Manabu Tange

Microbubbles Emission Flow Boiling in a Microchannel and Minichannel

This paper reports the results of experimental investigations on microbubbles emission boiling (MEB) in a microchannel and minichannel. MEB is a boiling phenomenon under high subcool and high heat flux condition. To understand the mechanisms and processes of MEB, pool boiling on a thin wire under subcooled condition was firstly performed. Under various subcooling condition, the experiments of subcool boiling were performed. From photographic observation, distributions of bubble diameters and their dependence on subcooling were investigated. To achieve better understanding of the process of MEB and to find the incipient subcooling of MEB, a sound of ebullition was recorded and analyzed. It was found that 30 to 40 K are the incipient subcooling of MEB on the thin wire. In the experiment of MEB in microchannel and minichannel, the special attention was paid to longitudinal transition of boiling behavior, since bulk liquid temperature increases in short length in case of subcooled flow boiling. Boiling curves for various channel height were obtained from experimental data, and pressure drop through whole channel was measured. In a minichannel, annular flow flushed out the whole channel from the downstream to the upstream and the pressure drop fluctuates, while in a microchannel, flow pattern was divided into two regions: bubbly flow in upstream and annular flow in downstream.Copyright

The Development of the Totalized Hydrogen Energy Utilization System for Commercial Buildings

We have proposed the Totalized Hydrogen Energy Utilization System(THEUS) for applying to commercial buildings. THEUS consists of fuel cells, water electrolyzers, metal hydride tanks and their auxiliaries. We evaluated the energy saving of the basic THEUS in view of an actual operation using thermal demand data of actual buildings. The THEUS have ability for achieving energy saving, in comparison with an ice storage system for cooling demand. We have developed the hydrogen storage system using metal hydride and unitized reversible cell (URC) combine the functionality of a fuel cell and an electrolyzer in a single device, these are important components of THEUS. The metal hydride tank designed and manufactured to evaluate that we assumed actual operation in the experiments. We developed the numerical simulation code, and simulation results are in good agreement with experimental data. The simulation about two tanks system was done by using this code. The heat utilization can be improved greatly. To achieve URC commercial use, improvement of durability was examined. It confirmed that our URC had durability for several thousand hours.

Microbubble Emission Boiling in a Rectangular Channel Flow

Highly subcooled flow boiling at high heat flux in a rectangular minichannel of 2 mm × 2 mm in dimension was experimentally investigated. The channel was heated only from the bottom wall of the channel and it is regarded as a model of cooling components on electric devices in mobile gears. Under the condition of high subcooling and high heat flux in the stagnant pool and conventional scale channel flow, many fine vapor bubbles are emitted from primary vapor bubbles on heated surfaces. This boiling regime is called microbubble emission boiling (MEB). If we realize MEB in a minichannel, high heat flux due to vaporization will be obtained and large pressure loss due to confinement of bubble will be avoided. This paper first reports the results of our early experimental investigations on MEB in a pool boiling system to introduce the appearance of MEB. In flow boiling experiment, we reports heat transfer characteristics and photographic observation.Copyright

A fractal-based 2D expansion method for multi-scale volume data visualization

Visualization of volume data is difficult to realize and control because the most common output device is a two-dimensional (2D) display and the most common input device is a mouse, which only allows 2D operation. For example, volume rendering projects the data structure onto a 2D image plane, but this type of view-dependent method gives rise to occlusion. In addition, 2D mouse operation does not allow direct selection of three-dimensional (3D) regions or coordinates. In this article, we propose a method that expands the octree structure of volume data onto a 2D plane. The proposed method uses the self-similarity of the fractal diagram and achieves multi-scale visualization of volume data in two dimensions. With this method, we can browse the entire domain of volume data without occlusion. For greater effectiveness, we combined the proposed method and existing 3D-based methods. Since each cell has a one-to-one correspondence with squares in the Sierpinski carpet, we can assign arbitrary 3D regions or positions by selecting the corresponding squares. This provides direct access to 3D regions and coordinates by 2D mouse operation. We propose some functions for interactive visualization and discuss how to exploit the advantages and lessen the disadvantages of the proposed method.Graphical Abstract

Combined measurement of temperature and velocity distribution of fluid flow

This paper proposes a combined method for two-dimensional temperature and velocity measurement using temperature sensitive particles (TSPs), a pulsed ultraviolet laser, and a high-speed camera. TSPs respond to temperature changes in a flow and can also serve as tracers for the velocity field. The luminescence from the TSPs was recorded at 15,000 frames per second as sequential images for a lifetime-based temperature analysis. These images were also used for the particle image velocimetry calculations. The temperature field was estimated using six images, based on the lifetime method. The decay curves for various temperature conditions fit well to exponential functions, and from these the decay constants at each temperature were obtained. The proposed technique was applied to measure the temperature and velocity fields in natural convection driven by a Marangoni force and buoyancy in a rectangular tank. The accuracy of the temperature measurement of the proposed technique was ±0.35∼0.40°C.Copyright

Boiling heat transfer surface capable of transient heating and nucleation control

