PROCESSES AND PROCESS VARIABLE
3.1
3.2
3.3
3.4
3.5
Mass and Volume
Flow rate
Chemical composition
Pressure
Temperature
(Chapter 3 of the Text Book)
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Week 2 : Part 1
3.1
3.2
3.3
Mass and Volume
Flow rate
Chemical composition
(Chapter 3 of the Text Book)
2
3.1 Mass and volume
q Density
– mass per unit volume ( kg/m3, g/cm3, lbm/ft3, ect.)
q Specific volume - inverse of density (m3/kg, cm3/g, ft3/lbm, ect.)
q Specific gravity - ratio of the density of substance (ρ) to the density of
reference (ρref); (SG = ρ/ρref)
SG
20 o C / 4 o C
 0 .6
* SG of subtance at 20oC with
reference to water at 4oC is 0.6.
Refer TABLE B.1 for SG of selected
compounds.
Commonly used ρref :
 H 2O ( l ) ( 4 o C )  1 . 000 g
cm 3
 1000 kg 3
m
 62 . 43 lb m 3
ft
3
3.1 Mass and volume (cont')
Try the following questions:
qTest your self (page 37)
qExample 3.1-1
qExample 3.1-2
4
3.2 Flow rate - Mass and volumetric flow rate
Density = mass/volume = mass rate/volume rate
  m  m 
v
v
Density of a fluid can be used to convert
a known volumetric flow rate to the mass flow rate
q Test your self (page 39)
5
3.2 Flow rate - Measurement
Flowmeter is a device to read flow rate in a process line.
Commonly used flowmeter – rotameter and orifice meter (pls refer Fig 3.2.1)
6
3.3 Chemical composition
3.3a Moles and molecular weight
Atomic weight – the mass of atoms of certain element (example: C = 12)
Molecular weight - sum of the atomic weight of elements
in the molecule of the compound
Example: atomic weight of oxygen (O) = 16
molecular weight of oxygen (O2) = 16x2 = 32
Refer Table B.1 for the molecular weight (MW) value of other compounds
7
3.3 Chemical composition
3.3a Moles and molecular weight
Types of mole:
Gram-mole = g-mole = mol
kg-mole = kmol
Ib-moles
ton-moles
Types of molecular weight:
Note as M or MW
kg/kmol
g/gmol
Ibm/Ib-moles
Example: Carbon monoxide (CO), its MW is 28. Hence,
1 mol of CO contains 28 g = 28 g/mol
1 kmol of CO contains 28 kg = 28 kg/kmol
1 Ib-mole of CO contains 28 Ibm = 28 Ibm/Ib-mole
1 ton-mole of CO contains 28 tons = 28 tons/ton-mole
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3.3 Chemical composition
3.3a Moles and molecular weight (cont')
MW can be used as a conversion factor that relates the mass
and the number of moles of the compounds
Example : To convert 34 kg of ammonia (NH3) to kmol (MW = 17)
34 kg
1 kmol
2.0 kmol NH3
17 kg
Please try the following questions:
q Example 3.3-1
q Test your self (page 42)
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3.3 Chemical composition
3.3b Mass and mole fraction and average molecular weight
Mass fraction :
Mole fraction :
xA 
yA 
mass of A  kg A
gA
Ibm A 
or
or
total mass  kg total g total Ibm total 
moles of A  kmol A
gmol A
Ib - moles A 


or
or
total moles  kmol total gmol total Ibmole total 
Average molecular weight :
M  y 1M 1  y 2 M
2
 ......
1
x
x2
 1 
 .....
M1
M2
M
Please try the following questions:
q Example 3.3-2
q Example 3.3-3
q Example 3.3-4
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3.3 Chemical composition
3.3b Mass and mole fraction and average molecular weight
Mass fraction can be converted to mole fraction by:
