Bapatla Engineering College: Bapatla
Department of Chemistry
1/4BTech-Engineering Chemistry; Semester-I: November -2016
Scheme of Evaluation( Common for all branches)
Paper Code: 14CY 103 (2016 Regulations)
1. Answer all questions
12X1M = 12 Marks
UNIT-I
2. a. Basic principle-1M
Equations- 4M
Procedure- 2M
Diagram-1M
b. Temporary hardness, 50mg/L – 4M
OR
3. a. Scales definition-1M
Formation-2M
Disadvantages and Removal-3M
b. Caustic embrittlement -4M, Phosphate conditioning-2M
UNIT-II
4. a. Definition- 1M Procedure- 2M
Diagram- 2M Advantages-1M
b. Phase diagram-2M
Explanation of the diagram-4M
OR
5. a. Explanation of curves of pure metal-2M
b. Explanation of curves of mixture-4M
UNIT-III
6. a. Process-4M
Diagram-2M
b. i) Anti-knocking agents-2M ii) Coal rank- 2M iii) Octane number-2M
OR
7. a. Analysis of C and H-2M
Analysis of N-2M
Analysis of S -2M
Analysis of Ash, O2-1M, Importance-1M
b. Composition of CNG -1M,
Uses of CNG-1M,
Composition of LPG -1M,
Uses of -1M
UNIT-IV
8. a. Refractoriness under load- 3M
Porosity- 3M
b. Viscosity index-4M
Cloud point-2M
OR
9. a. Explanation of fluid film lubrication- 4M
b. Explanation of particulate composite-3M
Explanation of thin film lubrication- 4M
Examples-1M
1
Scheme of Evaluation
12X1M= 12M
1. Answer all questions
a. Priming: The phenomenon of formation of wet steam by rapid or violent heating of the
water inside the boiler is called priming.
b. Eriochrome Black-T
c. Temporary hardness:
This is also known as carbonate or alkaline hardness. This is due to presence of dissolved
bicarbonates of calcium and magnesium.
It can be removed by boiling. During boiling, bicarbonates are decomposed forming
insoluble carbonates or hydroxides which will be removed by filtration.
Hardness which is easily removed by boiling is called temporary hardness
Permanent hardness
It is also known as non-carbonate or non-alkaline hardness. It is due to chlorides,
nitrates and sulphates of calcium and magnesium. As this type of hardness cannot be
removed by simple boiling, it is called permanent hardness.
It can be removed by suitable chemical methods like Lime-Soda, Zeolite and Ion-Exchange
processes.
d. Condensed Phase Rule: When the pressure of the system remains constant( ie., in which
vapour pressure is not considered), then the phase rule equation becomes F=C-P+1
e. Pb–Ag System: Eutectic Temperature + 3030C, Eutectic composition= 2.6%Agand 97.4%Pb
f. pH = 7.00 to 8.5
g. High or gross calorific value (HCV/GCV):
Total amount of heat produced, when unit mass or volume of the fuel is burnt completely and
the produced combustion has been cooled to room temperature (15°C or 60°F).
Example, hydrogen present in the fuel is converted into steam. They are condensed back
to room temperature. Thus the latent heat of condensation of steam is also included in the
measured heat.
Lower or net calorific value (LCV/NCV):
The net heat produced, when unit mass or volume of the fuel is completely burnt and the
products are allowed to escaped.
h. Cetane number:
Definition: The percentage of hexadecane in a mixture of hexadecane and α-methyl
naphthalene is known as cetane number
i. Dimensional stability: It is the resistance of a material to any volume changes, which may
occur on its expansion to high temperature, over a prolonged time. These changes may be
permanent(irreversible) or reversible.
j. Matrix phase: The continuous body constituent which encloses the composite and give it its
bulk form is called matrix phase.Matrix phase may be metal, ceramic or polymer.
Composites using these matrix are known as metal matrix composites (MMC), ceramic
composites (CMC) and polymer matrix composites (PMC) respectively.
Functions of matrix phase: (any two functions)
2
1. It binds the dispersed phase together by virtue of its cohesive and adhesive nature.
2. It acts as medium by which an externally applied load is transmitted and distributed to the
dispersed phase (fiber).
k. Oiliness:Oiliness generally indicates relative ability to operate under boundary lubrication
conditions. The term relates to a lubricant’s tendency or capacity to stick onto the surface
under conditions of heavy pressure or load. Good lubricating oil should have high oiliness.
Lubricating oils with poor oiliness will be easily squeezed out when the machines work
under heavy load.
l. Knocking:
Premature and instantaneous ignition of petrol-air (fuel-air) mixture in a petrol engine,
leading to the production of explosive violence known as knocking.
