Iisrt z abhijit devaraj

International Journal of Mechanical Civil and Control Engineering
Vol. 1, Issue. 3, June 2015 ISSN (Online): 2394-8868
27
Evaluation of efficiency and collector time constant of a
solar flat plate collector at various intensities of light
and constant wind speed by using forced mode
circulation of water
Abhijit Devaraj1
Abhishek Hiremath2
Akshay R Patil3
Krushik B N4
Department of Mechanical Engineering, BMS College of Engineering, Bangalore, INDIA
Abstract- The present attempt of the work is to calibrate the
efficiency and collector time constant of a flat plate collector
which is usedto heat water flowing through the pipes by forced
circulation at varying intensity of heat flux, when wind is
blowing at a constant speed. It was observed that these factors
affect the flat plate collector in a profound way. This work
helps us in giving an insight on practical scenarios where solar
collectors are usually placed at high elevations to receive heat
as high altitudes involve flow of wind across the collector.
Keywords: Flat plate collector, solar water heater, intensity of
sunlight, wind flow
I - INTRODUCTION
Solar Energy is one of the major alternative sources of
energy being used in the current world scenario. Processes
of industrialization and economic development require
important energy inputs. Reserves of fossil fuel are limited
and their large scale use is associated with environmental
deterioration.[2]
Solar energy is considered one of the main
promising alternative sources of energy to replace the
dependency on other fossil fuel resources[3] [4]
There are
adverse environmental effects caused by greenhouse gas
emissions from fossil fuel combustion.[5]
Solar energy is an
ecologically clean source of energy and freely available to
everyone over long time periods at all parts of the earth.[6]
Incoming solar radiation is converted into thermal energy
using black bodies which trap the excess heat emitted from
the sun in the form of infrared radiations Availability of
solar energy depends on day and night cycles and weather
conditions hence collectors are used to trap solar energy
radiated from the sun. Solar Water Heating (SWH) is the
conversion of sunlight into renewable energy for water
heating using a solar thermal collector. The heat collector
used here is a Flat-plate solar collector which is used to
collect heat for various applications such as space heating,
domestic hot water or cooling with an absorption chiller.
There are two types of solar water heating systems namely
passive and active. Flat plate collectors can be either glazed
or unglazed and either air or liquids can be used as heat
transporting fluids. [1]
This experiment involves an active
water heating system where a pump is used to circulate
water which allows us to have the collector tank above the
collector and also use drain back tanks.
The advantages of solar flat plate collector are that we
receive hot water throughout the year, it decreases our daily
fuel consumption and reduces our energy bills and also
reduces carbon emissions.
II – IMPLEMENTATION
FIGURE 1- Block Diagram of the experimental setup
Cold Water
Tank
Flat Plate Collector
Hot Water
Tank
Valve 5
Valve 1
Pump
Valve 7
Valve 3

28
FIGURE 2 – Experimental Setup of ECOSENSE water
heating systembased on solar flat plate collector.
FIGURE 3- Panel used to display input and output
parameters.
The setup consists of the following components:
Radiation meter: To measure the radiation level that is
received by the collector a radiation meter is supplied with
the system. It is a sensing based device. It can measure the
radiation level in the range of 0 to 200 W/m2
.
Thermometer: Four thermometers are connected to the
system. The sensors are RTD based platinum probe and
work on the principle of variation of resistance with
temperature. The probes are class A RTD and can measure
the temperature in the range of 200°C to 650°C. Pressure
Gauge: Two pressure gauges are there in the setup. They
work on the principle of generation of electric signal by
semi-conductor device due to exertion of pressure. Pressure
gauges can measure the pressure in the range of 101.3 to
650 KPa. Water flow meter: To measure the water flow
rate a panel mount flow meter with a mini turbine flow
sensor is connected near the collector inlet. It is a
programmable meter. It can measure the flow rate in the
range of 0.5 to 25 liters/minute. A temperature limit of
meter is up to 80°C. Pump: We are using an AC pump to
fill up the collector tank as well as to circulate the water
through the collector at some regulated speed. A continuous
regulator is there to maintain the flow rate. Anemometer:
An anemometer is supplied with the system. This can be
used to measure the air velocity and ambient air
temperature. The air flow sensor is conventional angled
vane arms with low friction ball bearing while the
temperature sensor is a precision thermistor. The
Anemometer can measure the wind velocity in the range of
0.5 to 45 m/s while the temperature range is 10 to 60°C.
Fan: One AC fan is integrated with the system to generate
artificial wind speed. To set the wind speed as per
requirement a regulator is there in the control unit. Valve:
Different valves are there to direct the water flow as per
requirement. [7]
A - Specifications
The specifications of the equipment are as follows:
 Tank capacity: 50 litres
 Collector area: 0.716m²
 Tungsten halogen fixture’s area: 0.72m²
 Halogen systemPower: 150 watt each
 Radiation meter range: 0 to 1999 w/m²
 Water pump power: 0.12hp
 Water flow range: 0.5 to 25 LPM.
 Water flow maximum pressure: 17.5 bar
 Thermometer sensor:class A sensor
 Thermometer range: 200 to 650˚C
 Anemometer range: 0.4 to 45 m/s
 Fan range: 0 to 5 m/s [7]

