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EXPERIMENTAL PERFORMANCE EVALUATION OF PARABOLIC TROUGH CONCENTRATOR

S. Umar+ ., U K Muhammad+, Garba M M*., H.N.Yahya*, and ** A.U Ali

+Department of Physics, Kebbi State University of Science and Technology Aliero.

*Sokoto Energy Research Center, Usmanu Danfodiyo University Sokoto.

**Department of Mathematics, Usmanu Danfodiyo University Sokoto.

Contact author: S. Umar,Dept. of Physics,Kebbi State University of science and technology, Aliero, P.M.B. 4411, Aliero, Nigeria. Tel. 234 3413 0968. E-Mail: umarmagajisadik@yahoo.com

ABSTRACT

Solar energy is currently represents the most abundant inexhuatible, non- polluting and free energy resources that could be used economically to supply man’s increasing energy demands. This paper presents the experimental performance study of a parabolic trough concentrator, which was constructed and investigated under climatic conditions of Dundaye at Sokoto Energy Research Center, Usmanu Danfodiyo university Sokoto, Nigeria.The collector was constructed using locally available materials with design parameters as : Focal distance of 0.15m, 1.82m length of the collector and depth of the collector as 0.33m.

The experimental test conducted to evaluate the collector showed that the maximum outlet water temperature attained was 110oc ,which is fairly acceptable, considering that it was an attempt to use local materials. Eventhough it encounter some problems such as inaccuracy in tracking the sun since it is manually tracked. However, the result obtained have shown that the temperature achieved is almost equivalent to the temperature at which the matter changes from liquid to gas (steam). In this case it can be said that when appropriate tracking mechanism is used, this collector could be used for steam generation which can turns steam turbine for electricity generation.

1. Introduction

Renewable energy is the most promising alternative sources of energy , that satisfy man’s energy needs for both domestic and industrial need.Solar energy currently represnts the most abundant renewable, inexhaustible, non-polluting and freeenergy resources that could beused economically to supply man’s increasing energy demands. Solar thermal energy could be a prominently sustainable means of power , lighting , heating , cooking etc. if properly harnessed, especially in the developing countries like sub saharan Africa . Nigeria being within the region

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is blessed with high solar irradiance and more aboundant in the northern region (Bashar et al, 1999) .Therefore her potential for deployment of solar concentrating collectors for steam generation is viable.

Different researches were conducted based on solar thermal technology for steam generation in their course to develop solar thermal technology as an alternative and most prospective, sustainable source of energy for steam production for both industrial and domestic application. Joshua (2009), in his effort to generate steam using solar energy ,parabolic dish collector was constructed using wood, aluminium sheet and plane mirror and a temperature 2000C was obtained.

The aim of this study was to investigate the performance of the already constructed parabolic trough concentrator at Sokoto Energy Research Center.

2. Parabolic Trough Concentrator Description and Principle of Operation

A parabolic trough solar concentrator was design, constructed and test at Sokoto Energy Research Center, Usmanu Danfodiyo University sokoto. The main basic principle adopted in the constrution was concave mirror and parabolic reflective surface principle, which takes the advantage of all parallel rays of light from the sun that incident on a concave or parabolic shaped mirror and converge after reflection to a point focus (escobar, 2011). This system consist of parabolic shaped mirror (reflecting surface) supporting arm and solar Radiation absorption system(pipe). The design specfications of the system is given in table 1

Table 1:Parabolic trough collector system specifications

Parameters Values Focal distance F 0.15m Depth of the parabolic trough

0.33m

Length of collector 1.82m Absorber Area 2.85cm2

a) Parabolic Mirror Shape

The parabolic trough collector uses mirror surface applied on a woody parabolic shape that linearly line and extends to the trough shape. The mirror was in to rectanngular shape of 8cmx 94cm and fixed with shinny side surface of mirror facing up , which in turns formed the parabolic mirror shape.The incident solar radiation is focused to a line (focus line). The mirror sheet used has a thickness of 3mm.

