Reduction of cavitation in the hydraulic jump pond of the cooling tower by stepping the end sill

Subject Areas : Hydrology, hydraulics, and water transfer buildings

Ehsan Behjati ¹ , Amir Khosrojerdi ² , Ali Saremi ³

1 - Ph.D. Candidate, Water Engineering Departments Islamic Azad university, Science and research Branch, Tehran, Iran.
2 - Associate Professor, Water Engineering Departments Islamic Azad university, Science and research Branch, Tehran, Iran.
3 - Assistance Professor, Water Engineering Departments Islamic Azad university, Science and research Branch, Tehran, Iran.

Received: 2022-07-09 Accepted : 2023-08-12 Published : 2023-04-21

Keywords: hydraulic jump, static pressure, Cooling water, cavitation,

Abstract :

Introduction: Cooling towers are an important and vital part of industrial units that are used for water cooling that is used in the cooling processes of systems in power plants, refineries and other industrial units. One of the important components of towers is the relaxation pool, the main role of which is to collect water for transfer to the system, the number of suction pools is usually designed according to the number of each pump. One of the important tasks of the relaxation pool structure in this structure is energy dissipation. In this regard, usually in this pond, the hydraulic structure of the hydraulic jump is used for energy dissipation. In the hydraulic jump process, the current changes from supercritical to subcritical. This causes a loss of flow energy. In cooling ponds, downstream slope is usually used to control the hydraulic jump. In cooling ponds, downstream slope is usually used to control the hydraulic jump. Various studies have shown that using stairs instead of ramps can greatly increase energy loss in the relaxation pool. In this study, by replacing the stepped surface with a sloping surface, the effects of this process on flow lines as well as its effects on cavitation are investigated.Method: In this research, the Fluent numerical model is used to numerically model the flow around the structure of the cooling tower calm pond. In this regard, the dimensions of the relaxation pool in the concrete cooling tower are very important from an engineering point of view and should be designed in such a way that the operating conditions of the pumps are safe. Existence of high velocities and pressure drop in the dischargers causes serious problems related to the occurrence of cavitation phenomenon. Since modeling a physical model usually requires a lot of time and money, a numerical model calibrated with laboratory data was used to follow this research. In this study, due to the recognition of destructive eddy currents created around the lower valve when the valve is opened, hydraulic optimization of the relaxation pool and the appropriate width of the relaxation pool in refineries is one of the objectives of this study.Results: The study of increasing the flow in numerical modeling showed that with increasing the flow due to the increase in energy loss due to the stepping of the end threshold, the water height in the calm pool decreases significantly. This drop is estimated at an average of about 67%. Also, the results of water level profiles showed that the threshold of the end of the pond in a stepped manner, has a greater drop than the sloping conditions. Also, in exchange for higher discharges, this drop will move to higher values. Therefore, in the numerical model, the flow conditions on the stairs were analyzed at minimum and maximum flow. Regarding the study of pressure drop in the relaxation pool, it can be stated that the development of flow in the pool section based on increasing the width and height of the duct increases the amount of velocity during the discharge, which has led to pressure drop. Conclusion: The results of the study of cavitation number along the pond indicate that for the ratio of water depth to the width of the pond less than 1.82, the possibility of cavitation during the pond will be reduced. Also, depleting blocks in the pond have a positive effect on improving hydraulic performance, which leads to increased energy dissipation and jump stabilization, reduced speed, length, height of hydraulic jump and also reduces the risk of cation compared to the case without depleting blocks.

References:

