Marcio Ricardo Salla                    Leonardo Vieira Soares                     José Eduardo Alamy Filho
Luiz Antonio Daniel                         Harry Edmar Schulz

1 Faculdade de Engenharia Civil. Universidade Federal de Uberlândia. Av. Engenheiro Diniz, 1178 - Cx. Postal: 593 - CEP: 38.400-902. Uberlândia. Minas Gerais. Brazil. E-mail: mrsalla@feciv.ufu.br; zeedu@feciv.ufu.br

2 Faculdade de Engenharia de São Carlos. Universidade de São Paulo. Av. Trabalhador Sãocarlense, 400 - Caixa Postal 359 - CEP: 13566-590. São Carlos. São Paulo. Brasil. E-mail: lvsoares@uol.com.br; ldaniel@sc.usp.br; heschulz@sc.usp.br

La sección transversal de una columna de ozonización posee influencia directa sobre las características hidrodinámicas de esa columna, lo que refleja en los fenómenos que dependen de la transferencia de masa en la interfase gas-líquido. En este estudio se utilizaron dos columnas con secciones transversales diferentes cuanto a la forma y al tamaño. La primera con sección transversal cuadrada de 0,19m y la segunda con sección transversal circular de 0,10m de diámetro. Se midieron las velocidades ascensionales de las burbujas y su concentración. Los resultados obtenidos muestran que el  aumento de la sección transversal en la proporción aquí estudiada no conlleva un aumento semejante de la sección transversal de la pluma ascendentes de burbujas, cuando son computadas las velocidades y concentraciones medias. Los resultados de velocidad media y de concentración media para la columna de sección más pequeña se mostraron independientes de la altura del líquido, mientras que los resultados de velocidad media y de concentración media obtenidos para la columna de sección más grande mostraron dependencia con la altura del líquido. La evolución de la razón de las áreas de la pluma a lo largo del eje longitudinal de las columnas se presenta y muestra  que esta razón disminuye en la dirección del tope de las columnas.

Palabras clave: Ozono, velocidad a láser no intrusiva, transferencia de masa gas-líquido, columna de burbujas, difusor.

ABSTRACT

The size of the cross section of an ozonization column influences its hydrodynamic characteristics, which, on its turn, has effects on phenomena that depend on the relative movement between gas bubbles and liquid. To observe the influence of the cross sectional area on gas concentration and bubbles velocity, two columns were used. The first column had a square cross section with side of 0.19m and the second had a circular cross section with diameter of 0.10m. The ascendant velocities of the bubbles and their concentration were measured in both columns and compared. The transversal spread of the plumes of bubbles was also quantified. The results show that the increase of the cross section of the column, in the proportion studied here, does not result in a similar increase of the cross section of the ascending plume of bubbles. Furthermore, the results of average velocities and concentrations obtained for the smallest cross section resulted independent of the liquid level in the column, while the results for the largest cross section showed to be dependent of this level. The ratio between the cross sectional areas of the larger and the smaller plumes of bubbles decreases for higher distances to the bottom of the columns.

Keywords: Ozone, non-intrusive laser velocimetry, gas-liquid mass transfer, bubble columns, diffuser.

ACKNOWLEDGMENTS

The authors wish to thank FAPESP (processes 01/13586-6 and 02/13378-7), CAPES (process 2201/06-2) and Faculdade de Engenharia Civil/Universidade Federal de Uberlândia, for the support of this research line.

REFERENCES

[1] S.S. Alves, C.I. Maia and J.M.T. Vasconcelos. "Gas-liquid mass transfer coefficient in stirred tanks interpreted through bubble contamination kinetics". Chemical Engineering and Processing. Vol. 43 Nº 7, pp. 823-830. 2004.

[2] A.K. Bin, B. Duczmal and P. Machniewski. "Hydrodynamics and ozone mass transfer in a tall bubble column". Chemical engineering science. Vol. 56 Nº 21, pp. 6233-6240. 2001.

[3] C.K.Z. Innocentini. "Estudo da transferência de oxigênio da fase gasosa para a fase líquida, usando difusor cerâmico poroso". Ph.D. Thesis, Universidade de São Paulo. São Carlos, Brazil. 1996.

[4] K.S. Jun and S.C. Jain. "Oxygen transfer in bubbly turbulent-shear flow". Journal of Hydraulic Engineering. Vol. 119 Nº 1, pp. 21-36. 1993.

[5] J. Levec and S. Pavko. "Mass transfer in square gas-liquid contractors". Chemical Engineering Science. Vol. 34, pp. 1159-1160. 1978.

[6] M. Motarjemi and G.J. Jameson. "Mass transfer from very small bubbles - The optimum bubble size for aeration". Chemical Engineering Science. Vol. 33, pp. 1415-1423. 1978.

[7] R.H. Perry and D.W. Green. "Perry's Chemical Engineers - HandBook". Sixth Edition. McGraw Hill. New York. 1984.

[8] P.C. Singer and C.S. Hull. "Modeling Dissolved Ozone Behavior in Ozone Contactors". AWWA Research Foundation and American Water Works Association. Denver. 2000.

[9] L.V. Soares. "Ozonização de esgoto sanitário: estudo da hidrodinâmica, transferência de massa e inativação de microrganismos indicadores". Ph.D. Thesis. Universidade de São Paulo. São Carlos, Brazil. 2007.

[10] R.E. Treybal. "Mass transfer operations".Third edition. McGraw-Hill Book Company. London. 1980.

[11] H. Zhou, D.W. Smith and S.J. Stanley. "Modeling of dissolved ozone concentration profiles in bubble columns". Journal of Environmental Engineering. Vol. 120 Nº 4, pp. 821-840. 1994.

[12] H. Zhou and D.W. Smith. "Ozone mass transfer in water and wastewater treatment: Experimental observations using a 2D laser particle dynamics analyzer". Water Research. Vol. 34 Nº 3, pp. 909-921. 2000.