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Energy and Environmental Technology
The Energy Engineering Department works on technologies related to new energy, energy conservation, and environmental protection. Some of the latest research topics are described below.
Silicon melt convection studies for development of high efficiency solar cells
Technology for the production of high quality silicon substrates is fundamentally important in the development of high efficiency solar cells. The Floating Zone (FZ) process is known to be better than other crystal growth processes (eg. Cochralski and Bridgeman methods) because it does not involve a crucible process. The main purpose of the research described here is to understand the effect of radio frequency (RF) heating, which is widely used in industry, on the flow and temperature fields in the melt.
Flow and temperature fields in the silicon melt in the FZ process have been investigated both numerically and experimentally. A typical numerical simulation result is shown in the Fig.1. It is clear that RF induced convection is dominant and opposite to Marangoni convection which can be seen near the feed and the crystal. RF induced convection is about 10 times that of Marangoni convection, and strong fluctuations are observed in both temperature and flow fields. Strong crystal striations are therefore to be expected. Experiments using X-ray radiography confirmed the numerical results.
Fig.1 Flow (left) and temperature (right) distribution in the RF-FZ silicon melt.
Clearly a melt convection control system is required to achieve high quality silicon crystals and an external system to apply a magnetic field during the RF-FZ crystal growth process is currently under development. [115]
Low Reynolds number flow problems in ceramic gas turbines
The Agency of Industrial Science and Technology is involved in a project to develop a 300kW ceramic gas turbine with target efficiency up to 42% and turbine inlet temperature of 1350℃. The high inlet temperature gives rise to low Reynolds (Re) numbers in the vicinity of the turbine section with consequent separation of the flow from the blade surface and end walls. The fundamental aerodynamic characteristics of turbine cascades at low Re are under investigation at MEL in order to improve turbine performance.
(a) Photograph (b) Trace of oil film
Fig.2 Flow pattern on suction surface (Re=6.0E+04)
Cascade wakes were measured using a hot wire probe and a five-hole pressure tube at Re numbers ranging 2.0E+04 to 12.0E+04. The Fig.2 shows the flow pattern on the suction surface of the annular turbine nozzle blade at Re=6.0E+04, obtained using oil film visualization. At low Re, the flow structure in the annular cascade is three-dimensional and quite complex. Moreover, the flow separation and boundary layers are strongly influenced by Re. The overall pressure loss increases significantly as Re is reduced, for example at Re=2.0E+04 the pressure loss is 1.67 times that at Re=12.0E+04. These results show the importance of correct design of turbine blades for low-Re conditions.
Ignition control of H2-02 mixtures using an ultra-violet laser (WE-Net Research)
Fundamental technologies for clean and efficient power generation systems have been developed at MEL as part of the WE-NET (International clean energy network using hydrogen conversion) project. WE-NET is a large-scale project which will provide a comprehensive solution to the global dilemma of producing and using energy while simultaneously preserving the environment.
Combined turbine systems using H2-02 Combustion with steam recirculation have potential to achieve high thermal efficiencies - up to 60%. Basic data for developing this type of turbine system have been obtained at MEL through research on the combustion characteristics of stoichiometric H2-02 - H20 mixtures. In this work, chemical kinetics simulations showed that burning velocities decrease monatonica11y as the pressure increases, even at high temperatures. Control of combustion is clearly important. [120]
As part of this work, techniques for combustion initiation using photochemical reactions are also under development. It was found that the threshold laser energy required to initiate combustion decreases drastically if ozone is added to the H2-02 mixture. Using a sheet of light from a UV laser we were able to achieve simultaneous ignition over a wide flat plane using a photochemical reaction, as shown in the Fig.3. The method has potential for control of bulk ignition using UV light.
Fig.3 Ignition process of flat ignition. (H2:66.7%, 02:33.3%, (03:1.4%), Frame speed 5,000,000f/s, Incident laser energy 569mJ, FIow speed of mixtures : 2.1m/s)
Hydrogen Internal Combustion Stifling Engine
A new hydrogen internal combustion Stirling engine has been proposed for efficient, small scale power generation in the future. Shown in the Fig.4, this engine uses catalytic combustion of a stoichiometric H2-02 mixture injected into the working fluid which may be hydrogen or helium. Combustion provides thermal input to the engine and the cycle finishes when water is removed from the engine at the cooler.