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b) Solar Radiation Absorption System

Solar radiation absorption system consist of a copper pipe, which is placed at focal line. The pipe diameter is 28.5mm and the wall thickness is small, so that quick transfer of energy from solar radiation to the working fluid is achieved. The outer surface of the pipe was pointed black which increases the absorbance of the incident solar irradiance and reduces, simultaneously the reflectance. At the edge of the absorbing pipe. The absorption pipe is supported to the focusing line by woody arm.

C ) Principle of Operation

Parabolic trough collectors are usually U like shape with reflective surface facing the sun, which are normally made up of either concave lens or mirror or any other reflecting material that are capable of concontrating solar radiation at a line (soteris, 2009). Whenever the parallel rays of solar radiation is incidence on a reflecting surface of the parabolic trough concentrator, the solar energy would be reflected and converge at a line called focal line or distance as shown in figure 1. The solar energy converge at focal line is absorbed to give rise to an increase in temperature, and generate higher temperature steam. The amount of which the collector concentrate solar energy is governed by optical property of the surface (Dascomb,2009)

Figure1: A typical parabolic trough concentrator

3. Concentrator Testing and Experimental Set Up

The manufactured Parabolic trough Concentrator was set for performance evaluation test at Sokoto energy research Center testing area and experiment was set as shown in figure 2.1. The water tank was elevated at 0.5m above the ground level in such a way that water can flow downstream to the absorber. The test was done at constant flow rate( mw) of 0.0177kg/min. The parameters recorded during the test were: water inlet temperature Ti, outlet temperature Tf , intensity of diffused solar radiation Id , global Ig , beam Ib , ambient Temperature Tamb , and

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wind speed in order to see their effect on the performance of the system. The thermocouple data logger was used for temperatures measurement of four different points, ambient, absorber, inlet temperature of water and out let temperature of water simultaneously. The ambient temperature was measured by placing the thermocouple terminal at the surrounding. The absorber temperature was also read and recorded by using a temperature resistive material to gum the thermocouple terminal on the absorber surface, the inlet and outlet water temperature was measured and recorded at 30 minutes interval during the sunshine hours of the day.

The collector efficiency is estimated by

�� = (�����)� � ��

��� (1)

Where A is Area of the collector and Cw is the specific heat capacity of water

Figure 2.1 parabolic trough collector set for test

a) Instrumentation and Measurement

The temperatures of water at inlet, outlet and ambient temperature were measured using digital thermocouple thermometer. The wind speed at parallel to the system was also measured using cfm thermo Anemomer.

Pyranometer was used to measure the solar radiation intensity.Pyranometer is the most frequently used sensor for measuring global or diffused solar radiation (Ahmad, 2001). The parabolic trough solar concentrator uses only beam solar radiation. Thus,the pyranometer of sensitivity (13.39x10-6V/wm-2) was used to measure the global (Total) solar radiation, and then

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another pyranometer of sensitivity (16.86x10-6 V/wm-2) was fitted with shading ring to read diffused solar radiation by covering the direct radiation flux see figure 2. Both global and diffused radiations were measured on surface parallel to the aperture of the parabolic trough reflector. The beam solar radiation flux was obtained by substracting diffused radiation flux from the global radiation flux.

Figure 2.2 :CMP3 Pyranometer With Shading Ring for Diffuse Radiation Recording

4. Results and Discussion

The experiments were carried out to investigate the performance of the parabolic trough solar concentrator every day from 9:00am to 4:00pm, during the experiment, which almost the period at which the sunset. Under climatic conditions of Dundaye Village in Sokoto state,Nigeria with latitude 13.0514 and Longitude 5.23140. The experimental result was presented in Figure 3.1-3.3 and Table 3.1 - 3.3 for different days at the same flow rate.

It can observe that, from Figure 3.1 the highest outlet temperature of 1100C was obtain, which was the highest temperature recorded for this parabolic trough collector at around 1:00pm, beam radiation and inlet temperature were 739w/m2 and 38.40C respestively.

The figure 3.1 shows a plot of temperatures variation with beam radiation in which the outlet temperature start droping down at 2:00pm as well as beam radiation, this significe that the higher the beam radiation, the greater the outlet temperature at the same time ambient temperature increases. Even though the figure does not present the ambient and wind speed but it can be seen in tables.

