Thermodynamics: An Engineering Approach 8th Edition

Published by McGraw-Hill Education
ISBN 10: 0-07339-817-9
ISBN 13: 978-0-07339-817-4

Chapter 15 - Chemical Reactions - Problems - Page 801: 15-113

Answer

$D=a n$ $E=b n$ $F=m / 2$ $J=3.76(1+B) A_{\text {ih }}$ $G=\frac{b n}{2}+B A_{\text {th }}$

Work Step by Step

The balanced reaction equation for stoichiometric air is $$ \mathrm{C}_n \mathrm{H}_m+A_{\mathrm{th}}\left[\mathrm{O}_2+3.76 \mathrm{~N}_2\right] \longrightarrow n \mathrm{CO}_2+(\mathrm{m} / 2) \mathrm{H}_2 \mathrm{O}+3.76 A_{\mathrm{lh}} \mathrm{N}_2 $$ The stoichiometric coefficient $A_{\text {出 }}$ is determined from an $\mathrm{O}_2$ balance: $$ A_{\mathrm{th}}=n+m / 4 $$ The reaction with excess air and incomplete combustion is $$ \mathrm{C}_n \mathrm{H}_m+(\mathrm{I}+B) A_{\mathrm{lh}}\left[\mathrm{O}_2+3.76 \mathrm{~N}_2\right] \longrightarrow a n \mathrm{CO}_2+b n \mathrm{CO}+(m / 2) \mathrm{H}_2 \mathrm{O}+G \mathrm{O}_2+3.76(\mathrm{I}+B) A_{\mathrm{th}} \mathrm{N}_2 $$ The given reaction is $$ \mathrm{C}_n \mathrm{H}_n+(\mathrm{I}+B) A_{\mathrm{th}}\left[\mathrm{O}_2+3.76 \mathrm{~N}_2\right] \longrightarrow D \mathrm{CO}_2+E \mathrm{CO}+F \mathrm{H}_2 \mathrm{O}+G \mathrm{O}_2+J \mathrm{~N}_2 $$ Thus, $$ \begin{aligned} & D=a n \\ & E=b n \\ & F=m / 2 \\ & J=3.76(1+B) A_{\text {ih }} \end{aligned} $$ The coefficient $G$ for $\mathrm{O}_2$ is determined from a mass balance, $\mathrm{O}_2$ balance:$$ \begin{aligned} (1+B) A_{\text {th }} & =a n+\frac{b n}{2}+\frac{m}{4}+G \\ (1+B)\left(n+\frac{m}{4}\right) & =a n+\frac{b n}{2}+\frac{m}{4}+G \\ \left(n+\frac{m}{4}\right)+B A_{\text {lh }} & =a n+\frac{b n}{2}+\frac{m}{4}+G \\ G & =n+B A_{\text {th }}-a n-\frac{b n}{2} \\ & =n(1-a)+B A_{\text {th }}-\frac{b n}{2} \\ & =n b-\frac{b n}{2}+B A_{\text {Lh }} \\ & =\frac{b n}{2}+B A_{\text {th }} \end{aligned} $$
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