29
B - Assumptions made in the setup
1. The collector is in steady state condition.
2. Headers cover a small area of the collector and can be
neglected.
3. Headers provide uniform flow to riser tubes.
4. Flow through the back insulation is one dimensional.
5. Temperature Gradients around the tube are neglected.
6. Properties of materials are independent of temperature.
7. No energy is absorbed by the cover.
8. Heat flow through the cover is one dimensional.
9. The covers are opaque to infra red radiation.
10. Same ambient temperature exists at both front and back
of the collector.
11. Dust effects on the cover are negligible.
12. There is no shadowing of the absorber plate.
13. Temperature drop across glass tube is uniform.
14. Solar radiation transmitted through glass cover is
reflected not absorbed. [7]
III – RESULTS AND DISCUSSIONS
A – Formulae
Calculations were performed using the following
formulae’s:
Heat Supplied= specific heat flux *area of collector
Water flow rate = 2.35 Lpm = 2.35/60
= 0.03916 Kg/s
Heat Radiated = Qrad = Q = σA∆T4
= σA(T1
4
-T∞
4
)
[8]
Collector Time Constant = R
R = [T3- T3(0)] / [ T4- T3(0)]
[8]
Collector Plate Efficiency = ɳ = (Qrad/ Qsup)*100
[8]
C – Methodology
The cold water tank 1 was filled with water at atmospheric
temperature. Valve 1 and valve 7 were opened which allows
flow from the cold water tank 1 to the Flat Plate Collector
inlet. The pump was switched on and the regulator was set
at the minimum power at which the pump can work. A
suitable flow rate was set whose value can be observed on
the flow meter screen. Valve 3 was opened which allows
flow from the Flat plate collector outlet to the hot water
tank. After waiting for some time to get a stable reading the
fan regulator was adjusted to get the desired wind speed
which in this case is 5 m/s. The wind speed was measured
using an anemometer. Once the flow rate and the wind
speed were set the initial readings of collector plate
temperature, water inlet temperature, water outlet
temperature and hot water temperature were noted down at
time= 0 sec. The Halogen system was then switched on and
the radiation was set to desired level which in the first case
is 100 W/m2
. The cold water was allowed to flow through
the Flat plate Collector which absorbed the heat and was
then allowed to flow into the hot water tank. The
temperature readings as mentioned above were noted down
for every one minute for a total duration of 10 minutes.
After the experiment was completed the pump was switched
off and the valve 1 was closed and valve 5 was opened
which allows the water to drain from the hot water tank to
the cold water tank. The water was allowed to cool for some
time. The experiment was repeated two more times by
following the exact same procedure but the flux rates were
set at 130 and 160 W/m2
for the next two trials respectively
and the readings were tabulated. The heat supplied was
obtained by multiplying the flux supplied by the collector
area. The collector time constant and radiative efficiency of
the collector were calculated using suitable formulae.
Graphs were plotted for efficiency vs. time and collector
time constant vs. time for various specific flux rates.