In figure 3.3 lowest beam radiation was recorded this is due to high diffuse radiation recorded which is as a result of non- clear sky that is the clound that covers the sky at that particular time, which also result to the low outlet temperature.

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The low performance recorded in some days at a particular period of time can be attributed to the thermal losses (convective and radiative) due to higher ambient temperature and wind speed and also lack of tracking device to focus the sun due to its lateral movement.

Figure 3.2 temperatures Variation with Beam radiation on 21/10/11

Figure 3.1 Temperatures variation with

Beam radiation on 20/10/11

0100200300400500600

020406080

100120

Beam

Rad

iatio

n w

/m2

Tem

pera

ture

0c

Local Time

inlet temp.

outlet temp.

beam rad.

0

100

200

300

400

500

600

700

0.0

20.0

40.0

60.0

80.0

100.0

120.0

Beam

Rad

iatio

n w

/m2

Tem

pera

ture

0C

Local Time

inlet temp.

outlet temp.

beam rad.

0100200300400500600700800900

0.020.040.060.080.0

100.0120.0

9:00

10:0

011

:00

12:0

013

:00

14:0

015

:00

16:0

0

Beam

radi

atio

n w

/m2

Tem

pera

ture

s 0C

Local time

inlet temp.

outlet temp.

beam rad.

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Figure 3.3 Temperature variation with

Beam radiation on 22/10/11

5. Conclusion and Recommendations

The parabolic trough solar concentrator was designed and constructed using local available materials, which si expected to produce steam above 1500C for domestic and industrial uses. The experimental result obtained by the parabolic trough collector was below the expectation and the maximum temperature produced by the system was 1100c , it is stil above that attained by (Umar,2012).This is also lower than that of international standard, but it can be said that a significant milestone was achieved. If the system can be modified and adopted mostly in the northern and midddle part of the country ( Nigeria), which are exposed to abundant solar radiation, therefore, a high pressure steam can be produce.

It is implicitly hoped, that as engineers and scientists venture in to serious research in various alternative energy sources (in which solar energy is the most potentially viable), the problem associated with the over dependence on fossil fuel as the only energy will be a history left to be told to future generation.

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However, base on this performance the following recommendation are here by proposed to improve it performance:

Ø Materials with higher reflectivety then mirror can be use since material with higher reflectance surface can concentrate more rays of sun, therefore this would increase the efficiency.

Ø There is need to improve the design by using special components such as gear box, parabolic mirror, electronic circuit specially manufacture for the purporse of fabricating the parabolic trough collector and automatic tracking device for proper solar radiation focusing.

References

Ahmad M.B.(2001). Design, Fabrication and Performance Evaluation of an Improved Solar

Concentrating Collector Using Slat-mirrors. Unpublished Msc (Eng). Thesis,

mechanical engineering department, Ahmadu Bello University,Zaria.

Bashiru G., Eboatu N.E., & Sambo A.S., (1999) The solar energy option. Sokoto energy

Research Center, Usmanu DanFodiyo University Sokoto. pp 3-17.

Dascomb J.(2009). Low cost concentrating solar collector for steam Generation.

unpoblished Thesis Submitted for the ward of Doctor of Philosophy, Department

of Mechanical Engineering,Florida State University. Retrieved on 6th may, 2011.

From http://esc.fsc.edu/documents/Dascomb JThesis.pdf

Escobar J.F.M., Vazquez S.,Montiel Y., Granados-Agustin F, Cruz-Martinez & Rodriquez

Rivere E.(2011) Building a Parabolic solar concentrator prototype. Journal of

Physics. Conference series 274 (2011). Retrieved on 5th August, 2011. From

iopscience.iop.org/1742-6596/274/012104. Pdf.

Joshua F.(2009). Design, Construction and Testing of Parabolic Solar Steam

Generator. Leonardo Electronic Journal of practices and Technologies. Retrieved on 16thDecember, 2010 from http://lejptacademicdirect.org/A14/115-133.pdf

Soteris K. (2009). Solar Energy Engineering processes and systems.British library

Cataloguing. Academic Press.Retrieved on 5th August, 2011 from

http://www.elsevier.com

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Umar S. (2013) Construction and Comperatives performance of three different parabolic

trough concentrator unpoblished Msc Thesis,Chemistry department, Usmanu

Danfodio University, Sokoto.

