kon dak shen

 for conduction, fourier's law is used,

q/A= K/(X2-X1) x (t1-t2)

q           ;heat transfer rate(w)
A          ;cross sectional area(m2)
k           ; Thermal conductivity
x2-x1    ;distance(m)
t           :temperature (K)

for the A is always different formula are used, this is because sometimes it is flat wall,hollow cylinder or sphere.

cylinder ; q= [(k)2pai L/ln(r2)(r1) ] / (t2-t1)

sphere   ; q =(t1-t2) / [(1/r1-1/r2)(4pai k )]