Design of a Combined Propeller and Venturi Tube System for Aquaculture Ponds

Abstract

The main objective of the study was to design and develop an aerator (a combined propeller and venturi tube system) and to evaluate its performance characteristics and oxygenating capacity. This system has certain advantages over existing methods of separate water circulation and oxygenation methods. The aerator was designed to perform two functions: circulation, and aeration. A large diameter propeller (0.45 m) rotating at a low speed (60 rpm), to move a large volume of water (0.093 m³/s), was aimed for circulation. The rotational speed was kept low enough to produce gentle water movement without disturbing or eroding the bottom soil. For oxygenation, a venturi tube was installed horizontally at the center of the propeller, at a depth of 0.5 m below water surface (1.0 m pond depth). The oxygenating experiments were conducted using accepted protocols for various operating parameters. The mixing of fine bubbles and strong current, accomplished by the rotating propeller, quickly transported the dissolved oxygen (DO) to a greater depth. The highest value of standard oxygen-transfer rate (SOTR) of the aerator tests in the range of scope and limitation was found to be 0.78 kg O₂/h, which is higher than other existing aerators, i.e. the paddle wheel aerators and propeller-aspiration-pump aerators. A dimensional analysis was conducted to find the relationship between the dependent variable, SOTR, and the independent variable in the form of PQ/V², where P is pressure inside venturi tube, V is water velocity, and Q is volumetric flow rate of water. The results show that the two variables have a linear relationship with R² = 0.93.