UNIT-I
2. a. Lime soda process:(Any one process)
8M
The basic principle in this process is to chemically convert all the soluble impurities into
insoluble precipitates which may be removed by settling and filtration. Calculated quantities of
suspension of lime (Ca (OH) 2) and soda (Na2CO3) are added.
When lime and soda are added to water, they react with hardness causing salts including other
impurities to form insoluble CaCO3 and Mg(OH)2. These precipitates are then filtered off to obtain soft
water.
Table: Chemical reactions involved in process:
S. No. Constituent
1
2
3
4
5
6
7
8
9
10
Ca(HCO3)2
(Temp.Ca)
Mg(HCO3)2
(Temp.Mg)
Ca2+
(Perm.Ca)
Mg2+
(Perm.Mg)
CO2
Reaction
Ca(HCO3)2 + Ca(OH)2
Mg(HCO3)2 + 2Ca(OH)2
Ca2+ + Na2CO3
2+
Mg + Ca(OH)2
Ca2+ + Na2CO3
CO2 + Ca(OH)2
+
H+ (free acids, 2 H + Ca(OH)2
2+
HCl, H2SO4) Ca + Na2CO3
Fe2+ + Ca(OH)2
FeSO4
(coagulant) Ca2+ + Na2CO3
3+
Al2(SO4)3 2Al + 3Ca(OH)2
(coagulant) 3Ca2+ + 3Na2CO3
NaAlO2 + 2H2O
NaAlO2
Need
2CaCO3  + 2H2O
2CaCO3+ Mg(OH)2↓
+ 2H2O
2+
CaCO3  + 2Na
2L
S
2+
Mg(OH)2 + Ca
CaCO3  + 2Na2+
CaCO3 + H2O
Ca2+ + 2H2O
CaCO3  + 2Na2+
Fe(OH)2 + Ca2+
CaCO3  + 2Na2+
2Al(OH)3 + 3 Ca2+
CaCO3  + 6Na2+
NaOH + Al(OH)3
(coagulant)
HCO3‾
2HCO3‾ + Ca(OH)2
(eg.NaHCO3)
L
CaCO3 + CO3 + H2O
L+S
L
L+S
L+S
L+S
-L
L-S
3
Calculation of required amount of Lime & Soda:
The amount of lime and soda requires can be calculated in terms of CaCO3 equivalents.
100 parts by mass of CaCO3 = 74 parts by mass of Ca(OH)2
X parts by mass of CaCO3 = How much lime, [Ca(OH)2]
74
Therefore, Lime required =
x (X)
100
Where X = sum of masses of impurities react with lime
74
Therefore, Lime required =
100
Temp.Ca2+ + 2xTemp.Mg2+ + Perm.Mg2+ +Fe2+ + Al3+
+ H+ + HCO3‾ + CO2 ─ NaAlO2 all in terms of CaCO3
equivalents
100 parts by mass of CaCO3 = 106 parts by mass of Na2CO3
Y parts by mass of CaCO3 = How much soda, [Na2CO3]
106
Therefore, Soda required =
x (Y)
100
Where Y = sum of masses of impurities react with soda
106
Therefore, Soda required =
Perm.Ca2+ + Perm.Mg2+ + Fe2+ + Al3+ + H+ ─ HCO3‾
all in terms of CaCO3 equivalents
100
There are various methods in lime soda process. They are
a. Cold lime soda process:
In this process, calculated quantity of chemicals (lime & soda) is mixed with water at room
temperature. At room temperature, the precipitates formed are very fine. They don’t settle down easily
and cause difficulty in filtration. So, it is need to add small amounts of coagulants like alum, aluminium
sulphate or sod.aluminate. They are hydrolyse to form aluminium hydroxide which entraps the fine
precipitate of CaCO3 and Mg(OH)2.
Method: Raw water and calculated amounts of lime soda and coagulants are taken in a circular vertical
chamber. It is provided with a stirrer, vigorous stirring ensures formation of precipitates. Precipitates
settle at the bottom. Softened water flows into outer chamber and it is filtered through wood fibre filter
to ensure complete removal of sludge particles.
Softened and filtered water rises up of the outer chamber and it is collected through the outlet.
Periodically sludge is removed through the sludge outlet. Cold lime-soda process provides water,
containing a residual hardness of 50-60 ppm.
4
b. Hot lime soda process:
It is similar to cold lime soda process except that the raw water is treated with chemicals
at a temperature of 80 ºC to 150 ºC.
There are three parts in hot lime-soda tank. Reaction tank, in which chemicals, raw water and
super heated steam are mixed thoroughly. Here the reactions are completed. Then the contents enter into
conical sedimentation tank where sludge is collected at the bottom. Softened water is passed through
sand bed which consists of three layers where sludge is completely removed. Filtered and softened water
comes out quickly. A soft water with 15-30 ppm of residual hardness is obtained.
