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EXPERIMENTAL ANALYSIS OF SOLAR WATER HEATER USING POROUS MEDIUM AND AGITATOR

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EXPERIMENTAL ANALYSIS OF SOLAR WATER HEATER USING POROUS MEDIUM AND AGITATOR Powered By Docstoc
					INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
  International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
  6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME
                         AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)                                                     IJMET
Volume 4, Issue 3, May - June (2013), pp. 273-280
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2013): 5.7731 (Calculated by GISI)                 ©IAEME
www.jifactor.com




        EXPERIMENTAL ANALYSIS OF SOLAR WATER HEATER USING
                  POROUS MEDIUM AND AGITATOR

                                         Dr. R. P. Sharma
                 Dept. of Mechanical Engineering, Birla Institute of Technology
                Mesra, Ranchi, 835215 India. E-mail: rpsharmabit123@gmail.com


   ABSTRACT

           The aim of the present study is to improve the thermal performance of flat plate solar
   collector using a novel cost effective enhanced heat transfer technique. The present work
   focuses on the process of energy conversion from the collector to the working fluid. This
   experimentally accomplished by using agitator in the riser tube ,packing of collector’s surface
   with pebbles and stainless steel chips. The basic purpose of agitator in the riser tube is to
   intensify heat transfer , packing of collector surface with pebbles and stainless steel chips is
   for longer heat retention and enhanced heat capture respectively .it has been found that the
   efficiency of collector with agitator and metal chips is highest among all other combinations.

   Keywords: Porous medium, pebbles, agitator, solar water heater etc

   1.     INTRODUCTION

           In performance of flat plate solar collectors used in modern domestic hot water
   systems have not changed significantly in past. In past in order to estimate the performance of
   solar water heaters, water circulating to storage by thermosyphon was investigated. The use
   of an optical element consisting of three specularly reflective surfaces and an infrared
   reflective surface finding towards the absorber of a plate solar collector has been designed
   [3]. By incorporating a panel of such optical elements in between the absorber and the
   window of the flat plate solar water collector, the radiation and convection heat losses were
   reduced.
           Afterward, more comprehensive studies to evaluate the thermal performance of a
   thermosyphone system were conducted. An experimental test ring, incorporating a system
   having fine thermocouple on the bottom surface of the water pipes and six thermocouples on

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME

the bottom surface of the water pipes and six thermocouple on the bottom surface of the
absorber plate was designed and tests performed. Thermocouples were also placed in the
storage tank [1, 2]. The performance of a thermosyphone system with vertical or horizontal
storage tank was maximized when the daily collector volumetric flow was approximately
equal to the daily load flow. Am experimental study was conducted in a water flat plate
collector with laminar flow conditions to analyze the flow distribution through the collector
[4].it was conducted that the flow distribution depends on the relation between energy loss on
the risers and the energy losses in the manifolds. To obtain a homogeneous flow distribution
to influence of the energy losses in the risers must control the system. Laminar flow in
internally formed tubes by assuming constant and uniform heat flux in tube and fin surface
has been analyzed using fins should great enhancement in thermal performed [5].

2. EXPERIMENTAL SETUP

        The experiments were conducted at the solar laboratory at the mechanical engineering
department, BIT Mesra. The coordinates of the place are 23.4120N, 85.4390E.The basic parts
of the working models are - Flat plate water heater, Insulated Water Storage Tank,
Instruments used, Eppley Pyranometer, Digital Thermometer, Agitator using Copper Wire,
Packing Media, Pebbles, Stainless Steel chips. The frame of the solar collector was cuboidal
in shape and made of plywood 10mm thick. The internal dimensions of the collector were
1.2m x 0.6m x 18cm. Five pieces of plywood were sawed off from a larger piece and then
attached to each other with nails. The top surface of the collector was left open for the glass
cover plate. Aluminium channels were nailed onto the top of the frame to secure the glass
cover. The corners and joints of the frame were sealed off by using putty-an epoxy adhesive.
The inside walls were painted black with black enamel paint. Aluminium sheet was used to
cover the entire floor area of the collector. This sheet has grooves to increase contact surface
between sheet and tubes. Channel was attached to the absorber plate using steel wires. The
Aluminium sheet along with pipes was painted black to increase absorptivity of heat. This
was fixed to the wooden box using nails. The tubes/channels were made using GI water
pipes. The riser tubes were of 0.5 in. internal bore diameter and header tubes with 1 in.
internal bore diameter. 5 holes were drilled in the header tubes at spacing of 12 cm. Agitator
made of Copper wire was inserted in the riser tube and were welded accordingly in the header
tube. Agitator was made by curling Copper Wires with approximate diameter of 1cm. Wires
were curled on a rod of diameter 1cm in the form of helix with a pitch of approximately
0.8cm. The stand was inclined at 22.5°. A glazed glass sheet measuring 1.20m x 0.60m x
4mm was used as the single glass cover for the apparatus. It was secured to the top of the
glass cover using epoxy adhesive (putty) for easy removal.
        A Thermocol sheet measuring 1.2m x 0.6m x 1cm was secured to the bottom surface
of the wooden frame by glue and a layer of Glass wool of thickness 2.5cm was secured using
steel net and nails. It was done to minimize heat loss from the absorber to the surroundings.
Water storage tank was made using GI sheet. It has two concentric tanks with air acting as an
insulator between them. The internal tank, measuring 72cm internal diameter and 72 cm
depth, is used for water storage. Outer tank measured 87cm internal diameter and 87cm
depth. Two holes are drilled at the bottom, one act as the inlet and other as the outlet. The
tank has a cover at the top to seal it. The whole water storage tank was covered with an
insulating material. A layer of pebbles used in construction sites is used to increase the heat
retention in the collector box. It has density of 6.9 gm/cubic cm. Iron Scraps from machining

