Calculate Thickness of Oak Layer to Limit Heat Loss to 740kJ/hr in Door

AI Thread Summary
To limit heat loss to 740 kJ/hr through a door with two steel layers, the user is attempting to calculate the necessary thickness of an oak layer using the equation H=area(temp1-temp2)/((thickness1/k1)+(thickness2/k2)). The user has encountered difficulties isolating the variable for oak thickness and is seeking guidance on potential errors in their calculations or conversions. Suggestions include solving the algebraic expression before inserting numerical values to minimize mistakes. The discussion emphasizes the importance of correctly applying thermal conductivity values and ensuring accurate unit conversions. Overall, the user is determined to find the solution with additional tips from the community.
Tonyuguccioni
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Warning! All queries in the Homework section must use the Posting Template provided when a new thread is started.
The information I am given is : a door has two steel layers both are .47 mm thick, the door itself is 725 mm by 1800mm. The question asks, how thick of a layer of wood (oak) would have to be put in the door to limit the heat loss to 740kJ per hour? Temp inside is 18C and outside is -20C

All work is done with only three significant digits.

I have been working with the equation ;
H=area(temp1-temp2)/((thickness1/k1)+(thickness2/k2))
Where; k is the thermal conductivity of the material
X is the unknown

I have run threw the equation several times but every time I either can't isolate the variable or end up with a wrong answer.

0.205kJ/sec= ((1.30m^2)(38C))/((9.40*10^-5m/43W/mC)+(Xm/0.17W/mC))

Is this the right equation and/or have I made a simple error with conversions ?

Please don't post full answer I want to find it but tips or suggestions would be awesome !
 
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thanks but it is still escaping me i feel like i am just one step away from getting it... very frustrating but it i will prevail ! :P
 
Did you try simply solving for X in your equation? (Note that it is usually easier not to make mistakes if you solve the algebraic expression first and insert numbers when this is done)
 
whats the next step? and what is the equation you started with was it H= -kA (dt/dx)
 

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