CFD & Electrical Capacitance Tomography Technology And Its Application In Downer Flow

With new areas developing in the industry, some conventional techniques of measurement appear limited in different fields. In order to reflect the state of multiphase flow, real-time measurement is very important. In order to analyze the hydrodynamic characteristics of the two-phase flow and heat transfer inside a tube, parameters such as velocity and concentration are important. Process tomography (PT) measurement is a new technology which has been developing since the late 1980's. PT can be widely used in many fields such as petroleum, chemical, metallurgy and electrical engineering. Electrical capacitance tomography (ECT) is typical technology of PT. ECT has several advantages such as simplicity, low cost and safety.This thesis presents a comparative study on two phase flow using CFD and ECT. For ECT, LBP method, iterative algorithm, fast iterative algorithm and regularization simulation method are applied to reconstruct the image. Experimental results show that each algorithm has its advantages and disadvantages. LBP method is faster than other method but often with poor image quality, iterative algorithm can characterize solid-gas flow behavior more accurately, fast iterative algorithm has the same image quality as iterative method but with much faster speed of image reconstruction. To verify the above methods, a sixteen-channel AC charged ECT system is used to measure the liquid-solid two-phase flow in a swirl barrel.Numerical simulations are carried out for the flow in a downer. In the simulation the gas phase is treated as the continuous phase and the turbulence is accounted for by a conventional k- e two equations model. Particle trajectory model is used to calculate the solids flow in three sections of the downer. Results indicate that, at the inlet of the downer, the solid concentration is high in the center area. As the particle flow downward, diffusion of the particles occurs that makes the concentration more uniform over the cross-sections.In accordance with the numerical simulations, ECT is applied to measure the gas-solid flow in the downer. Measure signals can be improved by using low permittivity material to calibrate. Experimental results illustrate that this method can successfully measure the volume fraction of gas-solid even when the flow is of lowconcentration (<0.1%). The numerical results agree reasonable well with those by ECT.