Since this process is carried out at boiling temperature of solution, the following advantages are
possible.
b. Problem 4M
100ml of the sample = 10ml of 0.1N HCl
=10X 0.1ml of 0.1N HCl
=1ml of 1N HCl
= 1X10-3L X 50mg of CaCO3
=5mg of CaCO3
1000ml of water = 5mg x 1000ml/ 100
= 50mg of CaCO3
Note: Hardness of water is temporary, since methyl orange indicator does not give the value for
permanent hardness.
3. a. i) Scales:
6M
These are the hard and adherent deposits on the inner surface of the boilers which are difficult to
remove.
This scale formation takes place due to the following reasons:
a. Decomposition of calcium carbonate: In low pressure boilers scale formation occurs due to the
formation of CaCO3 from Ca(HCO3)2.
5
Ca(HCO3)2
CaCO3 ↓ + H2O + CO2 ↑
Scale
However in high pressure boilers this CaCO3 is soluble due to formation of Ca(OH)2.
CaCO3 + H2O
Ca(OH)2 + CO2 ↑
Soluble
b. Deposition of CaSO4: The solubility of CaSO4 decreases with increase in temperature. CaSO4 is
soluble in cold water and is completely insoluble in super heated water. Therefore CaSO4 get
precipitated as hard scale in high pressure oilers.
c. Hydrolysis of magnesium salts: Dissolved magnesium salts at high temperature undergo hydrolysis
forming Mg(OH)2 as soft type of scale.
MgCl2 + 2H2O
Mg(OH)2 ↓ + 2HCl
Soft scale
d. Presence of silica: Very small quantities of SiO2 present in hard water react with Ca & Mg forming
CaSiO3 and/or MgSiO3. These calcium or magnesium silicate scales are very hard and are difficult to
remove.
Disadvantages
(i) Wastage of fuel: Scales have low thermal conductivity, so poor heat transfer from boiler to water
leading to increase in fuel consumption. The increase in thickness of the scale from 1.25 mm to 12
mm leads to increase in fuel consumption from over 50% to 150%.
(ii) Lowering of boiler safety: Due to the overheating of the boiler, different parts of the boiler become
weak and distorted and so the operation of the boiler becomes unsafe, particularly in high pressure
boilers.
(iii) Decrease in efficiency: Valves and condensers of the boilers are chocked due to scale formation
and boiler efficiency decreases.
(iv) Danger of explosion: The thick scales sometimes may be cracked due to uneven expansion, as a
result of this water comes in contact with overheated inner walls of boiler that lead to explosion
due to sudden development of high pressure.
Removal of scales:
The following methods are commonly used for the removal of the scales, depending upon nature of
scale.
(i) Loosely adhering scales can be removed by scraping using wire brush.
(ii) Scales which are brittle in nature can be removed by giving thermal shocks (i.e. heating the
boiler and then suddenly cooling with cold water).
6
(iii) Hard and adherent scales can be removed by dissolving in suitable chemical. Ex. CaCO3 scale
can be removed by using 5-10% HCl. CaSO4 scale can be removed by adding EDTA since CaEDTA complex is highly soluble in water.
b.
6M
i). Caustic Embrittlement:
It is the phenomenon during which the boiler material becomes brittle due to the
accumulation of caustic substances. It is a very dangerous form of stress corrosion occurring in mild
steel boilers exposed to alkaline substances at high temperatures. When water is softened by Lime-Soda
process, the excess sodium carbonate undergoes hydrolysis in high pressure boilers to form NaOH.
Na2CO3 + H2O
2NaOH + CO2
This makes water alkaline. The alkaline water flows into minute hair cracks and crevices by capillary
action. There the water evaporates and concentration of caustic soda (NaOH) increases progressively.
The concentrated alkali dissolves iron as sod.ferroate in crevices, cracks etc. where the metal is stressed.
This causes brittlement of boiler parts particularly stressed parts like bends, joints and rivets causing
failure of the boiler.
The caustic embrittlement of boiler may be explained by assuming the formation of concentration cell as
shown below.
- Iro n at
r iv e t s , jo in t s
etc.
co ncentrated
N aO H
s o lu t io n
d ilu t e
N aO H
s o lu t io n
+
Iro n at
p la n e
s u r fa c e s
Caustic Embrittlement can be avoided by
a. Using sod. Phosphate instead of Na2CO3 and
b. Adding tannin or lignin to boiler water which block the hair cracks& prevent infiltration of NaOH.
ii) Phosphate conditioning:
Different sodium phosphates like NaH2PO4, Na2HPO4 and Na3PO4 are added to high pressure boilers to
react with the hardness forming impurities to form soft sludge of calcium and magnesium phosphates
and finally this can be removed by blow down operation.
