Koji Kusano

A numerical analysis of solid-liquid phase change heat transfer around a single and two horizontal, vertically spaced cylinders in a rectangular cavity

In the present study, a new numerical model is proposed to analyze solid-liquid phase change heat transfer in a complicated geometry. The present model can treat the solid/liquid phase change heat transfer with/without porous media, as well as conventional transient natural convection with/without porous media. Solidification calculations of pure water (without porous media) around a single cylinder and two cylinders were performed to check the validity of the model. The interaction of two solidification layers were examined, and the effects of natural convection in the melt on the solidification process were also studied. The numerical results were found to be in excellent agreement with experimental data. It was also shown that for the initial water-temperature, Ti, of 0°C the solidification progresses more rapidly for the single cylinder than that for the two cylinders, but the reverse is true for Ti ⩾ 4°C.

Transient cooling of water around a cylinder in a rectangular cavity—a numerical analysis of the effect of the position of the cylinder

Abstract This paper reports the effect of the position of a cooled cylinder in a rectangular cavity on the cooling process of water around the cylinder. The governing equations are solved by a finite difference method, and the flow structure and temperature distributions are predicted. The initial water temperature, Ti, is varied at 4, 6, 8 and 12°C, while the temperature of the cylinder surface is fixed at 0°C. The obtained timewise variations of the temperature field and the velocity field as well as the mean Nusselt number over the cylinder surface are compared. The changes in the position of the cylinder and the initial water temperature largely affect fluid flows. Only an upward flow appears along the cylinder for Ti = 4°C, while for Ti > 4°C a downward flow is observed in early stages, and then the flow direction is changed to upward. Therefore, an averaged Nusselt number over the cylinder surface and averaged water temperature vary in a complicated manner with time for Ti > 4°C. The cooling rate of water is largely affected by the change of the position of the cylinder.

EFFECT OF DENSITY INVERSION ON COOLING OF WATER AROUND A CYLINDER IN A RECTANGULAR CAVITY

Transient natural convection in water around a cooled horizontal cylinder placed at the center of a rectangular enclosure has been studied. The governing equations were solved by a finite difference method, and the flow structure and temperature distributions have been predicted. The purpose of the present study was to examine the effects of the density inversion and the initial temperature of water on the cooling process. The initial water temperature was varied at 4, 6, 8, and 12°C, white the temperature of the cylinder surface was fixed at 0°C. The timewise variations of the temperature field and the velocity field as well as the mean and local Nusselt numbers on the cylinder surface were compared. Change in the initial water temperature largely affects fluid flows due to the density inversion of water. Complicated flow patterns are observed for initial water temperature higher than 4°; C. Cooling of water is most effective for an initial water temperature of 12°; C.

Solid/Liquid Phase Change Heat Transfer around Two Horizontal, Vertically Spaced Cylinders. An Experimental Study on the Effect of Density Inversion of Water.

Solid/liquid phase change heat transfer around cylinders occurs in many systems including latent heat thermal energy storage systems. In such systems, interaction of the heat transfer around the cylinders is often observed. Although several studies have reported on the heat transfer around a single cylinder, two or several cylinders, there have been no systematic studies to examine the effect of the initial superheat of water for solidification and the effect of the surface temperature of the cylinders for melting on the heat transfer. The purpose of the present study is to examine systematically the effects of the parameters mentioned above and the density inversion of water on the solid/liquid phase change heat transfer using two horizontal, vertically spaced cylinders.Solid/liquid phase-change heat transfer around cylinders occurs in many systems including latent-heat thermal-energy storage systems. In such systems, interactions of the heat transfer around the cylinders is often observed. Although several studies have reported on the heat transfer around a single cylinder and two or more cylinders, there have been no systematic studies to examine the effect of initial water superheat for the solidification and the effect of the surface temperature of the cylinders for the melting on the heat transfer. Therefore, in the present study, systematic experiments have been carried out to examine the effects of the parameters mentioned above and the density inversion of water on the solid/liquid phase-change heat transfer using a single and two horizontal, vertically spaced cylinders in a rectangular enclosure.

Flexural Properties Of All Bamboo\“green” Composites

This paper deals with the development and evaluation of environment-friendly composites that are composed of only bamboo. Japanese timber bamboo (Madake) is hot pressed in order to increase its mechanical properties, such as flexural strength and impact strength. The hot pressing conditions are varied from room temperature to 220°C. The flexural strength, flexural modulus, compressive strength and Izod impact strength increase with increasing the moulding temperature up to 160°C, showing the maximum peak values. The effect of moulding pressure on the mechanical properties is smaller than the effect of the moulding temperature. Extensive densification in both the vascular bundle and parenchyma cell regions is achieved by hot pressing and this increase in density results in the increased mechanical properties.

