ELEMENTARY PRINCIPLES OF

CHEMICAL PROCESSES

3rd Edition

Richard M. FelderRonald W. Rousseau

CHAPTER 2

INTRODUCTION TO ENGINEERING CALCULATIONS

UNITS AND DIMENSIONS

All measured property has a value and a unit

A dimension is a property that can be measured, or calculated by multiplying or dividing other dimensions.

Measurable units are specific values of dimensions that have been defined by convention, custom, or law.

Numerical values of two quantities may be added or subtracted only if the units are the same

Numerical values and their corresponding units may always be combined by multiplication or division

SYSTEMS OF UNITS

Base Units Multiple Units Derived Units

SI system CGS System American Engineering System

BASE UNITSQuantity Unit Symbol

Length Meter(SI)

Centimeter(CGS)

m

cm

Mass Kilogram (SI)

Gram(CGS)

kg

g

Moles Gram-mole mol or g-mol

Time Second s

Temperature Kelvin K

Electric Current Ampere A

Light Intensity Candela cd

Multiple Units

Tera (T) = 1012

Giga (G) = 109

Mega (M) = 10 6

Kilo (k) = 103

Centi (c) = 10-2

Milli (m) = 10-3

Micro (μ) = 10-6

Nano (n) =10-9

CONVERSION OF UNITS

CONVERSION OF UNITS

Conversion factors

1 cm 10 mm

10 mm 1 cm

Convert 36 mg to grams.

Conversion… the Chemical Engineer way!!

Convert 1 cm/s2 to it equivalent in km/yr2 .

The Gas Constant R= 8.314 m3-Pa/mol K. What is the value of R in lit-bar/mol K and cal/mol-K.

PROBLEM!!

A supersonic aircraft consumes 5320 imperial gallons of kerosene per hour of flight and flies an average of 14 hours per day. It takes roughly seven tons of crude oil to produce one ton of kerosene. The density of kerosene is 0.965 g/cm3. How many planes would it take to consume the entire annual world production of 4.02×109 metric tons of crude oil?

FORCE AND WEIGHT

Force = mass × acceleration Units: Newton (SI) ; Dyne (CGS);

Pound-force (FPS) 1 N ≡ 1 kg.m/s2

1 dyne ≡ 1 g.cm/s2

1lbf ≡ 32.174 lbm .ft/s2

More conversions……

What force would be required to accelerate a mass of 4 lbm at a rate of 9 ft/s2 ?

1 kg.m/s2 32.174 lbm.ft/s2

gc= =

1 N 1 lbf

DO NOT CONFUSE gc WITH g

g = acceleration due to gravity

= 9.8066 m/s2

= 980.66 cm/s2

= 32.174 ft/s2

Water has a density of 62.4 lbm/ft3 . How much does 2 ft3 of water weigh at sea level and in Colorado where the altitude is 5374 ft and the gravitational acceleration is 32.139 ft/s2 ?

PROBLEM 2.14

A poundal is the force required to accelerate a mass of 1 lbm at a rate of 1 ft/s2 and a slug is the mass of an object that will accelerate at a rate of 1 ft/s2 when

subjected to a force of 1 lbf. Calculate the mass in slugs and the weight in

poundals of a 175 lbm man on (i) earth and (ii) on the moon where the acceleration of gravity is one-sixth of its value on earth

A force of 355 poundals is exerted on a 25.0-slug object. At what rate (m/s2) does the object accelerate?

PROCESS DATA REPRESENTATION AND ANALYSIS

Interpolation or extrapolation can be done by

Two point linear interpolation/ extrapolation Graphical interpolation / extrapolation Curve fitting Linear regression or method of least squares

SCIENTIFIC NOTATION, SIGNIFICANT FIGURES AND PRECISION

Significant figures of a number are the digits from the first nonzero digit on the left to either

the last digit on the right if there is a decimal point or

the last nonzero digit of the number if there is no decimal point

RULES:

When two or more quantities are combined by multiplication and/or division, the number of significant figures in the result should equal the lowest number of significant figures of any of the multiplicants or divisors

When two or more numbers are added and or subtracted, the positions of the last significant figures of each number relative to the decimal point should be compared. Of these positions, the one farthest to the left is the position of the last permissible significant figure of the sum or difference.

CHAPTER 3

PROCESS AND PROCESS VARIABLES

MASS AND VOLUME

Density = mass per unit volume Kg/m3, g/cm3, lbm/ft3

Specific Volume = 1/density

Specific Gravity = ratio of density of a substance to the density of a reference substance at a specific condition (Units?)

Calculate the density of mercury in lbm/ft3. Specific gravity of mercury at 20°C is 13.546. Also calculate the volume in ft3 occupied by 215 kg mercury.

EFFECT OF TEMPERATURE

Temperature variation may be in either direction.

Perry’s Chemical Engineers’ Handbook,

pp. 2-128 to 2-131

FLOW RATE

Mass flow rate Volumetric flow rate