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME

processes can be used for packing the solar bed, which in turn can increase the thermal
efficiency by trapping solar radiation and reducing the conductive and convective losses from
top.




    Figure 1: Satellite image of the Solar lab,        Figure 2: Working model of the
                 BIT Mesra                               flat plate solar water heater




  Figure 3: Working model with agitator             Figure 4: Absorber plate with pipes
             and pebbles




      Figure 5: Pipes with Agitator                      Figure 6: Water storage tank



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 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME

3. RESULTS AND DISCUSSION

The following results are obtained and presented in tabular form given by using
Case 1: Agitator in the riser tube
Case 2: Packing of collector surface with pebbles
Case 3: Packing of collector surface with stainless steel chips


              Table 1: Flat Plate Water Heater with Agitator only (24th April)


                  Global          Diffused            Beam         Ambient        Temp. of
     Time        Radiation       Radiation          Radiation       Temp.          Water
                 (W/sq. m)       (W/sq. m)          (W/sq. m)      (deg. C)       (deg. C)
   09:00 am         730             144                586            25             28
   09:20 am         786             157                629            26             31
   09:40 am         863             177                686            27             32
   10:00 am         905             186                719            28             34
   10:20 am         956             200                756            29             38
   10:40 am         995             209                786            31             39
   11:00 am         846             177                669            32             40
   11:20 am        1023             214                809            33             42
   11:40 am         982             206                776            35             42
   12:05 pm        1135             244                891            36             44
   12:30 pm        1159             249                910            36             45
   01:20 pm        1206             265                941            37             49
   01:40 pm        1113             244                869            37             49
   02:00 pm         956             215                741            38             50
   02:20 pm         843             193                650            38             49
   02:40 pm         653             150                503            37             49
   03:00 pm         528             124                404            37             48
   03:20 pm         318              76                242            35             48
   03:40 pm         420             100                320            35             47
   04:00 pm         325              81                244            34             46
   04:20 pm         286              72                214            32             44
   04:40 pm         234              59                175            31             45
   07:40 pm                                                                          39
   10:00 pm                                                                          30


 Average Global Radiation = 784.63 W/sq.m ; Average Diffused Radiation = 170.09 W/sq.m ;
 Average Beam Radiation = 610.39 W/sq.m ; Efficiency = 17.38 %




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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME




  Graph1: Temp VS Time with agitator      Graph2: Intensity VS Time on 24th april,2013


    Table 2: Flat Plate Water Heater with Agitator and Pebbles as Packing Media
                                     (25th April)

                 Global        Diffused           Beam       Ambient        Temp. of
   Time         Radiation     Radiation         Radiation     Temp.          Water
                (W/sq. m)     (W/sq. m)         (W/sq. m)    (deg. C)       (deg. C)
 10:40 am         658            138               520          26            31.0
 11:00 am         813            170               643          28            32.5
 11:20 am         769            161               608          30            35.0
 11:40 am         837            180               657          31            35.5
 12:00 pm         863            186               677          32            37.0
 12:20 pm         995            218               777          32            38.4
 12:40 pm         740            163               577          33            39.0
 01:00 pm         925            203               722          34            40.0
 01:20 pm         870            196               674          37            41.0
 01:40 pm         230             52               178          37            42.0
 02:00 pm         736            166               570          37            42.5
 02:20 pm         708            163               545          37            42.5
 02:40 pm         650            152               498          36            43.0
 03:00 pm         410             98               312          36            43.5
 03:20 pm         140             35               105          36            43.5
 03:40 pm         420            105               315          35            43.4
 04:00 pm         348             89               259          35            43.3
 06:30 pm                                                       32            40.0
 10:00 pm                                                       24            33.0


Average Global Radiation = 653.65 W/sq.m
Average Diffused Radiation = 145.59 W/sq.m
Average Beam Radiation = 507.94 W/sq.m
Efficiency = 21.91 %


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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME




   Graph3: Temp VS time with agitator                Graph4: Intensity VS Time graph on
             and pebbles                                     25th April, 2013



