REDUCE EVAPORATION LOSSES FROM WATER RESERVOIRS

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1 Publshed by European Centre for Research Tranng and Developent UK ( REDUCE EVPORTION LOSSES FROM WTER RESERVOIRS 1 khudar abass dawood, 2 Farhan Lafta Rashd, 3 hed Hash 1, 2 Mnstry of Scence and Technology, Iraq-Baghdad 3 Babylon Unversty, Iraq BSTRCT: Evaporaton suppresson s the reducton of evaporaton by controllng the rate at whch water vapor escapes fro water surfaces. The need for water savng s greatest n areas of lttle ranfall and low runoff. Water losses by evaporaton fro storage reservors ust be nzed for greatest utlty of lted supples.usng trash of polyethylene wth dfferent denstes (800, 875 and 900 kg/3 as floatng cover to the water fllng cylndrcal contaner wth 8 c daeter led to reduce the evaporaton rate. sutable trash densty of 800 kg/3 gave reducton n evaporaton rate of 57% fro the theoretcal results calculated usng equaton (4 whch s a good result f copared wth prevous researches. KEYWORDS: Evaporaton Losses, polyethylene, floatng cover. INTRODUCTION Evaporaton of water fro reservors, rvers, and agrcultural felds results n ajor losses of crtcal water resources, especally n ard regons of the world. In ard regons, evaporaton can account for as uch as 25 to 30% of the total consuptve use of surface water. Because evaporaton s such a large part of the wa-ter budget n ard regons, evaporaton suppresson has been studed for decades. Research has shown that surfactants, whch odfy the surface tenson of the water surface, are very effectve n the laboratory n sup-pressng evaporaton. Recent research has shown that envronentally nnocuous surfactant onolayers coverng water surfaces can reduce the rate of evaporaton by as uch as 40 to 70%, resultng n substantal water resource savngs [1]. nnual loss of water fro storages through evaporaton can potentally exceed 40 per cent of water stored. Natonally ore than 7000 GL s stored n over two llon on-far storages, wth a further GL held n regstered large das. The loss of water causes lost agrcultural producton, leadng to fnancal stress for soe farers partcularly n tes of drought. Low water levels also lead to water restrctons beng posed on urban regons. Reducng the aount of water lost to evaporaton would prove water securty and lead to ncreased rrgaton producton [2]. Hardy [3] was the frst to suggest that onolayers were fored fro polar olecules consstng of a hydrophobc (water-repellng and a hydrophllc(water-attractng part, and hence that the onolayer olecules were orentated wth the hydrophllc part (a functonal group such as a hydroxyl-oh or carboxyl-cooh bured n the water, and the hydrophobc part (a hydrocarbon structuretendng to leave the water. Conclusve support for ths hypothess of orentatonwas provded by Langur [4]. Fnn and Barnes [5] use a suspended covers whch are horzontal sal-lke structures that are suspended over water surfaces and are supported externally by steel cables and poles. 14

2 Publshed by European Centre for Research Tranng and Developent UK ( Suspenson systes can be characterzed by ther span and ther cover weght. The cover ateral can vary fro porous shade screens to pereable plastc [6]. The cover reduces evaporaton by blockng ncong solar radaton ncdent upon the water surface, thus reducng theral energy nput nto the reservor surface waters, whch n turn reduces the water surface teperature and the potental for evaporaton. The covers also reduce surface wnd acton by lowerng the vapour pressure gradent over the water. The covers can also trap water vapour at the water surface that would otherwse be replaced by dry ar. Howard and Schdt [7] uses a Floatng covers nclude odular and flat sheet covers that float on the water surface. They reflect a proporton of the ncong solar radaton and act as physcal barrers to the passage of water vapour both vertcally and horzontally. Unlke suspended covers, the floatng covers are supported by the water tself. However, they do need to be fxed on the water surface usng soe for of anchorng echans when used on large das. Whle ost floatng cover products are desgned to wthstand strong wnd forces, t s evdent they have been desgned predonantly for sall storages and have not been rgorously tested on larger reservors. Heyann and Yoffe [8, 9] studed "the stablty of ultolecular fls of hydrocarbon ols, contanng spreaders, on water surfaces" and found that polyerzed spreaders for thck fls of ol that are uch ore stable than other spreaders; soe last as long as 18 onths f they are kept free fro dust. In ths paper trash of polyethylene wth dfferent denstes (800, 875 and 900 kg/3 used as floated cover to the water fllng the contaner n order to reduce the evaporaton rate. THEORETICL NLYSIS Fcks' Law of Dffuson and Stefan Proble [10]: Consder a non reactng gas xture of speces and B. Fcks' Law descrbes the rate at whch one speces dffuses through other. For the case of one densonal bnary dffuson, Fcks' Law on a ass bass s: Y ( D B B dy dx (1 Where. s the ass flux of speces ( kg / 2. s Y s the ass fracton D s bnary dffusvty ( 2 / s B Stefan assues the followng assuptons for equaton (1: 15

