A long glass cylinder of inner diameter = 0.03 m and outer

A long glass cylinder of inner diameter = 0.03 m and outer diameter = 0.05 m carries hot fluid inside. If the thermal conductivity of glass = 1.05 W/mK, the thermal resistance (K/W) per unit length of the cylinder is

Given data:
d₁ = 0.03 m

∴ r₁	d₁	=	0.3	= 0.015 m
	2		2

d₂ = .05 m
∴ r₂ = .025 m

K = 1.05	W
	mK

Thermal resistance

R_t =	1	log_e		r₂
	2πKL			r₁

=	1	log_e		.025
	2 × 3.14 × 1.05 × 1			.015

= 0.077 W/m