Technically, mechanical engineering is the application of the principles and problem-solving techniques of engineering from design to manufacturing to the marketplace for any object. Mechanical engineers analyze their work using the principles of motion, energy, and force—ensuring that designs function safely, efficiently, and reliably, all at a competitive cost. Mechanical engineers make a difference. That's because mechanical engineering careers center on creating technologies to meet human needs. Virtually every product or service in modern life has probably been touched in some way by a mechanical engineer to help humankind. This includes solving today's problems and creating future solutions in health care, energy, transportation, world hunger, space exploration, climate change, and more.Being ingrained in many challenges and innovations across many fields means a mechanical engineering education is versatile. To meet this broad demand, mechanical engineers may design a component, a machine, a system, or a process. This ranges from the macro to the micro, from the largest systems like cars and satellites to the smallest components like sensors and switches. Anything that needs to be manufactured—indeed, anything with moving parts—needs the expertise of a mechanical engineer.

1. SOLAR ENERGY COLLECTORS
Non Conventional Energy Sources
References : G.D RAI
J K Nayak

2. SOLAR COLLECTORS:
 Collector is a device which absorbs the incoming solar
radiation, converts it into heat, and transfers this heat to
a fluid (usually air, water, or oil) flowing through the
collector.

3. COLLECTORS
Collecting Fluids
Mounting
Flat (or)
Non
concentric
Adjustable
Stationary Gas (or) Air
Concentric
(or)
Focussing

4.  Flat-plate collectors, developed by
Hottel and Whillier in the 1950s, are the
most common type of solar collector
which are widely used for domestic
household hot-water heating , air
heating
 Temperature can be upto 900
 In the Non-concentrating type, the
collector area is the same as the
absorber area.
Flat or Non concentric type collector

5. Flat (or)
Non
concentric
Fluid Type Air Type
 FLUID TYPE : Heat Transfer medium is water or any other liquid
 AIR TYPE : Heat Transfer medium is air or gas.

6. A typical diagrams of
“ Flat plate solar thermal
collectors”

7. Components of Flat plate collector
GLAZING
ABSORBER
HEADERS
INSULATION
CONTAINER
** These can absorb both direct and diffused beam
radiations

8. GLAZING:
o Made of one or more covers of transparent material like glass or plastic..
o It is used to reduce convective and radiative heat losses from the absorber.
o It is opaque to the infrared radiations.
ABSORBER :
o It is usually made of copper or steel metal.
o The surface is covered with a thin coating of primer and then flat black paint of high absorptance huge
paint may increase the resistance to heat tranfer
o Coating is applied on the surface to maximize the absorptance of solar energy and minimizes the
radiation emitted by plate.
TUBES OR HEADERS :
o A tube that is attached to absorber or sometimes it is a part of absorber plate.
o If the working fluid is air , the flow passage should be below the absorber plate to minimize heat losses.

9. Insulation:
 These are some materials such as fiberglass and they are placed at the back and sides of
the collector to reduce heat losses. eg. wool, fiber etc...
Container :
 Which encloses the other components together and protects from the weather.

10. Flat plate collectors

11. Flat plate collector Fluid Type

12. Cross sectional arrangements through the
collector plates
Tube in strip type
Glazing
Riser
Absorbing plate
Insulation
A
B
Glazing
Riser
Absorbing plate
Insulation

13. C
Glazing
Riser
Absorbing plate
Insulation
D
Glazing
Riser
Absorbing plate
Insulation
Tubes brazed to absorber
Cross sectional arrangements through
the collector plates

14. Working Principle
Sunlight passes through the glazing
and strikes the absorber plate, which
heats up, and solar energy is
converted into heat energy.
This the heat is transferred to the
fluid passing through pipes attached
to the absorber plate by means of
convective heat transfer.

15. Glazing design
 Due to two glass sheets are used losses due to air convection are further reduced
, this is mainly used and important in windy areas.
 Radiation losses in infrared spectrum are reduced to 25% from 50% due to use of
two glass sheets.
 It is not economical to use more than two plates as if the plates increases it
reflects the solar radiation by 15 % and efficiency decreases.
 The air space between the cover and the absorber prevents heat loss by
convection
 However if one watches the electromagnetic spectrum

16.  As cover is made of glass
It allows the solar radiations of wavelength < 2µm
and is opaque for wavelength > 2µm
It is seen from electromagnetic spectrum that infrared
radiations having wavelength > 2µm
As a result infrared are opaque and does not pass
Soo heat is trapped inside the space between the cover and
absorber plate similar to green house effect and keeps it hot.
However some of heat occurs due to conduction , convection , and
radiation thereby effecting the overall efficiency.