3CaCl2 + Na3PO4
Ca3(PO4)2 ↓ + 6NaCl
A. Calgon conditioning: Calgon i.e., sodium hexa meta phosphate when added to boiler water, reacts
with scale forming CaSO4 and forms highly soluble complexes.
2CaSO4 + [Na4(PO3)6]2–
[Ca2(PO3)6]2– + 2Na2SO4
soluble complex
7
UNIT-II
4. a. De-Salination of Brackish Water:
6M
The water containing dissolved salts with a particular salty taste is called brackish
water. The process of removing extra common salt from the water is known as desalination. Sea water is
brackish water. It is unfit for drinking. Desalination can be done in many ways.
1. Electrodialysis:
It is a method in which the ions are separated from saline water by passing direct current through
saline water using electrodes and rigid membranes.
Consider a cell which is divided into three compartments using membranes. Two electrodes are
placed in outer compartments and saline water is taken in all compartments. When current is passed
through saline water, sodium ions move towards cathode and chloride ions move towards anode
through the membrane.
Hence the concentration of ions decreases in the middle compartment and the concentration of
ions increases in the side compartments. Desalinated water is obtained from middle compartment and
concentrated brine solution from outer compartments.
For more efficient separation, usually ion selective membranes are employed. An ion selective
membrane has permeability for only one kind of ions with specific charge. Thus, cation selective
membrane is permeable to cations only, while anion selective membrane is permeable to anions only. A
cation selective membrane contains fixed functional groups such as RSO3- or RCOO- which allow only
cations through the pores of the membrane. Similarly an anion selective membrane contains fixed
functional groups such as R4N+Cl- which allow only anions through the pores of the membranes.
8
An electrodialysis cell consists of large number of large number of paired sets of rigid
plastic membranes. Saline water is passed under a pressure of about 5-6 Kg/m2 between membrane pairs
and an electric field is applied perpendicular to the direction of flow of saline water. Just as magnets like
poles repel each other, cation selective membrane possess –vely charged functional groups and attract
cations but repel anions. Similarly anion selective membranes possess +vely charged functional groups
which attract anions and repel cations. Therefore, water in one compartment of the cell is deprived of its
salts and the alternative compartments are rich enough with ions. Thus, we get alternative streams of
pure water and concentrated water.
The membranes are usually polystyrene based containing sulphonic acid (cationselective) and tetra ammonium chloride (anion-selective) groups. These membranes possess high
transference values for cation and anions. Moreover they are very conducting and stable to chemical
attack.
Advantages:
1. It is a most compact unit.
2. The cost of installation of the plant and its operation is economical.
3. If electricity is easily available, it is best suited.
b. WATER SYSTEM: (One Component system)
6M
The water system consists of three phases, viz., ice, water and water vapour
Ice
Water
Water vapour
(S)
(l)
(g)
Since H2O is the only chemical compound involved, therefore, it is single or one-component system.
From the phase rule, when C =1,
F = C – P + 2 =1 – P + 2 = 3 – P
i. e. the degree of freedom depends on the number of phases present at equilibrium. Three different
cases are possible:
9
(i) P = 1;
(ii) P = 2;
(iii) P = 3;
F=2
F=1
F=0
(bivariant system)
(univariant system)
(invariant system)
From the above, it is clear that for any one-component system, the maximum number of degrees of
freedom is two. Therefore, such a system can be represented completely by a two-dimensional Diagram.
The most convenient variable are the pressure and the temperature.
The water system is shown in Fig. The diagram consists of:
1. Areas: The phase diagram consists of three areas viz., BOC AOC and AOB representing ice, liquid
and vapour respectively. Within these single-phase areas, the system in bivariant, because to locate
any point in an area, temperature as well as pressure co-ordinates need to be known. This also
following from phase rule equation
F = 3 – P = 3 – 1 = 2.
2. Boundary lines: There are three lines OA, OB and OC, connecting the point at which two phases can
co-exist in equilibrium. In order to locate any point on a particular line, either temperature or pressure
co-ordinate should be specified for which the second is automatically fixed.
In other words, any point on boundary lines has one degree of freedom or is univariant. This also
follows from phase rule equation
F = 3 – P = 3 – 2 = 1.
i. Curve OA: This curve is known as vapour pressure curve of water or vaporization curve. It represents
equilibrium between two phases i.e. liquid water and water vapour. The curve shows the vapour
pressure of liquid water at different temperatures. The curve OA has a natural upper limit at +374o C
and pressure 218 mm. This is the critical-point, beyond which the liquid phase merges into vapour
phase and they are no longer distinguishable from each other.
ii. Curve OB: This curve is known as sublimation curve of ice. Two phases, ice and its vapour coexist
in equilibrium along this curve. It gives the conditions under which water vapour is in equilibrium
with solid ice. The point B has a natural limit at -273oC, beyond which the two phases merge into
each other.
