Chapter 4, Problem 4.17P

Interpretation Introduction

(a)

Interpretation:

The flow-chart for the given process is to be drawn and labelled. Also, the degree of freedom analysis is to be done on the given system.

Concept introduction:

A flowchart is the complete representation of a process through boxes or other shapes which represents process units and arrows that represents the input and output of the process. The flowchart must be fully labelled to infer important data about the process involved.

Degree of freedom analysis is the procedure to analyze any missing information needed for material balance calculations. The procedure involves complete labelling of the flowchart representing the process and then determining number of unknown variables $\left(n_{\text{unknowns}}\right)$ and independent equations $\left(n_{\text{indep eqns}\text{.}}\right)$ from that flowchart.

Mathematically, degree of freedom $\left(n_{\text{df}}\right)$ is formulated as:

$n_{\text{df}}=n_{\text{unknowns}}-n_{\text{indep eqns}\text{.}}$ ......... (1)

A fuel-air mixture cannot be ignited if the fuel percent is below a certain value called the Lower flammability limit (LFL), also known as Lower explosion limit (LEL). Also, there is an Upper flammability limit (UFL) which is known as Upper explosion limit (UEL).

Between these limits, a fuel-air mixture can ignite when exposed to any spark or flame.

For propane in air mixture, LFL is $2.3{\text{ mol\% C}}_3{\text{H}}_8$ and UFL is $9.5{\text{ mol\% C}}_3{\text{H}}_8$.

Interpretation Introduction

(b)

Interpretation:

The minimum the molar flowrate of dilution air is to be calculated.

Concept introduction:

In a system, a conserved quantity (total mass, mass of a particular species, energy or momentum) is balanced and can be written as:

$input+generation-output-consumpumtion=accumulation$

Here, ‘ input’ is the stream which enters the system. ‘ generation’ is the term used for the quantity that is produced within the system. ‘ output’ is the stream which leaves the system. ‘ consumption’ is the term used for the quantity that is consumed within the system. ‘ accumulation’ is used for the quantity which is builds up within the system.

All the equations which are formed are then solved simultaneously to calculate the values of the unknown variables.

Molar flowrate of a component ${\left(\stackrel{•}{n}\right)}_{\text{S}}$ is given by:

${\left(\stackrel{•}{n}\right)}_{\text{S}}=\left(x_{\text{s}}\right)\stackrel{•}{n}$ ......... (2)

Here, $\stackrel{•}{n}$ is the molar flowrate of the stream and $x_{\text{s}}$ is the mole fraction of the substance in the stream.

A fuel-air mixture cannot be ignited if the fuel percent is below a certain value called the Lower flammability limit (LFL), also known as Lower explosion limit (LEL). Also, there is an Upper flammability limit (UFL) which is known as Upper explosion limit (UEL).

Between these limits, a fuel-air mixture can ignite when exposed to any spark or flame.

For propane in air mixture, LFL is $2.3{\text{ mol\% C}}_3{\text{H}}_8$ and UFL is $9.5{\text{ mol\% C}}_3{\text{H}}_8$.

Interpretation Introduction

(c)

Interpretation:

The actual flowrate of dilution air and the value calculated in part (b) is to be compared and explained.

Concept introduction:

A fuel-air mixture cannot be ignited if the fuel percent is below a certain value called the Lower flammability limit (LFL), also known as Lower explosion limit (LEL). Also, there is an Upper flammability limit (UFL) which is known as Upper explosion limit (UEL).

Between these limits, a fuel-air mixture can ignite when exposed to any spark or flame.

For propane in air mixture, LFL is $2.3{\text{ mol\% C}}_3{\text{H}}_8$ and UFL is $9.5{\text{ mol\% C}}_3{\text{H}}_8$.

The process in which a low concentration mixture is made from a high concentration mixture is called dilution.