Hideaki Kitagawa

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.

Ultrasonic Guided Wave Testing System for Piping

In the operation of electric power plant, it is necessary to understand the condition of the pipe quantitatively. The purpose is to prevent the accident caused of the wall thinning portion due to erosion or corrosion. The thickness of the pipe is partially measured with the ultrasonic thickness gage now. However, it is difficult to investigate the wall thinning portion in the pipe quantitatively without confirming it beforehand. In this study, for the purpose to identify the location of thinning, we have developed the ultrasonic testing system using the guided wave that was able to investigate partially the wall thinning portion of all aspects of pipe to be inspected at a time. This system propagates guided wave by using an electro-magnetic acoustic transducer. We understand the extensive condition of the pipe by using this system. Therefore, the efficient investigation of the pipe is available. For that reason, it is expected to contribute to the reliability improvement of facilities and the reduction of maintenance and repairs.Copyright

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.