Mechanical Engineering >> NCER

Question 1 : What is Renewable energy source. (Dec. 11, May 12)

Answer : Renewable energy source is the energy providing source which has infinite potential and by which energy can be generated without polluting the environment.
Renewable energy sources are:
1.Solar energy
2.Wind energy
3.Tidal Power
4.Geothermal
5.Biomass and Biogas
1.Solar Energy:
It has the highest potential than the other renewable energy sources. In this the energy of sun in the form of radiations can be converted into electricity with the help of solar panel which future may be utilised as per the requirement of applications.
2. Wind Energy:
In this wind velocity (K.E) can be used to rotate the wind turbine which further produce the electricity due to conversion of mechanical energy into electrical energy.
3.Tidal Power:
Periodic rise and fall of the water level of sea due to gravitational power of sun and moon on earth is called tidal and electricity produced due to this potential is called “Tidal Power”.
4.Geothermal
This is earths interior heat which is utilised for various applications (to generate electricity) by extracting it with the help of heat exchanger. 5.Biomass
It is produced from wastes like Municipal waste, agriculture waste, plant, forest residues and animal dung to converting it into biogas for various purpose.

Question 2 : Write the advantages of renewable energy source. (PTU: May 12, May 13)

Answer : Main advantages of renewable energy source are as give below:
1.It is totally pollution free as electricity produced by this does not pollute the environment.
2.Running cost is too low as compare to conventional sources.
3.All renewable energy sources have infinite potential.
4.Electricity also produced at small scale or even at home by using the home roof with the help of solar panels without any harmful effects.
5.Also applicable where availability of conventional energy sources are not possible.
6.More effective for that areas where convectional energy is not possible.

Question 3 : What are Beam and Diffuse radiation. (PTU: May 12)

Answer : Beam radiation:
Solar radiations received by the earth surface without being diffused by atmosphere is called Beam radiation. As shown in Fig 3.1.
It is also called Direct beam radiation.
Diffuse radiation:
Solar radiations received by earth surface after some of its parts are absorbed, scattered and reflected by the atmosphere like cloud, dust, air molecules and water vapors ect . As shown in Fig 3.1

Question 4 : What is Global radiation

Answer : Total radiations ie sum of beam and diffused radiation received by horizontal surface of earth from sun is called Global radiation.

Question 5 : Explain attenuation of solar radiation. (PTU: May 13)

Answer : Attenuation of solar radiation (weakness of radiation):
It is due to absorption, reflection and scattering of solar radiations by cloud, dust, air molecules, gases and water vapors present in the atmosphere, before reaching the earth surface.
Its again depends upon the quantities of dust particles and moisture present in the atmosphere.

Question 6 : What is Solar Constant. (PTU: May 12, May 13)

Answer : Rate of energy reached from sun to top atmosphere of earth is called Solar Constant. Its value is define as “average amount of energy received in a unit time on a unit area perpendicular to the sun direction at the mean distance of the earth from the sun”.
The value of Solar Constant is taken as 1353 W/m2(satellite measured yearly average value).

Question 7 : What are flat plate collectors? (PTU: Dec 11, May 12, May 13)

Answer : Flat Plate Collector:
1. It is a device to collect or absorb the incident solar radiation and convert it into some useful work, ie to heating collector fluid such as air, oil or water, which will further used for different useful works.
2. It is also called as Non- Concentrating type solar collector and in this collector area and absorber area are same.
3. It is used when temperature is below 90 degree.
4. It is of two types (based on the type of heat transfer fluid used) :
A. Liquid heating collector.
B. Air or gas heating collector.
5. It consist of below mention main components :
a. Transparent cover
b. An absorber plate
c. A series of tubes, carry a heat transfer fluid (water or air)
d. Housing with thermal insulation as shown in fig. 7.1.

Question 8 : Explain the main components and design procedure of flat plate solar collector. (PTU: Dec 11, May 12, May 13)

Answer : Main Components of Flat Plate Collector are:
1. Transparent cover
2. An absorber plate
3. A series of tubes, carry a heat transfer fluid (water or air)
4. Housing with thermal insulation, as shown in fig. 7.1.
Design Procedure of main components:
In this a box/housing with proper insulation is used and absorber plate (having high absorbtivity) with black surface with liquid tubes as an integral part or welded with it are used. In this the absorber plate is enclosed in a box/housing and when solar radiations impinges on the absorber plate after passing through the transparent plate(s) the large amount of radiation is absorbed by the fluid in the tubes. Which will further used as usable energy. The housing is well insulated to reduce the conduction losses. The fluid used in tubes may be water or air. The most common material used for absorber plate is copper as it has good corrosion resistance, high tensile strength and thermal conductivity. It is mainly used for space heating, water heating and space cooling.

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