EXPERIMENTAL INVESTIGATIONS OF OXYGEN STRIPPING FROM FEED WATER IN A SPRAY AND TRAY TYPE DE-AERATOR

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1 International ournal of Automotive an Mechanical Engineering (IAME) ISSN: (Print); ISSN: (Online); Volume, pp , anuary-une 00 Universiti Malaysia Pahang DOI: EXPERIMENTA INVESTIGATIONS OF OXYGEN STRIPPING FROM FEED WATER IN A SPRAY AND TRAY TYPE DE-AERATOR K.V. Sharma,4, K.V. Suryanarayana, P.K. Sarma 3, M.M.Rahman, M.M.Noor, an K. Kairgama Faculty of Mechanical Engineering, Universiti Malaysia Pahang, 6600 Pekan, Kuantan, Pahang, Malaysia. kvsharma@ump.eu.my Department of Chemical Engineering, Sri Venkateswara Engineering College, Suryapet 5083, Inia. 3 International Director, GITAM University, Visakhapatnam , Inia 4 Centre for Energy Stuies, NTUH College of Engineering, Hyeraba , Inia ABSTRACT The influence of various parameters on oxygen stripping for a two stage spray an tray type e-aerator is analyze experimentally. It is observe that increasing the mass flow rate of water leas to an increase in heat an mass transfer coefficients in both stages. There is no significant influence of e-aerator pressure an length of the secon stage on the heat transfer coefficients in the range teste. The increase in e-aerator pressure enhances the mass transfer coefficient by 4 percent, whereas the increase in length of the secon stage has no significant influence. The empirical correlations available in the literature preict the mass transfer coefficients satisfactorily in the experimental range teste. The total length of the e-aerator is a significant parameter influencing the quantity of oxygen remove from the fee water. Keywors: thermal e-aerator, spray an tray combination, conensation heat an mass transfer coefficients, oxygen strippe INTRODUCTION Boiler fee water may contain significant amounts of issolve oxygen in the make-up water an/or ue to seepage of air at the conenser. Corrosion ue to pitting an iron eposition will be forme if the gas/air is not remove. Removal of the air takes place in a e-aerator, as even small quantities of issolve gas can cause significant corrosion. The high temperature of the boiler fee water will enhance corrosion ue to issolve oxygen, if left untreate. In spray an an tray type e-aerators, the incoming water is passe through a hollow cone spray nozzle which is locate at the top of the e-aerator. The liqui thus emerging from the nozzle forms a conical sheet at the nozzle outlet ue to its tangential, raial an axial momentum forces. After traversing a small istance from the nozzle, the sheet breaks into ligaments an finally into roplets ue to estabilizing forces. The roplets accumulate on a tray an flow as a jet through holes in it an finally collect at the bottom of the e-aerator. The water is then pumpe to the boiler. Experimental investigation of conensation of steam on a spray of water roplets was conucte by Brown (95) in the iameter range of 0.5 to 0.50 mm an obtaine heat transfer coefficients of the orer of 7,000 W/m K. For an ekic 46