A GPU-3 Stirling engine equipped with a conventional catalytic combustor was simulated using an adiabatic model. It was assumed that the catalytic combustion was diffusion controlled and that there was no interaction between the flow pattern predicted by the adiabatic model and the small amount of injected gas. The simulation showed that a conventional catalytic combustor has sufficient performance to suppress 02 Concentrations to a safe level but that high H20 concentrations may cause condensation in the regenerator. The work also showed that, while an increase of 5% in boiler efficiency is possible due to direct thermal input to the working fluid, the work required to compress the injected gases is not negligible for this type of engine. Several problems remain to be solved including condensation in the regenerator and the work necessary to compress the injected gases. The simulations are continuing together with experimental studies in order to assess the feasibility of this engine. [124]
Fig.4 Concept of hydrogen internal combusion Stirling engine.
Tyre characteristics on icy roads
Tyre performance on an icy road depends very much on the characteristics of the ice, and tests on different ice tracks can give rise to different results. It is important to find a scale to provide reliable characterisation of the ice to make tyre performance tests consistent.
Work of MEL showed that the electrical conductivity of water made by melting ice on the road surface may be used as an indicator of the properties of the ice. An even quicker measure is to simply measure the surface resistivity of the ice. The Fig.5 shows crystals in two different ice samples and their conductivities (μS/cm).
Fig.5 Pictures of Ice Crystal used for Tests.
Fig.6 Coefficient of Friction vs. slip Ratio Curves.
Tests on an indoor tyre test rig confirm that the tyre characteristics are affected by the ice (Fig.6 (a)). In order to understand this phenomenon better, it was simulated numerically using a model based on the friction heat generated between the tyre and the ice. Here, friction is mainly determined by the thickness of the thin film of water generated under the tyre by friction. The results of the simulation agree well with test results (Fig.6 (b)). [102]
DeNOx catalysts for diesel engines
Studies of selective deoxidisation catalysts (DeNOx catalysts) are in progress towards development of techniques to control nitrogen oxides in diesel exhaust emissions. Ag/Alumina catalytic converters with a trap oxidiser have been tested in an attempt for simultaneous reduction of NOx and particulate emissions. The effects of reaction temperature, the hydrocarbons used as reducing agents, space velocity, and gas velocity on the reaction characteristics were analysed experimentally. The Fig.7 shows the surface profile of an Ag/Alumina catalytic converter obtained with a STM. It was found that the NO reduction ratio of the converter approaches 100% under ideal conditions, and that space velocity has the most critical effect on reduction ratio.
Fig.7 STM surface profile of Ag/Alumina catalytic converter.
Wind turbine generator performance in complex terrain
The Wind energy group at MEL has measured the performance of the NEDO 500kW prototype wind generator at Tappi. The average annual wind speed is about 10m/s, but it is very difficult to obtain an accurate performance measurement due to the complex terrain, and even the IEC standard for performance measurement to be published in 1998 is unable to describe this situation adequately. In this work, a reference meteorological mast was used to obtain accurate site calibration data. By calibrating the wind characteristics and processing the generator performance data with the "method of bins", the performance of the generator was successfully analysed even in this complex terrain (black half-circles on the power curve in the Fig. 8). This method of performance measurement will be used to help complete the IEC Standard on Power Performance Measurement in complex terrain. [110]
Fig.8 Power performance of NEDO-500kW WTGS (U:wind speed, P:output power)
Any enquiries regarding this project should be directed to e-mail: energy0@mel.go.jp
List of Publications (1997)
Energy and Environmental Technology
102) M. Nihei and K. Shimizu
Effect of Frictional Heat in Tire Characteristics on Ice
Trams. of the Soc. of Automotive Engineers of Japan 28-1 (Jan. 1997), pp. 89〜94
