A pipe of 25 mm outer diameter carries steam. The heat transfer c
A pipe of 25 mm outer diameter carries steam. The heat transfer coefficient between the cylinder and the surrounding is 5 W/m2K. It is proposed to reduce the heat lost from the surrounding pipe by adding insulation having a thermal conductivity of 0.05 W/mK. Which of the following statements is true?
A. <p>The outer radius if the pipe = the critical radius</p>
B. <p>The outer radius of the pipe is less than the critical radius</p>
C. <p>Adding the insulation will reduce the heat lost</p>
D. <p>Adding the insulation will increase the heat lost</p>
Please scroll down to see the correct answer and solution guide.
Right Answer is: C
SOLUTION
Concept:
In order to provide effective insulation, the radius of insulation must be greater than the critical radius of insulation as at a critical radius of insulation maximum heat loss takes place.
Calculation:
Given:
r2 = 0.125 m = 12,5 mm, ki = 0.05 W/mK
ho = 5 W/m2K
\(r_c = \frac{{{k_i}}}{{{h_o}}} = 10mm\)
\(r_c < r_2,\)the addition of insulation will reduce heat loss
