Chapter 8, Problem 8.36P

Interpretation Introduction

Interpretation:

The rate at which the energy is lost due to breathing in $\text{J/day}$ is to be determined.

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.

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

$\mathrm{input}+generation-output-consumpumtion=accumulation$

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.

The equation for energy balance is:

$\Delta H+\Delta E_{\text{k}}+\Delta E_{\text{p}}=Q-W_{\text{s}}$   ....... (1)

Here, $\Delta H$ is the change in the enthalpy of the system, $\Delta E_{\text{k}}$ is the kinetic energy change of the system, $\Delta E_{\text{p}}$ is the potential energy change of the system, $Q$ is the net energy which is transferred to a system and $W_{\text{s}}$ is the word done by the shaft.

The mole fraction of a species $\left(y_i\right)$ in a mixture is given by:

$y_i=\frac{p_i}{p_{\text{total}}}$   ....... (2)

Here, $p_i$ is the partial pressure of the species in the mixture and $p_{\text{total}}$ is the total pressure of the mixture.

The formula to calculate relative humidity is:

$h_r=100\times \frac{p_{{\text{H}}_2\text{O}}}{p_{{\text{H}}_2\text{O}}{}^{\ast }\left(T\right)}$   ....... (3)

Here, $p_{{\text{H}}_2\text{O}}$ is the partial pressure of ${\text{H}}_2\text{O}$ and $p_{{\text{H}}_2\text{O}}{}^{\ast }\left(T\right)$ is the equilibrium pressure of ${\text{H}}_2\text{O}$ at temperature $T$.