hi ,
how do i calculate the thermal resistance for a black anodized aluminum sheet with dimension of 100 x 50 x 5mm.
Considering 167W/m3 of thermal resistance for alu , I reach at 0.0041750 for the sheet intended for my application , but that's the thermal resistance for heat transfer within the aluminum , I need to calculate for aluminum sheet to ambient air at 40C .
I need to dissipate a total of 6W , any help will be highly appreciated .......
how do i calculate the thermal resistance for a black anodized aluminum sheet with dimension of 100 x 50 x 5mm.
Considering 167W/m3 of thermal resistance for alu , I reach at 0.0041750 for the sheet intended for my application , but that's the thermal resistance for heat transfer within the aluminum , I need to calculate for aluminum sheet to ambient air at 40C .
I need to dissipate a total of 6W , any help will be highly appreciated .......
Thermal resistances simply add, like resistors serie connected.
The most important thermal resistance is at the boundary of the aluminium and air.
This resistance depends a lot of whether that is still air or moving air. So it depends of the position of the heat sink, best is vertical and long with fins chaneling air down up thanks to air convection. Worse is the heat sink flat and enclosed.
A gentle breeze from a underpowered fan makes a lot of difference versus still air.
This is pretty variable, there exist charts to give figures, in these different cases.
Search for "heat sink air convection heat transfer".
There are heat sinks where they give the thermal resistance to ambient air, assuming it is in the right position to let free moving air. I do not like heat sinks set flush againt the PCB, a couple of large holes to let air go through the PCB is a worthwhile improvement.
Your dimension of 100 x 50 x 5mm in case it has fins seems ok for 6W. You can try, keeping a hand on it, and see wether it goes too hot.
The most important thermal resistance is at the boundary of the aluminium and air.
This resistance depends a lot of whether that is still air or moving air. So it depends of the position of the heat sink, best is vertical and long with fins chaneling air down up thanks to air convection. Worse is the heat sink flat and enclosed.
A gentle breeze from a underpowered fan makes a lot of difference versus still air.
This is pretty variable, there exist charts to give figures, in these different cases.
Search for "heat sink air convection heat transfer".
There are heat sinks where they give the thermal resistance to ambient air, assuming it is in the right position to let free moving air. I do not like heat sinks set flush againt the PCB, a couple of large holes to let air go through the PCB is a worthwhile improvement.
Your dimension of 100 x 50 x 5mm in case it has fins seems ok for 6W. You can try, keeping a hand on it, and see wether it goes too hot.
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"100 degrees C per Watt per Square Inch."
(Sorry for the antique unit, but I learned this long ago.)
100x50 is 4"x2" or 8 square inches, one side. If both sides get fresh air, 16 square inches. 1 Watt on 16sqin is about 6 deg C rise. 6 Watts is 38 deg rise. This seems OK.
I have often been surprised how hot sinks run from such rule-of-thumb estimates. And 38C rise on your (reasonable for Mexico) 40C ambient makes 78C, which here in Maine is 178 degrees F, which is HOT. Too hot for drinking coffee. Too hot to hold. If it is inside a case it will run hotter. When I did such a thing using the case as heatsink, I didn't like it for live recording because if I carelessly set my hand on it, it hurt.
(Sorry for the antique unit, but I learned this long ago.)
100x50 is 4"x2" or 8 square inches, one side. If both sides get fresh air, 16 square inches. 1 Watt on 16sqin is about 6 deg C rise. 6 Watts is 38 deg rise. This seems OK.
I have often been surprised how hot sinks run from such rule-of-thumb estimates. And 38C rise on your (reasonable for Mexico) 40C ambient makes 78C, which here in Maine is 178 degrees F, which is HOT. Too hot for drinking coffee. Too hot to hold. If it is inside a case it will run hotter. When I did such a thing using the case as heatsink, I didn't like it for live recording because if I carelessly set my hand on it, it hurt.
When I get back to NJ will post a nomograph of heat sink resistance for aluminum and copper -- no access to it right now.
One of they young men in the neighborhood got some industrial heatsinks on a dumpster dive near Carnegie Mellon University -- to these I attached a Dale power resistor with screws and thermal compound. Cooked the babies and plotted the temperature rise without forced air, just suspended above the workbench.
One of they young men in the neighborhood got some industrial heatsinks on a dumpster dive near Carnegie Mellon University -- to these I attached a Dale power resistor with screws and thermal compound. Cooked the babies and plotted the temperature rise without forced air, just suspended above the workbench.
Rule of thumb: if you can just keep your finger on it for 10 seconds, it's probably between 45 and 50 C.
Jan
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