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Convention for Work

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Work is a positive quantity when work is performed on the system
...


At a constant volume:
ΔV = 0
W = – P · ΔV = 0 J
ΔU = Q + W = Q
Heat, State Change, Calorimetry

Mixtures with no Change of State
The heat gained or lost by a solid or liquid substance, provided there is no change of state,

is determined by the equation, Q = m c ΔT
...
Thus
power generation processes and energy sources actually involve conversion of energy from one form to another, rather than
creation of energy from nothing

2nd Law of Thermodynamics
The second law is concerned with entropy, which is a measure of disorder
...
This temperature depends on the pressure on the surface of the
liquid
...

Latent heat
Heat that causes a change of state of a substance without changing its temperature
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This steam has no moisture
contents
...
This
steam has a moisture content express in dryness fraction
...
(ie
...

Dryness fraction expresses the percent of dry steam as compare to water in that wet steam
...
it is the percent of the latent
heat for the wet steam at that pressure)

Define the following terms:
Saturation temperature
The temperature at which a liquid reaches its boiling point
...

Saturated steam
Steam at the saturation temperature corresponding to a particular pressure and saturated with sensible and latent
heat
...

This steam has a moisture content express in dryness fraction
...
5 degree Celsius, what would the temperature be of 50
% wet steam at the same pressure?
The temperature will and remains the same @ 133
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State, in the form of an equation, the relationship between the heat released by fuel during combustion in
a boiler, the heat given to the steam in the boiler, and the boiler thermal efficiency
...

Boiler efficiency = m

s × (h1– h2)
mf × c
...


Where:
ms = mass flow rate of steam
h1 = enthalpy of steam produced in boiler
h2 = enthalpy of feedwater to boiler
mf = mass flow rate of fuel
c
...
= calorific value of fuel

Calculate the heat required to produce 1 kg of wet steam at 350 kPa from water at 20 Degrees C if the
steam is 95 % dry
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96 kJ/kg
Enthalpy of steam @ 95% dry = hf @ 350 kPa + (hfg @ 350kPa × dryness fraction)
= 584
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1 kJ/kg × 0
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025 kJ/kg

The amount of heat required to produce 1 kg of wet steam at 95% dry from feedwater at 20°C =
Enthalpy of steam @ 95% dry - Enthalpy of feedwater

= 2625
...
96 kJ/kg
= 2541
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Interpolation for enthalpy of superheated steam @ 250 kPa & 200°C:

 h @ 250 kPa & 200°C
= {[(h@ 300 kPa & 200°C – h @200 kPa & 200°C) / (300 kPa –200 kPa)] × (250 kPa – 200 kPa)} + h
@200 kPa & 200°C
= {[( 2865
...
5 kJ/kg ) / 100 kPa] × 50 kPa}+ 2870
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05 kJ/kg

MODULE 20 (AC)

BASIC CONCEPTS ABOUT MATTER

Define matter and explain the states of matter
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Matter can exist in three different physical states: solid, liquid, or gas
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Physical properties are those characteristics used to describe a substance, of those properties that ca be
observed without a change in the composition of the matter
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For example, a block of ice is composed of a hydrogen and oxygen compound in the solid state
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Define and give an example of the chemical property of a substance
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They are those properties
that matter exhibits as it undergoes a change in its composition
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For example, iron will combine with oxygen ton produce rust, a new substance
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Magnesium reacts with oxygen to produce magnesium oxide, a white powder
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Physical changes occur when physical properties are altered without a change in chemical composition
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A change in physical
state (for example, changes in water from a liquid to solid or gaseous state) is perhaps the most common
type of physical change
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Chemical change involves a change in the chemical composition of a substance
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Each new substance is different both
chemically and physically from the original
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When fuel gases
react with air in a combustion reaction, carbon dioxide and water are formed as products
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Define and give an example of:
an element
Elements are pure substances that cannot be decomposed into simpler forms of matter
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a compound
A compound is a pure substance that consists of two or more elements, chemically bound together in fixed
proportions by mass
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a mixture
They are combinations of two or more pure substances that aren’t chemically bound to each other
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Briefly describe how the Periodic Table of the Elements is organized
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THERMODYNAMICS OF STEAM

With reference to the production of steam, define the terms:
Saturation temperature
The temperature at which a liquid reaches its boiling point
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Sensible heat

Heat that causes a change in the temperature of a substance without changing its state
...


Define the terms:
Dry saturated steam
Steam that is saturated with all the possible sensible heat and latent heat for that pressure
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Wet steam
Steam that is saturated with all the possible sensible heat, but only partially with the latent heat for that pressure
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Superheated steam
This is dry saturated steam with further sensible heat added
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The temperature of the steam is higher than its
saturation temperature)

Define the term “dryness fraction”

Dryness fraction expresses the percent of dry steam as compare to water in that wet steam
...
it is the percent of the latent heat for the wet steam at that pressure)
Define the following terms:

Saturation temperature

The temperature at which a liquid reaches its boiling point
...


Saturated steam
Steam at the saturation temperature corresponding to a particular pressure and saturated with sensible and latent
heat
...

This steam has a moisture content express in dryness fraction
...
5 degree Celsius, what would the temperature be of 50
% wet steam at the same pressure?

The temperature will remains the same @ 133
...


State, in the form of an equation, the relationship between the heat released by fuel during
combustion in a boiler, the heat given to the steam in the boiler, and the boiler thermal
efficiency
...


Boiler efficiency = ms (h1– h2)
mf c
...

Where:
m = mass flow rate of steam
s
h = enthalpy of steam produced in boiler
1
h = enthalpy of feedwater to boiler
2
m = mass flow rate of fuel
f
c
...
= calorific value of fuel

Calculate the heat required to produce 1 kg of wet steam at 350 kPa from water at 20
Degrees C if the steam is 95 % dry
...
96 kJ/kg
f
Enthalpy of steam @ 95% dry = hf @ 350 kPa + hfg @ 350kPa dryness fraction
= 584
...
1 kJ/kg 0
...
025 kJ/kg
The amount of heat required to produce 1 kg of wet steam at 95% dry from feedwater at 20C
= Enthalpy of steam @ 95% dry - Enthalpy of feedwater
= 2625
...
96 kJ/kg
= 2541
...

Interpolation for enthalpy of superheated steam @ 250 kPa & 200C: h @ 250 kPa &200C
= (h@ 300 kPa & 200C – h @200 kPa & 200C) / (300 kPa –200 kPa) (250 kPa – 200 kPa) + h @200 kPa & 200C
= 2865
...
5 kJ/kg / 100 kPa 50 kPa + 2870
...
05 kJ/kg



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