2 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) (97) evelope a correlation for the estimation of the growth of liqui roplets uring conensation of steam in irect contact for three ifferent iameters using high-spee photography. The experiment was conucte at various roplet temperatures below the saturation temperature of take into consieration unsteay state heat transfer. They moelle the roplet as a sphere with negligible heat transfer at the interface. Sunararajan an Ayyaswamy (987) have carrie out experimental stuies on the effect of resience time on roplet size by introucing a non-imensional conensation parameter, which consiers the steam properties at far-stream along with the instantaneous surface temperature of the rop. They observe the value of the conensation parameter to ecrease with an increase in time an roplet size. Experiments on irect contact conensation of steam with water sprays characterize by roplet size varying between 0.30 an.8 mm, velocities between 0.85 to 9.0 m/s an operating pressure up to 0.6 MPa were unertaken by Celata et al. (99). The experiments inclue the continuous measurement of the average roplet temperature along the axis of the spray. They obtaine a conensation efficiency higher than that preicte by the pure conuction an internal circulation moels. An empirical approach for the evaluation of the liqui mixing in the roplet has been unertaken by them an presente this efficiency as a function of the moifie Peclet number. A comparison of the that moel with the experimental ata is foun to be quite satisfactory. Mayinger an Chavez (99) conucte experiments on the growth of sub coole spray roplets in a pure saturate vapour using the pulse laser holography technique. The experimental values obtaine by them preict high heat transfer coefficients in both sheet an roplet regions. Takahashi et al. (00) stuie the mechanism of conensation from a spray nozzle both theoretically an experimentally. They conclue from their analysis that the turbulence moel preicte heat transfer in the first zone closer to the experimental ata than i the pure conuction moel. Nosoko et al. (00) conucte experiments on oxygen absorption using a single column horizontal tube bank of 6 mm iameter an 84 mm wette length. They foun that the Sherwoo number increases with an increase in tube spacing from to 5 mm an then levels off at 0 mm or higher. They conclue that the volume of a horizontal tube absorber coul be /. to /.8 times lower compare to vertical orientation for the same heat uty. Experimental evaluations of conensation heat transfer coefficient from sprays by inucting non-conensable gas into the vapour region have been unertaken by many. However, in the literature, heat an mass transfer stuies with a non-conensable gas such as oxygen getting strippe from the boiler fee water are quite limite in number. Hence, it is propose here to stuy the influence of various operating parameters such as the flow rate of water, e-aerator length, e-aerator pressure, water temperature, oxygen concentration in the inlet water, etc., on the heat an mass transfer coefficients by conucting experiments with a spray an tray type e-aerator. EXPERIMENTA SETUP The experimental setup consists of a column of 0.5 m ia. an. m length with a flexibility to enhance the total length to. m using spacers as shown in Figure. A nozzle locate at the top of the e-aerator sprays water over a istance of 0.55 m, referre to as the first stage. 47

3 Experimental investigations of oxygen stripping from fee water in a spray an tray type e-aerator VENT WATER INET Slanting ength, S Breakup length, B Inner raius, R I Outer Raius, R O ID.8 54 ETS IN EACH TRAY OF II STAGE NO OF TRAYS=4 SPRAY ength of Secon Stage, mm. Config. No STEAM INET 50 0 WATER OUTET No. of Rivets on each tray = Figure : Schematic iagram of spray an tray type e-aerator 48

4 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) A provision to ajust the spacing between trays with spacers of 00 an 300 mm length is available in the secon stage of the e-aerator. The trays can be use either iniviually or in combination to vary the total height of the e-aerator. The water emanating from the nozzle gets accumulate on the first tray. The trays with holes as shown in Figure allow water to flow from one to another as jets. The experiments were conucte at various flow rates, ifferent e-aerator heights an pressures, inlet water temperatures, inlet concentrations an vent locations to evaluate the heat an mass transfer coefficients. VENT TT3 P3 P SRV DPR STEAM FROM PRDS FCV- VENT SURGE TANK SRV P DE- AERATOR TT DRAIN 3 4 I STAGE II STAGE FCV- SRV F STEAM TRAP TT CV DO METER WATER OUTET WATER STORAG E TANK WATER BATH WATER INET DRAIN PUMP DRAIN CV : Check Valve DPR : Dome oae Pressure Regulator DO : Dissolve Oxygen Meter FCV : Flow Control Valve F : Flow Meter : Manual Valve P : Pressure Gauge TT : Temperature Transmitter PRDS : Pressure Reucing & Distribution System SRV : Safety Relief Valve Figure : Process an instrumentation iagram of e-aerator experimental set-up 49

