Influence of Throat Length and Flow Parameters on a Venturi as an Aerator

Venturi system helps to air drawn into a flowing stream of water transferring the oxygen from air to water till they reach the water surface and burst due to Bernoulli's principle in form of bubbles. The efficacy of venturi as an aeration device is primarily dependent on the geometry and the flow conditions prevailing inside. Presently, the diameter and placement of holes in a venturi under different flow conditions was studied to determine the performance of the venturi as an aerator. To evaluate the results, SOTR and SAE were calculated and compared for analyse their performance. The study involved selecting 5 different throat lengths each having multiple hole of 1 mm diameter. The hole distance from the start of the throat section, which has been characterised as the effective distance (ED) has been so selected that all the ED's are different. The ED's selected for study varied from 2 mm to 46 mm under three different discharges of 1.72 m³/h, 2.02 m³/h and 2.38 m³/h. Firstly, it was observed from the experiments that the venturi performs best when the ED is less. Secondly, it was also observed that both SOTR and SAE are more for higher discharge. Next, it was also found that increasing the throat length beyond a certain value has a negative effect on the SOTR and SAE. It was also observed that among all the possible combinations the best was for the 10 mm throat section with the hole situated just adjacent to the start of the throat section and performing at a high discharge.

Venturi aeration is a novel scheme of air water mixing at throat section. Other than the position of throat hole was foundthat the chief factor influencing the air entrainment rate and the oxygen transfer efficiency.