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Experimental investigation of a double slope solar still with a latent heat
 

Experimental investigation of a double slope solar still with a latent heat

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    Experimental investigation of a double slope solar still with a latent heat Experimental investigation of a double slope solar still with a latent heat Document Transcript

    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEME AND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online)Volume 4 Issue 1 January- February (2013), pp. 22-29 IJMET© IAEME: www.iaeme.com/ijmet.aspJournal Impact Factor (2012): 3.8071 (Calculated by GISI)www.jifactor.com ©IAEME EXPERIMENTAL INVESTIGATION OF A DOUBLE SLOPE SOLAR STILL WITH A LATENT HEAT STORAGE MEDIUM Ajeet Kumar Rai *, Vivek Sachan and Maheep Kumar Department of Mechanical Engineering, SSET, SHIATS-DU Allahabad, U.P., India *E-mail raiajeet@rediffmail.com ABSTRACT Single basin solar still is a very simple solar device used for converting available brackish or water into fresh drinking water. This device can be fabricated easily with locally available materials. The maintenance is also cheap and no skilled labor is required. The device may be a suitable solution to solve drinking water problem but because of its low productivity it is not popularly used. Number of works are undertaken to improve the productivity of the still. The use of latent heat storage system using phase change material (PCMs) is an effective way of storing thermal energy and has the advantage of high energy density and the isothermal nature of the storage process. Double slope single basin solar still is experimented by adding a heat reservoir in the basin using Zinc Nitrate Hexahydrate. It is a material which changes its phase during addition and removal of heat. It is observe that an increment of 33.5 % is observed in the collection of distillate when the still is used with PCM as Zinc Nitrate Hexahydrate. Key Words: double Slope Solar Still, Phase Change Materials 1.INTRODUCTION Water is the primary source of life. Next to oxygen, fresh water is the most important substance for sustaining human life. Water shortage is a worldwide problem, where 40% of the world population is suffering from water scarcity [1]. Although Water is one of the most abundant resources on Earth, covering approximately three-quarters of the planets surface. About 97% of the Earths water is salt water in the oceans. 3% of all fresh water is in ground water, lakes and rivers, which supply most of that needed by humans and animals. 22
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEME However, rapid industrial-growth and the population explosion world-wide haveresulted in a large escalation of the demand for fresh water. Added to this is the problem ofpollution of rivers and lakes by industrial wastes and the large amounts of sewage discharged.On a global scale, man-made pollution of natural sources of water is becoming the singlelargest cause for fresh-water shortages. Besides the only inexhaustible sources of water arethe oceans. Their main drawback, however, is the high salinity of such water. It would beattractive to tackle the water-shortage problem with desalination of this water, which may bemixed with brackish water increase the amount of fresh water and reduce the concentration ofsalts to around500 ppm [2]. Solar distillation has been practiced for many generations. All desalination methodsrequire fossil fuel or electrical energy but solar distillation is one of many processes that canbe used to produce fresh water by using the heat of the sun directly in a simple equipment topurify water. The equipment, commonly called a solar still [3,4]. Solar still is most simpledevice to get potable/fresh distilled water from impure water. Among other available designsof solar still, the Double Slope Solar Still is most popular. The construction and design of thissolar still is simple. The problem is poor productivity. A large number of attempts are madeto improve the productivity from solar still. Studies are performed to predict the performanceof solar still [5]. Effect of variation of parameters on the total output is also studied byvarious researchers [6].They have analyzed the effect of water depth on the performance ofDSS. Due to intermittent nature of solar energy, distillate production is not continuous andnight time production is almost nil. By using energy storage mediums, distillate may beproduced during non-Sunshine hours. These energy storage systems may store heat energy intwo ways (i) Sensible Heat (ii) Latent Heat. Thermal energy can be stored as a change ininternal energy of a material as sensible heat, latent heat or combination of these two. Insensible heat storage (SHS), thermal energy is stored by raising the temperature of a solid orliquid. SHS utilizes the heat capacity and the change in temperature of the material during theprocess of charging and discharging. The amount of heat stored depends on the specific heatof the medium, the temperature change and the amount of storage material [7]. ்௙Q=‫்׬‬௜ ݉‫ܶ݀݌ܥ‬ (1) =݉‫݌ܥ‬ሺ݂ܶ െ ܶ݅ሻ (2)LHS is based on the heat absorption or release when a storage material undergoes a phaseChange from solid to liquid or liquid to gas or vice versa. The storage capacity of the LHSsystem with a pcm medium is given by- ்௠ ்௙Q=‫்׬‬௜ ݉‫ ݐ݀݌ܥ‬൅ ݉ܽ݉∆݄݉ ൅ ‫்׬‬௠ ݉‫ݐ݀݌ܥ‬ (3)Q=݉ሾ‫݌ݏܥ‬ሺܶ݉ െ ܶ݅ሻ ൅ ܽ݉∆݄݉ ൅ ‫݌݈ܥ‬ሺ݂ܶ െ ܶ݉ሻሿ (4)Due to the compactness of PCMs the latent heat is much higher than the sensible heat. Thesematerials are still a point of interest for researchers. Lorsch et. al. [8], Lane et. al. [9] and 23
