View
225
Download
0
Category
Preview:
Citation preview
7/30/2019 units and dimension in chemical engineering
1/15
Basic Chemical Engineering
Lecture - 2
7/30/2019 units and dimension in chemical engineering
2/15
Basic Concepts of Chemical
Engineering
Units & Dimensions
What are Dimensions:
Dimensions are our basic concepts of measurement such as length,
time, mass, temperature, etc.
But dimensions alone cannot suffice for our requirements. We
need to quantify these concepts of measurement for our day to day use.
7/30/2019 units and dimension in chemical engineering
3/15
Basic Concepts of Chemical
Engineering
Units & Dimensions What is a Unit:
A unit of measurement is a definite magnitude of a physical quantity,
defined and adopted by convention and/or by law, that is used as astandard for measurement of the same physical quantity.
Unit is how you define a quantity under discussion. If we say thatweight of the computer is 10 kilogram, weight of the computer is thequantity under discussion & 10 kilogram is its unit.
Similar Common examples of Units are meter, Co, Km/hr, etc.
Units are determined relative to a physical quantity, which is taken as astandard.
7/30/2019 units and dimension in chemical engineering
4/15
Common Systems of Units
Over time a lot of international unit systems have
evolved, few of which are in use worldwide.
7/30/2019 units and dimension in chemical engineering
5/15
7/30/2019 units and dimension in chemical engineering
6/15
Basic Mathematic Operations on Units
Add or Subtract Units & Dimensions are SAME
5 kilograms + 3 kilograms = ? Possible
10 kilograms 6 joules = ? Not Possible20 kilograms + 10 pounds = ? Possible
7/30/2019 units and dimension in chemical engineering
7/15
Basic Mathematic Operations on Units
Multiply or Divide Units are NOT SAMEBut You cannot cancel them with each other unless they are the same.
20 centimeter 5 seconds = 4 cm/s Possible
4 kilogram x 20 miligram = 80 kg Not Possible
10 Newton x 3 meter = 30 N.m Possible
50 ft2 2 ft = 25 ft Possible
2 horsepower 746 Watt = Not Possiblewatt
hp
746
2
7/30/2019 units and dimension in chemical engineering
8/15
Unit Conversion & Conversion Factors
Conversion Factors
7/30/2019 units and dimension in chemical engineering
9/15
Unit Conversion & Conversion Factor
Dimensional Equation
Example 1.2:
If a plane travels twice the speed of sound (assumethat the speed of sound is 1100 ft/s), how fast it is
going in miles per hour?
Practice Yourself: Convert 20 gal/hr to m3/s.
7/30/2019 units and dimension in chemical engineering
10/15
Unit Conversion & Conversion Factor
Example 1.3:
Change 400 in3/day to cm3/min.
Practice Yourself: Convert 25 ft3/year to m3/s.
7/30/2019 units and dimension in chemical engineering
11/15
Units for Constants Used in Equations
Units for Constants vary according to the System ofUnits being used.
Let us consider the example of the equation
F m a
F = C m a
F = Force
C= Constant of Proportionality
m = Mass
a = acceleration
am
FC
7/30/2019 units and dimension in chemical engineering
12/15
Units for Constants Used in Equations
Example 1.4 Use of gc:
One hundred pounds of water is flowing through a pipe
at the rate of 10 ft/s. What is the kinetic energy of thiswater in (ft)(lbf)?
Practice Yourself:
What is the potential Energy in (ft)(lbf) of a 100 lb drumhanging 10 ft above the surface of the earth withreference to the surface of the earth?
7/30/2019 units and dimension in chemical engineering
13/15
Being Careful About Units
Some times Units may sound the same but
they belong to different dimensions, you have
to decide based on common sense.
A man is 6 feet tall but has only two feet.
N . m vs. m . N
m . s (meter . Second) vs. ms (Milli Second)
7/30/2019 units and dimension in chemical engineering
14/15
Course Outline for
BSc. Chemical Engineering CHE116 Basic Chemical Engineering
Introduction to chemical engineering: Introduction to Engineering Profession.
Responsibilities and ethics for engineers. Role of chemical engineer. History of
profession and future directions. Career opportunities in Chemical Engineering.
Basic concepts of Chemical Engineering: Units and dimensions, conversion of
units. Process variables; pressure, temperature, concentrations and Compositionof mixtures.
Material balances: Fundamentals of material balances; Program of analysis of
material balance problems, material balance calculations, Balances on non
reactive systems, balance on reactive systems and Processes, Recycle, By-pass and
purge calculations, Case studies on balances for important industrial processes.
Ideal gases, equations of state for real gases. The compressibility factor equationof state.
Energy Balance: Concepts and units, Forms of energy: The first law of
thermodynamics. Calculation of enthalpy changes. Applications of the general
energy balance without reactions occurring.
Ethics: Professional ethics: The ethics challenge and ethical case studies.
Credit hours/ Contact Hours - 2
7/30/2019 units and dimension in chemical engineering
15/15
Quick Review
Differentiate between Units & Dimensions?
Units are determined relative to a _________, which is taken
as a standard.
Solve Practice Yourself Questions on Notebook.
Recommended