10
iii. Curve OC: This curve is called fusion or melting curve of ice, because it indicates how the melting
temperature of ice or the freezing temperature of water varies with the pressure. Along this curve
ice and liquid water coexist in equilibrium. The slope of OC towards the pressure axis shows that
the melting point of ice is decreased by increasing pressure.
3. Triple point: The three curves OA, OB, and OC meet at O, at which solid, liquid and vapour are
simultaneously at equilibrium. This point at 273.16 k is called a triple – point. Since three phases coexist, the system is invariant (F=3-3=0). In other words, there is no degree of freedom at O, i.e.,
neither pressure nor temperature can be altered, even slightly, without causing the disappearance of
one of the phase.
o
4. Metastable curve OA': As water does not always freeze at 0 C, so if the vessel containing water and
vapour is perfectly clean and free from dust, it is possible to super – cool water several degrees below
its freezing point 0. The dotted curve OA', a continuation of vaporization curve AO, represents the
vapour pressure curve of super cooled water.
This curve represents a metastable system. On slight disturbance, the super cooled water at once
changes to solid ice and the temperature rises to 0oC. It may be noted that metastable vapour pressure
of supper cooled water is higher than the vapour pressure of ice.
OR
5. a. Cooling curves 6M
1. When a pure substance in the fused or liquid state is allowed to cool slowly and the temperature
noted at definite time, a curve of the type shown in Fig.(a) is obtained. During the initial stage the
fall in temperature is continuous. When solidification starts, the solid makes its appearance
indicated by break (point ‘b’) in the continuity of cooling curve and the temperature remain
constant until point ‘c’ is reached. Thereafter, the fall in the temperature will again become
continuous.
2. If a mixture of two solids in the fused state be coo led slowly and the cooling curve is obtained in a
similar manner. The cooling curve is continuous as long as the mixture is in the liquid state. When
a solid phase begins to form, the rate of cooling abruptly alters and the cooling curve exhibits a
break (point ‘b’). However, the temperature is not remaining constant. It decreases continuously in
the part ‘bc’ but at different rate with liberation of heat.
11
At point ‘c’, which is the eutectic point, the remaining liquid solidifies as a whole, i.e., both
components crystallize out separately and the temperature remain constant from ‘c’ to‘d’. The
system now becomes in variant from the point of the view of the phase rule. There after the fall of
the temperature becomes uniform along ‘cd’, but the rate of fall is quite different than the previous
one.
Study of cooling curves of Bi-Cd Compostion:
Prepare number of (eight) mixtures of Bi and Cd ranging in composition 100% Bi to 100% Cd.
Place each of these mixtures separately in fireclay or graphite crucible and then melt in an electric
furnace in an inert atmosphere of nitrogen. After melting and thorough agitation, a thermocouple is
inserted in each melt and the furnace is allowed to cool slowly. Temperature and time reading are taken,
until the charge in the crucible is completely solidified. Then prepare the plots of temperature versus
time for each mixture. Figure shows a set of cooling curves obtained for various compositions of Bi-Cd
mixtures.
Explanation of cooling curves:
When a body is cooled slowly and uniformly, a smooth cooling curve is obtained, till the
temperature approaches that of room. However when some transformation (or transition) that
liberates heat occur during cooling, the slope of the curve is reduced suddenly. The nature of the
reduction depends on the degree of freedom (F) of the system. A single phase (p=1) with F=2 exhibits a
continuous curve, but when a phase appears, the degree of freedom (F) is reduced to one and the heat
liberated by the formation of the new phase results in the discontinuity in the curve, due to the change of
slope for the cooling of one phase to a lesser slope corresponding to the cooling of two phases. Again,
when the third phase appears, F=0, the temperature of the system must remain constant, until one of the
phases disappears. This in-turn results in a flat portion on the cooling curve. Finally, when solidification
is complete, the system regains a degree of freedom; thereby the cooling curves once again exhibit
continuous variation of temperature versus time.
12
b. i. phases-3, components=1, degrees of freedom-zero
ii. phases-2, components=1, degrees of freedom-1
UNIT-III
6. a. SYNTHETIC PETROL: Bergius Process
6M
Coal is a raw material in bergius process. In this process, the low ash coal is powdered and made
into a paste with heavy oil and catalyst (tin or nickel oleate).
The paste is heated with hydrogen at 4500C and 200-250 atm pressure for about one and half an
hour. The coal undergoes hydrogenation to form saturated hydrocarbons that decompose at high
temperature and pressure to form low-boiling liquid hydrocarbons. The liberated gases are led to
condenser where a liquid resembling crude oil is obtained. This on fractionation gives (a) gasoline (b)
middle oil and (c) heavy oil.
