SEMESTER TWO FOR BSC PTI ENGINEERING PROGRAMMES
TEST PAPERS:
ml 4201 ENERGY CONSERVATION AND MANAGEMENT
DATE: 16TH NOVEMBER, 2022
TIME ALLOWED: 2Hours
Instructions to Candidates:
This test paper contains five Questions
Attempt any Five Question
QUESTION ONE
a). Explain briefly what is meant by Energy audit. (5marks)
An energy audit is an inspection, survey and analysis of energy flows for identification of
energy savings opportunities in a building, process or system to reduce the amount of energy
input into the system, without negatively affecting the output(s).
b). Outline five reasons for undertaking an Energy audit. (1Omks)
•
To improve energy performance and minimise the environmental impacts of the
organisation’s operations.
•
To identify behavioural change opportunities by evaluating current operations and
maintenance practices.
•
To identify technical opportunities by evaluating significant process energy-using
components or utilities including boilers, refrigeration plant, ventilation systems,
building performance and fleet efficiency.
•
To provide clear financial information regarding energy savings opportunities in order
to prioritise these items for the organisation’s decision-making process.
•
To gain a greater understanding of a part or all of the organisation’s energy usage
patterns.
•
To identify potential for using renewable energy supply technologies.
•
To achieve compliance with legal requirements such as the Energy Efficiency
Directive, Industrial Emissions Directive or the Environmental Protection Agency’s
waste license requirements.
•
To comply with corporate social responsibility goals.
•
To meet customer and shareholder expectations.
•
To inform a strategic plan aimed at minimising the organisation’s carbon footprint
c). Write down five steps involved in phase one of preparation & pre analysis of the
Energy audit process. (5marks) Phase 1 Preparation & Pre-analysis
✓ Step 1 Introductory meeting to agree approach
✓ Step 2 Confirm scope and collect preliminary data
✓ Step 3 Identify key personnel and schedule site visit
✓ Step 4 Develop energy use baseline and measurement plan
✓ Step 5 Develop audit checklist Step
✓ to Phase 2
✓ Step 6 Conduct site audit and record findings
✓ Step 7 Undertake analysis of current energy practices and usage onsite
✓ Step 8 Develop graphic interpretation of energy opportunities and threats
✓ Step 9 Develop final report with contextualised graphic information
OUESTION TWO
a)
Define the following terms as applied to basics of heat transfer:
Heat is the form of energy that can be transferred from one system to another due to a
temperature difference or gradient.
i)
Conduction
Conduction refer to the thermal energy transfer that
will occur across a medium, which may be a solid or a
fluid due to a temperature difference.
ii)
Convection
Convection refer to the thermal energy transfer
between a surface and a moving fluid when they are at
different temperature levels.
iii)
Radiation
Thermal radiation refers to the net transfer of thermal
energy between two surfaces at different temperature
levels, in the absence of an intervening medium
between them. This occurs due to electromagnetic
waves emitted from a hot body.
b)
Write down the basic equation for thermal conduction and state Fourier 's law.
(4marks)
The basic equation for thermal conduction is the Fourier’s law.
It states that the heat flux(Heat Transfer rate per unit area) is directly proportional to the
temperature gradient.
q = dT/dx or q ═ - k dT/dx
Where, k - thermal conductivity (W/m.K)
dT/dx - temperature gradient
q - heat flux (W/sq. m)
𝐐 = −𝐤𝐀 𝐝𝐓/ 𝐝X.
Assumptions of Fourier’s Law
1. Steady state conduction – temp. does not change with time.
2. Uni-directional heat flow.
3. Constant temp. gradient and linear temp. profile.
4. No internal heat generation.
5. Bounding surfaces are isothermal in character.
6. Isotropic and homogeneous material.
Thermal energy transfer by convection is classified as:
1. Natural (Free) convection and 2. Forced convection.
✓ Forced convection is the transfer of thermal energy when the flow is caused by
external means, such as a fan, a pump or atmospheric winds.
✓ Natural convection is induced by buoyancy forces due to density variations as a result
of temperature differences.
The basic equation for convection heat transfer is known as Newton’s law of cooling:
𝑄 = ℎ𝐴(𝑇𝑠 − 𝑇∞) Where,
𝑇𝑠 is the surface temperature,
𝑇∞ is the fluid temperature and A is the surface area of the solid.
h is the convection heat transfer coefficient in (𝑊/m2 k )’
h is also called film heat transfer coefficient or surface conductance.
c). Give an outline of the three distinct phases of the mechanism of heat flow by radiation.
