Chap. 1 Introduction to Engineering Calculations

7/28/2019 Chap. 1 Introduction to Engineering Calculations

1/21

Introduction to EngineeringCalculations

Chapter1


2/21

After completing this chapter, you should

be able to:

Identify units commonly used to express both

mass and weight in SI and Americanengineering system

Perform unit conversions

Apply the concept of dimensional homogeneityof equation


3/21

Units and Dimension

Conversions of Unit

Systems of Units

Force, Weight and Mass

Whats in this chapter


4/21

Introduction

Describe the basic techniques for the handling of

units and dimensions in calculations.

Describe the basic techniques for expressing the

values of process variables and for setting up andsolving equations that relate these variables.

Develop an ability to analyze and work engineering

problems by practice.


5/21

CHEMISTVS

CHEMICAL ENGINEER


6/21

SEPARATION PROCESS

REACTION PROCESS

SEPARATION PROCESS

RAW MATERIALS

INTERMEDIATE PRODUCT

INTERMEDIATE PRODUCT

FINAL PRODUCT

Chemical process


7/21

You need to:

Minimize production of unwanted

byproducts

Separate the good (product) from the

bad (byproducts)

Recover the unused reactants

Maximize profit, minimize energy

consumption, minimize impact on the

environment

Role of chemical engineer


8/21

petroleum and petrochemical

pharmaceuticals

polymers

energy

food

consumer products

biotechnology

electronic and optical materials.


9/21

Dimensions are: properties that can be measured such as length,

time, mass, temperature,

properties that can calculated by multiplying ordividing other dimensions, such as velocity(length/time), volume, density

Units are used forexpressing the dimensions such asfeet or meter for length, hours/seconds for time.

Every valid equation must be dimensionallyhomogeneous: that is, all additive terms on both sidesof the equation must have the same unit

1.1 Units and dimension


10/21

1.2 Conversion of units

A measured quantity can be expressed in terms ofany units having the appropriate dimension

To convert a quantity expressed in terms of one unitto equivalent in terms of another unit, multiply thegiven quantity by the conversion factor

Conversion factor a ratio of equivalent values of aquantity expressed in different units

Let say to convert 36 mg to gram


11/21

1.2.1 Dimensional equation

1. Write the given quantity and units on left

2. Write the units of conversion factors that cancel

the old unit and replace them with the desired

unit3. Fill the value of the conversion factors

4. Carry out the arithmetic value


12/21

Convert 1 cm/s2 to km/yr2

1 cm s2 h2 day2 m km

s2 h2 day2 yr2 cm m

1 cm 36002 s2 242 h2 3652

day21 m 1 km

s2 12 h2 12 day2 12 yr2 100 cm 1000 m

(3600 x 24 x 365) 2 km=

9.95 x 109 km/ yr2

100 x 1000 yr2


13/21

1.3 Systems of units

Components of a system of units: Base units - units for the dimensions ofmass, length, time,

temperature, electrical current, and light intensity.

Multiple units- multiple or fractions of base unit

E.g.: for time can be hours, millisecond, year, etc.

Derived units - units that are obtained in one or two ways;

a) By multiplying and dividing base units; also referred to as

compound units

Example: ft/min (velocity), cm2(area), kg.m/s2 (force)

b) As defined equivalent of compound unit (Newton = 1 kg.m/s2)


14/21

3 systems of unit:

a) SI system

b) American engineering system

c) CGS system


15/21

Base Units

Quantity SI Symbol American Symbol CGS Symbol

Length meter m foot ft centimeter cm

Mass kilogram kgpoundmass lbm gram g

Molesgram-mole mole pound mole lbmole gram-mole mole

Time second s second s second s

Temperature Kelvin K Rankine R Kelvin K

Table 1: SI, American and CGS Units


16/21

Multiple Unit Preferences

tera (T) = 10 12 centi (c) = 10 -2

giga (G) = 10 9 milli (m) = 10 -3

mega (M) = 10 6 micro () = 10 -6

kilo (k) = 10 12 nano (n) = 10 -9


17/21

Derived SI Units

Quantity Unit Symbol Equivalent to the Base Unit

Volume Liter L 0.001m3 = 1000 cm3

Force Newton

(SI)Dyne(CGS)

N 1 kg.m/s2

1 g.cm/s2

Pressure Pascal Pa 1 N/m2

Energy/WorkJouleCalorie

Jcal

1 N.m = 1 kg.m2/s2

4.184 J =4.184 kg.m2/s2

Power Watt W 1 J/s = 1 kg.m2/s3


18/21

1.4 Force and weight

Force is proportional to product of mass and acceleration

Usually defined using derived units ;

1 Newton (N) = 1 kg.m/s2

1 dyne = 1 g.cm/s2

1 Ibf = 32.174 Ibm.ft/s2

Weight of an object is force exerted on the object by

gravitational attraction of the earth i.e. force of gravity, g.

Value of gravitational acceleration:

g = 9.8066 m/s2

= 980.66 cm/s2

= 32.174 ft/s2


19/21

gc is used to denote the conversion factor

from a natural force unit to a derived

force unit.

gc = 1kg.m/s2= 32.174

lbm.ft/s2

1N 1 lbf


20/21

1.5 Dimensional homogeneity and

dimensionless quantities

Every valid equation must be dimensionally

homogeneous: that is, all additive terms on both

sides of the equation must have the samedimensions


21/21

Exercises

Problems 2.1, 2.2, 2.8, 2.9, 2.26

Chap. 1 Introduction to Engineering Calculations

Documents

Transcript of Chap. 1 Introduction to Engineering Calculations