WATER AERATION USING FINE AIR BUBBLES GENERATORS

Transcription

1 WATE AEATION USING FINE AI BUBBLES GENEATOS Beatrice TĂNASE, areş PĂUN, Nicolae BĂAN, Giovani OZA Politehnica Univerity of Bucharet, Faculty of Mechanical and Mechatronic Engineering, Bucharet, omania Abtract. For efficient water aeration, it i neceary to contruct fine air bubble generator in which the main element i the plate with orifice for the introduction of air into the water. The reearch team contructed a fine bubble generator having orifice with Ø. mm, which can be obtained by park-eroion or micro-drilling. An experimental plant ha been deigned and built to ee how the generator operate and the preure lo that occur when the air pae through it. The theoretical and experimental reearch on increaing the diolved oxygen concentration in water led to atifactory reult. Keyword: water aeration, fine air bubble generator.. INTODUCTION Bubble aeration device can be claified into three major categorie, a follow: I. Fine bubble generator made of ceramic, platic; II. Fine bubble generator made of perforated elatic membrane; III. Fine bubble generator with perforated plate made with coordinate micro drilling machine with Ø <. mm drill. Fine air bubble are obtained by dipering air in the water; conequently the water aeration equipment include: A) Compreor or blower; B) Air tranport and ditribution pipeline; C) Meauring and control device to enure the proper functioning of the aeration ytem; D) Air dipering device in water; thee device are porou media of variou hape: circular plate, rectangular plate, tube, panel, dome or elatic membrane. Oxygen tranfer into watewater i an important problem in ewage technology; the ue of fine bubble aeration optimize the amount of introduced air, reulting in ignificant energy aving. Fine air bubble are obtained with the ue of fine bubble generator (F.B.G.) made of ceramic material; thee type of generator are known in the literature [] a porou ceramic diffuer. The ue of porou diffuer in ceramic ha the following diadvantage: The emiion of air bubble take place through air bubble of unequal diameter; Air bubble appear irregularly only on certain portion of the porou diffuer area; Porou diffuer exhibit high preure loe. In recent year, reearche on water oxygenation ha been geared toward obtaining fine bubble generator at which air to water inlet have a diameter of d < mm. F.B.G. with the perforated plate made an unconventional proce (park-eroion) wa contructed; thi proce enure a uniform ditribution of the orifice on the plate urface and an equal diameter of the orifice. The contruction olution of F.B.G. made by park-eroion and their performance are preented in the paper [] []. The orifice ize i a critical parameter of the F.B.G. becaue it directly affect the air preure inlet in the F.B.G. The air preure at the entrance to the fine bubble generator i a very important parameter in the election, evaluation and monitoring of fine bubble generator, regardle of the hape or material from which it i built.. FINE BUBBLE GENEATOS MADE BY MICO-DILLING In the laboratorie of Politehnica Univerity of Bucharet were deigned and built fine bubble generator (F. B. G.) on which the orifice plate i made by park-eroion (Ø <. mm). In thi cae, the orifice are equal and evenly ditributed in the xoy plane. TEMOTEHNICA /7 69

2 Beatrice TĂNASE, areş PĂUN, Nicolae BĂAN, Giovani OZA Two type of technologie can be ditinguihed for performing orifice in the microbubble generator plate (M.B.G.): I) Micro technologie machining that can create orifice of Ø> μm; II) Nanotechnologie machining producing orifice of Ø < μm; It i known from the literature [4][] that with the reduction of the air bubble diameter, the oxygen tranfer rate to the water i higher; the diameter of the air bubble i a function of the orifice diameter in the perforated plate of M.B.G. The ga bubble immered in water come from the following ource: Atmopheric air (% O + 79% N ); Atmopheric air + oxygen from the cylinder; Low nitrogen-containing air (oxygen concentrator). Thee ga bubble can be claified a follow (Fig. ): Ø increae O cre?te m m mm mm mm Microbubble Bule bubble fine Bule bubble medii Bule bubble groiere Bule bubble foarte Fine Medium Nanobubble Croae Large Nanobule Microbule mari I II III Fig.. Claification of ga bubble according to their diameter (Ø) I - the area where the ga bubble can be oberved under the microcope; II - the area where ga bubble can be oberved with difficulty; III - the area where ga bubble can be oberved with the naked eye. The paper preent a microbubble air generator, in which the plate ha orifice with d = μm. A a reult of the reearch in the field of micro technologie, air bubble can be called "micro bubble".. CONSTUCTION OF THE FINE BUBBLE GENEATO To obtain fine bubble or microbubble, the diameter of the orifice hould be a mall a poible (d < mm) and the ditribution of the orifice in the plate hould be uniform. Thee two condition can be achieved with the help of advanced technologie or modern microproceing technologie [6] [7] [8]: Spark eroion proceing; Electrochemical proceing; Laer proceing; Electron beam proceing; Drill in coordinate, with Ø. mm drill. The microbubble generator ha a diperion element, a metal plate of rectangular hape, which i called M.B.G. Figure how a plan view of M.B.G. of rectangular hape. Figure how the contructive olution of the microbubble generator (M.B.G.) to be ued in experimental reearche. The orifice in the perforated plate were made by micro drilling machine KEN Micro. Thi machine ha an accuracy of ±. μm and can proce part with a height of mm and a diameter of mm. A 4 6 A-A d =. mm 8 A d= a) b) Fig. 4. M.B.G. perforated plate: a) plan view; b) cro ection. 7 TEMOTEHNICA /7

