Unit Operations of Chemical Engineering
Unit Operations of Chemical Engineering
7th Edition
ISBN: 9780072848236
Author: Warren McCabe, Julian C. Smith, Peter Harriott
Publisher: McGraw-Hill Companies, The
Question
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Chapter 10, Problem 10.1P
Interpretation Introduction

Interpretation:

The equivalent thickness of air layers in millimeters is to be calculated.

Concept Introduction:

The law of heat conduction states that the heat transfer rate through any material is proportional directly to the negative of the temperature gradient and the area of the heat flow.

  Q=kA(T2T1)x..... (1)

Here, x is the thickness of the material, T1 is the temperature of the hot side of the wall, T2 is the temperature of the cold side of the wall, A is the area of the heat conduction, and k is the thermal conductivity of the material.

For N materials present in series in a wall, the rate of heat transfer is taken same throughout the wall. The heat transfer equation will now become:

  Q=A(T2T1)iNxiki..... (2)

Expert Solution & Answer
Check Mark

Answer to Problem 10.1P

The air layer thickness is calculated as, xair=298 mm .

Explanation of Solution

Given information:

Thickness of the refractory fireclay brick, xA=200 mm

Thickness of the kaolin brick, xB=100 mm

Thickness of the steel pipe, xC=6 mm

Thin layers of air are between brick and steel.

Fire side refractory temperature, T1=1150C

Temperature of the outside of steel side, T2=30C

Heat loss from the wall per meter square of the wall, Q=300 Wm2

For the appendix 11, take the thermal conductivity of fireclay brick, kaolin brick, steel plate, and air as:

  kA=1.7 WmCkB=0.11 WmCkC=45.34WmCkair=0.11WmC

Let the thickness of air layer be xair . Use equation (2) for 1 m2 of wall area to calculate the air layer thickness as:

  Q=(T2T1)xAkA+xBkB+xCkC+xairkair300 Wm2=(30C1150C)200 mm×m1000 mm1.7 WmC+100 mm×m1000 mm0.11 WmC+6 mm×m1000 mm45.34WmC+xair0.11WmCxair=0.298 mxair=298 mm

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Unit Operations of Chemical Engineering
Chemical Engineering
ISBN:9780072848236
Author:Warren McCabe, Julian C. Smith, Peter Harriott
Publisher:McGraw-Hill Companies, The