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3/7/2015 1
M.A.A. Shoukat Choudhury, PhDProfessor
Department of Chemical Engineering, BUET
ChE 111 – Chapter 3Processes and Process Variables
February 2015
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Process
• Process: A process is any operation by which a particular objective is accomplished.
• Materials that enter a process is referred to as the input or feed and that which leaves the process is called output or product.
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Process and Input/Output
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Chemical Engineering, BUET Dr. M. A. A. Shoukat Choudhury 4
Mass and Volume
density: mass per unit volume, kg/m3
Specific volume: volume per unit mass, m3/kg
Specific gravity:
SG = /ref
The most commonly used reference material is water at 4 oC
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Chemical Engineering, BUET Dr. M. A. A. Shoukat Choudhury 7
Mass and Volumetric Flow Rates
flow
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Chemical Engineering, BUET Dr. M. A. A. Shoukat Choudhury 8
Mass and Volumetric Flow Rates
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Chemical Engineering, BUET Dr. M. A. A. Shoukat Choudhury 9
Flow Rate Measurement
Rotameter Orifice meter
A flow meter is a device mounted in a process pipe that provides
a continuous reading of the flow rate in the pipe line
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Flow Rate Measurement
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Chemical Composition
Mole and Molecular Weight
- Atomic Weight
- Molecular weight
- g-mole or mole
- lb-mole
- Kmole
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Mass Fraction and Mole Fraction
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Conversion using Mass and Mole Fractions
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Mass composition to Molar Composition
Example 3.3-3
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Example 3.3-3 (solution)
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Average Molecular Weight
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Mass Concentration and Molar Concentration
• Mass Concentration = density
• Molar concentration = number of moles per unit volume
• Molarity = molar concentration expressed in gmoles per Litre, e.g.
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ppm and ppb
• ppm – Parts per million
• ppb – parts per billion
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Example 3.3-5
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Solution to example 3.3-5
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Figure 3.4-1: Fluid pressure in a tank and a pipe.
PressureFluid Pressure and Hydrostatic Head
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Figure 3.4-2: Pressure at the base of a fluid column.
PressureHydrostatic Head
Hydrostatic Pressure/Head :
The pressure exerted by the fluid at
the base of the tank. Here, P.
Show that (by force balance):
Since A does not appear in this
equation, the formula is a
applicable to any column of fluid
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Equivalence betn Head and Pressure
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Pressure Equation as Head
Equation 3.4-1 as fluid head (e.g., mercury):
Example 3.4-2:
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Atmospheric Pressure
• Atmospheric Pressure: The pressure of the atmosphere can be thought of as the pressure at the base of a column of fluid (air) located at the point of measurement (sea level). Equation 3.4-1 can be used for calculation with Po= 0 and average values of air density and gravitational acceleration.
• Typical Values of atmospheric pressure at sea level are 760 mm Hg, 14.7 psi or 1 atm
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Atmospheric Pressure, Gauge Pressure,Absolute Pressure
• Relationship between absolute and Gauge pressure
• Conventionally, psia and psig are used to denote absolute and gauge pressure in psi units
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Fluid Pressure Measurement
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Figure 3.4-3: Bourdon gauge.
Pressure Measuring Device
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• A manometer is a U-shaped tube partially filled with a fluid of known density
Manometer
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Elementary Principles of Chemical Processs, 3/E by Richard M. Felder and Ronald W. RousseauCopyright © 2005 by John Wiley & Sons, Inc. All rights reserved.
Figure 3.4-5 (p. 58)Manometer variables.
Manometer Equation Derivation
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Manometer Equation Derivation
• The pressure at the height of the lower surface of the manometer fluid is same at the both arms of the manometer
• General Manometer Equation
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Elementary Principles of Chemical Processs, 3/E by Richard M. Felder and Ronald W. RousseauCopyright © 2005 by John Wiley & Sons, Inc. All rights reserved.
Example 3.4-3(1) (p. 59)
Differential Manometer Equation
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Special Cases of Manometer Equation
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Example 3.4-3
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Temperature
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Temperature (cont’d)
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Relation Between Temperature Scales