Coal dust suspended in heavy oil + H2
Mixture of hydrocarbons
Condensation
Crude oil
Heavy oil is used again for making paste with fresh coal dust. Middle oil is hydrogenated in vapor phase
in the presence of solid catalyst to give more gasoline. The yield of gasoline is about 60% of the coal
dust used.
b.
6M
i. Antiknocking agents
The octane number if IC fuels can be raised by addition of such extremely poisonous materials as
tetra ethyl lead, (C2H5)4Pb or TEL and diethyl telluride,(C2H5)2Te, (CH3)4Pb-TML.
TEL is converted into a cloud of finely divided lead oxide particles in the cylinder and these react
with any hydrocarbon peroxide molecules formed, thereby slowing down the chain oxidation
13
reaction and thus, decreasing the chances if any early detonation.however, deposite of lead oxide is
harmful to the engine life, a small amount of ethyle dibromide is also added to petrol where it
removes lead oxide as volatile lead bromide.
ii. Classification of coal by rank or Coal Ranking:
Various types of coal commonly recognized on the basis of rank or degree of alteration or coalification
from the present material, wood, are
c.
d.
-------->
-------->
------->
-------->
-----------Moisture content, H, O, N, and S Content, Volatile Matter---------------------------------------------Carbon content, calorific value and hardness --------------------->
The progressive transformation of wood to anthracite results in: 1) decrease in the moisture content; 2)
decrease in hydrogen, oxygen, nitrogen and sulphur contents, with a corresponding rie in carbon
content, 3) decrease in volatile matter content, 4) increase in calorific value 5) increase in hardness.
iii. Octane number:
The performance of gasoline in internal combustion engines is related on the basis of octane number.
Definition: The octane number of gasoline is defined as the percentage of isooctane present in a mixture
of isooctane and n-heptane having same knocking characteristics as gasoline sample, under same set of
conditions.
The straight chain hydrocarbon i.e. n-heptane that has poor combustion characteristics and
knocks badly is arbitrarily given an octane number of zero where as the branched chain hydrocarbon i.e.
isooctane that has an excellent combustion characteristics and very little knocking tendency is given an
octane number of 100.
Fuel
n-heptane
Octane number
0
Combustion
characteristics
Poor combustion
characteristics
Excellent combustion
characteristics
Knocking
characteristics
Knocks severly
High resistant to
knocking
CH3
CH3-CH2-CH2-CH2-CH2-CH2-CH3
CH3-CH-CH2-C-CH3
n-heptane
CH3
CH3
2,2,4-trimethyl pentane ( Iso-octane)
80-octane fuel is one which has the same combustion characteristics as a 80:20 mixture of
isooctane and n-heptane.
OR
7. a. Ultimate Analysis:
8M
Isooctane
100
a). Carbon and Hydrogen:
14
About 1-2 gm of accurately weighed coal sample is burnt in a current of oxygen in a combustion
apparatus. C and H of the coal are converted into CO2 H2O respectively The gaseous products of
combustion are absorbed respectively in KOH and CaCl2 tubes of knownj weights. The increase in
weightsof these are then determined.
C+O2
CO2;
2KOH + CO2
CaCl2+7H2O
H2 + 1/2O2
H2O
K2CO3+H2O
CaCl2.7H2O
Increase in weight of KOH tubex12
Percentage of C = ---------------------------------------------- x100
Weight of sample takenx44
Increase in weight of CaCl2 tubex2
Percentage of H = --------------------------------------------- x100
Weight of sample takenx18
b): Nitrogen
About 1 gm of accurately weighed powdered coal is heated with concentrated H2SO4 along with
K2SO4(catalyst) in a long-necked flask(called Kjeldahl’s flask). After the solution becomes clear, it it is
treated with excess of KOH and the liberated ammonia is distilled over and adsorbed in a known volume
of standard acid solution. The unused acid is then determined by back titration with standard NaOH
solution. From the volume of acid used by ammonia liberated, the percentage of N in coal is calculated
as follows.
Volume of acid used x Normality x1.4
Percentage of N = ---------------------------------------------------Weight of sample taken
c). Sulphur:
It is determined from the washings obtained from the known mass of coal, used in bomb
calorimeter for determination of calorific value. During the determination, S is converted into sulphate.
The washings are treated with barium chloride solution, when barium sulphate is precipitated. This
precipitate is filtered, washed and heated to constant weight.
Weight of BaSO4 obtained x 32
Percentage of S = ---------------------------------------------x100
Weight of sample taken x 233
d) Ash:
The residual coal in the crucible is then heated without lid in a muffle furnace at700+-50oC for
1/2hour. The crucible is then taken out, cooled first in air then inside desiccator and weighed. Heating,
cooling and weighing is repeated until a constant weight is obtained. The residue is reported as ash on
percentage basis. Thus,
Wt of ash left
Percentage of ash = ------------------------ x 100
Wt of coal taken
e). Oxygen:
It is obtained by difference.