17.  This can be met by following steps :--
 It can be reduced by using "water white glass" with low iron content
 Reflection which is order of 15% can be met by gentlly itching the
glass surface hydro flouric acid.
Glazing design considerations

18. Absorber design
 Coating done on the absorber surface is called "selective coatings "
 "Black chrome" is extensively used coating which is of 2µm
thickness
Heat transport sytem
 Heat generated in the absorber is continuosly taken by the flow of
medium through tubes.

19. ?
?
?

21. Non porus absorber : Air flows above and beneath the absorber.
Porus Absorber : Air flows through the absorber.
Air Heaters
Non porus
Absorber
Porus
Absorber

22. Non Porus Air heater

23. Air Type Flat plate collectors
 Used commonly for space heating and agricultural
heating applications.
A Typical
Flat plate collector
Solar air heater

24. Collectors with porus absorbers

25.  Design of Air plate collector
 Heavily insulated material like mineral wool is coated beneath the
surface of absorber
 The most favourable orientation of the panel is facing due south with
an inclination of 15o latitude with the horizontal.
 Air as medium of heat transfer eliminates the corrossion and
freezing problems which are more when water is used.
 Air is passed through the baffles arranged in zig zag pattern
between the absorber and insulation where fins provides the more
contact area thereby more amount of heat to transfer.

26. Applications
Flat Plate collectors
Air collectors
Heating Buildings
Drying Agricultural Products
Heating Green houses.
Heat source for heat engines.
Both Beam and Diffuse radiations
orientation need not be towards sun
little maintaince
simplier than concentric plate type
Advantages

27.  Thermal Analysis of Flat Plate Collectors

28. Thermal Analysis of Flat Plate Collectors
 If I is the intensity of solar radiation, in W/m2 , incident on the aperture plane of the
solar collector having a collector surface area of A, in m2
 Then the amount of solar radiation received by the collector is :
 However, as it is shown Figure 2, a part of this radiation is reflected back to the sky,
another component is absorbed by the glazing and the rest is transmitted through the
glazing and reaches the absorber plate as short wave radiation.
 Therefore the conversion factor indicates the percentage of the solar rays penetrating
the transparent cover of the collector (transmission) and the percentage being
absorbed.
 Basically, it is the product of the rate of transmission of the cover and the absorption
rate of the absorber and is given by

29. Thermal Analysis of Flat Plate Collectors
 As the collector absorbs heat its temperature is getting higher than that of
the surrounding and heat is lost to the atmosphere by convection and
radiation.
 The rate of heat loss (Qo) depends on the collector overall heat loss
coefficient (UL) and the collector temperature.

30. Under steady state conditions
 The rate of useful energy extracted by the collector (Qu), expressed as
Thermal Analysis of Flat Plate Collectors
It is also known that the rate of extraction of heat from the collector may be
measured by means of the amount of heat carried away in the fluid passed
through it, that is:

31.  It is convenient to define a quantity that relates the actual useful energy
gain of a collector to the useful gain if the whole collector surface were at
the fluid inlet temperature. This quantity is known as “the collector heat
removal factor (FR)” and is expressed as:
Thermal Analysis of Flat Plate Collectors

32. Concentric type collector :

33. simple concentric collector

34.  Types of concentric collectors
 a) Flat plate collector with adjustable mirrors
 b) Compounded parabolic collector
 c) Cylindrical parabolic collector
 d) Mirror strip reflector (or) Moving reflector with fixed concentrator
 e) Fresnel lens collector
 f) Parabolic trough collector

36.  Beam radiation is reflected from the
number of individual mirrors called
heliostats to the central receiver at the top.
 Upto 20000C
Cylindrical parabolic trough collector

37. Fresnel Lens Collector
It is flat on one side and has
fine longitudinal grooves on
the other
The angles of these grooves
are such that the radiation is
brought to the focus
Lens are made of plastic
sheets.
Used upto 4000C

38. Parabolic trough collector
 solar radiation coming in a
particular direction is collected
and is collected on the focus of
the parabola

39. Thermal Analysis of concentrate collectors
 Under the steady state conditions we have :
 Equation is written assuming that the contribution of diffuse beam
radiations are negligible

40.  And Q1 the overall loss coefficient can be given as :

41. CONCLUSION
Long lasting
Cheaper than other water heating systems.
However,they requires large areas
Also solar energy is free
If we do not include the initial cost for installation and the maintenance.
Finally; besides these we should remember by using solar energy we can
protect nature

42. The End