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Heat Transfer Calculations 
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#1
Jan2511, 01:33 PM

P: 1

I would be grateful for your help with a small project I am involved in at work. I would like to set up an excel spread sheet to calculate either the thickness of insulation required to reduce the temperature of say a furnace wall from the inside to the outside, or calculate the resultant outside wall temperature, knowing the insulation details and inside temperature. I have come across several different formulas on the net, which unfortunately have left me a little confussed.
An application I am currently looking at involves adding a piece of equipment to a furnace roof. This equipment consists of an outer stainless steel cylinder having an outside diameter of 750 mm, a wall thickness of 3 mm, and externally subjected to a temperature of 650 deg C. Inside the cylinder is another cylinder again constructed with stainless steel with a wall thickness of 5 mm. I need to sandwich a sufficient thickness of insulation between the cylinders, to achieve a temperature within the internal cylinder of +/ 60 Deg C. Any help would be much appreciated. 


#2
Jan2611, 06:29 AM

P: 1,235

Hello PWoolfall,
If I understand correctly:
If there is cool air flowing in the inner cylinder, then the design is possible but needs more information:
If you chose a insulation material with heat conductivity of 0.04 W/K.m, if you use an insulation thickness of 0.1 m, then the cold air inside the inner tube should take out an amount of heat of at least q=236 W/m²: since q = 0.04/0.1 * (65060) W/m² if you pipe is 1 meter long, its surface would be 4.7 m², and this would imply a cooling power of Q = q*4.7 = 1100 W = 1.1 kW This would only be possible if the cooling fluid is cold enough and has a sufficient velocity. Before further calculations, please check these comments. 


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