CFD simulation of venturi aerator

การใช้ซอฟต์แวร์ CFD ในการศึกษาเครื่องเติมอากาศแบบ Venturi

Name: Donlaporn Songwatthana

Organization : King Mongkut's University of Technology Thonburi. Faculty of Engineering. Chemical Engineering

keyword: Computational Fluid Dynamics

; เครื่องเติมอากาศ

; Venturi aerator

Abstract: Aeration in aquaculture has the main purpose of maintaining dissolved oxygen (DO)concentrations in a pond. When the DO level becomes supersaturated due tophotosynthesis, the widely used surface aerator transfers oxygen not from the air to the pond water, but instead disperses dissolved oxygen from the pond water back to the air.However, aerator is essential for aquaculture to aerate the pond during the nighttime when no photosynthesis takes place and to enhance convection of oxygen. For thesereasons, venturi aerator that can switch between mixing in the daytime and oxygenation to gether with the mixing during the nighttime could be a good alternative to the surfaceaerator. This venturi aerator works by sucking air into its venturi and mixes it with water before ejecting the water-air stream to the pond. The oxygen transfer occursmainly in the outlet pipe and in the surrounding area. Switching aeration mode is simply turning on and off the air inlet valve of the venturi aerator. Since commerciallyavailable venturi aerators are specifically designed for deep waste treatment pond, anew design for shallower shrimp pond is required.A Colnputational Fluid Dynamics (CFD) software package CFX (ANSYS, USA) wasused to study the effects of venturi aerator configuration on velocity profile and flowbehavior of the fluid in order to design a new prototype for use in shrimp culture ponds.The venturi aerator type FLI JA from Flow line Manufacturing Co., Ltd was used as thebase case for simulation. The simulation started with one phase, namely water, as apreliminary study of the system before being expanded to a more complicated modelwith two-phase flow involving water and air. The effects of these venturi configurationssuch as nozzle diameter, air inlet position, air inlet pipe diameter, mixing tube diameter,mixing tube length, and water inlet pipe diameter were analyzed by means ofdiinensional analysis method. The nozzle diameter was found to significantly anddirectly affect the velocity profi le and water flow pattern. Smaller nozzle producedhigher average velocity of fluid flow in the venturi aerator. Position of air inlet showed110 influence on the velocity profile, although it significantly affected the water .flowpatteni. While air inlet pipe diameter had no effects on the velocity, the mixing tubediameter is another significant parameter affecting the mixing flow in the venturiaerator. Only slight variations of velocity profiles in mixing and diffuser zone werel'ound with different lengths of mixing tubes. On the other hand, expansion of themixing zone which might enhance the oxygen transfer occurred when the mixing tubelength was increased. The water inlet pipe diameter clearly demonstrated that the waterinlet pipe diameter strongly affected the flow pattern of the venturi aerator and thevelocity increased as the water inlet pipe diameter increased. Simulation results showedthat the key parameter affecting the average velocity was the mass flow rate of thesucked air.The CFD model predictions had been validated with experiments. The pressure waslneasured at four locations in the venturi by pressure transducers, and the air velocitywas measured by a thermal flow meter at the air inlet pipe. The CFD and theexperimental results showed similar trends, but the CFD model over-predicted thetrend5 by 10 - 30 percent. These errors might come from the inaccurate boundarycotidition at the venturi aerator entry which could not be directly measured. Moremeasurements are required in order to improve the simulation.

King Mongkut's University Technology Thonburi. Library

Address: กรุงเทพมหานคร (Bangkok)

Email: info.lib@mail.kmutt.ac.th

Name: Wiwat Ruenglertpanyakul

Role: Advisor

Created: 2004

Issued: 2007-07-18

Modified: 2007-07-26

วิทยานิพนธ์/Thesis

ISBN: 9741838042

CallNumber: CHE1524

eng

DegreeName: Master of Engineering

Level: Master's Degree

Descipline: Chemical Engineering

Grantor: King Mongkut's University of Technology Thonburi

©copyrights King Mongkut's University of Technology Thonburi

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