Fundamentals of Heat and Mass Transfer
Fundamentals of Heat and Mass Transfer
7th Edition
ISBN: 9780470501979
Author: Frank P. Incropera, David P. DeWitt, Theodore L. Bergman, Adrienne S. Lavine
Publisher: Wiley, John & Sons, Incorporated
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Chapter 11, Problem 11.1P

In a fire-tube boiler, hot products of combustion flowing through an array of thin-walled tubes are used toboil water flowing over the tubes. At the time of installation, the overall heat transfer coefficient was 400  W/m 2 K . After 1 year of use, the inner and outertube surfaces are fouled, with cot-responding foulingfactors of R f , i n = 0.0015 and R f , o n = 0.0005  m 2 K/W ,respectively. Should the boiler be scheduled for cleaning of the tube surfaces?

Expert Solution & Answer
Check Mark
To determine

Whether the boiler should be scheduled for cleaning of the tube surfaces.

Answer to Problem 11.1P

Scheduled cleaning is essential.

Explanation of Solution

Given information:

The overall heat transfer coefficient at the time of installation: U=400 W/m2.K

Fouling factors of inner and outer tube surfaces after 1 year of use:

  Rf,i"=0.0015 m2.K/WRf,o"=0.0005 m2.K/W

Calculations:

  Fundamentals of Heat and Mass Transfer, Chapter 11, Problem 11.1P

The overall heat transfer coefficient after one year is calculated as:

  1U=1hi+1hO+Rf,i''+Rf,o''.since,1hi+1hO=1400 W/m2K

  1U=1400 W/m2K+(0.0015+0.0005)m2K/W=0.0045 m2K/WU=222 W/m2K

Thus, periodic cleaning is essential for efficient boiler operation.

Conclusion: The boiler should be scheduled for cleaning of the tube surfaces

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Chapter 11 Solutions

Fundamentals of Heat and Mass Transfer

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