Question

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

• A. 0.031
• B. 0.077
• C. 0.17
• D. 0.34

Answer 1

The correct option is B 0.077

Given data:
$d_1=0.03m$
$\therefore r_1=\frac{d_1}{2}=\frac{0.03}{2}=0.015m$
$d_2=0.05m$
$\therefore r_2=\frac{d_2}{2}=\frac{0.05}{2}=0.025m$

k = 1.05 W/mK



Thermal resistance,
$R_t=\frac{1}{2\pi kl}lo{g}_e\frac{r_2}{r_1}$

$=\frac{1}{2\times 3.14\times 1.05\times 1}lo{g}_e\frac{0.025}{0.015}=0.077K/W$