Question

122 Thermal Properties of Matter
28. Two coaxial cylinders of radius r and 3r are made
of material of thermal conductivity
K, and K2
respectively. The equivalent thermal conductivity of
substance for axial heat flow may be
130
4(K, +K2)
Kq+6K2
(1)
9
Kq +8K2
(4) Ki + K₂

plz can anyone solve it​

Answer 1

Answer:

answer the questions option c.

Answer 2

Answer:

(k1+8k2)/9

Explanation:

keff=(k1a1+k2a2)/a1+a2

a1=πr^2

a2=π(3r)^2-π(2r)^2

=8πr^2

keff=(πr^2k1+8πr^2 k2)/πr^2+8πr^2

={πr^2(k1+8k2)}/9πr^2

=(k1+8k2)/9