山口 義幸

A uniform inlet velocity profile is widely used in the numerical simulations of fluid flow and heat transfer in ducts for both incompressible and compressible flows. In incompressible flows, the calculated fluid pressure at the inlet edge is extremely high and affects the calculation of the average pressure. In compressible flows, the fluctuation of pressure in the flow direction results in the fluctuation in the velocity. This has motivated this study to numerically investigate a physically realistic velocity profile at the inlet of a pipe rather than using a uniform velocity profile. The numerical simulations were based on the control volume-based power law scheme and the semi-implicit method for pressure-linked equations (SIMPLE) algorithm. The continuity and momentum equations for a flow in a pipe with the rounded inlet corner were solved to obtain a physically realistic inlet velocity profile. The obtained inlet velocity profile was expressed by a simple expression in the range of Reynolds number from 100 to 2000. Using this velocity profile, both the incompressible and compressible flows in a pipe were numerically investigated. The results resolved the previously observed inconsistencies in the pressure that were previously observed in the numerical simulations with uniform inlet velocity profiles.

Two different analytical models were developed on water type Stirling engine. One is the resonance model which qualitatively clarifies the relationship between performance and resonance tube length, and the other is the heat transfer model considering heat transfer between working gas and the tube walls of heating and cooling units. These analyses and experiments were carried out changing the resonance tube length variously, then it was confirmed that the resonance tube length which maximizes the water column amplitude of the power piston agrees well and the oscillations of water columns at that resonance tube length also agrees. In addition, a series of analysis using the heat transfer model was carried out with changing cross sectional area of the resonance tube, loss factors of the elbows, heat transfer area of heating and cooling unit, and pressure of working gas. By this numerical investigation, the effect on the resonance tube length and the work at the length in which these parameters maximize the amplitude of power piston water column was clarified.

It is well known that moist fire protection materials show good fire resistance characteristics. For this reason, these materials are usually made of mixtures of perlite-mortar and high-water-content materials such as silica gels or moist perlites. The latent heat of water plays an important role in the resistance of heat propagation in these materials. A superabsorbent polymer gel that absorbs calcium chloride solution contains much water, and it is one of these high-water-content materials. In this study, numerical simulations of fire resistance tests were conducted for materials of different mixing ratio of perlite-mortar and the super absorbent polymer gel to investigate the effect of the mixing ratio on the fire resistance characteristics. The effective thermal conductivity and the water content of the materials were measured and those values were used for computations. One of the test materials shows excellent fire resistance characteristics, and its fire resistance time at 60 mm thick is about 300 min. The relations of thermal properties and composition of the test material and the effects of mixing ratio of the gels and the perlite-mortar on the fire resistance characteristics are discussed.

Three-dimensional natural convection heat transfer characteristics in a vertical air layer partitioned into cubical enclosures by partition walls of finite thermal conductivity and finite thickness were obtained numerically. The air layer is differentially heated from each surface. In this work, the analyses were performed using finite thickness and finite conductivity of the partition wall for Ra=10(4) and 10(5), and for wide range of thickness and the conductivity of the partition wall. The results were presented in the form of overall convection and total heat transfer coefficient. From the comparison of the results with the traditional ideal boundary conditions such as "conduction, " "adiabatic," and "no-thickness," the correlation of the heat transfer with the actual partition wall and the ideal boundary conditions were developed. After examinations of the results, it was shown that the proportion of the heat transfer quantity in the partition wall to the total heat transfer quantity from the hot wall is a function of a product of the thermal conductivity and the thickness of the partition wall.

It is known that moist fire protection materials show good fire resistance characteristics. For this reason, these materials are usually made of mixtures of cement mortar and high water content materials such as silica gels or moist perlites. The latent heat of water plays an important role in the resistance of heal propagation in these materials. In this study, a fire resistance test of a material with high water content is conducted and the temperature response of the test is obtained. Also, the water content of the test materials is measured. The test material consists of a mixture of perlite mortar and gel. The gel absorbs the aqueous solution of calcium chloride, which serves as a water storage mechanism. The numerical predictions to simulate the fire resistance test were conducted and the results were compared with the experimentally obtained temperature responses. (C) 2000 Elsevier Science Ltd. All rights reserved.

