COMPARISONS OF NUMERICAL METHODS FOR FLUID FLOW SIMULATIONS IN A MICROORGANISM INCUBATING CHAMBER

摘要

A microorganism incubator has been developed by a prototype performance tests and computational fluid dynamics (CFD) simulations. The microorganism incubator is useful to supply the high quality of fertilizer to agricultural industries. Particularly, a small-sized, movable incubator is desired to be produced for personal agriculturalists. Since the incubator is basically designed as a type of mixing tank for mixing water and powder of microorganism, the decision of an impeller type and size, positions, size of internal parts such as baffles for an efficient mixing process should be considered. To produce the effect of turbulence on the efficient mixing, the location and size of baffles on the chamber wall is particularly significant to the mixing chamber design process. Multiphase CFD simulations are performed to describe the mixing flows inside the tank and the flow physics and patterns are studied in order to find out the optimal conditions for the microorganism incubating. Since water with powder of microorganism is partially filled with the chamber, air-water two phase flows should be considered in the CFD simulation. To simulate such flows, the volume of fluid (VOF) scheme is used. Both steady-state and time-transient simulations are performed and their results between two different time derivative considerations are compared, which enables us to clearly understand the effects of unsteady flow characteristics on the whole flow phenomena in the chamber. Additionally, comparisons of the turbulence modeling for the rotating flows in the chamber will be performed to describe the complex flow phenomena around the rotating impeller and the stationary baffles on the chamber wall. Prior to performing CFD study for the real type of the chamber, the flow simulations for the mixing chamber whose flow characteristics were already studied by experiments are performed with respect to the change of the turbulence modeling and numerical methods. Thus, the proper numerical methods and turbulent modeling are then determined. After validations of the turbulent modeling and numerical schemes, the flow phenomena occurred at the real prototype of the microorganism chamber corresponding to the change of design parameter of the chamber such as the change of the chamber bottom shape, an impeller blade length and the number of baffles will be analyzed.