WaterSubject

Dissolved oxygen (DO) is a measure of the free oxygen dissolved in water. The concentration of DO is an important indicator of water quality. DO concentrations can range from 0 to 15 mg/L, depending on atmospheric pressure, temperature and salinity. The ecological quality of water depends largely on the amount of oxygen water can hold. The higher the level of DO, the better the quality of the water system. By measuring DO, scientists determine the quality of water and healthiness of an ecosystem. Oxygen enters water by air entrainment. Air entrainment and aeration efficiency of hydraulic structures have been studied experimentally by a number of investigators. These studies were reviewed by. Venturi aeration is another method of aeration that has become popular in recent years. Recently studied the use of venturi tubes in plunging water jet aeration systems. In venturi aeration, a pressure difference between the inlet and outlet ports of a venturi tube creates vacuum inside the venturi, which initiates air suction through the suction port. Air that is entrained into the water is momentarily forced downstream in the form of small air bubbles. The dissolution of oxygen into the water results from the air suction at the throat portion of the venturi tube. Moreover, high pressure in venturi tubes also facilitates the dissolution of oxygen into the water.

Aeration systems with a venturi device can be used to solve the following environmental problems:

Moreover, venturi tubes can be used to inject chemicals into an irrigation system. Chemical application through irrigation systems is called chemigation. The vacuum pulls the chemical solution into the venturi port where it is mixed with the passing water and introduced into the system. Chemigation has been practiced for many years especially for fertilizer application (fertigation). In recent years, other chemicals have also been applied through irrigation systems with increasing frequency. The primary reason for chemigation is economy. It is normally less expensive to apply chemicals with irrigation water than by other methods. The other major advantage is the ability to apply chemicals only when needed and in required amounts. This ‘prescription’ application not only follows plant needs much more closely than traditional methods, but also minimizes the possibility of environmental pollution. Through chemigation, chemicals can be applied only in the amounts needed, and thus large quantities are not subject to leaching losses if heavy rainfall follows applications. Additional advantages of chemigation include less operator hazard and possibly reduced amounts of chemicals.

This paper describes an experimental investigation into the air and liquid injection rate of venturi tubes, and, in particular, the effects of the inlet diameter of the venturi tube, the ratio of the throat diameter of the venturi tube to the inlet diameter of the venturi tube, pipe length downstream of the venturi tube, diameter of the suction pipe at the throat portion of the venturi tube, angle of the pipe downstream of the venturi tube, flow velocity at the inlet portion of the venturi tube and density and viscosity of liquid injected into the venturi tube.

When a minimal amount of differential pressure exists between the inlet and outlet sides of a venturi tube, a vacuum (air and liquid suction) occurs at the suction holes of the venturi tube. When a pressurized operating (motive) fluid, such as water, enters the venturi tube inlet, it constricts towards the throat portion of the venturi tube and changes into a high-velocity jet stream. The increase in velocity through the throat portion of the venturi tube, as a result of the differential pressure, results in a decrease in pressure in the throat portion. This pressure drop enables air and liquid to be injected through the suction holes and become dynamically entrained into the motive stream. As the jet stream is diffused towards the venturi tube outlet, velocity is reduced and reconverted into pressure energy (but at a level lower than the venturi tube inlet pressure). Venturi tubes are highly efficient, requiring less than 20% differential to initiate suction.