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Su damıtma işleminde güneş enerjisinden yararlanma ve güneş enerjili havuz tipi damıtıcıların incelenmesi

Utilization of solar energy in water distillation and basin type solar stills

  1. Tez No: 21983
  2. Yazar: OSMAN BEZK
  3. Danışmanlar: DOÇ. DR. ABDURRAHMAN KILIÇ
  4. Tez Türü: Yüksek Lisans
  5. Konular: Enerji, Energy
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1992
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 159

Özet

ÖZET BU DAMITMA İŞLEMİNDE GÜNE© ENERJİSİNDEN YARALANMA VE GÜNES ENERJİLİ HAVUZ TİPİ DAMITICILAR Günümü 2 dünyasında, yüksek nüfus artısı ve endüstrileşmeye paralel olarak artan su tüketimi karcısında, deniz, okyanus v.b. büyük su kütlelerinin arıtılarak alternatif su kaynakları oluşturulması kaçınılmazdır. Uygulamalardaki arıtma tesislerinin hemen hemen tamamen fosil esaslı yakıtlara bağımlı olduğu göz önüne alınırsa, artan enerji maliyetleri özellikle fosil esaslı yakıtlara bağımlılığı azaltmanın hatta ortadan kaldırmanın gerekliliğini ortaya çıkarmaktadır. Bu amaçla su damıtma işleminde güneş enerjisinin kullanımı ideal bir çözümdür. Bu araştırmada su damıtma işleminde güneş enerjisinden ya rarlanma, güneş enerjili su damıtıcıları özellikle bu sistemlerin temelini teşkil eden havuz tipi güneş- enerjili damıtıcılar 'geniş bir şekilde incelenmektedir. Başlangıçta su gereksinimi., problem ve çözümleri hakkında bilgi verilerek konuya girilmekte, su damıtma işleminde güneş enerjisinin devreye girmesi anlatıldıktan sonra güneş enerjili damıtıcı çeşitleri ve yöntemler hakkında bilgi verilmektedir. Daha sonra, havuz tipi güneş enerjili damıtıcılar incelenmekte, damıtıcı elemanları, damıtıcı konstrüksiyon özellikleri ve uygulamadaki damıtıcı konstrüksiyonları, damıtma işlemine etki eden faktörler ayrı ayrı detaylarıyla incelenmektedir. Bir başka bölümde, güneş enerjili havuz tipi damıtıcıların teorik a- nal izi yapılmaktadır. Sistemin ısı dengesi içinde yer alan tüm e- lemanlar ve faktörler incelenmekte ayrı ayrı formülüze edilerek sistemin termal denge denklemleri oluşturulmaktadır. Bu teorik a- nal iz kapsamında yer alacak şekilde sistem ısı dengelerinden, genel denge denklemlerinden yararlanılarak bir güneş enerjili havuz tipi damıtıcı için, damıtıcının taşıdığı özelliklere göre sistemin önemli karakteristik özelliklerini hesaplayabilen bir bilgisayar programı geliştirilmeye çalışılmış ve programdan elde edilen çıkışlar incelenmiştir. Takip eden bölümde, güneş enerjili damıtıcı sistemlerin ekonomik analizi yapılmaktadır. Bu analiz içinde güneş enerjili havuz tipi damıtıcıların performansının arttırıla bilmesi için yapılan çalışmalar ve geliştirilen yöntemler açıklanmaktadır. Ayrıca sistemin ekonomik yapısı gözden geçirilmekte sistem maliyetine etki eden faktörler belirtilmektedir. Daha sonra ise araştırma sonuçları ve yapılan değerlendirme belirtilmekte dir. X

Özet (Çeviri)