Abbaspour A, Hosseinzadeh Dalir A, Farsadizadeh D, Sadraddini AA (2009). Efect of sinusoidal corrugated bed on hydraulic jump characteristics. J Hydro Environ Res Elsevier B.V 3(2):109–11.
Alfatlawi, T. J., & Alshaikhli, H. I. (2015). Prediction the coefficient of discharge for stepped morning glory spillway using ANN and MNLR approaches. International Journal of Civil and Environmental Engineering, 37(2), 1701-8285.
Baharvand, S., Jozaghi, A., Fatahi-Alkouhi, R., Karimzadeh, S., Nasiri, R., & Lashkar-Ara, B. (2021). Comparative study on the machine learning and regression-based approaches to predict the hydraulic jump sequent depth ratio. Iranian Journal of Science and Technology, Transactions of Civil Engineering, 45(4), 2719-2732.
Campbell, F. B., and B. Guyton. (1953). Air demand in gated outlet works.” In Proc., 5th IAHR Congress. A Joint Meeting of Int. Association for Hydraulic Research and Hydraulics Div., 529–533. Reston, VA: ASCE.
Dettmers, D. (1953). Beitrag zur Frage der Belüftung von Tiefschützen (A Contribution to the Aeration of High-head Gates). [In German.]
Hannover, Germany: Franzius-Institut Technische Hochschule.
Hager WH, Bremen R, Kawagoshi N (1990) Length of rollerRessaut hydraulique classique: Longueur du rouleau. J Hydraul Res 28(5):591–608.
Hannover. Douma, H. 1955. “Hydraulic design criteria for reservoir outlets. In Proc., 6th IAHR Congress, 1–20. Reston, VA: ASCE.
Falvey, H. T. 1980. Air-water hydraulic flow in structures. Engineering Monograph No. 41. US Dept. of the Interior. Denver: Water and Power Resources Service.
Finnemore, E., Franzini, J. (2002). Fluid mechanics with engineering applications. New York: McGraw-Hill, 2002.
Fiorotto, V., & Rinaldo, A. (1992). Turbulent pressure fluctuations under hydraulic jumps. Journal of Hydraulic Research, 30(4), 499-520.
Hohermuth, B. (2019). Aeration and two-phase flow characteristics of low-level outlets. VAW-Mitteilung 253, edited by R. M. Boes. Zurich, Switzerland: ETH Zurich.
Hohermut, B. Schmocker, L. Boes, R. M. (2020). Air demand of low-level outlets for large dams. Journal of Hydraulic Engineering, 146(8), 04020055, https://doi.org/10.1061/(ASCE)HY.1943-7900.0001775.
Hughes W, C., Flack, J, E., (1984). Hydraulic jump properties over a rough bed. J Hydraul Eng 110(12):1755–1771.
Jesudhas, V., Balachandar, R. (2019). Turbulent shear flow in symmetric spatial submerged hydraulic jump. 11th International Symposium on Turbulence and Shear Flow Phenomena (TSFP11) Southampton, UK.
Kindsvater, C, E., (1944). The hydraulic jump in sloping channels. Transactions of the American Society of Civil Engineers, 109(1), 1107-1120.
Liu, Z. P., Guo, X. L., Xia, Q. F., Fu, H., Wang, T., & Dong, X. L. (2018). Experimental and numerical investigation of flow in a newly developed vortex drop shaft spillway. Journal of Hydraulic Engineering 144(5), 04018014.
Sabeti, P., Karami, H., & Sarkardeh, H. (2019). Analysis of the Impact of Effective Length of Morning Glory Spillway on Its Performance (Numerical Study). Journal homepage: http://iieta. org/journals/i2m 18(2), 211-221.‏
Savage, B. M., & Johnson, M. C. (2001). Flow over ogee spillway: Physical and numerical model case study. Journal of hydraulic engineering 127(8), 640-649.
Sualaheldin, T. M., Imran, J., & Chaudhry, M. H. (2004). Numerical modeling of three-dimensional flow field around circular piers. Journal of Hydraulic Engineering 130(2), 91-100.
Salehi, S., Mostaani, A., & Azimi, A. H. (2021). Experimental and Numerical Investigations of Flow over and under Weir-Culverts with a Downstream Ramp. Journal of Irrigation and Drainage Engineering, 147(7), 04021029.
Salehi, S., & Azimi, A. H. (2022). Effects of spoiler and piggyback on local scour under single and twin submerged pipes. Ocean Engineering, 261, 112137.
Vischer, D., and Hager, W. H., (1998). Dam hydraulics. Chichester, UK: Wiley.
Yakhot, V., & Smith, L. M. (1992). The renormalization group, the ɛ-expansion and derivation of turbulence models. Journal of scientific computing 7(1), 35-61.‏