An experimental study to evaluate the efficacy of air entrainment holes on the throat of a venturi aeration system

Abstract

Dissolved oxygen (DO) is a vital nutrient for the health of water bodies such as streams, rivers, and ponds, as it is used in respiration and other biological activity of aquatic animals. Natural replenishment of oxygen through photosynthesis in aquatic bodies is insufficient to meet the high requirements for an intensive aquaculture system, which compels farmers to use aeration systems to supplement the natural process of DO accumulation. When the demand for oxygen (KgO2/h) is lower, venturi aerators may be more effective than other aerators. The venturi device is an aeration system which is highly efficient in providing an adequate supply of DO, and is flexible in nature and easy to operate. To evaluate the efficacy of air entrainment holes on the throat of a venturi, aeration experiments were conducted for different throat lengths (Lt) of 20, 40, 60, 80 and 100 mm, varying the number of air holes according to throat length while maintaining a constant air hole diameter of 2 mm. Aeration efficiency was found to increase with an increasing number of air holes. The highest oxygen transfer coefficients for throat lengths of 20, 40, 60, 80 and 100 mm were 0.497 h−1, 0.756 h−1, 1.045 h−1, 0.627 h−1 and 1.072 h−1, respectively, with the maximum number of air holes (NH). The maximum standard aeration efficiency was found to be 1.25 × 10−2 kgO2/kWh for a throat length of 100 mm with the maximum number of air holes (NH17). Hence, the physical properties of throat length, number of air holes, and distribution of air holes on the throat section were proven to be key factors controlling the performance of the venturi aeration system.