3 ASSESSMENT METHODS THEMODYNAMICS OF COGENEATION PLANTS Compreed air Fig.. Air microbubble generator: - compreed air tank; - ealing gaket; - the orifice plate; 4 - Ø 8 mm pipe with compreed air; - connection for the meaurement of the air preure in the tank; 6 - perforated plate fatening crew. In order to achieve thi M.B.G., which i an original contructive olution, it took a theoretical and experimental work revealed by [9] []. In the cae of the tudy, the air i continuouly introduced into the tank for ', o the regime i non-tationary, the diolved oxygen concentration will increae in time. In non-tationary regime, the meaured amount will be the concentration of oxygen in water in time. Meaurement: water and air temperature, ga flow rate at the tank inlet and ga preure in the M.B.G. body. The tank i hown in Figure 4. Compreed air Fig. 6. Water tank into which the microbubble generator i inerted; the generator i fixed: V =.7 m ; VHO =. m ; tranparent plexigla tank; microbubble generator (M.B.G.); air upply pipe. 4. THE DEVELOPMENT OF A POGAM FO CALCULATING THE FUNCTION C = f (τ) FO DIFFEENT COMPOSITIONS OF THE GAS INJECTED INTO THE WATE The equation of the oxygen tranfer rate in water i []: L C C C C e a k ( ) () In thi equation mut be known: C the initial concentration of diolved O in water; C diolved O aturation concentration in water for a given water temperature; ak L the oxygen tranfer volumetric coefficient [ - ] or [min - ] determined by one of the chemical, electrical method. The value of C = f (τ) i calculated on the bai of a calculation program decribed in Figure. The operation of M.B.G. of rectangular hape with orifice of Ø. mm i hown in Figure 6. M.B.G. i provided with a perforated plate, with Ø. mm orifice performed by micro drilling.. COMPAISON OF THE THEOETICAL ESULTS WITH THE EXPEIMENTAL OBTAINED DATA Following the computation program in Figure, a erie of data reulted. Baed on thee data, the curve () of Figure 7 wa plotted. After the experimental reearch, the curve () of Figure 7 wa plotted. TEMOTEHNICA /7 7

4 WATE AEATION USING FINE AI BUBBLES GENEATOS STAT dy Define: f ( x, y) dx dc ak L ( C C d ) ead: C =.84 mg/dm ; C =8.4 mg/dm ; a k L =.47; h= ; τ= min i ; x C C ; akl i Ci C C Ci e x x h i i Fig. 9. Diolved O concentration for atmopheric air: curve baed on theoretical data; - curve baed on experimental data. Nu i 4 Da H eult STOP Fig. 7. Logical diagram for the function: C = f(τ). Fig. 8. Scheme for meaurement: water tank; compreed air inlet connection; the plate orifice; 4 digital thermometer; - digital indication manometer; 6 - MBG body. 6 Between the curve and of Figure 7 a atifactory concordance i oberved. 6. PESSUE LOSSES AT POOUS CEAMIC GENEATOS The orifice being ditributed in parallel, the lo of preure on each will be equal. Figure 8 how a chematic diagram for determining preure loe at the MBG [9]. The compreed air preure in the tank (6) i p and it mut cover: p ph pt pp () Fig. 8. M.B. G. with orifice Ø. mm in operation. p H hydrotatic load, H = mm H O; Δp t lo of preure to overcome uperficial tenion; Δp p the preure drop that occur when the air pae through the orifice to the dry plate. From experimental meaurement reulted: p = 8 mmh O; p H = mmh O. 7 TEMOTEHNICA /7