Table3.1 : Measured data on 20/10/11

Time glob.rad diff.rad. beam rad.

Amb. Temp.

inlet temp.

Absorber temp.

outlet temp.

Wind speed

9:00 607 199 408 34.1 28.9 46.8 53.9 0.89

9:30 781 210 571 34.5 30.9 60.1 62.1 0.76

10:00 850 212 638 34.7 31.9 70.0 72.5 1.02

10:30 911 297 614 36.8 34.5 80.9 87.7 0.92

11:00 780 254 526 36.8 34.8 89.4 99.7 0.25

11:30 986 267 719 38.2 35.3 78.3 85.3 0.52

12:00 994 255 739 39.5 36.5 95.9 96.3 0.15

12:30 1041 247 794 40.5 37.4 98.5 99.7 1.14

13:00 1008 269 739 40.8 38.4 103.7 110.0 1.11

13:30 1018 470 548 41.8 39.5 107.4 100.0 0.41

14:00 964 239 725 41.3 40.3 103.3 100.0 0.71

14:30 887 287 600 42.7 41.0 73.5 83.2 0.81

15:00 521 245 276 41.5 41.1 67.4 69.2 0.97

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15:30 367 215 152 39.5 40.6 63.9 63.0 1.06

16:00 453 228 225 40.1 40.4 60.8 58.9 0.64

Table 3.2:Measured data on 21/10/11

Time glob. rad. diff.rad

beam rad. Amb.temp.

inlet temp.

Collect. temp.

Outlet temp.

Wind speed

9:00 541 221 320 35.1 29.5 55.5 41.1 0.54

9:30 652 261 391 35.4 30.6 58.1 50.5 0.84

10:00 687 275 412 35 31.0 61.4 50.0 0.78

10:30 772 280 492 37.1 32.6 72.5 62.2 1.07

11:00 829 283 546 39.5 35.9 79.8 69.0 0.68

11:30 896 289 607 40.9 35.4 80.8 70.2 1.41

12:00 903 294 609 44.2 38.1 84.4 66.0 1.43

12:30 949 298 651 44.0 38.0 88.3 99.8 1.04

13:00 907 313 594 46.4 39.4 91.8 100.2 0.05

13:30 882 300 582 46.9 41.2 85.6 101.0 0.34

14:00 766 278 488 45.8 41.2 77.6 86.8 0.30

14:30 749 279 470 46.1 41.0 74.9 82.7 1.00

15:00 708 250 458 47.3 41.2 71.1 75.4 0.44

15:30 568 210 358 45.9 41.7 66.5 69.2 0.53

16:00 475 187 288 44.6 41.8 63.7 65.6 0.23

Table 3.3: Measured data on 22/10/11

Time Glob. rad.

diff. rad.

Beam radiation

Amb .tempt.

Inlet temp.

collect. temp.

outlet temp.

Wind speed

9:00 294 221 73 31.3 28.6 43.7 46.1 1.93

9:30 524 335 189 33.2 29.4 50.4 52.3 1.52

10:00 337 244 93 32.8 29.8 49.2 53.6 0.77

10:30 584 377 207 33.9 30.6 54.4 57.1 2.23

11:00 574 368 206 36.0 31.1 58.6 63.4 1.03

11:30 698 435 263 35.9 32.6 51.5 61.5 1.36

12:00 743 405 338 37.3 33.3 59.4 73.9 2.23

12:30 867 408 459 39.9 35.0 72.1 86.0 0.84

13:00 894 349 545 41.0 36.5 89.0 95.9 0.95

13:30 905 349 556 40.1 37.3 85.9 99.3 2.41

14:00 818 367 451 39.4 37.8 72.4 83.4 0.94

14:30 802 363 439 40.8 38.1 68.6 80.2 1.61

15:00 764 317 447 41.4 38.2 62.1 69.5 0.47

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15:30 445 204 241 38.5 37.9 57.6 63.6 0.28

16:00 507 199 308 40.2 38.0 56.7 61.9 0.97