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Percentage of Oxygen = 100 - percentage of ( C+ H+S + N)
Importance of ultimate analysis:
a) Carbon and Hydrogen: Greater the percentage of C H, better is the coal in quality and calorific
value.
b). Nitrogen: It has no calorific value and hence its presence is undesirable.
c). Sulphur: Presence of S is highly undesirable in coal to be used for making coke for iron industry.
Oxides of sulphur pollute the atmosphere and leads to corrosion.
d). Oxygen: It decreases the calorific value of coal. Thus a good quality coal should have low
percentage of oxygen.
b.
4M
Compressed Natural Gas (CNG)
CNG is natural gas compressed to a high pressure of about 1000 atmospheres. A steel cylinder
containing 15 kg of CNG contains about 2 x 104 L or 20 m3 of natural gas at 1 atmospheric pressure. It
is derived from natural gas and the main constituent of CNG is methane (88.5%). Its calorific value is
8000-14000 Kcal/m3.
Properties:
1) CNG is comparatively much less pollution causing fuel as it produces less CO, ozone and
hydrocarbons during combustion.
2) During it s combustion, no sulphur and nitrogen gases are evolved.
3) No carbon particles are ejected during combustion.
4) It is less expensive than petrol and diesel.
5) The ignition temperature of CNG is 550 C.
6) CNG is a better fuel than petrol/diesel for automobiles.
7) CNG requires more air for ignition.
Uses:
As CNG is the cheapest, cleanest and least environmentally impacting alternative fuel. In Delhi,
it is mandatory for all buses, taxis and auto to use CNG as a fuel.
Liquified Natural Gas:LPG
LPG or bottled gas or refinery gas is obtained as a by-product during the cracking of heavy oils or
from natural gas. LPG is dehydrated, desulphurised and traces of odorous organic sulphides (mercaptans)
are added to give warning of gas leak. LPG is supplied under pressure in containers under the trade name
like Indane, Bharat gas, etc. Its calorific value is about 27,800 kcal/m3.
It consists of hydrocarbons of such volatility that they can exist as gas under atmospheric
pressure, but can be readily liquefied under pressure. The main constituents of LPG are n-butane
(38.5%), isobutene (36.7%), and propane (24.7%), with little or no propylene and ethane. Its calorific
value is 25000 Kcal/m3.
Uses: 1. Use as a domestic fuel and industrial fuel.
1.Nowadays used as motor fuel.
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UNIT-IV
8. a.
6M
Refractoriness Under Load (RUL):
Refractories used in metallurgical operation and industries have to withstand varying loads. So
refractories should have high mechanical strength under operating temperatures. The load bearing
capacity of a refractory can be measured by means of RUL test.
In RUL (Refractoriness Under Load) test a constant load (1.75 kg/cm2 or 3.5 kg/cm2) is applied
to the sample refractory specimen of rectangular shape (base 5 cm2 & height 75 cm) and heated at
standard rate of 10 oC/min in furnace. The temperature at which atleast 10% of the specimen standard
get destroyed is taken as the RUL value. A good refractory should have high RUL value.
Porosity:
Porosity of refractory material is the ratio of pore volume to bulk volume. All refractories contain
pores. However, refractories with high porosity are not preferred for furnace lining because
 Molten charge, gases and slag penetrates through the pores and decreases the life of refractory.
 Penetration of slag may change the physical nature of the inner side of the material and may
result in development of internal stress during heating.
 Refractory with high porosity has less strength, poor resistance to abrasion and greater
tendency to be corroded by slags.
However pores trap air and hence increase the resistance to thermal spalling because the trapped
air acts as a non-heat conducting material. A good refractory material in general has low porosity.
b)
6M
Viscosity Index:
The most important physical property of a lubricant is its viscosity. Viscosity may be defined as
the internal resistance of fluid during flow. The viscosity of oil is the time in seconds for given quantity
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of oil to flow through a standard orifice under the specified set of conditions. The higher the flow rate,
lower is the viscosity of oil.
The viscosity can be measured using Red-wood viscometer or Saybolt viscometer. It is
expressed in centipoises (cP), centistokes (cSt), or seconds Saybolt universal (SSU). In most liquids,
viscosity drops appreciably with rise of temperature as a result of decrease in intermolecular attractions.
This variation of viscosity with temperature is indicated by viscosity-temperature curve or by means of
an arbitrary scale known as the Viscosity Index (VI).
