Parameters effecting solar lfpc performance

Parameters effecting
solar LFPC
performance
GURUDATH G PRABHU
MTECH I YEAR RET

CONTENTS
• LFPC
• CONSTRUCTION
• VARIOUS PARAMETERS
• KEY INVESTIGATIONS
• CONCLUSION
Saturday, April 16, 2016 2

LFPC (Liquid Flat Plate Collector).
 Most common type of collector.
 Simple in design and constructing.
 Used for domestic water heating applications.
 If the fluid is liquid then it is liquid flat plate collector.
 Usually LFPC are stationery and they do not need any tracking.

VARIOUS PARTS OF LFPC ANDTHEIR CONSTRUCTION

Constructional Features
• Usually rectangular case, open at top side, insulation at sides and bottom.
• Heat transfer fluid flowing through the conduits( headers, tubes) which are
attached over or underneath the absorber plate.
• There is transparent cover closing the face of LFPC.
• LFPC casing is usually made up of wood or aluminium.
• Insulation material is glass wool( due to its stability at high temperatures) and it
is up to 25mm-100mm thick.
• Mineral wool, rock wool is also used as insulation material.
• Absorber generally is made of copper metal due to its high conductivity and is
0.2mm to 0.7mm thick.
Saturday, April 16,
2016 5

Constructional Features(cont’d)
• aluminium , steel is also used as absorber material.
• Absorber is spray painted black, and heat treated to improve bonding with
surface or coated with black metal oxides.(nickel oxide, chromium oxide).
• Conduits are same material that of absorber.
• Tubes are of diameter 10-15mm , they are brazed , soldered or pressure bonded
with absorber plate.
• Headers are of 20-25mm diameter.
• Cover is low ferric oxide toughened glass.
• Glass glazing is 2-5mm thick, gap b/w absorber and cover is 15-30mm.
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2016 6

The thermal performance of a collector can be calculated from a first-
law energy balance. according to the first law of thermodynamics, for
a simple flat-plate collector an instantaneous steady-state energy
balance is[1] :
 Useful energy = energy absorbed – heat loss to
gain (Qu) by the collector surroundings

• Absorbed energy = AC FR S
• Lost energy = AC FR UL (Ti-Ta)
where ;
AC = Collector area, m2
FR = Heat removal factor, unitless
S = Absorbed solar radiation, J/m2
UL = Heat transfer loss coefficient, J/m2 °C
Ti = The mean absorber plate temperature, °C
Ta = The ambient temperature, °C.

Useful gain energy equation

    aiLTRcu TTUGFAQ  
   
T
aiLR
R
Tc
u
i
G
TTUF
F
GA
Q
n

 
 
Tc
ip
i
GA
TTCm
n


0'

THREE LOSS COEFFCIENT
• Top loss coefficient( Covers, upper parts)
• Side loss coefficient( through sides)
• Bottom loss coefficient.(bottom such as insulation)
• TOP HEAT LOSS ACCOUNTS MORETHAN 70% OFTOTAL
LOSS AND IS CONTAINS ABSORPTIVITY, EMISSIVITY,
MATERIALVARIANCE, WIND SPEED ETC .

TOP LOSS COEFFCIENT
As the wind loss coefficient increases,
more amount of heat is dissipated to
atmosphere and consequently lower
efficiency can be expected.

BOTTOM LOSS COEFFCIENT

SIDE LOSS COEFFCIENT

PARAMETERS EFFECTING PERFORMANCE
Heat Transfer System
• Heat from the absorber plate is removed from fluid.
• Usually cool fluid enters and gets heated up and is passed.
• Usually thermosiphon principle is used, otherwise external
pumping may be adopted.
• It also depends on type of fluid used.
• Some fluids used are: Ethanol, Methanol, water, Acetone etc.
• Medium inside the collector.
• Usually air, sometime inert gases are filled.

Selective Surfaces
• Absorber plate surfaces which provides high absorptivity for
incoming solar radiation and low emissivity for outgoing solar
radiation is termed as selective surface.
• Solar radiation lies short wavelength band up to 4micro meter,
while the absorber plate the long wave radiation of wavelength
8.3 micro meter.
• No natural surface has this selective surface radiation
characteristics.
• A successful selective surface can be developed by a thick
metallic oxide base on a metal base.
• A good selective surface will have 0.95 absorptivity , 0.1
emissivity.

