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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

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  • 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 273 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 INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) 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) www.jifactor.com IJMET © I A E M E
  • 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 274 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
  • 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 275 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
  • 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 276 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) 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 % Time Global Radiation (W/sq. m) Diffused Radiation (W/sq. m) Beam Radiation (W/sq. m) Ambient Temp. (deg. C) Temp. of Water (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
  • 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 277 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) Time Global Radiation (W/sq. m) Diffused Radiation (W/sq. m) Beam Radiation (W/sq. m) Ambient Temp. (deg. C) Temp. of Water (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 %
  • 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 278 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) 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 % Time Global Radiation (W/sq. m) Diffused Radiation (W/sq. m) Beam Radiation (W/sq. m) Ambient Temp. (deg. C) Temp. of Water (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
  • 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 279 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.
  • 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 280 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.