5 Experimental investigations of oxygen stripping from fee water in a spray an tray type e-aerator A 00 liter fee water storage tank, a steam jacket on the e-aerator water inlet pipe for regulating its temperature, an a pump for circulating water are other accessories. In the steam circuit a pressure regulator an a steam trap are connecte to a buffer tank for removal of water roplets after steam expansion in the pressure regulator. A water bath of 5 liters capacity with a copper coil to ecrease the temperature of the sample water to vary between 30ºC an 40ºC is connecte to a issolve oxygen (DO) meter, an flow components such as valves, flow meters, pressure gauges an thermocouples are provie. The process an instrumentation iagram of the experimental setup is shown in Figure. ANAYSIS OF HEAT AND MASS TRANSFER COEFFICIENTS Estimation of Heat Transfer Coefficient at Stage The etermination of roplet size an hence the number of roplets can be preicte when the sheet (s) or breakup length ( B ) is known. The sheet length can be estimate using the empirical relation given by Eq. (ee an Tankin, 984) C6 C5We C C3 We C4 A C a e B 0 () 6 where C 6.5, C 0.7, C3 30, C an We 750, C. 5 5 an C We 750, C an C The spray Weber number in this stuy varies between 790 We 50 an corresponing mass flow rate between m From the geometry of triangles, if the half cone angle ( ) of the nozzle an B are known, the slanting length (S) an outer raius ( R O ) of the sheet can be estimate. The sheet thickness ( s ) at the location of breakup is estimate by Eq. (Takahashi et al., 00): m R V () s O N For the swirl cone angle of the nozzle ( ), the slanting length is calculate by Eq. 3: S B / Cos (3) Using these values, the sheet volume can be estimate as in Eq. 4: v s O I ( R R ) 3 (4) s The roplet iameter can be estimate accoring to the empirical relation of Dombowski an Munay (967) for known conitions of e-aerator pressure, flow rate of water, which is expresse as Eq. 5: FN / 0 P (5) 50

6 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) where FN.08x0 m / P /000 D an P is the pressure rop across the nozzle. The number of roplets ( N ) forme can be estimate as Eq. 6: 3 N 6vs (6) The surface area of N roplets can be estimate with Eq. 7: A N (7) The heat transfer area is the sum of the areas of sheet an roplets: A A s A (8) The variation of roplet raius with time ue to conensation can be estimate with the theoretical relation erive by Rao an Sarma (985): r r / con E (9) where / 3 ) r con ( a ; E [ a exp( )] 3 The value of can be expresse as Eq n where q exp n ln q n n (0) of Thus Eq. 9 with the ai of Eq. 0 provies an explicit relation for the estimation r. The conensate flow rate of the first stage is C P To Ti m H fg m C () The heat transfer coefficient ue to conensation in the first stage an the temperature at the exit of first stage of e-aerator can be estimate with the help of Eq. () to Eq. (4). h con fg T C S i H m A T T () Q h A T (3) T con S i i T i ( Q / mc P ) (4) The energy transferre to water in the e-aerator is the sum of the energies transferre in both stages: Q E P o i Q Q m C T T (5) 5

7 Experimental investigations of oxygen stripping from fee water in a spray an tray type e-aerator Estimation of Heat Transfer Coefficient at Stage A mathematical treatment of conensation on laminar an turbulent liqui jets taking into account the variation of flow rate over the jet cross section has been presente by Mochalova et al. (988). They compare their analysis with the experimental ata of Mills et al. (98) an presente an explicit solution for the estimation of heat transfer coefficient in terms of the Reynols, Prantl, an Weber numbers in aition to other geometric parameters governing the flow. For laminar flow, the explicit equation for the Stanton number is given by Mochalova et al. (988) as Eq. (6a): For turbulent flow, 0. 8 f f f 0. a D St 004 for Re H 500 (6a) a D Re Fr St B H Pr ; 0.00 a ; 500 Re H 0,000 ; Pr 50; 50 Fr 5, 000 (6b) where B if the initial velocity profile is plane B.8 D 0. if the initial profile is parabolic f Re H ; f.05 Pr D ; f3.05 C Re H We D C Re H We for We. 5 ; f C Re H We D for We. 5 ; C g D 3 8 ; Re H V D ; Pr ; We V D ; Fr V g D ; h T St V CP h The heat transfer coefficient T for liqui jets in the secon stage can be valiate with the overall energy balance equation, if the surface area for heat transfer can be etermine. The surface area for heat transfer epens on the phenomenon of liqui jet breakup. The hyraulic break up length of the jet emerging from.8 mm iameter holes of the tray is estimate by Eq. 7 accoring to the empirical correlation of Celata et al. (989), hb D 9.9 We. (7) The volume of water in the jet up to the break-up length can be estimate as: v D 4 (8) hb Spherical roplet formation takes place on the breakup of the liqui jet. The iameter an volume of the roplet forme on breakup can be estimate as (Hinze, 955): 5

