Chapter 1

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Dr. M. K. O. Hadj-Kali / ChE315. 1. Transport Processes and. Separation Process Principles. (Geankoplis). CHE315. Dr. Mohamed Kamel Omar Hadj-Kali ...
Transport Processes and Separation Process Principles (Geankoplis)

CHE315 Dr. Mohamed Kamel Omar Hadj-Kali 1 Dr. M. K. O. Hadj-Kali / ChE315

Chapter 1 Introduction to Engineering principles and units

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Arrangement of the book • The reference book (Geankoplis) is arranged in two parts: – Transport Processes : Momentum, heat and mass. – Separation Process Principles (which includes Unit Operations)

The module CHE315 deals only with the first part 3 Dr. M. K. O. Hadj-Kali / ChE315

Fundamental transport processes • Many of the chemical separation processes have certain fundamental and basic principles in common.

• According to transfer processes, we can make the following classification: – Momentum transfer: filtration – Heat transfer: Drying – Mass transfer: liquid – liquid extraction 4 Dr. M. K. O. Hadj-Kali / ChE315

Main systems of basic units • There are three main systems of basic units employed at present in engineering and science: length

– SI system – English system – cgs system

m ft cm

mass

kg lbm g

time

s s s

• For the SI system of units, the other standard units (N, J, W, Pa) are derived from these basic quantities. • In the English system, the pound force (lbf) is considered as a basic unit  introduction of the proportionality factor gc. 5

Dr. M. K. O. Hadj-Kali / ChE315

Methods of expressing temperature • There are four temperature scales in common use in Chemical Engineering: °C, °F, °R and K. • The following equations can be used to convert from one scale to another: °F °C °R K

= 32 + 1.8 (°C) = 1/1.8 (°F – 32) = °F + 459.67 = °C + 273.15 6

Dr. M. K. O. Hadj-Kali / ChE315

Mole and mass units • There are many methods to express compositions in gases, liquids and solids. One of the most useful is molar fractions since chemical reactions and gas laws are simpler to express in terms of molar units. • The mole fraction of a particular substance A in the mixture is obtained by the expression:

xA = nA / nTot Where nA is the number of moles of A and nTot the total number of moles.

• In like manner, the weight or mass fraction (wA) is expressed by:

wA = mA / mTot Dr. M. K. O. Hadj-Kali / ChE315

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Concentration units for liquids • When one liquid is mixed with another miscible liquid, the volumes are not additives. Compositions of liquids are expressed as weight or mole percent or molarity which is defined as gmol of a component per liter of solution. • The most common method expressing total concentration per unit volume is density (kg/m3, lbm/ft3, …) or specific gravity (defined as the density of the solution at its given temperature divided by the density of a reference substance at the same temperature. 8 Dr. M. K. O. Hadj-Kali / ChE315

Gas law and vapor pressure • Ideal gas are supposed to obey the following conditions: – made of rigid spheres, – occupy no volume, – do not exert force on one another

• No real gases obey these laws exactly, but at ordinary T° and P we can suppose that these laws are sufficiently accurate for engineering problems. • Ideal Gas law of Boyle is expressed as follows

pV = nRT P: absolute pressure (N/m2) / T: absolute temperature (K) V: Volume of the gas (m3) / n: Kg moles of the gas R: Gas law constant = 8314.3 (kg * m3) / (kg mole * s2 * K) Dr. M. K. O. Hadj-Kali / ChE315

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Ideal gas mixtures • Dalton’s law for mixtures of ideal gases states that the total pressure of a gas mixture is equal to the sum of the individual partial pressures:

P = PA+ PB+ PC+ ... • Since the number of moles of a component is proportional to its partial pressure, the mole fraction of a component A is:

yA = PA/ P = PA/ (PA + PB + PC + ...) • •

Gas mixtures are almost always represented in terms of mole fraction and not weight fractions. For engineering purposes, Dalton’s law is sufficiently accurate for actual mixtures and at total pressures of a few atmospheres or less. 10

Dr. M. K. O. Hadj-Kali / ChE315

Vapor pressure of liquids • When a liquid is placed in a sealed container, molecules of liquid will evaporate into the space above the liquid and fill it completely. After a time, an equilibrium is reached. This vapor will exert a pressure that we call the

vapor pressure of the liquid. • The vapor pressure of a liquid increases markedly with temperature. The plot of this vapor pressure vs temperature does not yield a straight line but a curve. Psat

Ln(Psat) For moderate T

T Dr. M. K. O. Hadj-Kali / ChE315

1/T

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Conservation of mass • The total mass of all materials entering any process must equal the total mass of all materials leaving plus the mass of any materials accumulating or left in the process:

input = output + accumulation • In steady state process, there is no accumulation, so:

input = output “What goes in must come out” 12 Dr. M. K. O. Hadj-Kali / ChE315

Simple material balances • To solve a material balance problem, it is advisable to proceed by a series of definite steps: – Sketch a simple diagram of the process by a simple box diagram showing each stream entering

– Write the chemical equations involved (if any) – Select a basis for calculation – Make a material balance

Please show the different examples given in the book Dr. M. K. O. Hadj-Kali / ChE315

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