The oil is said to posses low VI, if its viscosity decreases rapidly as the temperature is raised. If it
is slightly affected with temperature, the oil is said to posses high VI. The Pennsylvanian oil exhibits a
relatively small change in viscosity with rise in temperature and are arbitrarily assigned a VI value of
100. Oils of Gulf origin exhibit a larger change in viscosity with rise in temperature and are arbitrarily
assigned a VI value of 0.
The test oil is compared at 38 oC (100 oF) with zero VI oil and 100 VI oil, both having the same
viscosity as the test oil at 99 oC (210 oF).
V.I. = L-U/L-H x 100, where, U = Viscosity of test oil at 38 oC
L = Viscosity of low viscosity index oil at 38 oC
H = Viscosity of high viscosity index oil at 38 oC
Cloud point:
The lubricating oils are derivatives of petroleum and contain dissolved paraffin wax and other resinous impurities.
These impurities tend to separate from the oil at lower temperatures. The solidification of lubricant causes
jamming of machines.
“The temperature at which the impurities begin to separate from the solution and lubricating oil becomes cloudy
or hazy in appearance is called cloud point”
“The cloud point is the temperature at which crystallization of solids in the form of cloud or haze first becomes
noticeable, when the oil is cooled at a standard rate.”
Significance:
The cloud point indicates stability of lubricants in cold conditions.
Cloud point is useful for estimating the temperature at which filter screens in the fuel intake system of diesel
engine clogged because of separation of wax.
9. a.
8M
Fluid film or Thick-layer or Hydrodynamic lubrication:
The sliding / moving surfaces are completely separated by applying a thick uniform film of
lubricant between them. The thickness of fluid film is at least 1000 °A. This thick film of lubricant
covers all the irregularities on the moving surfaces and prevents contact between moving surfaces. Thus
the formation of welded junctions is prohibited.
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Since the fluid film comes in contact with the surfaces, it offers resistance to motion due to its
viscosity. Therefore the lubricants so chosen should have sufficient viscosity under working conditions
and at the same time it should remain in place and separate the surfaces.
In such a type of lubrication, when load is applied, the corresponding pressure is developed in
the lubricant is sufficient to keep moving surfaces apart. Therefore this type of lubrication is known as
hydrodynamic lubrication. Light machines like watches, clocks, guns, sewing machines etc., are
provided with this type of mechanism.
Hydrocarbon oils are generally considered as satisfactory lubricants for fluids film lubrication.
Petroleum oils are mixed with additives to maintain the viscosity of oil in all seasons.
Boundary lubrication or Thin film lubrication:
This kind of lubricant is employed where a continuous film of lubricant cannot persist and direct
contact between sliding surfaces is possible due to some reasons. Typical cases are movement of a shaft
from rest, low speed or heavy load and the viscosity of the oil is low. Under such conditions the
thickness of a fluid film should less than 1000 °A. Such thin layer consists of one or two molecular
layers. To form a thin film, the lubricant has to be adsorbed (surface attached) by physical or chemical
reaction or both to the metallic surface. The oil film keeps the metallic surfaces apart known as
boundary film.
Vegetables and animals oils are usually used for this type of lubrication process as they possess
the property of adsorption. For boundary lubrication the lubricant molecules should have long
hydrocarbon chains and polar groups (-COOH) which react with metal surface to form continuous thin
film of lubricant.
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Good boundary lubrication is observed using blended oils. Solid lubricants like MoS2 and
graphite are also useful in boundary lubrication.
b. Particle-reinforced composites:
4M
These are made by dispersing particles of varying size and shape of one material in a matrix of
another material. The process can be carried out by adding particles to a liquid matrix material, which
later solidifies or may be pressed together. The matrix transfers some of the applied stress to the
particles, which bear a fraction of load.
These are again two types
A. Large particle composites:
In these composites, the particulate phase is harder and stiffer than the matrix. These
particles restrain the movement of the matrix phase in the vicinity of each particle. For effective
reinforcement, the particle should be small and evenly distributed throughout the matrix. The
mechanical properties are enhanced with increasing particulate content.
Ex: Polymers with fillers, concrete, cements.
The composite formed from ceramic with metal is known as cermets.
Tungsten carbide or titanium carbide embedded in a metal like cobalt or nickel is an example of
cermet. It is used as cutting tool for steel.
B. Dispersed- Hardened composites:
0.01 to 0.1u size particles are dispersed in the matrix. The volume percentage of the particles
is also smaller (15%). The most widely used materials of this class are the precipitation-hardened alloys.
Ex: Age-hardening of aluminum alloy (95.5%Al + 4.5%Cu). This alloy is heated to high temperature
so as to form solid solution and then quenched when a hard constituent like CuAl2 is precipitated in fine
particle form.
The high temperature strength of nickel alloys may be enhanced by the addition of 3% volume of
Thoria (ThO2) as fine dispersed particles. This is known as TD nickel.
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