Selective Surfaces
Table : Characteristics of absorptive coatings

Number of covers
• To minimize the convection and radiation loss the solar
collector is covered with a transparent glass sheet over a
absorber plate.
• Solar radiation incident on glass passes through it and glass
cover.
• Thus the glass sheet cover reduces the heat loss coefficient up
to 10W/m^2 K.
• It is seen that with two glass covers the heat loss coefficient
was still reduced to 4W/m^2 K.

Number of covers
Table : Charactericts of cover plate materials

Transmissivity Absorptivity Product
S is absorbed radiation and it is equal to:
are the view factors from the
collector to the sky and from the collector to the ground, respectively.
The subscripts b,d, and g represent beam, diffuse, and ground ,
respectively. is transmittance and absorptance product.Rb is
the ratio of beam radiation on the tilted surface to that on a horizantal
surface at any time.
Equation 4.2 Absorbed solar radiation[6].
)2/cos1(),2/cos1(  
 

Spacing
• Spacing between the absorber plate and the cover or
between two covers also influence the performance.
• The operating performance varies with space as well as tilt
and service conditions.
• There is no exact way to express spacing.
• The experiments have revealed that 4cm to 8cm will give
good results.
• Large spacing reduces collector area requirements.

Glazing
• Low iron clear glass of 5 mm thickness is used as glazing panel.
• The experiment was conduction to check
Optimum glazing covers and space.
• 5 mm , 10 mm, 15mm space with 1, 2, 3
Glazing covers

(finandtubeareofsanemalerial)

Geometric Parameters
• Spacing: Lower the gas conductivity, the smaller the volume
required for maximum efficiency.
• Tube thickness: Improvement in efficiency when using 1.0 mm
thick tubes instead of 0.5 mm because of the changed
Reynolds number.
• Helical pipe collector gives higher temperature in hot water
tank.

Materials Used for construction
• Absorber plate material : Low cost galvanized iron as absorber
material can give efficiency comparable to copper.
• Tube and header material : Low cost coated stainless steel tube and
aluminium tube gives same performance as copper.
• Absorber coating material : Higher outlet temperature and higher
efficiency for black chrome followed by the matt black and sol
chrome.
• Working fluid : Acetone gives higher efficiency than methanol and
ethanol. Water gives higher efficiency than methanol.

Other things
• Use of PCM :The temperature of water in PCM filled FPC is much
higher.
• Porous aluminium absorbers : Maximum efficiency for the more
porous and thicker absorber at the highest air mass flow rate, but
at very low air flow rates the absorber porosity shows a reversed
effect.

CONCLUSION
• MAJOR LOSSES OCCUR INTOP LOSS.
• LOT OF SCOPE FOR REDUCING ABSORBER AREA.
• OPTIMUM GLAZINGWILL REDUCE LOSSES.
• BEST INSULATION MATERIAL WILL REDUCE LOSSES.
• SELECTION OF RIGHT MATERIAL WILL GIVE US DRASTIC CHANGE IN
EFFICIENCY.
• Solar energy is free if we do not include the initial cost for
installation and the maintenance.

• PERFORMANCE STUDIES OFTUBULAR FLAT PLATE COLLECTORS"
Md. SakhawatHusain International Centre forTheoretical Physics,Trieste, Italy.
INTERNATIONALCENTRE FORTHEORETICAL PHYSICS
• EVALUATION OF HEAT LOSS COEFFICIENTS IN SOLAR FLAT PLATE COLLECTORS
Y. Raja Sekhar1, K.V. Sharma1 and M. Basaveswara Rao2
1Centre for Energy Studies, J. N.T. U. H. College of Engineering, Kukatpally, Hyderabad, India
2Department of Mechanical Engineering, S.V. I.T, Secunderabad, India
• RENEWABLE ENERGY SOURCES AND EMERGINGTECHNOLOGIES
By D.P. KOTHARI, K. C. SINGAL, RAKESH RANJAN
• Recent investigations in solar flat plate collectors P A Kulkarni1, S P Sabnis2, R Sarangi3
Mechanical, DBIT, Mumbai, India
REFERENCE

Parameters effecting solar lfpc performance

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