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEMEHumphries and Griggs [10] have suggested a wide range of PCMs that can be selected as astorage media. Latent Heat storage systems are having advantage of their isothermal nature ofstoring heat energy. Kuznik et. al [11] has given a good explanation of how PCM stores andreleases latent heat. The external heat supplied to a PCM is spent in breaking the internalbonds of lattice and thereby it absorbs a huge amount of latent heat at phase temperature.Abhat et.al.[12] has given a detailed classification of PCMs along with their properties.Dinser and Rosen [13] have also exercised the same. A large number of phase changematerials (organic, inorganic and eutectic) are available in any required temperature range.El-Sebaii et al [14] and Shukla et al [15] have used phase change material as a energy storagemedium to study the performance of a single slope solar still. In the present study,performance of a double slope solar still with Zinc Nitrate Hexahydrate as PCM has beeninvestigated in outdoor conditions in the month of October. Thermophysical properties ofZinc Nitrate Hexahydrate are given. Melting temperature 36.10C specific heat (solid) 1.34kJ/kg0C, specific heat (liquid) 2.26kJ/kg0C, Latent Heat of fusion 147.0 kJ/kg, Thermalconductivity 0.464W/mK at 39.90C.2. EXPERIMENTAL SET-UP AND PROCEDURE2.1 Set-up Figure 1 shows the photograph of two Double Slope Solar Still of same size andshape. One DSS is without PCM and another DSS is having PCM in the basin. The DSSconsist of a passive solar distillation unit with a glazing glass cover inclined at 260 having anarea of 0.048m x 0.096 m. The tilted glass covers are of 3 mm thickness, Transmit solarenergy and work as an insulator of heat. It works as a condensing surface for the vaporgenerated in the basin. Still basin, made up of Galvanized Iron, has an effective area of 0.72m2. The basin of the distiller was blackened to increase the absorptive of the basin liner. Adistillate channel was provided at each end of the basin for the collection of distillate output,a hole was drilled in each of the channels and plastic pipes were fixed through them with anadhesive (Araldite). An inlet pipe and outlet pipe was provided at the top of the side wall ofthe still and at the bottom of the basin tray for feeding saline water into the basin and drainingwater from still for cleaning purpose, respectively. All arrangements are made to make thestill air tight. Water gets evaporated and condensed on the inner surface of glass cover. It runsdown the lower edge of the glass cover. The distillate was collected in a bottle and thenmeasured by a graduated cylinder. The distillate is collected from two sides of the still. PhaseChange Material is filled in the tubes and placed in the basin of the still. Tubes are made ofaluminum to offer little resistance to the heat transfer between water and PCM. Tubes are ofdia 10 mm and length as that of the basin inner side. Thermocouples were attached indifferent locations of the still to record the temperatures of inside glass cover, watertemperature in the basin and ambient temperature. All experimental data are used to obtainthe internal heat and mass transfer coefficient for double slope solar still. The effect of use ofphase change material is also studied by comparative analysis. 24
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEMEFig.1 Photograph showing experimental set-up (Double Slope Solar Still with and without PCM)2.2 Procedure The experiments were conducted in the campus of Sam Higginbottom Institute ofAgriculture, Technology and Sciences- Deemed University, Allahabad, India. Allexperiments were started at 08:30 AM at local time and lasted for 08.30 hours. Water, glass,water vapor and PCM temperatures were recorded with the help of calibrated Copper –Constantan thermocouples having a least count of 10C. The ambient temperature is measuredby a calibrated mercury (ZEAL) thermometer having a least count 10C. The distillate outputwas recorded with the help of a measuring cylinder of least count 1 ml. The solar intensitywas measured with the help of calibrated solarimeter of a least count of 2 mW/cm2. Thehourly variation of all above mentioned parameters were used to evaluate average values ofeach for further numerical computation. 25