1. Assuming basis of calculation a mass of the mixture (eg. 100kg)
2. Use the mass fraction to calculate mass of each component
3. Convert the mass of each component to mole using its MW
4. Calculate the total mole of the mixture
5. Take the ratio of the moles of each component to the total mole of mixture
6. Hence mole fraction can be determined.
Example 3.3-3 : Basis 100 g (mtotal)
Component
i
Mass fraction
xi (g/g total)
Mass (g)
mi = xi*m(total)
MW
Mi(g/mol)
Moles
ni =mi(g)/Mi(g/mol)
Mole
fraction
yi=ni/n(total)
O2
0.16
16
32
0.50
0.15
CO
0.04
4
28
0.14
0.04
CO2
0.17
17
44
0.39
0.12
N2
0.63
63
28
2.20
0.69
Total
1.00
100
3.28
1.00
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3.3 Chemical composition
3.3c Concentration
Mass concentration : mass of component per unit volume (g/cm3, kg/in3)
Molar concentration : mole of component per unit volume (kmol/m3)
Molarity : gmoles of solute per liter of solution
(2 molar solution A = 2 mol A/liter solution)
Please try the following question:
q Example 3.3-5
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3.3 Chemical composition
3.3d Part per Million and Part per Billion
Part per million (ppm)
Part per billion (ppb)
Use to express trace species in gas or liquid
Example:
15 ppm SO2 in air = 15 parts per million SO2
Every million moles of air contains 15 moles of SO2
Mole fraction of SO2 in air = 15 x10-6
Please try : Test your self (page 47)
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END OF WEEK 2: PART 1
Week 2 : Part 2
3.4
3.5
Pressure
Temperature
(Chapter 3 of the Text Book)
15
3.4 Pressure
3.4a Fluid pressure and hydrostatic head
q Pressure - ratio of a force to the area on which the force acts.
Unit - N/m2, Pa (SI), dynes/cm2, Ibf/in2 or psi
q Fluid pressure – (F/A) where F is the minimum force exerted on the
frictionless plug in the hole (A) to keep the fluid from emerging
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3.4 Pressure
3.4a Fluid pressure and hydrostatic head
q Hydrostatic pressure –
When;
# the P of the fluid at the based of the column
# the force that exerted on the base divided by the base area A
Where;
Force (total) = force top surface + weight of fluid in the column
Hence;
Po
P = Po + ρgh
h
ρ
P
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3.4 Pressure
3.4a Fluid pressure and hydrostatic head
q Hydrostatic head (head of fluid)
The height of the column of the fluid exerted the pressure at its base
and the pressure at the top is zero
Hence;
P = ρgh where Po = 0
Po
h
Please try the following questions:
q Example 3.4-1
q Example 3.4-2
ρ
P
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3.4 Pressure
3.4b Atmospheric pressure, absolute pressure and gauge pressure
Pabsolute = Pgauge + Patmospheric
Patmospheric = 1 atm (standard pressure)
Pgauge = pressure from pressure-measuring devices
Pabsolute = Pgauge when (Patm = vacuum)
Standard atmospheric pressure: 760 mmHg, 1 atm
Please try Test yourself (page 50)
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3.4 Pressure
3.4c Fluid pressure measurement
Categorizes of pressure-measurement devices:
q Elastic-element methods – Bourdon tubes, bellows or diaphragms
q Liquid-column method – manometers
q Electrical methods – strain gauges
Strain gauge
Bourdon gauge – suitable to measure fluid
pressures from vacuum to 7000 atm
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3.4 Pressure
3.4c Fluid pressure measurement
Manometer give more accurate measurement (pressure < 3 atm)
Barometer when P1 = Patm (absolute pressure @ sealed end)
P1
P1
P1
P2
P2
P2
ρ1
sealed-end
opened-end
Types of manometers
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3.4 Pressure
3.4c Fluid pressure measurement
P1
General manometer equation:
P1 + ρ1gd1 = P2 + ρ2gd2 + ρfgh
when fluid 1 and 2 are the same,
ρ1 = ρ2 = ρ
Manometer
variable
P2
ρ2
d2
d1
ρ1
ρf
Differential Manometer equation:
P1 - P2 = (ρf - ρ)gh
If either fluid 1 or 2 is gas at moderate pressure, part ρgd can be neclected
Manometer formula for gasses:
P1-P2 = h
Please try the following equations:
q Test yourself (page 53)
q Example 3.4-3
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3.5 Temperature
Temperature mearsuring devices:
o resistance thermometer
o thermocouple
o pyrometer
o thermometer
Temperture scales:
o Celsius
o Fahrenheit
o Kelvin
o Rankine
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3.5 Temperature
Temperature conversion & conversion factor:
T(K) = T(oC) + 273.15
T(oR) = T(oF) + 459.67
Kelvin (K)
Rankine (R)
T(oR) = 1.8T(K)
T(oF) = 1.8T(oC)+32
Conversion factor for temperature interval:
1.8 o F 1.8 o R 1o F 1o C
,
, o ,
o
1K
1 C
1 R 1K
Please try the following equations:
q Test yourself (page 55)
q Example 3.5-1, 3.5-2 and 3.5-3
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END OF WEEK 2: PART 2
• Try exam questions Dec 2016 (Q1 & Q2)
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