SUMMARY UTILIZATION OF SOLAR ENERGY IN WATER DISTILLATION AMD BASIN TYPE SOLAR STILLS I. CONTENT OF THE STUDIES In this exploration, utilizing solar energy in water distil lation process, solar stills especially basin type solar still has been examined on a large scale. At the beginning, taking place of solar energy in water distillation process has been explained, and it has been informed about solar distillation methods and so lar stills. Then, basin type solar still has been investigated; elements of still constructions in practice, the factors that ef fect the system performance has been separetely examined with de tails. Then it has been made theoretical analysis of the basin type solar stills; all elements and factors taking place in heat balance of the system is examined, separetely formalizing a,l 1 of these elements, system thermal heat balance equations has been formed in comprising of this theoretical analysis, utilising heat balance equations of the system, a computer program which 4. can compute important characteristic properties of the system according to fixed properties of the still has been tried to be developed for a basin type solar still and it has been examined outputs of this program. In another section of this exploration, economical analysis of the solar stills has been made in this section, studies and developed methods to improve the performance of the basin type solar stills have been explained. Besides, economical situation of the system has been examined and it has been indicated the effecting factors then, results and evaluation of the exploration has been explained in the last section. II. TAKING PLACE OF SOLAR ENERGY IN WATER DISTILLATION One of the most important problem of the world we live in is the potable water problem. The rapidly increasing of the world's population, industrialisation of the communities, increasing social life standart have coused continiously increasing water consumption and this situation has brougt out a problem of providing domestic water, all around the world. For This reason, in time people will be obliged to find new water source other than consuming of the present water source. In this stage unusable water mass like oceans,sees etc. can be seen as an alternative water sources. Utilising the water of this sources by distillation will have on influence in solving the water problem. Very different water distillation methods have been applied, single or multi stage flash evaporation, vapour compression, ion exchange, multi effect evaporation, electrodialysis, electrochemical threatments, freezing and cristalyzation etc. But almost all of these methods- requires energy such as heat or elecricity and since energy is one of the most important problem too, increasing energy costs XIdecreasing of fosil based fuels such as petroleum etc. have brought out that it is necessary to decrease even to remove the dependence of this type of fueTs in water dis-ti 1 1 ati on. For this purpose, utilization of solar energy in water distillation is an ideal solution for this problem. III. TYPES OF SOLAR STILLS For utilization of solar energy in water distillation, two main approaches had been formed. One approach reproduces on a small scale the pure water separation portion of the hydro! ogic cycle while the other uses the solar energy to energise distillers which &re also capable of operating on other types of energy. Different solar distillation systems have been devoloped at the end of the explarations. The ones wiedly used in practice; İ. Basin type solar stills 2. Wick type solar stills 3. Solar multistage flash desalination systems The basin type solar stills that is a method that has been applicated for centuries is simple and system consists of a basin which is closed by a transparent cover such as glass or plastic: with & base line covered by a black material. In operation, absorbing the solar radiation passing through the transparent cover by the basin and the water permits heating and evaporation of the water basin. The formed vapour condensates on the cover and with the slope of the cover slides down the edges of the still then is collected by the help of the troughs installed of these places. So, distil lated water is produced. Mick type solar stills may be compared solar collectors instead of the basin in the basin type solar stills, a kind of wick is used. The brakish or salt water is abrosbed with cappilar effects by this wick and then evaporated on it. The latent heat of the distil lated water instead of being discharged to the ambient is utilized to preheat of the brakish or salt water in multistage flash distillation systems, so more effective solar energy utulization is obtained. This kind of stills consist of multistage evaporation and distillation system with a high efficiency solar collector sytem. This type of systems consist of three parts. Energy collection, accumulation and distillation by utilization of this energy. The solar energy collected by the solar collectors is accumulated in a tank, the hot water stored in this tank heats the water which will be distil lated (brakish or salt water) by a heateschanger. The brakish water heated in the heat exechanger is send to a multistage evaporator which the presure keeps on decrease from stage to stage. Condensing the vapour obtained by this evaporator in a condencer of which the water to be distilled