103) B. Burtsitsig, A. Yabe and N. Wakayama
Quantitative Analysis of Convective Flow of Nitrogen Gas and Air under Magnetic Field
Grandient Trams. JSME (Ser. B) 63- 607 (Mar. 1997), pp. 141〜147
104) A. Yabe, K. Nakagome, M. Tanaka, F. Takemura, Y. Kobayashi and Per- Erling FRIVIK
Microscale Analysis of Crystals in Ice Slurry Made from an Antifreeze Protein Solution
Trans. JSME (Ser. B) 63- 607 (Mar. 1997), pp. 283〜288
105) A. Yabe
Evaluation Methods of Global Environment Protection Technologies: Current Status and Their Importance
Proc. JSME Anual Meeting (V) (Mar.-Apr. 1997), pp. 78〜79
106) Q. Jiang, N. Aya and F. G. Shi
Nanotube Size-dependent Melting of Single Crystals in Carbon Nanotubes
Appl. Phys. A 64 (Apr. 1997), pp. 627〜629
107) S. Grandum, A. Yabe, A. Nakagome, M. Tanaka, F. Takemura, Y. Kobayashi,
K. Ikemoto and Per-Erling FRIVIK
Investigation of the Characteristics of Ice Slurry Containing Antifreeze Protein for Ice Storage Applications
Trans. JSME (Ser. B) 63- 609 (May 1997), pp. 282〜288
108) K. Yamashita and A. Yabe
Electrohydrodynamic Enhancement of Falling Film Evaporation Heat Transfer and its Long -Term Effect on Heat Exchangers
J. Heat Trans. 119 (May 1997), pp. 339〜347
109) Y. Kawaguchi, H. Daisaka, A. Yabe, K. Hishida and M. Maeda
Existence of Double Diffusivity Fluid Layers and Heat Transfer Characteristics in Drag Reducing Channel Flow
Proc. 2nd Int. Symp. Turbulence, Heat and Mass Trans., (Delft)(Jun. 1997), pp. 157 〜166
110) H. Matsumiya, H. Imamura and K. Tsuchiya
Wind Measurements and Performance Analysis of a WTGS in Complex Terrain
Proc. Int. Conf. on Fluid Eng. ICFF'97 V (Jul. 1997), pp. 1557〜1562
111) A. Yabe
Advanced Heat Recovery and Energy Tramsport Technologies for Eco-energy City Concept
Proc. JSME Thermal Eng. Symp. [No.97-6] (Jul. 1997), p.1
112) S. Grandum, A. Yabe, M. Tanaka and F. Takemura and K. Nakagomi
Characteristics of Ice Slurry Containing Anti-freeze Protein for Ice Storage Applications
J. Thermophysics And Heat Trans. 11-3 (Jul.-Sep. 1997), pp. 461〜466
113) M. Shiraishi, N. Nakamura, K. Seo and M. Murakami
Visualization Study of Velocity Profiles and Displacements of Working Gas Inside a Pulse Tube Refrigerator
Pulse- Tube Modeling and Diagnostic Measurements (1997), pp. 355〜364
114) A. Yabe, S. Terakado, J. P. Longtin, M. C. Hipwell and Chang-Lin Tien
Thermoelectric Characteristics of Microscale Thin Film Thermocouples
Microscale Thermophysical Eng. 1 (1997), pp. 53〜60
115) T. Munakata and I. Tanasawa
Flow Field under RF Heating on FZ Crystal Growth Process
Proc. 1st Int. Symp. on Flow Visualization and Image Processing 2 (1997), pp. 627〜632
116) A. Murakami
An Attempt of Moving Bottom Auxiliary Combustion Chamber to Reduce Diese Particulate and NOx
SAE Paper 970316 (1997), pp. 1〜11
117) J. Y. Koo, S. T. Hone, Joseph Shakal and S. Goto
Influence of Fuel Injector Nozzle Geometry on Internal and External Flow Characteristics
SEA Paper 970354 (1997), pp. 245〜257
118) T. Kagazyo, K. Kaneko, M. Akai and K. Hizikata
Methodology and Evaluation of Priorities for Energy and Environmental Research Projects
Energy 22 (2/3), ( 1997), pp. 121〜129
119) M. Akai, N. Nomura, H. Waku and M. Inoue
Life Cycle Analysis of Fossil Power Plant with CO2 Capture and Sequestering System
Energy 22 (2/3) (1997), pp. 249〜255
120) N. Iki, H. Furutani, J. Hama, S. Takahashi, O. Kurata and H. Ryu
Laminar Burning Velocity of Stoichiometric Hydrogen- Oxygen- Steam Mixture under High Pressure
Proc. 4th Japan- Korea Joint Symp. '97 on Hydrogen Energy (1997), pp. 148〜155
121) S. Grandum, Y. Kobayashi, A. Yabe, S. Matsumoto, F. Takemura,
K. Nakagome and Per-Erling Frivik Molecular Dynamics Simulation of Ice Crystal Growth from A Surface Containing Adsorbed Antifereeze Protein
DSC- Vol.62/HTD- Vol.354, Microelectromechanical Systems (MEMS) ASME 1997 (1997), pp. 191〜197
122) F. Takemura, M. Nishio and A. Yabe
Multi-phase Flow Study in Energy Department of Mechanical Engineering Laboratory, AIST, MITI
Japanese J. Multiphase Flow 11- 1( 1997), pp.77〜80
123) M. Hasegawa, A. Yabe and H. Nariai
Numerical Analysis of Electrohydrodynamical Enhancement Mechanism of Forced Convection Heat Transfer in Duct Flow
HTD- Vol.348, National Heat Trans. Conf. Vol.10 ASME1997 ( 1997), pp. 11〜15
124) S. Takahashi et al
Internal Hydrogen Combustion Engine (in Japanese)
1st Stirling Engine Symp. ( 1997) , pp. 37〜39
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