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Caculating heat loss from cooling fins? 
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#1
Oct1911, 04:58 AM

P: 12

Hello,
I am currently studying transformer design, in particular cooling methods. I am tyring to calculate the cooling effect (increased heat transfer) of adding cooling fins to a transformer. Does anyone know of some general equations/methods for calculating the increased heat radiation achieved by adding cooling fins. Thanks, Rob 


#2
Oct1911, 02:25 PM

P: 688

Basically, fins increase the heat transfer rate by adding surface area. But there is an efficiency associated with the fins. The heat transfer rate is:
q_Total = Nfin * eff * hfin * Af * (Tsurface  Tsurr) + hbase * Ab * (Tsurface  Tsurr) q_Total = heat transfer rate Nfin = number of fins eff = fin efficiency hfin = convection heat transfer coefficient of fin Af = surface area of one fin Tsurface = surface temperature Tsurr = surroundings temperature hbase = convection heat transfer coefficient of base Af = surface area of base Notice the first term in the above equation is the heat transfer from the fin and the second term is from the base. These calculations are a bit of an art. The trick is to make simplyfying assumptions that do not introduce too much error. Let me know if you need help getting started. 


#3
Oct1911, 03:09 PM

PF Gold
P: 244

Just have in mind that adding metals close to a transformer will generally reduce the transformers efficiency. When a heat sink is placed upon a toroide transformer for example, the transformer is "seeing" a short circuit secondary winding because the magnetic field wants to induce electric current through the heat sink. As the heat sink (usually made by copper or aluminum) is a good conductor, it will for sure reduce the efficiency of the transformer  which in turn makes it even hotter than without heat sink at all.
Vidar 


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