understanding of Watts than BTU/hour. I used W/(m^2-°C) for the convection coefficient and m/s for the air velocity because that's what the chart and formula I used were based on.

That also seems logical. Thanks again.

I tried to use this tool for checking the performance of an aluminum heat sink that I used on an older project of mine. I did not know how to calculate the required dimensions and shape of such a heat sink and so I just did an educated guess for both parameters. It has worked quite well for my project but without employing the math, it may actually be too large rather than too small. After I have some time to spend on it, I'll let you know how well this tool worked for me.

Q: I did not know how to calculate the required dimensions and shape of such a heat sink.
A: If the part is in CAD then there is usually a way to automatically get volume and surface area for the part. If it's a part of uniform cross section, then you could use Algodoo and the code in one of the objects in Thermal Convection to get perimeter (P) and area (A). Surface area = P * L + 2 * A. Volume = A * L. If it's just size and shape you're after, then I would just scale up or down a standard heat sink. I would expect a scaled heat sink ability to dissipate heat to be directly proportional to its surface area.

It is generally accepted that the lum­ped system analysis is applicable if the Biot number < 0.1. If that's not true, then the approach in this scene is not applicable.

My best guess is that if the heat sink uses natural convection then lumped analysis applies.

Unfortunately, the part is not in CAD. It was simply cut from a larger stock of finned aluminum. The application isn't at all critical. The heat sink is used to cool two power FET's which generate ultrasonic power to a hand-held ultrasonic transducer which has a small knife blade attached to it. It's used for cutting plastics and other semi-rigid materials. The heat sink gets only slightly warm to the touch after about 20 minutes of heavy cutting, and so I believe that the surface area of the sink is correct for this application. It is fan cooled.

Thanks very much for the advice. I appreciate it.