3 Publshed by European Centre for Research Tranng and Developent UK ( 1. Gas B s nsoluble n lqud ( B =0 2. Steady state. 3. Lqud level s constant or nterface regresses so slow, that ts oveent can be neglected. dy Y DB dx Y D B dy dx (2 Rearrange equaton (2 and ntegrate: x x0 D B dx Y Y, 1 dy (1 Y, x D B (1 Y ln (1 Y, (3 Y 1 (1 Y, exp( D x B Boundary condtons: t x=l Y for equaton (3: Y, D L B (1 Y, ln (1 Y, (4 Equaton (4 can be used to calculate the theoretcal evaporaton rate per unt area 16

4 Publshed by European Centre for Research Tranng and Developent UK ( Where s evaporaton rate per unt area s the average gas densty n the contaner (Fg.(1 and can be calculated fro: ( R P u / MW P s the atospherc pressure T R u s Unversal Gas Constant L s the nterface depth fro the top of contaner T s Gas Teperature MW 0.5( MW x MWx,, Fgure (1 Dffuson of Vapor through a Stagnant Colun of Gas B,.e., the Stefan Proble 17

5 Publshed by European Centre for Research Tranng and Developent UK ( Experental Part Fgure (1 shows the contaner (8 c daeter, flled wth water at depth of 3 c fro the top of the contaner at whch our experents were take place, usng trash of polyethylene for dfferent denstes ranged fro 800 to 900 kg/ 3 putted n a float layout at the nterface (x=0 to reduce water evaporaton fro the surface and take the easureents whch nvolve teperature and net weght of the water n the contaner by usng senstve balance, n each easureent we report the te fro startng evaporaton n order to dvde the net weght on the te to gve evaporaton te. RESULTS ND DISCUSSIONS Calculatons of evaporaton rate for dfferent trash denstes were obtaned and copared wth theoretcal results obtaned fro equaton (4, we can see fro fgure (2 that t shows the relatonshp between evaporaton rate wth teperature, an ncrease n water teperature led to an ncrease n evaporaton rate, also nu evaporaton rate take place wth usng trash of lower densty (800 kg/ 3 and ncreased wth ncreasng trash densty. Fgure(3 shows the relatonshp between evaporaton rate wth te, one can observe that an ncrease n evaporaton te wll ncrease the evaporaton rate, also nu evaporaton rate take place wth trash of low densty (800kg/ 3 and ncrease wth ncreasng trash densty. Fgure (2 Varaton of Evaporaton Rate wth Teperature Fgure (3 Varaton of Evaporaton Rate wth Te 18

6 Publshed by European Centre for Research Tranng and Developent UK ( CONCLUSIONS Fro the present work, we can deduce the followng conclusons: 1. n ncrease n evaporaton te and teperature wll lead to ncrease n evaporaton rate. 2. Reducng the trash densty wll reduce the evaporaton rate. 3. Usng trash densty of 800 kg/ 3 wll reduce evaporaton rate 57% REFERENCES 1. Mke Hghtower and Gary Brown(2004, Evaporaton Suppresson Research and pplcatons for water anageent, Identfyng Technologes to Iprove Regonal Water Stewardshp: North-Mddle Ro Grande Corrdor. 2. Ea Pre et al. (2012,New Technology to reduce Evaporaton fro Large Water Storages. 3. Hardyw, B.,(1919, The Tenson of Coposte Flud Surfaces and the Mechancal Stablty,(1913,The Tenson of Coposte Flud Surface,No.2.Proc, Roy.Soc., Ser.., Vol LNGMUIR, I. (1917, The shapes of group olecules forng the surfaces of lquds. Proc. Nat. cad. Sc., vol. 3, no. 4, p Fnn, N. and Barnes, S. (2007. The benefts of shade-cloth covers for potable water storages. CSIRO Textle and Fbre Technology. 6. Martínez Álvarez, V., González-Real, M.M. Balle,. and Molna Martínez, J.M novel approach for estatng the pan coeffcent of rrgaton water reservors: pplcaton to South Eastern Span. grcultural Water Manageent. 7.Howard, E. and Schdt, E. (2008. Evaporaton control usng Ro Tnto's Floatng Modules on Northparks Mne, Landloch and NCE. Natonal Centre for Engneerng n grculture Publcaton /1, USQ, Toowooba. 8. Heyann, E., and Yoffe,., 1942, Te stablty of ultolecular fls of hydrocarbon ols, contanng spreaders, on water surfaces: Faraday Soc. Trans., v. 38, p Heyann, E., and Yoffe,., 1943, The equlbru between lens and unlayer n the syste hydrocarbon ol-olec acd-water, n relaton to the nterfacal fl: Faraday Soc. Trans., v. 39, p