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 (Ph.D. Candidate, Water Engineering Departments Islamic Azad university, Science and research Branch, Tehran, Iran.)
Amir Khosrojerdi ² (Associate Professor, Water Engineering Departments Islamic Azad university, Science and research Branch, Tehran, Iran.)
Ali Saremi 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.

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