(6marks)
The mechanism of heat flow by radiation consists three distinct phases:
1. Conversion of thermal energy of the hot source into electromagnetic waves. Photons are
propagated through the space as rays.
2. Passage of wave motion through intervening space. Photons travel with unchanged
frequency in straight paths with speed equal to that of light.
3. Transformation of waves into heat. Reconversion of wave motion into energy occurs in the
receiving surface which may partly absorbed, reflected or transmitted through.
c)
A horizontal steel pipe having a diameter of 10 cm is maintained at a temperature
of 600C in a large room where the air and wall temperature are at 200C with average
heat transfer coefficient 6.5 W/m2k. The emissivity of the steel is 0.6. Calculate the total
heat lost from the pipe per unit length. (Stefan-Boltzmann constant = 5.67xl 0-8 W/m2.K4)
(5mark)
d)
List down the parameters to be monitored for calculation of boiler efficiency by
direct method.(5marks)
Question One
a) Explain briefly what is meant by energy audit.
[3 marks)
An energy audit is an inspection, survey and analysis of energy flows for identification of
energy savings opportunities in a building, process or system to reduce the amount of energy
input into the system, without negatively affecting the output(s).
b) Outline four reasons for undertaking an Energy audit.
•
[4 marks)
To improve energy performance and minimise the environmental impacts of the
organisation’s operations.
•
To identify behavioural change opportunities by evaluating current operations and
maintenance practices.
•
To identify technical opportunities by evaluating significant process energy-using
components or utilities including boilers, refrigeration plant, ventilation systems,
building performance and fleet efficiency.
•
To provide clear financial information regarding energy savings opportunities in order
to prioritise these items for the organisation’s decision-making process.
•
To gain a greater understanding of a part or all of the organisation’s energy usage
patterns.
•
To identify potential for using renewable energy supply technologies.
•
To achieve compliance with legal requirements such as the Energy Efficiency
Directive, Industrial Emissions Directive or the Environmental Protection Agency’s
waste license requirements.
•
To comply with corporate social responsibility goals.
•
To meet customer and shareholder expectations.
•
To inform a strategic plan aimed at minimising the organisation’s carbon footprint
c) State five steps involved in phase one of preparation & pre analysis of the energy
audit process.
[S marks]
✓ Step 1 Introductory meeting to agree approach
✓ Step 2 Confirm scope and collect preliminary data
✓ Step 3 Identify key personnel and schedule site visit
✓ Step 4 Develop energy use baseline and measurement plan
✓ Step 5 Develop audit checklist Step
✓ to Phase 2
✓ Step 6 Conduct site audit and record findings
✓ Step 7 Undertake analysis of current energy practices and usage onsite
✓ Step 8 Develop graphic interpretation of energy opportunities and threats
✓ Step 9 Develop final report with contextualised graphic information
d) State two appropriate portable measuring equipment for each of the following
systems that could be tested during an Energy' audit.
i.
Electrical
• Multimeter • Voltmeter • Ammeter • Power Mete
ii.
Temperature measurement
Surface Pyrometer • Portable Electronic • Thermometer • Thermocouple Probe • Infrared
Thermometer • Infrared Camera
iii.
Buildings
• Light Meter • Measuring Tape • Thermal Image Camera
iv.
Combustion
[2 marks each]
• Combustion Analyser.
Question Two
a) Define the following terms as applied to basics of heat transfer:
i. Conduction ii. Convection
[2 marks each]
b) Discuss the surface properties that radiation heat transfer depend on.
Radiation heat transfer depends on the surface properties such as colors, surface orientation
and fourth power of the absolute temperature (T4 ) of the surface.
c) A horizontal steel pipe having a diameter of 10 cm is maintained at a temperature of
600Cin a large room where the air and wall temperature are at 200C with average
heat transfer coefficient 6.5 W /m2 .k. The emissivity of the steel is 0.6. Calculate the
totalheat lost from the pipe per unit length.
(Stefan-Boltzmann constant = 5.67x 10 -8 W/m2 .K4) [5 marks)
d) An electric current is passed through a wire 1mm diameter and 10 cm long. This wire
is submerged in liquid water at atmospheric pressure, and the current is increased until
the water boils. For this situation h = 5000 W/m2. 0C, And the water will be 1000C.