Using MEMS technique, we develop a novel boiling heat transfer surface with three types of circuits: a heater, a bubbling trigger, and thermocouples. This paper presents the design of the heat transfer surface and experimental results of bubbling behavior on this surface during highly subcooled boiling at high heat flux. The heater makes superheated liquid layer transiently. Then the bubbling trigger make a tiny hydrogen bubble playing a role of a nuclei of a boiling bubble. The thermocouple signal reveals a growth of superheated liquid layer, vaporization of the liquid layer beneath the bubble, and rewetting. It has been known that highly subcooled boiling at high heat flux results in atomization of vapor bubbles on heat transfer surfaces due to the violent condensation. Parametric experiments were conducted to clarify the occurrence condition of the atomization by changing heat flux and heating time before nucleation. Bubbling behavior was categorized into four patterns: Oscillating, Not-Oscillating, Single-bubble emission, and Multi-bubbles emission.© 2010 ASME

Topics on Boiling: From Fundamentals to Applications

This chapter deals with the various topics on boiling with regard to aspects of the fundamentals and applications to introduce the development of each author’s research in recent decades. The first four sections investigate the physics of boiling as phase change phenomena, including thermodynamic phase equilibrium state (Section 6.1), molecular dynamics of phase change (Section 6.2), computational analysis of boiling in micro-nano scale (Section 6.3), and transient boiling under rapid heating (Section 6.4). Section 6.5 deals with two-phase distribution measurement using neuron radiography. The following three sections then examine a specific boiling regime during highly subcooled boiling, called microbubble emission boiling (MEB). Each section treats the overall characteristics of MEB (Section 6.6), the occurrence conditions of MEB (Section 6.7), and vapor collapses in subcooled liquid related to MEB (Section 6.8). The next four sections are devoted to heat transfer augmentation with various techniques: thermal spray coating (Section 6.9), porous media (Section 6.10), patterned wettability refinement (Section 6.11), and self-rewetting fluid (Section 6.12). The last seven sections describe topics on applications of boiling. Sections 6.13 and 6.14 introduce boiling research in steel industries. Sections 6.15 and 6.16 explore vapor explosion. Boiling of refrigerant is discussed with heat pump systems in Section 6.17 and with automobile air conditioners in Section 6.18. Boiling related to emergency cooling core systems is considered in Section 6.19.

Design Concept and the Performance of a Metal Hydride Hydrogen Storage Tank in Totalized Hydrogen Energy Utilization System

We have proposed the Totalized Hydrogen Energy Utilization System (THEUS) for applying to commercial buildings. THEUS consists of fuel cells, water electrolyzers, metal hydride tanks and their auxiliaries. The basic operation of the THEUS is as follows: In the nighttime, hydrogen is produced by water electrolysis and stored in metal hydride tanks. In the daytime, it conducts fuel cell power generation using the stored hydrogen to meet the electric power demand of a building. The chilled and hot water generated in this process are also utilized. It is also possible to use the electric power from renewable energy. That is, THEUS has not only the load leveling function but the function to stabilize the grid system. The metal hydride tank is an important component of THEUS as hydrogen storage. The tank was designed as a thermally driven type, which be able to absorb/desorb hydrogen at normal temperature and pressure and utilize the endothermic reaction during hydrogen desorption as chilled water for air-conditioning. The tank with 50 kg AB5 type metal hydride alloy was assembled to investigate the hydrogen absorbing/desorbing process. The experimental results of the heat utilization ratio using this metal hydride tank are about 43%. Since the reaction heat is consumed to heat and to cool the tank up to the temperature of possible heat utilization. The heat utilization ratio can be improved by reduced the heat capacity of the tank and exchanging heat with multiple tanks.Copyright

The Actual Operation of Multiple Metal Hydride Hydrogen Storage Tanks in Totalized Hydrogen Energy Utilization System

As a method for simultaneously increasing efficiency of energy use and stability of energy supply in commercial buildings, we have proposed Totalized Hydrogen Energy Utilization System (THEUS) that uses hydrogen as a high potential for energy carrier. The hydrogen storage method used by this system adopts metal hydride that excels in volumetric storage density. In this paper, as the model case for electric power load leveling operation, the optimum design and optimum operation method for multiple metal hydride tanks are described with a mathematical model which can simulate operation of the metal hydride tank and experimental equipment. As a result, the combination of tank specifications and operating conditions that produce the effective simultaneous utilization of 1) hydrogen, 2) metal hydride and 3) heat are identified. Furthermore, an operating method to make the most of the metal hydride tank flexibility with respect to tank selection is determined.Copyright

Fractal map: fractal-based 2D expansion method for multi-scale high-dimensional data visualization

Visualization of high-dimensional data is difficult to realize and manipulate with 2D display. For example, visualizing time-varying volume data (4D) with volume rendering and animation has spatial and temporal shielding, and data of 5 or more dimensions cannot be visualized on 2D display with existing methods. In this paper, we propose a method that expands high-dimensional data onto a 2D image plane. The proposed method uses the self-similarity of the fractal shape and achieves multi-scale high-dimensional data visualization on 2D display. With this method, we can visualize the entire domain of high-dimensional data without occlusions. Also, one-to-one correspondence in the elements of high-dimensional data and its 2D expansion enables us to manipulate high-dimensional data with 2D expanded result as an interface.