Thermal Characteristics OfPLA-bamboo Composites

The effective properties for the thermal characteristics of polylactic acid (PLA) bamboo composites, such as thermal conductivity, density and porosity were investigated experimentally. The thermal insulation characteristics are significantly dominated by these parameters. The thermal conductivity was measured by the transient hot wire method and the steady state method. The measured data was compared with each other and also used for the verification of the validity of Russell’s theoretical thermal conductivity model for green composites. The results show that the thermal conductivity of PLA-bamboo depends on the direction of fiber alignment as well as the direction of stacking. The thermal conductivity decreases gradually with decreasing the porosity (i.e., increasing the density of fiber). It was also clear that the theoretical estimation based on Russell’s model is adaptable to the anisotropic PLA-bamboo composites. All of the thermal conductivity measured by using the steady state method is lower than that measured by using the hot wire method. The thermal conductivity through the thickness direction is lower than that of surface plane averaged thermal conductivity. Due to the anisotropicy of its low thermal conductivity, the PLA-bamboo “green” composites have excellent insulation properties.

Prediction and Improvement of Artificial Ground Freezing

The aim of present study is to establish the numerical model for the solidification or melting of water saturated soil and to clarify the effect of thermal and physical parameters on the artificial soil freezing by comparing between the numerical and experimental results. First, the numerical model has been modified to adapt for freezing of soil. By comparing between obtained numerical solutions and experimental data, the validity of the model has been checked and certified. Next, the effect of physical property of soil, initial and boundary conditions of soil and freezing pipes, the velocity of groundwater, and the arrangement of freezing pipes on soil freezing have been examined. As the results, it was found that the water content of soil and ground water affect the volume of solid, besides the groundwater also especially changes the profile of solid/liquid interface. The rate of the interface growth would gradually stop provided that the flow speed exceeds certain limits. The knowledge obtained from our study will be useful to predict solid volume, decrease in thermal energy consumption and minimize the influence to ambience on artificial ground freezing precisely.Copyright

Natural convection of miscible two phases due to density difference in saturated porous media

Understanding of natural convection of miscible two phases in porous media is of great importance to problems of geological storage of carbon dioxide. We consider saltwater-freshwater fingering instabilities in a saturated porous medium. Plastic resin particles with an average diameter of 320 μm or 440 μm were packed 50 mm in height in a tube with the inter diameter of 32 mm. Development of the fingering due to instabilities and natural convection of freshwater and saltwater in porous media have been imaged by means of micro-focused X-ray computer tomography (CT) every three minutes. At early stages of convective mixing, ripples appear on the contour surface of the concentration of sodium iodine and grow to be fingers which extend vertically downwards with time. As fingers proceed downwards, the concentration of sodium iodine in fingers are reduced. As a result the convective mixing is rapidly suppressed. With an increase in the density difference and the permeability, the development of the natural conve...

Transient Natural Convection of Water around a Cylinder in a Rectangular Cavity. Effect of the Density Inversion on Cooling of Water.

Transient natural convection in water around a cooled horizontal cylinder placed at the center of a rectangular enclosure has been studied. The governing equations were solved by a finite difference method, and the flow structure and temperature distributions have been predicted. The purpose of the present study was to examine the effects of the density inversion of water and the initial temperature of water on the cooling process of water. The initial water temperature was varied 4, 6, 8 and 12°C, and the timewise variations of the temperature field and the velocity field as well as the mean and local Nusselt numbers on the cylinder surface were compared. The change in the initial water temperature largely affects fluid flows due to the density inversion of water. Complicated flow patterns are observed for initial water temperatures larger than 4°C. The cooling of water is most effective for an initial water temperature of 12°C.

Solid/liquid phase-change heat transfer around two horizontal, vertically spaced cylinders -- An experimental study on the effect of density inversion of water

Solid/liquid phase change heat transfer around cylinders occurs in many systems including latent heat thermal energy storage systems. In such systems, interaction of the heat transfer around the cylinders is often observed. Although several studies have reported on the heat transfer around a single cylinder, two or several cylinders, there have been no systematic studies to examine the effect of the initial superheat of water for solidification and the effect of the surface temperature of the cylinders for melting on the heat transfer. The purpose of the present study is to examine systematically the effects of the parameters mentioned above and the density inversion of water on the solid/liquid phase change heat transfer using two horizontal, vertically spaced cylinders.Solid/liquid phase-change heat transfer around cylinders occurs in many systems including latent-heat thermal-energy storage systems. In such systems, interactions of the heat transfer around the cylinders is often observed. Although several studies have reported on the heat transfer around a single cylinder and two or more cylinders, there have been no systematic studies to examine the effect of initial water superheat for the solidification and the effect of the surface temperature of the cylinders for the melting on the heat transfer. Therefore, in the present study, systematic experiments have been carried out to examine the effects of the parameters mentioned above and the density inversion of water on the solid/liquid phase-change heat transfer using a single and two horizontal, vertically spaced cylinders in a rectangular enclosure.