Determine the electric power that must be supplied to the wire to maintain the wire
surface at 1140C
[5 marks)
Ouestion Four
a) State five basic colours associated with the visible portion of the electromagnetic
spectrum and explain what distinguishes this part of the electromagnetic spectrum
from the rest. [6 marks]
b) With aid of illustrations, explain the three general types of reflection.
c) State four different types of high intensity discharge lamp. [4 marks]
d) Using illustrations, explain the difference between diffuse reflectance and
transmission
[4 marks)
QUESTION FIVE
a) Write short notes on the following properties of liquid fuels
i.
Density
ii.
Calorific value
iii.
Specific heat
[2 marks each]
b) Explain briefly the "three T's" of combustion
[6 marks]
Find out the efficiency and evaporation ratio of the boiler by direct method with the
data given below:
Question six
a) Outline five ultimate sources of useful energy
✓ hydroelectricity or hydro energy
✓ solar energy
✓ geothermal energy
✓ biomass
✓ biogas
[5 marks]
b) State three environmental and social problems of fossil fuels. [3 marks)
✓ Non renewable energy source.
✓ Produce greenhouse gases.
✓ Due to mining of coal, Natural habitats are destroyed.
c) Discuss the importance of renewable energy resources and technologies for
sustainable development.
✓ Hydroelectricity is non polluting sources of energy
[6
marks]
✓ Dams used in production of hydroelectricity, is also used in irrigation
purposes
✓ Burning of alcohol or producer gas produce less amount of pollutant gases.
✓ Biomass present in large amount.
✓ Help to reduce waste
✓ Produce organic waste
✓ Burn without smoke
d) State three examples on each of the following.
i. Renewable energy resources
For example, solar energy, wind energy, bio-fuels, hydro energy, geothermal
energy, wave & tidal energy.
ii. Non-renewable energy resources.
For example, nuclear energy, coal, petroleum, natural gas etc.
Question Seven
a) Outline four characteristics of steam that make it popular and useful to
Industry. [4 marks]
b) Differentiate between the following:
I.
Liquid enthalpy and enthalpy of evaporation [4 marks]
II.
Sensible and latent heat
[4 marks]
THE SOLUTION IS ABOVE
c) State four factors to be considered in the design of a good steam distribution system.
[4 marks]
d) State two factors that limit distribution pressure of steam and explain why steam
will inevitably lose pressure as it passes through the distribution pipe work.
Question One
a). Define the following terms:
i) photo electric effect
The phenomenon of emission of electrons from metal surface exposed to light (of suitable
frequency) is known as Photo – electric effect.
ii) work function
In a metal ,electrons are bound by attraction force of nucleus. So, a certain minimum
energy is required to pull out the electron from the surface of metal. It is called Work
Function of the metal.
iii) photon
(2marks @)
Radiant energy is quantized into localized bundles moving with velocity c and having
energy proportion to the frequency Eph = hv
These particles like bundles are called photons.
b). Mention the categories of energy resources classified on the basis of sources.
(4marks)
On the basis of sources energy are classified into categories, renewable energy resources
and non-renewable energy resources.
i)
Renewable energy resources: These energy resources are also known as non
conventional energy resource, which can be regenerated continuously. It can be used
again and again in an endless manner because these resources are available in large
amount. For example, solar energy, wind energy, bio-fuels, hydro energy,
geothermal energy, wave & tidal energy.
ii)
Non renewable resources: These energy resources are also known as conventional
(traditional) energy resources. It cannot be replenished when these sources are
exhausted because these resources are present in limited amount and take a long
period of time to re-synthesize. For example, nuclear energy, coal, petroleum,
c). Describe briefly the following steps involved in generation of biogas by anaerobic
digestion of organic wastes;
Hydrolysis: In this step, macromolecule like fats, proteins, carbohydrates are broken down
through hydrolysis into fatty acids, amino acids and sugars respectively.
Acid formation: in this step, fatty acids, amino acids and sugars are fermented by acid
producing bacteria under anaerobic condition into acetic acid, carbon dioxide and hydrogen.
Gas production: In this step, methanogenic bacteria produce methane either by fermenting
acetic acid to form methane and carbon dioxide or by reduction of carbon dioxide into
methane.
Question two
a). Write short notes on each of the following:
(i). Nuclear fission (4marks)
Nuclear Fission: In this case nuclear energy is produced by bombardment of slow
neutrons or thermal neutrons on heavy atom like Uranium. On bombardment
Uranium get excited and split into two medium weight nuclei and liberate large
amount of energy (more than 200 MeV of energy).