passes trough the pipes, latent evaporation heat of the xiidistil lated water is used to preheat the water to be distilled so important economy of energy is obtained. IV. CONSTRUCTION AND STRUCTURE OF THE BASIN TYPE SOLAR STILLS When we examined the basin type solar still we see that it consists of three main parts s İ. Transparent cover 2. Basin 3. Collecting troughs The properties asked for transparent cover which permits to reach the solar flux to the basin and on which the vapour condense are high wettability, allowing to pass through all of the solar flux as well as possible without absorbing it, high reflection property for long wave (thermal) radiation, to be cheap and- safe. There are two* options in practice; glass and plastic. The basin is a part in which the water to be distil lated is collected, heated and evaporated by absorbing the solar energy. In order to increase the absorbtion of the solar energy, it is °( covered or painted with a black coloured material. It is applied heat and water insulation in the basin line and sides. All joints- is sealed with special seal en ts to make all the system vapour and weather proof. One of the most important point taking into consideration is that the basin must be flat as well as possible to prevent the dry spots to be formed because of the low water depth. The water condensing on the transparent cover and sliding down to the edges with the slope of the cover is collected by the troughs. One of the important point to be considered is to prevent reevaporation in the troughs by keeping them away from the direct solar radiation. As a result of explorations being made, different types of constructions has been improved for the basin type solar stills. General properties asked for the constructions are long operation life, low cost, lightness, easiness in set up, operation and. maintenance. V. THE FACTORS THAT EFFECT THE PERFORMANCE OF THE BASIN TYPE SOLAR STILLS The factors that effect the performance of the basin type solar stills can be explained as fallows : XI IX1) Atmospheric Conditions: a) Solar Radiation Solar energy is the unique energy come from outside of the system so, higher solar radiation results in higher performance. b) Clear Day-Cloudy Day Ratio For The Place Of The Stills This ratio widely effects the solar radiation. Higher ratio results in higher performance and efficiency. c) Ambient Tenperature: High ambient temperature couses to increase the system efficiency by decreasing the heat loss from the system to the ambient and forming high basin temperature. d) Wind Velocity: Increasing the velocity up to a definite value ( 32 K'm/h) results in high efficiency by increasing the heat transfer from the cover to the ambient. But higher velocities then this value couse to decrease the system performance by increasing the heat losses. e) Other Atmospheric Factors That Effect The Solar Radiation {Latitude, etc.) 2} The Effect Of The Water Depth In The Basin: Higher depth of the water in the basin causes to increase the amount of water in the basin and the thermal capacity (thermic inertia) of the system. So the most of the solar radiation is used for increasing the water temperature, distillation delays, temperatures being obtained are low and consequently system performance and efficiency decrease. 3} Effect Of The Type And Properties Of The Covers High transparency, low absorbtion of the solar energy, high wettability, low reflection of the long wave radiation of the cover results in high efficiency and performance. 4) The Temperature Difference Between The Basin And The Cover : Wien we examine the heat balance equations of the system, it may be seen that increasing basin temperature, decreasing cover teiftperature consequently increasing temperature difference between the basin and the cover increases the performance of the system. H75) Properties Of The Construction: Thermal capacity of the system, heat instil ati on, weather and vapour proofing, form and slope angle of the cover, air circulation in the system, radiation absorbtion ratio of the basin line, way of the still effect the performance of the system VI. THEORETICAL ANALYSIS OF THE BASIN TYPE SOLAR STILLS When it is made theoretical analysis of a basin type solar still, the heat fluxes taking place in the thermal c.onsruction of the system can be indicated as fallows. a) Radiation Heat Transfer From Basin To Cover [Qr3: 4 4 Qr=Fs*a#(Tw -Tg ) (1) Fs=i/C ( l/ew)+Ar* ( JL/eg-1 ) 3 (2) b) Convection Heat Transfer From Basin To Cover [Qc3s Qc=hc*(Tw-Tg) (3) 1/3 hc=0.884* [Tw-Tg+ (Pw-Pg ) / ( 2. 65*Pt-Pw ) *Tw3 ( 4 ) c) Evaporation Heat Transfer From Basin To Cover And The Amount Of Water Produced CQe^mb]? Qe=mb*hfg (5) mb=0. 