If a foam insulation is added to a 4 cm outer diameter

If a foam insulation is added to a 4 cm outer diameter pipe as shown in the figure, the critical radius of insulation (in cm) is ________.

K_foam = 0.1	W
	mK

h₀ = 2	W
	m²K

Critical radius, r_c =	K_foam	for a pipe
	h₀

=	0.1	= 0.05 m = 5 cm
	2