5 ASSESSMENT METHODS THEMODYNAMICS OF COGENEATION PLANTS Overpreure required for bubble formation [][]: pt () σ the urface tenion of water / air at C, the value of σ i: σ = 7 N / m. the radiu of the bubble when it i detached from the orifice plate. Note: d = r and D = ; D =. m; ρ HO = kg / m. Air denity i determined from the tate equation []: p kg / m (4) T kg / m D HO 6d aer D [m] g.8 m () The relation () become: 7 p t N / m p g h N / m t HO t p 78.4 t ht 8.4 m HOg 9.8 Equation () become: t (6) h 8.4 mmh O (7) p p (8) h mmh O (9) t The firt term to the right of equation (8) i the overpreure required to overcome the hydrotatic load, the econd to overcome the uperficial tenion and the third refer to the required preure for an air bubble in the compreed air tank of MBG to pae through the plate into the water volume.. CONCLUSIONS. The paper preent a new type of microbubble (MBG.) which ha the following advantage compared to porou diffuer made of ceramic material [9]: Provide a uniform ditribution of air bubble in the water body. All bubble emitted by the microbubble have the ame diameter. The preure lo of air paage through thi type of MBG i lower than at porou diffuer.. The contruction of a microbubble generator, where the perforated plate ha orifice with Ø μm, i a firt in the field of water aeration.. With a maller diameter of the air bubble in the water, ak L will increae, o it will increae the oxygen tranfer rate to the water; 4. The paper [] compare the theoretical and experimental reult for fine bubble generator, where the perforated plate ha orifice Ø<.mm, it i hown that the mot efficient generator i the one with the mallet orifice diameter.. The lo of preure in a porou diffuer i. mh O [], and at a MBG i.64 mh O; a a reult, the energy conumed for compreed air i much lower in the cae of MBG. 6. The theoretical and experimental reearch preented above lead to a very good concordance (Figure 7), which reveal the correctne of thee reearche. EFEENCES [] G. Oprina, I. Pincovchi, Ghe. Băran, Hidro-Gazo- Dinamica Sitemelor de aerare echipate cu generatoare de bule, Ed. POLITEHNICA PES, Bucureşti, 9. [] G. Mateecu, Hidro-gazodinamica generatoarelor de bule fine, Teză de doctorat Facultatea de Inginerie Mecanică și Mecatronică, Univeritatea POLITEHNICA din București,. [] Al. S. Pătulea, Influenţa parametrilor funcţionali şi a arhitecturii generatoarelor de bule fine aupra eficienţei intalaţiilor de aerare, Teză de doctorat, Univeritatea Politehnica din Bucureşti,. [4] G. Mateecu, A. Marinecu, N. Băran, A new Contructing Fine Buble Generator, Bulletin Of The Tranilvania Univerity Of Braşov, vol., 9, pp.9-67, Braov. [] N. Băran, Gh. Băran, G. Mateecu, eearch egarding a New Type of Fine Bubble Generator, evita de Chimie, vol.6, nr.,, pp [6] I. Gavrilaș, N. I.Marinecu, Prelucrări neconvenționale în contrucția de mașini, Editura Tehnică, București, 99. [7] A. Nanu, Tehnologia materialelor, Editura Didactica și Pedagogică București 977. [8] N. Ceaușecu, I. Popecu, Tehnologii neconvenționale, Editura Scriul omânec, Craiova, 98. [9] M. Contantin, N. Băran,. Păun, G. oza, Theoretical and Experimental eearch about the Preure Lo of a New Type of Fine Bubble Generator, International Journal of Emerging eearch in Management & Technology, ISSN 78-9, Volume 6, 7, pp. -. [] Al. Pătulea, I. M. Căluşaru, N. Băran, eaearche regarding the meaurement of the diolved concentration in water, Advanced Material eearch, Tran Tech Publication, Switzerland, vol. -,, pp [] Al. Dobrovicecu, N.Băran, și col., Colecția Bazele Termodinamicii tehnice, vol. I Elemente de termodinamică tehnică, Editura POLITEHNICA PESS, București, 9. TEMOTEHNICA /7 7