   Table 3: Flat Plate Water Heater with Agitator & Metal Chips as Packing Media
                                     (26th April)

               Global         Diffused              Beam        Ambient      Temp. of
    Time      Radiation      Radiation            Radiation      Temp.        Water
              (W/sq. m)      (W/sq. m)            (W/sq. m)     (deg. C)     (deg. C)
  10:20 am      857             172                  685          30.0         34.9
  10:40 am      924             185                  739          32.0         36.7
  11:00 am      903             181                  722          32.0         38.3
  11:20 am      950             200                  750          33.0         40.0
  11:40 am      320              70                  250          34.0         41.5
  12:00 pm      975             205                  770          34.0         42.5
  12:20 pm      940             188                  752          35.0         45.0
  12:40 pm      850             171                  679          35.0         45.0
  01:00 pm      520             114                  406          36.0         45.0
  01:20 pm      500             100                  400          36.0         46.0
  01:40 pm      550             121                  429          36.5         46.5
  02:00 pm      670             134                  536          37.0         47.0
  02:20 pm      600             138                  462          37.0         47.5
  02:40 pm      530             127                  403          35.0         47.6
  03:00 pm      150              31                  119          34.0         47.1

Average Global Radiation = 682.6 W/sq.m
Average Diffused Radiation = 142.5 W/sq.m
Average Beam Radiation = 540.1 W/sq.m
Efficiency = 22.19 %


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6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME




   Graph5: Temp VS time with agitator               Graph6 : Intensity VS Time on
          and metal chips                                 26th April, 2013



Temperature Variation in Water Tank with Height




  Graph7: Temperature gradient at 11:00 am         Graph8: Temperature gradient at 3:00pm


        The Temp-time graph of first model (using agitator only) dips more than that of
second model (using agitator and pebbles) during later part of the day. This justifies better
heat retention capacity and longer duration purpose fulfillment over a day of second model as
compared to first model. As it can be seen from the thermal gradient curve, temperature of
water rises with height. This can be attributed to the property of warm water to stay above
cold water layer because of difference in density. The hottest layer is slightly below the top
layer, this is due to conduction and convection losses from the top layer, which is in contact
with air. This graph can be utilized practically in drawing hot water from the point slightly
below the point of hottest layer.




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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME

5. CONCLUSIONS

        Present experimental work has been performed with the aim of enhancing the heat
transfer in a passive flat plate solar water collector using cost effective techniques that could
be easily applied in a typical (conventional) flat plate collector without changing or
redesigning its shape. Such technique would allow the reduction of the solar collector area
and its associated manufacturing costs. The presence of the copper agitator inside the
channels changed the flow pattern in such a way which increased heat transfer from fluid
present in the near-wall zone to the internal layers of the water. The efficiency has been
further improved by packing the collector box with a layer of pebbles. This presented an
added advantage that warm water was retained for a longer duration of time till 10:00 PM in
night. Hence this model can be used to fulfill requirements of hot water even after dusk. Also
this model has a very good scope of implementation in rural areas where there is lack of
electricity. The model also shows a good result by using metal chips as packing media. It
improved the heat transfer coefficient considerably. It has a promising industrial scope.
Overall conclusion from the experimental work undertaken is that using such a low cost
modifications in design, using a metallic agitator insertion, pebbles and metallic chips as
packing media, considerably improves the performance of the solar collector.

REFERENCES

1. KS Ong, “A finite-difference method to evaluate the thermal performance of a solar
   water heater”, Solar Energy, Vol. 18, 181-191, 1974.
2. KS Ong, “An improved computer program for the thermal performance of a solar water
   heater”, Solar Energy, Vol. 18, 183-191, 1976.
3. Schmidt C, Goetzberger A, Schmid J., “Test results and evaluation of integrated collector
   storage system with transparent insulation”, Solar Energy, Vol. 41, 487-494, 1988.
4. V. Weitvrecht, D. Lehmann and A. Richter, “Flow distribution in solar collectors with
   laminar flow conditions”, Solar Energy, Vol. 73, 433-441, 2002.
5. M. H. Hu and Y. P. Chang, “Laminar flow in internally finned tubes under constant and
   uniform heat flux”, Journal of Heat Transfer, Vol. 95, 332, 1973.
6. Ajay Kumar Kapardar and Dr. R. P. Sharma,, “Experimental Investigation of Solar Air
   Heater using Porous Medium”, International Journal of Mechanical Engineering &
   Technology (IJMET), Volume 3, Issue 2, 2012, pp. 387 - 396, ISSN Print: 0976 – 6340,
   ISSN Online: 0976 – 6359.
7. Ajay Kumar Kapardar and Dr. R. P. Sharma, “Numerical and Cfd Based Analysis of
   Porous Media Solar Air Heater”, International Journal of Mechanical Engineering &
   Technology (IJMET), Volume 3, Issue 2, 2012, pp. 374 - 386, ISSN Print: 0976 – 6340,
   ISSN Online: 0976 – 6359.




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