(ii).
Nuclear fusion (4mks)
Nuclear Fusion: In this case, two lighter atoms like deuterium atom combine at extremely
high temperature to form heavier nuclei helium (stable) atom and release large amount of
energy.
b). Explain briefly 3 ways of generating energy from biomass. (6marks)
Energy generation from biomass
a) Combustion or burning is most common method to obtain energy directly from
biomass.
b) Fermentation: in this process, biomass (carbohydrate) is converted into alcohol in
presence of bacteria or yeast.
c) Biomass gasification: In this process, biomass is converted into combustible fuel like
producer gas (CO+H2) and small amount of methane through incomplete combustion.
Advantage of biomass energy
✓
✓
✓
✓
It is also a renewable source of energy.
Burning of alcohol or producer gas produce less amount of pollutant gases.
Biomass present in large amount.
Help to reduce waste
Disadvantage of biomass energy
✓
✓
✓
Direct combustion of biomass generates pollutant gases like fossil fuel.
Cause deforestation.
Not efficient like fossil fuel.
c). State the advantages and disadvantages of using biogas. (6 marks)
Advantage of biogas
✓
✓
✓
✓
Produce organic waste
Burn without smoke
Renewable
Help to reduce waste.
Disadvantage of biogas
✓
✓
Methane is health hazardous.
Not efficient like fossil fuel.
Question Four (2() marks)
a). Outline the functions performed by most air conditioning systems. (4marks)
Most air conditioning systems perform the following functions:
✓ Provide the cooling and heating energy required
✓ Condition the supply air, that is, heat or cool, humidify or dehumidify, clean and
purify, and attenuate any objectionable noise produced by the HVAC&R equipment
✓ Distribute the conditioned air, containing sufficient outdoor air, to the conditioned
space
✓ Control and maintain the indoor environmental parameters–such as temperature,
humidity, cleanliness, air movement, sound level, and pressure differential between
the conditioned space and surroundings—within predetermined limits
b). Discuss four areas that utilize process air conditioning systems.
1. In textile mills, natural fibres and manufactured fibres are hygroscopic. Proper control of
humidity increases the strength of the yarn and fabric during processing. For many textiles
manufacturing processes, too high a value for the space relative humidity can cause problems
in the spinning process. On the other hand, a lower relative humidity may induce static
electricity that is harmful for the production processes.
2. Many electronic products require clean rooms for manufacturing such things as integrated
circuits, since their quality is adversely affected by airborne particles. Relative-humidity
control is also needed to prevent corrosion and condensation and to eliminate static electricity.
Temperature control maintains materials and instruments at stable condition and is also
required for workers who wear dust-free garments
3. Precision manufacturers always need precise temperature control during production of
precision instruments, tools, and equipment. Bausch and Lomb successfully constructed a constant temperature control room of 68+_ 0.1°F (20 0.56°C) to produce light grating products
in the 1950s.
4. Pharmaceutical products require temperature, humidity, and air cleanliness control. For
instance, liver extracts require a temperature of 75°F (23.9°C) and a relative humidity of 35
percent. If the temperature exceeds 80°F (26.7°C), the extracts tend to deteriorate. Highefficiency air filters must be installed for most of the areas in pharmaceutical factories to
prevent contamination.
5. Modern refrigerated warehouses not only store commodities in coolers at temperatures of
27 to 32°F (2.8 to 0°C) and frozen foods at 10 to 20°F (23 to 29°C), but also provide relativehumidity control for perishable foods between 90 and 100 percent. Refrigerated storage is used
to prevent deterioration..
c). List down the components of a central hydronic air conditioning system. (5marks)
A central hydronic air conditioning system consists of
✓ an air system,
✓ a water system,
✓ a central heating
✓ cooling plant,
✓ and a control system.
Question five
(a) .Give the symbols and units respectively for each of the following photometric
quantities
(i). luminous energy
(ii).
symbol
units
Illuminance
(iii). radiant intensity and (iv). luminous intensity
(b)Differentiate between the following.
(i) Radiant and luminance
(ii) Radiant intensity and luminous intensity
(iii) Radiant exitance and irradiance
Question Seven (20 marks)
a). Mention three general classes of electric light sources used for providing illumination.
(6 marks)
b). State four different types of high intensity discharge lamp. (4marks)
Differences between incandescent and tungsten halogen lamps