Analysis of aeration efficiency of dissolved oxygen through hydraulic jump in rectangular channel

Abstract

The amount of dissolved oxygen (DO) content in a water body is one of the most important parameters to determine the water quality and hence a measure of the ability of water to sustain aquatic life. Micro-organisms such as bacteria need a high concentration of oxygen in the water to the ability to continue their lives healthfully. In this case, the concentration of the DO in the water body should be greater than 5 mg/l. A hydraulic jump is formed whenever there is a rapid or sudden change of flow from a super-critical to sub-critical flow in an open channel. Oscillating jump is detected in channels, canals below sluiceways, at the spillway bases, or during an immediate decrease in a slope like steep to flatter. In such transition, the water surface suddenly rises, surface rollers are simultaneously formed, the air is rapidly entrained, extreme mixing occurs, and energy is dissipated. The hydraulic jump is used as an effective natural mechanic mixer for the oxygen transfer and it can increase the amount of DO in the water by creating turbulent conditions. The main reason for this oxygen transfer is the air entrainment into the flow through a large number of air bubbles that helps in air-water transfer. To design and implement a hydraulic arrangement wherein a hydraulic jump is developed, it is important to identify the jump position and jump length and the quantum of energy to be disseminated. The present study investigates the effect of hydraulic jumps on their aeration efficiency and energy dissipation. The hydraulic jump is studied as an aeration agent. Hydraulic jump, herein, is formed by adjusting a tail gate in a rectangular flume. In the study, several experiments are carried out to find out the jump characteristics and the aeration efficiency while the jump is made to occur at five different discharges ranging from 15 lps to 35 lps and three different bed slopes (horizontal, 3° and 6°). Experiments are done by varying the discharge and bed slope of water from minimum to maximum within the range of measurement and different jump characteristics are observed. The DO was measured at the water surface level throughout the jump profile. The dependence of jump parameters with varying discharge and bed slope is measured and quantified. The DO was measured using a hand-type oxygen meter. With the variation of these parameters the jump height, jump length, and DO vary. The observations and outcomes reveal a linear relationship between the aeration efficiency and energy dissipation rate. The hydraulic jump attained an aeration efficiency of 0.4175. From these results, the hydraulic jump is found to be efficient for oxygen transfer and energy dissipation. This new procedure could have practical implications for predicting hydraulic jump aeration efficiency. This study may find applications where changing stream water DO significantly affect the jump characteristics.