8 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) v. 89D ; 6 (9) The number of roplets N forme from each jet in the secon stage can be estimate as: N v v (0) The surface area of 54 liqui jets emanating from each tray is the sum of the areas up to the breakup length an that of the roplets forme thereafter At 54 D hb N () As the height of the jet between the thir an bottom tray is only 0.05 m an less than the breakup length, the surface area expose to steam is taken for consieration. Hence, the total heat transfer area of the secon stage consiering all the trays is A 3 A t 54(0.05 D ) () The heat transferre in the secon stage of the e-aerator can be estimate from the ifference relation Q Q (3) E Q The overall heat transfer coefficient of the secon stage can be estimate accoring to Newton s law h E S i The total heat transferre can be estimate as: Q A T T (4) Q T con T T h A T T h A (5) S i T S i The values obtaine from Eq. (5) are valiate with the energy balance, Eq. (5). A regression equation for the estimation of the overall heat transfer coefficient has been evelope with 85 experimental values an with an average eviation of 3% an stanar eviation of 4% as m C A T T D U Re 3 (6) g. P S i N vali for the operating conitions m 0. 5 kg/s, 350 / D 600 an. T / T.4. S i N 53

9 Experimental investigations of oxygen stripping from fee water in a spray an tray type e-aerator Estimation of the Mass Transfer Coefficient at Stage The objective of the present analysis is to estimate the quantity of oxygen iffusing from the solvent water. This is formulate as one relate to the iffusion of oxygen from the roplet centre to its surface. In this formulation, the assumptions are as follows:. The configuration of the roplet is a perfect sphere.. Diffusion occurs uner non-isothermal conitions, i.e., the major resistance for iffusion is within the roplet an the resistance ecreases as the temperature of roplet increases. 3. The resistance for iffusion of gas from the interface to steam is negligible. The component continuity equation can be written as follows: 3 6 X ( t) t k C (7) The oxygen concentration ( C A ) in the inlet water can be expresse as Eq. (8) in terms of the bulk ensity of water an the mass fraction of oxygen issolve in it., A C X (8) A For flow past a single sphere, the mass transfer coefficient uner force an free convective conitions, accoring the to well establishe imensionless equation of Steinberger an Treybal (960), is Sh (Re Sc ) Sh (9) vali in the range 0.6 Sc 4000 an.8 Re 60 The initial Sherwoo number Sh 0 can be evaluate as follows: Gr Sc Gr Sc Sc Sh for Gr Sc Sh for Gr 0 (30) Eq. 7 can be rewritten with the ai of Eq. 8 an Eq. 9 as X 5 Sc t t 6 ( Sh D X ( t)) 0.6 A (3) 6 where D (7.480 ( T )) /( v ) with the initial conition at t 0, X X i. AV Integration of Eq. 3 yiels X ( t) X i exp 6 Sh D t (3) 54

10 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) Estimation of the Mass Transfer Coefficient at Stage The following assumptions are mae in the analysis to evaluate the quantity of issolve oxygen remove when the liqui emanates as a jet:. The jet is cylinrical in configuration.. The iffusion process occurs uner non-isothermal conitions of jet, i.e., the major resistance for iffusion is within the liqui jet an the resistance ecreases as jet temperature increases. 3. The resistance for the iffusion of oxygen from the interface of the jet to the steam environment is negligible. From the component continuity equation we obtain 4 D hb X ( t) t k, CA D hb (33) The empirical correlations for falling films in the laminar- wavy-, transition- an turbulent flow regime are liste as follows (Mayinger, 98): 4.6 Sh Sc for Re 70 an Sc.30 / Re (34a) 3 Sh Sc for 70 Re 400 an Sc.80 / Re (34b) 7.5 Sh Sc for Re 400 an.470 / Re (34c) Re Re Re.5 Sc Eq. 33 can be arrange an solve in conjunction with Eq. 34 for the initial conition t 0, X X i to give i 55 X ( t) X exp 4 Sh D t D (35) Eqs. 3 an 35 have been solve for ifferent values of inlet mass flow rates, eaerator lengths an inlet oxygen concentration in the experimental range an the results are presente here. A regression equation has been evelope, Eq. 36, for the estimation of the Sherwoo number in the experimental range of m 0. 5 kg/s, 350 / D 600 an. T / T. 4: N Sh Reg S i Re Sc D T T (36) N i N i N S i with an average eviation of.54% an stanar eviation of 3.84%. RESUTS AND DISCUSSION The temperature an concentration at the en of the first stage are evaluate using Eqs. 4 an 3, respectively, an the salient results presente. Figure 3 shows the effect of mass flow rate of e-aerator water on conensation heat transfer coefficient. It can be observe that an increase in the mass flow rate of the e-aerator water increases the heat transfer coefficients in the first an secon stages. The rate of increases are more in the first stage than in the secon ue to the higher temperature potential between the steam

