heat sink surface area

[nithin.kundapur]

Hi I want to calculate heatsink surface area and formula to reduce heat of 90` to 50 digree celcius. Wat s the surface area required for that and formula. Material s. Aluminium

 

[tpetar]

What pump heat to heatsink and what is power of that pump (read semiconductor) ?
In other words tell us more about heat source, calc depends of that.

 

[nithin.kundapur]

i want to calculate surface area for LED. So System heat is 120' and i want to reduce it to 50' so how much surface area heatsink required and formula to calculate it.
power is 3W.

 

[tpetar]

You do not want a led chip to run over 90C. Therefore a heat sink should be chosen such that its thermal resistance will keep the temperature of the attached regulator below that maximum tolerable temperature. Therefore the maximum thermal resistance acceptable can be calculated according to the following formula:

Max. Heatsink Thermal Resistance = (90 - AmbientTemp) / Power


Example: room temp is 30C, LED power is 3W would require a heatsink with a thermal resistance of less than (90 - 30) / 3 = 20C/W.

If thermal resistance of heatsink smaller that means that heatsink have capabilities for better cooling.

You can use some smaller PC CPU heatsink, and you can calc thermal resistance for that heatsink if you dont have such data for that heatsink. Some 486 or chipset heatsink will be fine for this purpose, or if there is space you can use some bigger heatsink. You should remember that higher temp shorten life of led, you can see datasheet curve life span / temp, max allowed temp, about particular product provided by manufacturer. Also read manufacturer advices and suggestions for heatsink and how to choose it.

My suggestion is max temp of 80C!!! for 3W led.


Thermal resistance of a heatsink
- Its size
- The number of fins
- The total surface area - a ribbed fin design will be smaller than one using flat fins for the same thermal resistance
- Thermal resistance within the aluminium itself - the actual alloy used, its thickness, etc
- The colour - matt black is best, and other colours are all worse
- The orientation of the fins - vertical is best, any horizontal position is worse
- Availability of unrestricted air flow
- Its temperature!

Thermal Resistance = 50 / SQRT(A) Where A is the total surface area in cm²


The heat dissipation performance depends on the surface contact conditions between the 3W led aluminum base and the heat sink. If the 3W has insufficient contact with the heat sink due to uneven heat sink surface, the measuring point temperature will exceed 80℃ (approved upper temperature limit). In case of the upper temperature limit being exceeded, be sure to decrease the measured temperature below 80℃ by inserting a heat dissipation sheet or applying heat dissipation paste between the aluminum base and the heat sink.

Measure the temperature by attaching the thermocouple to the Single 3W aluminum base completely until the measured temperature stabilizes.


Some photos of led heatsink examples :




There is stronger leds with stronger power and heatsink needs.
See this heatsink for 200W power led with about 14000-15000 lumens :

Cant attach photo sorry, reached limit of 10 attachment per post.







See this alternative material :
**broken link removed**