Question

The thermal conductivity of brick is 1.7 W m^-1k^-1 and that of cement is 2.9 W m^-1k^-1 . What thickness of cement will have same insulation as the brick of thickness 20 cm.

Answer 1

Given :     

K_B = 1.7 W m⁻¹ K⁻¹ 

K = 2.9 W m⁻¹K ⁻¹ 

d = 20 cm 

d_c = ?

From formula the heat flow is given by

Q=KA\(\frac{Δ\theta}{d}t\)

For same insulation by the brick and the cement, Q, A, ∆θ and t don’t change. Hence should be a constant.

or  \(\frac{K_{\theta}}{d_{\theta}}\)=\(\frac{K_{c}}{d_{c}}\)

or  d_c=\(\frac{K_{C}}{K_{B}}d_{B}\)

=\(\frac{2.9}{1.7}\times20=34.12cm\)