11 Experimental investigations of oxygen stripping from fee water in a spray an tray type e-aerator an water. An increase in the e-aerator pressure an length of the secon stage has a negligible effect on the heat transfer coefficient. An increase in the non imensional roplet raius estimate with Eqs. 9 an 0 of Rao an Sarma (985) at the exit of the first stage, an that calculate with ata from experiments using energy balance Eq., are shown plotte in Figure 4. The close agreement between the two estimates, varying by less than %, ensures the reliability of the present ata. Figure 5 shows a comparison of the experimental heat transfer coefficients evaluate with the energy balance equation with those estimate with the theoretical analysis of Mochalova et al. (988) for the secon stage. A goo agreement of estimate values with experimental stuy is observe. Figure 3: Effect of mass flow rate of e-aerator water on conensation heat transfer coefficient estimate from theories of ifferent authors Figure 4: Comparison of first stage imensionless roplet raius r+ estimate with Eq. 0 at the exit with experimental ata 56

12 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) Figure 5: Comparison of experimental values of conensation heat transfer coefficients with values estimate using Eq. A comparison of the heat transferre from both stages estimate from the energy balance Eq. 5 with the values estimate using Eq. 5 shows goo agreement as can be seen from Figure 6. This valiates the heat transfer coefficients estimate with Eqs. an 6 for the first an secon stages, respectively. The overall conensation heat transfer coefficient of two stage spray an tray type e-aerator is foun to vary between 400 an 600 W/(m K). Values estimate from the regression Eq. 6 are shown in Figure 7, which is in goo agreement with the values evaluate with the energy balance equation, U Q A( T T ). E E / S i Figure 6: Comparison of total heat transfer estimate from theory with values from experiments 57

13 Experimental investigations of oxygen stripping from fee water in a spray an tray type e-aerator Figure 7: Comparison of the overall conensation heat transfer coefficients estimate using the regression equation with the experimental ata The increasing trens of mass transfer coefficients shown in Figures 8 an 9 for the first an secon stages of the e-aerator with an increase in the mass flow rate of water is similar to the increases in the heat transfer coefficient as can be seen from a comparison with Figure 3. The rate of increase is more in the first stage than in the secon ue to the higher concentration potential between steam an water. The increase in e-aerator pressure from 0. to 0. MPa enhances the mass transfer coefficient in the secon stage. This may be attribute to the squeezing of oxygen from the water at higher pressure. The increase in length of the secon stage has a negligible effect on the mass transfer coefficient. Figure 8: Effect of mass flow rate of e-aerator water on mass transfer coefficient uner ifferent operating conitions of the first stage 58

14 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) The variation of the Reynols number with Sh Sc for ifferent operating conitions in the secon stage of spray an tray type e-aerator is shown in Figure 0. The experimental values are in goo agreement with the values estimate with the equation of Bakopoulos (980) for the secon stage. However the author has not presente information as to the quantity of oxygen remove. The values of the Sherwoo number estimate with the regression equation is in goo agreement with the experimental values as shown in Figure emonstrating the valiity of the propose Eq. 36. The effect of e-aerator length on the variation of oxygen concentration in inlet water is shown in Figure. The oxygen concentration ecreases rapily initially in a length of 0.4 m an remains constant thereafter. Figure 9: Effect of mass flow rate of e-aerator water on mass transfer coefficient uner ifferent operating conitions of the secon stage Figure 0: Effect of Reynols number on Sherwoo Schmit prouct uner ifferent operating conitions of the secon stage 59