0006847*hc * ( Pw-Pg ) ( 6 ) d) Convection Heat Transfer From Cover To Ambient £Qca3' Qca=hca#(Tg-Ta) (7) hca=5.7+3.8*V ' (8) e) Radiation Heat Transfer From Cover To Ambient [Qra3: 4 4 Qra=sg#P*(Tg -Ts ) (9) XVf) Heat Transfer From Basin Line To Ambient [Qb3: Qb=hb*(Tw-Ta) (.10) g) Thermal Capacity of The System For basin : Qw=Cw*dTw/dt (.11 ) For covers Qg=Cg*dTg/dt (12) h) Other Heat Losses: These heat losses can be substituted in the hea-.t balance equations with a. multiplying factor IKS] Taking into consideration all of these heat fluxes, heat balance equations can be set up; 1) The Heat Balance Equation At The Basin: awtZ *Qs=Cw*dTw/dt + Qe + Or + Qc + Qb (13) 2) The Heat Balance Equation At The Cover: Qe + Qc +. Or + ag*Qs= Oca + Qra + Cg*dTg/dt (14) 3) System Heat Balance Equation (Basin + Cover): (öw+ t h f g / O s (17) Utilising all of these equations being indicated., variation of the basin and the cover temperatures can be computed by two methods. By one of the methods, variation of the basin and the cover- temperature can be approximately computed by using definite empirical equations. According to these statements: In variation of the basin temperatures In cooling or after sun set: STw ( t ) =R*Qo*e>: p ( -t / tc ) ( 18 ) In heating or between sun rise and sun sets 6Tw( t)=R*Qsma>;/[l+(w*tc)2 3*[w*tc#e>;p(-t/tc )-w*tc*cos(w*t ) +sin(w*t> (19) w=ti / tg j tc=R*Cw/36C>0 ( 20 ) ( 21 ) In variation of the cover temperature: Tg=[ ( 0.026I2*Tw2 -1 5. 76*Tw+2392 ) *Tw+Ar*hca*Ta+Ar* ( 0. 04S*Ta-9 ) *Ts3 / E ( 0.026i2*Tw* -15. 76*Tw+2392 ) +Ar *hca+Ar* ( 0. 048*Ta-9 ) 3 +«g*Qs/ ( 0. 0238*Tw* -13. 3S*Tw+1961 ) ( 22 ) By other method,, first the cover temperature is estimated, then basin temperature is computed according to this estimated cover temperature (Using the system heat balance equation). The temperatures being obtained is substituted in the heat balance equation at the basin, temperatures providing this equation is appointed as the basin and the cover temperature. A computer program which can compute the characteristic properties of the basin type solar stills by utilising the equations in theoretical analysis of the system. By this program, for a basin type solar still inputting the datas related with the still (Place of the still, slope angle of the cover, max. solar radiation, values related with the cover and the water to be distalleted etc.) in any month of the year, taking into 3TVİİFor consideration of the day which re-fleets the average property of the month ambient temperature, basin and cover temperature, solar radiation and evaporation heat transfers from basin to cover, amount of distil 3 ated water can be computed with £ t time steps Besides daily, monthly and yearly total values can be separetely computed. VII. PERFORMANCE IMPROVEMENT IN THE BASIN TYPE SOLAR STILLS When the basin type solar stills is compared to other distillation methods, it can be seen that, their efficiency and performans is lower, the cost of the water being produced is higher than others, it can not be obtained higher capacities, this reason, in order to improve the performance of the basin type solar stills, several methods have been applied. Let us explain some of them. 1. F'erf ormance improvement of the basin type solar stills using various dyes * In order to eliminate the problems coused by shallow basin type solar stills, this method is applied to improve the performance of the deep basin type solar stills. Adding the water saluable dyes to the system, the solar energy is absorbed by the layer about 2 cm thickness near the surface of the water in the basin. So increasing the water surface temperature, higher performance is obtained. At the same time, it is obtained to accumulate the salt being formed in operation at the base line. of the basin without preventing the absoption of the solar enrgy. 2. Performance improvement of the basin type solar stills forming dried and forced air bubbling This treatment shortly is a method which ensures that the performance improvement with an effective evaporation absorbing the water molecules which transferee) to the interface (free surface) in evaporation by that air bubbling being formed. 3. The use of waste heat in basin type solar stills This is a method.which aims, especially in the places where the gasoline or diesel engines is available to preheat the feeding water to be distill ated by the waste heat of these sources. 4. Performance improvement with the multieffect basin type solar stills These are stills which is developed in order to utilise the latent evaporation heat of the distil lated water in the system. The main structure of the multieffect unit is identical to the corresponding standart still. The e>:tra effects are obtained XVlxXthrough evaporation of the source water placed in transparent basins (one or several) set between cover and main basin of the structure. Evaporation in each basin is energised by condensation on its under surface. 5. Performance improvement of the basin type solar stills using porous and black coloured material such as charcoal pieces. VIII. THE COST ANALYSIS IN SOLAR DISTILLATION In the case of solar distillation, the cost of energy is a very small fraction of the total, since the energy other than solar is only that required to operate the pumps and controls. Thus the major share of the water cost in solar distillation is that of amortization of the capital cost. In this exploration, utilisation of so3ar energy -in water distillation and especially the basin type solar stills which constitute the basis of the system had been examined on a large scale properties, construction structure,, the factors that effect the system, theoretical analysis and the computation of the values of the performans economical analysis had been investigated with details. I hope that these studies will help the next researchs in this field. When we consider the conditions at the present time, solar distillation will be more attractive in a near future. XU£

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