Question

A thin metallic wall may be constructed using copper (properties
are given in the table). The piping is required

to have a radius r = 0.008 m and carries steam at 385 K. The wall
is inside a room surrounded by air at a temperature

of 298 K. The wall is insulated with a material (properties are
given in the table).

Properties |
Copper |
Insulation material |

Thermal Conductivity (W/m per ˚C) |
385 |
0.071 |

Density (kg/m |
8940 |
453 |

i. If the external the convective heat transfer coefficient, h=
4.0 W/m2.K, what is the critical thickness of insulation?The
conductive resistance due to the wall of the copper wire may be
assumed to be negligible. **(answer: 17.8 mm)**

ii. Determine radial heat transfer per meter length of copper tube
for the following cases:

a. Insulation thickness = 4 mm **(answer: 20.12
W/m)**

b. When the insulation thickness reaches the critical

value r_{crit }**(answer: 20.10
W/m)**

c. Insulation thickness = 50 mm **(answer: 17.33
W/m)**

Answer #2

Answer for the first question is given for **CRITICAL
RADIUS OF INSULATION.** But the question is about
**CRITICAL THICKNESS OF INSULATION.** so please check
that.

And regarding the answers of second question.

They are nearly obtained correct.But the first two answers are given wrong in your problem.

The heat transfer at critical radius of insulation must be more than the heat transfer at 4mm thickness of insulation.

Finally,what is meant to say is follow the answers provided by me in the solution.They are correct and followed the principle.

Hope it helps.

Thank you.

answered by: anonymous

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