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEME3.PRODUCTIVITY AND EFFICIENCY OF THE SOLAR STILL Energy balance equations are written for the different components of a double slopesolar still without PCM in the basin[5], [6] and with PCM in the basin [14].The hourly and daily productivity of solar still isMewh = hewh (Tw-Tgin)/L (5)Mewd = ∑24 hrsmewh (6)The instantaneous efficiency of the solar still is:ηi = [ hewh (Tw-Tgin)/I (t)]x 100% (7)ηd = [Mewd hew/(Ap∑I)(∆t)]x 100% (8)4. RESULTS AND DISCUSSION 1000 900 Solar intensity East Solar Intensity (W/m2) 800 Solar intensity West 700 600 500 400 300 200 100 0 Time Of the Day (hr) Fig. 2. Variation of solar intensity with time of the dayVariation of solar intensity falling on the east and west side glass covers of the double slopesolar still for a particular day (17-10-12) is shown in fig.2. It is observed that the solarintensity falling through east side glass cover is higher till 01:30 hrs. Maximum value isobserved around11:00 hrs on east glass cover. 26
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEME 70 Glass cover temp. East with PCM Glass cover temp. East without PCM 60 50 Temperature (C0) 40 30 20 10 0 Time of the day (hr) Fig.3 Variation of East glass covers temperatures of DSS with PCM and without PCMVariation of east glass cover temperatures of DSS with PCM and without PCM is shown infig 3. It is observed that the DSS with PCM tubes will have higher glass cover temperature incomparison to that of without PCM. This difference is higher in afternoon session. This isdue to thermal inertial effect produced by PCM tubes. This is also true for the west side glasscover. A slight rise in temperature of the west side glass cover with PCM is shown in fig.4.This little difference is due to low solar intensity on west side glass cover. 70 Glass cover temp. West with PCM Glass cover temp. West without PCM 60 Temperature (C0) 50 40 30 20 10 0 Time of a day (hr) Fig. 4. Variation of West glass covers temperatures of DSS with PCM and without PCM 27
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEME 250 total output. with PCM Total output. without PCM 200 Distillate output (ml) 150 100 50 0 Time of the day (hr) Fig.5.Variation of total distillate output from DSS with PCM and without PCMHourly distillate output is measured in the daytime only from 08:30 AM till 5:00 PM. Lastreading shows total distillate collected during 5:00 PM to 8:00 AM. From fig. 5 it is clear thatoutput will increase due to use of PCM as heat reservoir. Total gain of 33.5% is observed inoutput. Where daytime gain is 34.7% and nocturnal gain is of 31.7%.5. CONCLUSION This study explores the possibility of using latent heat energy storage mediums inconventional solar still to ensure the continuous production of fresh water even after sunset.Result shows that productivity increases by 30 to 35% with Zinc Nitrate Hexahydrate asPCM. This can be further improved by a PCM with high latent heat of fusion and increasingthe mass of the PCM in the basin.REFERENCES[1]Abdullah S., Badranb O. & Abu-Khaderc M. M. (2008), Performance evaluation of amodified design of a single slope solar still. Desalination 219pp. 222–230[2]MalikMAS,Tiwari GN, Kumar A, Sodha MS.Solar distillation.Oxford: PergamonPress,1985.[3]Tiwari, G.N., Tiwari, A.(2007), Solar Distillation Practice for Water DesalinationSystems, Anamaya, New Delhi,.[4]Argaw N. ( 2001),"Renewable Energy in Water and Wastewater Treatment Applications".National Renewable Energy Laboratory[5] Shukla S.K. and Rai A. K. (2008), “Analytical thermal modeling of double slope solarstill using inner glass cover temperature” Thermal Science,vol 12,(3), 139-152.[6] Rai Ajeet Kumar, Kumar Ashish and Verma Vinod Kumar (2012), “Effect of water depthand still orientation on productivity of passive solar still”IJMET, vol 3, (2), 740-753.[7] Rai Ajeet Kumar, Kumar Ashish (2012),” A Review on phase change materials and theirapplications”IJARET, vol. 3,(2), 214-225. 28
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 1, Jan - Feb (2013) © IAEME[8] Lorsch HG, Kauffman KW, Denton JC, “Thermal Energy Storage for Heating and AirConditioning, Future energy production system”. Heat Mass Transfer Processes; 1: pp 69-85(1976).[9] Lane GA, Glew DN, Clark EC, Rossow HE, Quigley SW, Drake SS, et al. “Heat of fusionsystem for solar energy storage subsystems for the heating and cooling of building”.Chalottesville, Virginia, USA, 1975.[10] Humphries WR, Griggs EI. “ A designing handbook for phase change thermal controland energy storage devices.” NASA Technical Paper, p. 1074, (1977).[11] Kuznik F., Virgone, J. and Noel, J.: Optimization of a phase change material wallboardfor building use. Applied Thermal Engineering 28 (2008), 1291-1298.[12] A. Abhat, Low temperature latent heat thermal energy storage: heat storage materials,Solar Energy30, pp 313-332 (1983).[13] Dincer I., Rosen M.A. , Thermal energy storage, Systems and Applications John Willeyand Sons Chichester (England), 2002.[14] El-Sebaii A. A., Al-Ghamdi A.A., Al-Hazmi F.S. and Faidah A.S. (2009), Thermalperformance of a single basin solar still with PCM as a storage medium, Applied Energy,86,1187-1195.[15] Al-Hamadani A.A.F. and Shukla S.K. (2011), Modeling of solar distillation system withphase change material(PCM) storage medium, thermal science, 29