Chapter 17: Electrical Properties
ISSUES TO ADDRESS.
How are electrical conductance and resistance
characterized?
What are the physical phenomena that distinguish
conductors, semiconductors, and insulators?
For metals, how is conductivity affected by
i
THE P AND I DIAGRAM
The P and I diagram shows the arrangement of the process equipment, piping, pumps,
instruments, valves and other fittings. It should include:
1. All process equipment identified by an equipment number. The equipment should
be drawn rou
Heat Pumps
A heat pump is a device for raising low grade heat to a temperature at which the heat can
be utilised. It pumps the heat from a low temperature source to the higher temperature
sink, using a small amount of energy relative to the heat energy re
Block diagrams
A block diagram is the simplest form of presentation. Each block can represent a single
piece of equipment or a complete stage in the process. Block diagrams were used to
illustrate the examples in Chapters 2 and 3. They are useful for show
Development of absorber model
The methods found in the literature for the modeling of packed columns generally belong to
either of two types. In the first type the packed height is divided into a number of segments.
Within each segment the conditions are
ENTHALPY-CONCENTRATION DIAGRAMS
The variation of enthalpy for binary mixtures is conveniently represented on a diagram.
An example is shown in Figure 3.3. The diagram shows the enthalpy of mixtures of
ammonia and water versus concentration; with pressure
PURGE
It is usually necessary to bleed off a portion of a recycle stream to prevent the build-up of
unwanted material. For example, if a reactor feed contains inert components that are not
FUNDAMENTALS OF MATERIAL BALANCES 53
separated from the recycle st
Integral heats of solution
Heats of solution are dependent on concentration. The integral heat of solution at any
given concentration is the cumulative heat released, or absorbed, in preparing the solution
from pure solvent and solute. The integral heat o
Heat exchange
The most common energy-recovery technique is to utilise the heat in a high-temperature
process stream to heat a colder stream: saving steam costs; and also cooling water, if
the hot stream requires cooling. Conventional shell and tube exchan
RECYCLE PROCESSES
Processes in which a flow stream is returned (recycled) to an earlier stage in the processing
sequence are frequently used. If the conversion of a valuable reagent in a reaction process
is appreciably less than 100 per cent, the unreacte
Cooler-condenser
The sources of heat to be considered in the balance on this unit are:
1. Sensible heat: cooling the gases from the inlet temperature of 234C to the required
outlet temperature (the absorber inlet temperature) 40C.
2. Latent heat of the wa
CONSERVATION OF ENERGY
As for material (Section 2.3), a general equation can be written for the conservation of
energy:
Energy out = Energy in -f generation consumption accumulation
This is a statement of the first law of thermodynamics.
An energy balance
MATERIALS SCIENCE AND ENGINEERING
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Classification of Natural Fibres
Natural Fibres
Plant fibre
Non-wood
fibre
Seed/Fr
uit
Cotton
Kapok
Coir
Organ
ic
Inorganic
Animal
fibre
Wool
Silk
Wood
fibre
Hardwoods / Softwoods
Ba
st
Flax
Hem
MATERIALS SCIENCE AND ENGINEERING
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Creep
Creep may be defined as a time-dependent
deformation at elevated temperature and
constant stress
Occurs when material supports a load for very long
period of time, and continues to deform
MATERIALS SCIENCE &
ENGINEERING
POLYMERS
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Polymers
2
Polymer
Poly
many
mer
repeat unit (building blocks)
repeat
unit
repeat
unit
H H H H H H
C C C C C C
H H H H H H
H H H H H H
C C C C C C
H Cl H Cl H Cl
Polyethylene (PE)
Poly(vin
Other Fibres:
Ceramics
Ceramic fibres, usually in the form of very short
whiskers are mainly used in areas requiring high
temperature resistance.
They are more frequently associated with
nonpolymer matrices such as metal alloys.
Natural
Fibrous plant m
INFLUENCE OF FIBRE LENGTH
The mechanical characteristics of a fiber-reinforced composite
depend not only on the properties of the fiber, but also on the
degree to which an applied load is transmitted to the fibers by
the matrix phase.
Magnitude of the int
MATERIALS SCIENCE AND
ENGINERRING
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Molecular Weight of Polymers
Due to existence of different sizes of molecular
species molecular weight averages are used to
express the size of synthetic polymers.
Different average molecular w
HW 11
Problem 18.14
a. To Find:
(a) Determine 0 and a in Equation 18.10 for pure copper, using the data in Fig.18.8
(b) Determine A in Equation 18.11 for nickel as an impurity in copper, using the data in Figure
18.8
(c) Estimate the electrical resistivit
HW 9
Problem 14.5
a. To Find:
(a) The number-average molecular weight
(b) The weight-average molecular weight
(c) The degree of polymerization
for the given polypropylene material
b. Given:
Molecular Weight
Range (g/mol)
xi
wi
8,00016,000
0.05
0.02
16,000
HW 10
Problem 15.1
a. To Find:
Elastic modulus and tensile strength of poly(methyl methacrylate) at room temperature [20C
(68F)]. Compare these with the corresponding values in Table 15.1.
b. Given:
Figure 15.3 is accurate; the elastic modulus and tensile
HW #4
Problem 6.8
a. To Find:
The diameter of the test cylinder,d0.
b. Given:
Load, F = 6660 N (1500 lb)
Modulus of elasticity, E = 110 GPa (16 *106 psi)
Yield strength, y = 240 MPa (35,000 psi)
Initial length of rod,l0 = 380 mm (15.0 in)
Elongation, l =
HW 8
Problem 10.2
a. To Find:
(a) The expression for total free energy change for a cubic nucleus, critical cube edge length,
a*, and G*
(b) Compare G* for a cube with that for a sphere
b. Given:
Nucleus is cubic; edge length of the cubic nucleus = a unit
HW 7
Problem 9.13
a. To Find:
The phases and the compositions of these phases, in a binary Cu-Zn alloy, at various
temperatures.
b. Given:
Composition of alloy: 74 wt. % Zn 26 wt % Cu
c. Assumptions:
(i) The alloy is cooled/heated very slowly to attain th
HW #5
Problem 7.12
a. To Find:
Does the single crystal yield under the given applied stress? If not, at what stress will it yield?
b. Given:
= 43.1
o
o
= 47.9
CRSS = 20.7 MPa
Applied stress = 45 MPa
c. Assumptions:
(i) The applied force is uniaxial
(ii)
HW #3
Problem 5.7
a. To Find:
The distance from the high-pressure side at which the concentration of nitrogen in steel equals
2.0 kg/m3 under conditions of steady-state diffusion.
b. Given:
o
D = 6 10-11 m2/s at 1200 C
J = 1.2 10-7 kg/m2-s
Concentration o
HW #6
Problem 8.2
a. To Find:
Theoretical fracture strength of the given material
b. Given:
o = 1200 MPa
a = 0.25 mm
-3
t = 1.2 X 10 mm
c. Assumptions:
(i) Surface crack; semi-elliptical crack
(ii) Applied stress is perpendicular to the crack/ crack lengt
HW A
Problem 2.14
a. To Find:
The bond energy between two ions (EO) expressed as a function of three parameters
A, B and n.
b. Given:
The equation representing variation of the net potential energy between two adjacent
ions (EN) with inter-ionic spacing (