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Basic Chemical Engineering

Lecture - 2

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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.

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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.

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Common Systems of Units

Over time a lot of international unit systems have

evolved, few of which are in use worldwide.

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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

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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

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Unit Conversion & Conversion Factors

Conversion Factors

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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.

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Unit Conversion & Conversion Factor

Example 1.3:

Change 400 in3/day to cm3/min.

Practice Yourself: Convert 25 ft3/year to m3/s.

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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

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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?

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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)

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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

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Quick Review

Differentiate between Units & Dimensions?

Units are determined relative to a _________, which is taken

as a standard.

Solve Practice Yourself Questions on Notebook.