15 Experimental investigations of oxygen stripping from fee water in a spray an tray type e-aerator Figure : Comparison of Sherwoo number from regression equation with experimental values Figure : Effect of e-aerator length on oxygen concentration in fee water from theory an comparison with experiment ata Figure 3 shows a comparison of the values of oxygen remove ue to stripping with that calculate with theory using Eqs. 3 an 35 for the first an secon stages, respectively. It can be observe that the values obtaine from experiments are higher than the values preicte from theory. This may be ue to re-absorption of oxygen at the en of the secon stage for the flow rates conucte. Hence, the possibility of re- 60

16 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) absorption of oxygen cannot be prevente, if the height of the secon stage an liqui flow rates are not maintaine at the esign conitions. The re-entry of oxygen can be avoie if a separate secon stage is provie. Figure 3: Percentage of oxygen remove comparison of experimental values with theory CONCUSIONS The following conclusions can be rawn from the analysis of spray an tray type eaerators: a) The influence of the mass flow rate of water on the heat an mass transfer coefficients of both stages of the e-aerator are significant. b) There is no significant influence of e-aerator pressure on the heat transfer coefficients in both stages of the e-aerator c) An increase in length of the secon stage has no significant effect on the heat an mass transfer coefficients. ) Increases in e-aerator pressure from 0. to 0.MPa enhance the mass transfer coefficient in the secon stage by %. e) The oxygen removal rate from the fee water is large initially ue to large concentration ifference an ecreases slowly thereafter. f) Mayinger s empirical correlations can be use to estimate the Sherwoo numbers of the first an secon stages. g) Regression Eqs. 6 an 36 can be use for the estimation of heat an mass transfer coefficients useful in the esign of the e-aerator. h) The preicte values of oxygen concentration are higher than the experimental values. 6

17 Experimental investigations of oxygen stripping from fee water in a spray an tray type e-aerator ACKNOWEDGEMENTS The financial support by the Universiti Malaysia Pahang an Sri V. Satyener, Secretary of Sri Venkateswara Engineering College, Suryapet, Inia are gratefully acknowlege. REFERENCES Bakopoulos, A. (980) iqui sie controlle mass transfer in wette-wall tube. German Chemical Engineering, 3: 4 5. Brown, G. (95) Heat transmission by conensation of steam on a spray of water rops. Proceeings of General Discussion on Heat Transfer, Institute of Mechanical Engineering,pp Celata, G.P., Cumo, M., D Annibale, F. an Farello, G.E. (99) Direct contact conensation of steam on roplets. International ournal of Multiphase Flow, 7(): 9. Celata, G.P., Cumo, M., Farello, G.E. an Focari, G. (989) A Comprehensive analysis of irect contact conensation of saturate steam on sub coole liqui jets. International ournal of Heat an Mass Transfer, 3(4): Dombrowski, N. an Munay, G. (967) Biochemical an Biological Engineering Science, onon: Acaemic Press. For,.D. an ekic, A. (97) Rate of growth of rops uring conensation, International ournal of Heat an Mass Transfer, 6: Hinze,.O. (955) Funamentals of the hyroynamic mechanism of splitting in ispersion processes. American Institute of Chemical Engineers ournal, (3): ee, S.Y. an Tankin, R.S. (984) Stuy of liqui spray (water) in a conensable environment (steam). International ournal of Heat an Mass Transfer, 7(3): Mayinger, F. (98) Strömung un Wärmeübergang in Flüssigkeitsgemischen. Berlin: Springer Verlag. Mayinger, F. an Chavez, A. (99) Measurement of irect-contact conensation of pure saturate vapor on an injection spray by applying pulse laser holography. International ournal of Heat an Mass Transfer, 35(3): Mills, A.F., Kim, S., eininger, T., Ofer, S. an Pessran A. (98) Heat an Mass Transport in Turbulent iqui ets. International ournal of Heat an Mass Transfer, 5(6): Mochalova, N.S., Kholpanov,.P. an Malyusov, V.A. (988) Heat transfer in vapor conensation on laminar an turbulent liqui jets taking account of the inlet section an variability of the flow rate over the jet cross section. Institute of New Chemical Problems, Acaemy of Sciences of USSR, Moscow, 54(5): Nosoko, T., Miyara, A. an Nagata, T. (00) Characteristics of falling film flow on completely wette horizontal tubes an the associate gas absorption. International ournal of Heat an Mass Transfer, 45: Rao, V.D. an Sarma, P.K. (985) Direct contact heat transfer in spherical geometry associate with phase transformation a close-form solution. International ournal of Heat an Mass Transfer, 8(0):

