Kenichi Okui

Lattice Boltzmann simulation of natural convection in porous media

This paper confirms the reliability and the computational efficiency of the lattice Boltzmann method in simulating natural convection in porous media at the representative elementary volume scale. The influence of porous media is considered by introducing the porosity to the equilibrium distribution function and by adding a force term to the evolution equation. The temperature field is simulated by a simplified thermal energy distribution function which neglects the compression work done by the pressure and the viscous heat dissipation. A comprehensive parametric study of natural convective flows is carried out for various values of Rayleigh number, of Darcy number, and of porosity. The comparison of solutions between the present model and earlier studies shows good quantitative agreement for the whole range of Darcy and Rayleigh numbers.

The effect of aggregation on rheological characteristics of an electrorheological fluid of the particle dispersion type

A study was conducted on the effect of particle aggregation on the rheological characteristics of an electrorheological (ER) fluid of the BaTiO3 type as a colloidal ER fluid. Increasing viscosity by applying an electric field was measured using a rotating viscometer. The experimental data was compared with the theoretical analysis taking into account either uniform particle dispersion or particle aggregation. The effect of aggregation on the rheology of the ER fluid was clarified and the increasing viscosity was quantitatively determined by a formula based on the aggregation model.

RHEOLOGY OF ERF ON VARIOUS FLOW FIELDS

This paper is concerned with the experimental investigation of electrorheological effect (ER effect) on apparent viscosity and yield stress obtained from hydrodynamic characteristics of electrorheological fluid (ERF) in various flow fields. Our conducting flow fields are made by using rectangular duct, concentric cylindrical pipe, rotating disk and rotating concentric cylinder. The measured parameters of the former two cases are pressure difference at a given volumetric flow rate, and the latters are torque at a given angular velocity. Our using ERF is suspension type. We arrange these data to obtain increment of apparent viscosity and yield stress with and without a supplying D.C. electric field by using integral method of rheology. It is clarified that qualitative values of increment of apparent viscosity and yield stress are different at each flow field. In addition, the quantitative ER effects of shear rate and electric field strength on the increment of apparent viscosity and yield stress are clarified.

Heat Transfer and Pressure Drop Characteristics of Finned Tube Banks in Heat Exchanger for Gas Turbine

In recent years the requirement for reduction of energy consumption has been increasing to solve the problems of the global warming and the shortage of petroleum resources. For example in the power generation field, as the thermal power generation occupied 60% of the power generation demand, the improvement of the thermal efficiency is required considerably. This paper described the heat transfer and pressure drop characteristics of the finned tube banks used for the heat exchanger in the thermal power generation. The characteristics were clarified by testing the serrated finned tubes banks for improvement of higher heat transfer and the conventional spiral finned tube banks under the same test conditions. The equations to predict heat transfer coefficient and pressure drop which are necessary on design of the heat exchanger were proposed.© 2004 ASME

Lattice Boltzmann Simulation of Nucleation

We propose a lattice Boltzmann model capable of simulating nucleation. This LBM modifies a pseudo-potential so that it recovers a full set of hydrodynamic equations for two-phase flows based on the van der Waals-Cahn-Hilliard free energy theory through the Chapman-Enskog expansion procedure. Numerical measurements of thermal conductivity and of surface tension agree well with theoretical predictions. Simulations of phase transition, nucleation, pool boiling are carried out. They demonstrate that the model is applicable to two-phase flows with thermal effects. Using finite difference Lattice Boltzmann method ensures numerical stability of the scheme.Copyright