che 111 chapter 2
TRANSCRIPT
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