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Rectangular tank surface aerators: scale up criteria and energy conservation

  • A. R. Rao
  • B. Kumar
Article
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Abstract

Surface aeration experiments were conducted in two types of rectangular tanks of aspect ratios i.e., length to width ratio (L/W) of 1.5 and 2 and developed simulation equations to correlate the oxygen transfer coefficient, k and power number, P0 with a parameter governing theoretical power per unit volume X. The parameter X is defined as equal to F4/3R1/3, where F and R are impellers’ Froude and Reynolds numbers respectively). Results have shown that the P0 can not be simulated singularly with either Reynolds number, R or Froude number, F, which results in scale-effects; there appears to be a need to incorporate the effects of both F and R. It was found that P0 is uniquely related to X for rectangular aeration tanks of both aspect ratios, however, such relationships are different depending upon the aspect ratios. It has been demonstrated that energy can be saved substantially if the aeration tanks are run at relatively higher input powers. It is also demonstrated that smaller sized tanks are more energy conservative and economical when compared to big sized tanks, while aerating the same volume of water, and at the same time by maintaining a constant input power in all the tanks irrespective of their size.

Keywords

Froude number oxygen transfer coefficient power number power per unit volume Reynolds number surface aerators water and wastewater treatment 

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References

  1. Cook, A. L. and Carr, C. C., (1947). Elements of electrical engineering. 5uh. Ed. Wiley. New York.Google Scholar
  2. Grisafi, F., Brucato, A. and Rizzuti, L., (1994). Solid liquid mass transfer coefficients in mixing tanks: influence of side wall roughness. Instn Chem. Engn Symp. Ser., 136, 571–578.Google Scholar
  3. Holland, F., (1964). Scale-up in chemical engineering, Chem. Proc. Eng., 45, 1214.Google Scholar
  4. Hsieh, Ch. Ch., (1991). Estimating volatilization rates and gas/liquidmass transfer coefficients in aeration systems. Ph.D. thesis, Dept. of Civil Engg., University of California, Los Angeles, USA.Google Scholar
  5. Johnstone, R. E. and Thring, M. W., (1957). Pilot plants, models and scale-up methods in chemical engineering. New York, McCraw-Hill Book Company, Inc.Google Scholar
  6. Johnson, A. I. and Huang, Ch. J., (1956). Mass transfer studies in an agitated vessel. AICHE J., 2, 412–419.CrossRefGoogle Scholar
  7. Lee James, M., (1992). Biochemical engineering, Prentice Hall.Google Scholar
  8. Lewis, W. K. and Whitman, W. G., (1924). Principles of gas absorption. Ind.Eng. Chem., 16(12), 1215–1220.CrossRefGoogle Scholar
  9. Maise G., (1970). Scaling methods for surface aerators. J. sanitary engg. Division, ASCE SA5, 1079–1083.Google Scholar
  10. Perry, R. H., Green, D.W. and Malony, J.O., (1984). Perry’s Chemical Engineers’ Handbook, 6th. Ed., McGraw-Hill, New York.Google Scholar
  11. Rao, A. R. K., (1999). Prediction of reaeration rates in square, stirred tanks. Journal of Environmental Engineering, ASCE, 125(3), 215–233.CrossRefGoogle Scholar
  12. Rao, A. R. K., Bharathi, B.V., Laxmi and Subba Narasiah, K., (2004). Simulation of oxygen transfer rates in circular aeration tanks. Water Qual. Res. J. Canada, 39(3), 237–244.Google Scholar
  13. Rao, A. R. K. and Jyothish. S., (1997). Oxygen transfer in circular surface aeration tanks with and without Baffles, The International Conference on Industrial Pollution and Control Technologies, held at Jawaharlal Nehru Technological University (JNTU), Hyderabad, India, Nov. 17–19.Google Scholar
  14. Rushton J. H., (1952). Applications of fluid mechanics and similitude to scale-up problems-part1. Chem. Engg. Progress. 48, 33–38.Google Scholar
  15. UdayaSimha L., Shrma K. V. N. S. and Rao A. R. K., (1991). Effect of geometrical parameters for overall Oxygen transfer coefficient. Proc. Symp. On Environmental Hydraulics, University of Honkong, 1577–1581.Google Scholar
  16. WEF and ASCE Manual of practice for water pollution control (1988). Aeration a waste water treatment process. Water Environment Federation, Alexandria, Va., and ASCE, New York.Google Scholar

Copyright information

© Islamic Azad University 2006

Authors and Affiliations

  1. 1.Department of Civil EngineeringIndian Institute of ScienceBangaloreIndia

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