30
B - Tables
Table 1: Readings for a specific Heat flux of 100 W/m2
Table 3: Readings for a specific heat flux of 160 W/m2
Heat
Supplie
d (Qin)
in watts
Wind
Velocity
(V) in
m/s
Time
in sec
Flow
Rate (ṁ)
in Kg/s
Plate
Temp (T1)
in °C
Inlet
Water
Temp
(T2) in
°C
Outlet
Water
Temp
(T3) in
°C
Hot
Water
Temp
(T4) in
°C
Heat
Radiated
(Qrad) in
watts
Collector
Time
Constant
(R)
Efficiency
of plate
ɳ (in % )
71.6 5
0 0.03916 38.8 30 31.8 32.6 32.39 0 45.23
60 0.0383 37.7 29.2 32.5 32.8 27 0.7 37.71
120 0.037 36.6 29.2 32.2 33 21.6 0.33 30.16
180 0.0386 36.3 29.1 32.1 33.1 20.23 0.2307 28.25
240 0.0408 36 29.1 31.9 33.2 18.79 0.0714 26.24
300 0.0408 35.9 29.1 31.9 33.3 18.31 0.0667 25.57
360 0.04 35.7 29.1 31.9 33.3 17.36 0.0667 24.24
420 0.0391 35.7 29.1 31.9 33.3 17.36 0.0667 24.24
480 0.0383 35.7 29.1 31.9 33.3 17.36 0.0667 24.24
Heat
Supplied
(Qin) in
watts
Wind
Velocity
(V) in
m/s
Time
in sec
Flow
Rate
(ṁ) in
Kg/s
Plate
Temp (T1)
in °C
Inlet
Water
Temp
(T2) in
°C
Outlet
Water
Temp
(T3) in
°C
Hot
Water
Temp
(T4) in
°C
Heat
Radiated
(Qrad) in
watts
Collector
Time
Constant
(R)
Efficiency
of plate
ɳ (in % )
93.08 5
0 0 44.7 29.3 32.6 33 62.27 0 66.9
60 0.0167 42.6 29.4 33.5 33.2 51.44 1.5 55.26
120 0.022 39.6 29.2 33 33.2 36.34 0.667 39.04
180 0.0195 38.4 29.2 32.9 33.3 30.42 0.428 32.68
240 0.0225 37.9 29.2 32.7 33.3 27.98 0.1413 30.06
300 0.0204 37.7 29.2 32.8 33.4 27 0.25 29
360 0.02 37.6 29.3 32.7 33.5 26.52 0.111 28.49
420 0.0175 37.6 29.3 32.8 33.6 26.52 0.2 28.49
480 0.017 37.6 29.3 32.8 33.6 26.52 0.2 28.49
Heat
Supplied
(Qin) in
watts
Wind
Velocity
(V) in m/s
Time
in sec
Flow
Rate
(ṁ) in
Kg/s
Plate
Temp
(T1) in °C
Inlet
Water
Temp
(T2) in
°C
Outlet
Water
Temp
(T3) in
°C
Hot
Water
Temp
(T4) in
°C
Heat
Radiated
(Qrad) in
watts
Collector
Time
Constant
(R)
Efficiency
of plate
ɳ (in % )
114.56 5
0 0.03 42.4 33 33.1 33.5 50.42 0 44.01
60 0.0104 42 30.5 36.9 33.6 48.39 7.6 42.24
120 0.0175 41.7 30.2 36.3 33.9 46.87 4 40.91
180 0.0175 40.8 30 35.5 34.1 42.33 2.4 36.95
240 0.0216 40 29.9 34.2 34.2 38.33 1 33.46
300 0.0212 40 29.7 34 34.4 38.33 0.692 33.46
360 0.0179 39.9 29.6 33.6 34.5 37.83 0.357 33.03
420 0.0191 39.9 29.6 33.7 34.6 37.83 0.4 33.03
480 0.02 39.8 29.6 33.7 34.6 37.34 0.4 32.59
Table 2: Readings for a specific heat flux of 130 W/m2

31
C – Efficiency of Collector
FIGURE 4 – Plot of Efficiency vs. time for a flux of 100
W/m2
W/m2
W/m2
The plots of efficiency v/s time for each specific flux rate
(figure 4, figure 5, and figure 6) showed that the efficiency
decreased as time increased. This was due to wind blowing
constantly over the Flat plate Collector which reduced the
collector plate temperature resulting in reduced heat
radiation. This resulted in decreased efficiency. The graph
after a certain time interval becomes almost linear. This was
because after some amount of cooling of the Flat plate
Collector had taken place, the plate attained an almost
steady temperature which gave steady heat radiation and
almost constant efficiency.
D – Collector time Constant
FIGURE 7 – Plot of Collector time constant vs. time for a
flux of 130 W/m2
0
10
20
30
40
50
0 60 120 180 240 300 360 420 480
Efficiencyin%
Time (seconds)
Efficiency v/s time plot for 100 W/m2 flux
Efficiency
0
10
20
30
40
50
60
70
80
0 60 120 180 240 300 360 420 480
Efficiencyin%
Time (seconds)
efficiency
0
5
10
15
20
25
30
35
40
45
50
0 60 120 180 240 300 360 420 480
Efficiencyin%
Time (seconds)
efficiency
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
60 120 180 240 300 360 420 480
R
Time (seconds)
R v/s time for flux of 100 W/m2