Heat transfer and fluid flow characteristics in a rotating two-pass square passage with a sharp 180-degree turn are investigated numerically. The channel is aligned with a skew angle to a rotating axis. The configuration simulates the internal air cooling of a turbine blade. The present study focuses on the combined effects of rotation and skew angle on the two-pass passage with a sharp 180-degree turn. The computational procedure solves full three-dimensional Navier-Stokes equation using a finite volume method with the SIMPLE algorithm. Computations were performed for the Reynolds number in the range from 100 to 500, for the Prandtl number of 0.717, for the Rossby number in the range from 2.55 to infinity and for the skew angle in the range from 0 to 45 degrees. The flow patterns, the overall pressure drop, the peripheral averaged Nusselt number and the bulk temperature at the outlet of the passage are presented as a function of the governing parameters.

It is empirically well known that a moist fire protection material shows a good fire resistant characteristics. From this fact, a fire protection material is made of a mixture of cement mortar in which water storage materials such as silica gels or moist perlites are mixed. The latent heat of water in the fire protection material plays an important role in the resistance of temperature rise. In this study, the fire resistance tests for a fire protection material of high water content is conducted and the temperature response of the test material is obtained. The test material consists of the perlite motar in which the gels which absorbed the aqueous solution of calcium chloride are mixed as the water storage material. The water content of the test materials were also measured. And also the numerical predictions for the fire resistance test were conducted and the results were compared with the experimentally obtained temperature responses.

A fire wall is made of a mortar wall in which water storage materials are mixed. However, the mortar fire wall is relatively heavy. A nonorganic insulator for middle and high-temperature ranges such as a calcium silicate board is expected as a good material for the fire wall because of a light weight. Usually, a nonorganic insulator such as the calcium silicate board consists of a hydrate which contains free water, physically adsorbed water, and crystalline water. Behavior of such waters should be considered for a numerical model which is used to predict thermal responses of a fire wall. A simple one-dimensional numerical model to predict thermal response of a fire wall which is made of a nonorganic hydrate insulator, is developed. The numerical computations to simulate the thermal responses for a standard fire resistance test were performed for a sand wall of five percent volume of moisture and two calcium silicate boards which contains free water, adsorbed water and crystal line water. The experiments for the sand wall and the calcium silicate boards were also performed. The numerical results were compared with experiments. The proposed model well predicts the thermal responses of the walls.

A fire wall usually contains moisture. When the wad is exposed to flame, water in the wad evaporates into vapor. The latent heat of water plays an important role in the resistance to heat propagation. A wad of high water content is therefore expected to have good fire-resistant characteristics. in this study the thermal responses of a fire wall that consists of a porous material, its pores partially filled with wafer, are investigated numerically. A simple one-dimensional numerical model developed in the authors' previous study ir simplified to reduce the computational parameters. The parameteric study is conducted to investigate the effects of thermal diffusivity, moisture, and density ratio on wall thicknesses of 1, 2, and 3 hours of fire resistance. The correlation between the wad thickness and fire resistance time is obtained.

Combined heat transfer characteristics are obtained numerically for three-dimensional natural convection and thermal radiation in a long and wide vertical porous layer with a hexagonal honeycemb core. The porous layer is assumed to be both homogeneous and isotropic. The pure Darcy law for the fluid flow and Rosseland's approximation for the radiation are employed. The numerical methodology is based on an algebraic coordinate transformation technique and the transformed governing equations are solved using the SIMPLE algorithm. The effect of radiation on the heat transfer characteristics is investigated in a wide range of radiation numbers and emprerature ratios, for two Darcy-Rayleigh number values (Ra^*=100,1000), and for a fixed aspect ratio of H/L=1. The results are presented in the form of combined and convection heat transfer coefficients, and are compared with the corresponding values for pure natural convection.

Unsteady three-dimensional natural convection heat transfer in an inclined air slot with a hexagonal honeycomb enclosure is investigated numerically. The numerical methodology is based on an algebraic coordinate transformation technique that maps the hexagonal cross section onto a rectangle. The transformed governing equations are solved with a control volume discretization scheme using a fully implicit method with time. The computations are performed for inclination angles in the range of 60 to 80 deg for Ra = 104, and in the range of 45 to 80 deg for Ra = 105, for Prandtl number of 0.7, and for a fixed aspect ratio of H/L = 5. A conductive thermal boundary condition for the honeycomb side walls is considered. Both periodic and nonperiodic oscillating solutions are obtained depending on the inclination angle and Rayleigh number. The complex flow patterns are presented inform of particle trajectory maps and are compared with the flow visualization results using microcapsulated liquid crystals. © 1995 by ASME.