18 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) Steinberger, R.. an Treybal, R.E. (960) Mass transfer from a soli soluble sphere to a flowing liqui stream. American Institute of Chemical Engineers ournal, 6: 7 3. Sunararajan, T. an Ayyaswamy, P.S. (987) Conensation on a moving rop: Effect of time epenent rop velocity. Proceeings of the 8 th National Conference on Heat an Mass Transfer, Visakhapatnam, Inia, pp Takahashi, M., Arun Kumar, N., Kitagawa, S.I. an Murakoso, H. (00) Heat Transfer in irect contact conensation of steam to subcoole water spray. International ournal of Heat an Mass Transfer, 3: NOMENCATURE A total surface area for heat transfer, m A 0 cross sectional area of nozzle orifice, m B parameter efine in Eq. 6b C parameter efine in Eq. 6a C A concentration of oxygen, (= X ) kg/m 3 C P specific heat, /kg K roplet iameter, m D iameter of the spray nozzle or jet, m D iffusion coefficient or iffusivity of oxygen in water, m /s E parameter efine in Eq. 9 f f parameters efine in Eq. 6a f 3 FN flow number, m 3 /[s (N/m ) / ] Fr Froue number g local acceleration of gravity, m/s Gr Grashof number, g 3 ) h heat transfer coefficient, W/ m K H latent heat of conensation, / kg fg ( V a acob number of liqui at inlet, C P ( TS Ti ) / H fg k mass transfer coefficient, m/s length, m B sheet break-up length, m hb hyraulic break-up length of the jet, m m mass flow rate of water, kg/s m C mass flow rate of conensate, kg/s P D e-aerator pressure, N /m P pressure rop across the nozzle, N /m Pr Prantl number of liqui jet in stage, q parameter efine in Eq. 0 Q heat transfer, W r time epenent raius of the roplet, m r raius of the roplet at time zero, m 0 63

19 Experimental investigations of oxygen stripping from fee water in a spray an tray type e-aerator r imensionless variable raius of the roplet, r r0 r imensionless raius of the roplet uring conensation con R I inner raius of sheet, RO s, m R O outer raius of sheet, S sin 30, m Re roplet Reynols number, V / V / Re Reynols number of liqui jet in stage for mass transfer, H V D Re Reynols number of liqui jet in stage for heat transfer, Sc Schmit number, / D S slant height, m Sh initial Sherwoo number 0 Sh roplet Sherwoo number, k, D Sh Sherwoo number of the liqui jet, k, D St Stanton number, h T V CP t resience time, s T temperature, K T AV average temperature, ( T T ) / O i, K U overall heat transfer coefficient, W/m K v volume of liqui, m 3 v molecular volume of oxygen, m 3 / kg-mol A V Velocity of liqui, m/s We Weber number of liqui, V D X mass fraction of O in water, ppb Greek symbols thermal iffusivity, m /s coefficient efine in Eq. 0 volumetric flow rate per jet perimeter, m /s imensionless time, 4 t 3 Nusselt film thickness (= ( 3 / g) s sheet thickness, m kinematic viscosity, m /s viscosity, kg /m s ensity, kg/m 3 ), m 3 surface tension, T Subscripts i, N / m A AV C oxygen or non-conensable gas average conensate 64

20 K.V. Sharma et al. / International ournal of Automotive an Mechanical Engineering (00) con conensation E energy balance EXP experiment roplet H heat transfer i inlet jet liqui N nozzle o outlet Reg regression equation s sheet S saturation t tray T theoretical V water vapour 0 initial first stage secon stage 65