32
FIGURE 8 – Plot of Collector time constant vs. time for a
flux of 130 W/m2
FIGURE 9 – Plot of Collectortime constant vs. time for a flux of 160W/m2
Collector time constant is required to evaluate the transient
behavior of a collector. It can be calculated from the curve
between R and time as shown above. The plots of Collector
time constant R v/s time for each specific flux rate showed
that R decreased as time increased. The graph for a fluxrate
of 100 W/m2
becomes almost constant or linear between the
time interval of 240 and 480 seconds and hence R = 0.75 for
figure-7. The graph for a flux rate of 130 W/m2
becomes
almost constant or linear between the time interval of 420
and 480 seconds and hence R = 2 for figure-8. The graph for
a flux rate of 160 W/m2
becomes almost constant or linear
between the time interval of 360 and 480 seconds and hence
R = 0.35 for figure-9.
IV - CONCLUSIONS
In the present study on Flat plate Collector’s the potential
barriers to using them in practical scenarios at high
elevations involving wind flow was determined. From the
readings obtained and the graphs plotted it was inferred that
the Collector Time Constant R decreased as time increased.
Also as time increased the temperature of Flat Plate
Collector decreased due to which the heat radiated
decreased. This resulted in a decrease in efficiency. The
temperature drop was due to cooling of the Flat Plate
Collector due to the constant wind blowing over it. Also the
efficiency decreased as heat flux incident normally on the
collector plate decreased. Hence in practical scenarios
maximum efficiency is obtained at noon when maximum
normal heat flux is incident on the Flat plate Collector.
This particular study helped us understand the influence
of day night cycles and wind flow velocity on flat plate
collectors. It gave us estimation that for solar collectors to
heat water to higher temperatures and generate more
efficiency, the collectors should be kept at a high altitude to
receive more sunlight and also at a location where the wind
is blowing at minimum or negligible speed to avoid cooling
and temperature drops.
REFERENCES
[1] Amirhossein Zamzamian, Mansoor Keyanpour Rad,
Maryam Kiani Neyestani, Milad Tajik Jamal-Abad., “An
experimental study on the effect of Cu-synthesized/Eg
nanofluid on the efficiency of flat plate collectors”,
Renewable Energy, vol. 71, pp 658-664, 2014.
[2] F.Cruz-Peragon, J.M.Palomar, P.J.Casanova,
M.P.Dorado, F.Manzano-Agugliaro, “Characterization of
solar flat plate collectors”, Renewable and sustainable
energy reviews, vol. 16, pp 1709-1720, 2012.
[3] R. Manzano-Agugliaro F, Montoya FG, Gil C, Alcayde
A, Gomez J. Banos, “Optimization methods applied to
renewable and sustainable energy: a review”, Renewable &
Sustainable Energy Reviews, vol. 15, pp 1753–66, 2011.
[4] Ssen Z, “Solar energy in progress and future research
trends”, Progress in energy and combustion science, vol. 30,
pp 367–416, 2004.
[5] Gurveer Sandhu, Kamran Siddiqui, Alberto Garcia,
“Experimental study on the combined effects of inclination
angle and insert devices on the performance of a flat plate
solar collector”, International Journal of Heat and Mass
Transfer, vol. 71, pp 251-263, 2014.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
60 120 180 240 300 360 420 480
R
Time (seconds)
R v/s time for a flux of 130 W/m2
0
1
2
3
4
5
6
7
8
60 120 180 240 300 360 420 480
R
Time (seconds)
R v/s time for a flux of 160 W/m2

33
[6] Ljiljana.T.Kostic, Zoran.T.Pavlovic, “Optimal position
of flat plate reflectors of solar thermal collector” Energy and
Buildings, vol. 45, pp 161-168, 2012.
[7] – Insight Solar Manual by ECOSENSE
[8] – Ynus.A.Cengel, Afshin.J.Ghajar, “Text book on Heat
and Mass transfer”.

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