Mechanical-drive steam turbines have the heavy deposition of fouling materials on blade and nozzle path surfaces due to contaminated materials such as silica and sodium in steam. As a result, turbine performance tends to be deteriorated gradually. This first paper introduces this fouling phenomena and actual conventional washing procedure in order to prevent the fouling problem and its practical disadvantage by showing thermodynamics analysis. In the second report, the new online washing technology by water injection nozzles is introduced and the most important design factors of this washing system are discussed by showing the results of detail analysis and online washing test results.

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In this paper, a new method for measuring flow velocity has been proposed. It adopts periodic heating as an input signal, and flow velocity is deduced from the phase delay of output signal, coming from adjacent temperature sensors. Since this method doesn't use absolute values of the temperature, but only phase delay, it has a strong robustness against possible noise. We have developed a simplified model based on a quasi-steady state of thermal convection in fluid, and compared the model predictions with experimental results. It's found that the model is able to explain the experimental results qualitatively. The proposed method, which makes use of a micro sensor manufactured by MEMS technique, provides a wide dynamic-range of flow velocity measurements with a simple electronic circuit.

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We are carrying out an investigation on the technology which can extract energy from biomass wastes. This technology combines the pyrolysis and reforming processes to produce clean fuel gas from biomass wastes. In this research, we investigated the influence of fuel properties on gasification performance by comparing wood chips, mushroom bed wastes and fowl droppings as fuels. The experimental results showed that pelletized fuels are effective for stable gasification. And also increase of the air ratio together with increase of the steam ratio to keep the temperature constant at the bottom of the gasifier is effective for increasing the heating value of the pyrolysis gas. The optimum air ratio is different for each kind of fuel.

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Nanoparticles formed in motor vehicle exhaust have received increasing attention due to their potential adverse health effects. But there are a lot of uncertain points for chemical properties and formation mechanisms of diesel nanoparticles. The objective of this study was to characterize nanoparticles emitted from a light-duty diesel engine operated on a dynamometer. Diesel nanoparticles which typically range in diameter from 3 to 30 nm were observed only under idling, high load and deceleration conditions. The formation characteristics of diesel nanoparticles under idling and high load conditions depended mainly on fuel distillation characteristics and sulfur content in fuel, respectively while fuel-cut control of fuel injection in deceleration process had a strong influence on those under deceleration condition. Nanoparticles under idling and deceleration conditions were composed mainly of high boiling point hydrocarbons (heavy hydrocarbons) in fuel and/ or lubricating oil and those under high load conditions consisted of sulfuric acid. The formation characteristics of diesel volatile nanoparticles was controlled by number concentration of accumulation mode particles.

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This study was focused on the volatile nanoparticles consisting of hydrocarbons under idling and deceleration conditions. Diesel nanoparticles were collected on aluminum substrates using an impactor (MOUDI and Nano-MOUDI) and were analyzed with a gas chromatography-mass spectrometry (GC/MS) and a time-of-flight secondary ion mass spectrometry (TOF-SIMS). Main components of the volatile nanoparticles under idling and deceleration conditions were some combination of the lubricating oil and the fuel heavy hydrocarbons (> C₁₉). Oxygenated fuel hydrocarbons and > C₃₅ lubricating oil hydrocarbons which had lower volatility than the main components had were detected in the volatile nanoparticles under idling and deceleration conditions respectively. We could simulate the volatile nanoparticles were formed via homogeneous nucleation of these lower volatile molecules, considering the existence of the lower volatile molecules in engine-out exhaust. It was concluded that the lower volatile molecules (oxygenated fuel hydrocarbons and > C₃₅ lubricating oil hydrocarbons) were nucleation materials and the formation of the volatile nanoparticles consisting of hydrocarbons was dominated by homogeneous nucleation.

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This paper proposes a numerical method for solving the unsteady incompressible Navier-Stokes equation at high Reynolds number by a modified fractional step finite element method. This method is based upon the velocity correction method and uses two concepts to conduct intermediate velocity. The first is the streamline method, which provides an accurate multidimensional generalization, and the second is the balancing tensor diffusivity, which is used as the artificial diffusion for the stabilization techniques. The accuracy of this method for the advection-diffusion equation is demonstrated for the rotating cone problem. The unsteady incompressible viscous flows, such as square cavity flow at Re ≤10000 and flow past a circlar cylinder at Re ≤2000, are simulated without any numerical instability.

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We investigate the influence of numerical diffusion for the Ghost Fluid Method (GFM) in which the interface is captured with the level set method. The shock-bubble interactions are simulated using several numerical schemes for the reinitialization procedure of the level set function. It is shown that the interface is not captured accurately using the GFM without the reinitialization of the level set function. The numerical diffusion in the reinitialization procedure affects the formation of a re-entrant jet and vortex structures after a shock wave impacts the bubble; higher order scheme is needed to discretize the convection terms in the reinitialization equation. It is also shown that the accurate interface capturing is realized by using the hybrid particle level set method. The results with the hybrid particle level set method agree well with the experiments by Hass & Sturtevant.

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The present work is concerned with the improvement of the Ghost Fluid Method (GFM) for gas-liquid two-phase compressible flows. We have improved the GFM by correcting velocities, pressure and density at boundary nodes using the Riemann solutions to avoid numerical oscillations near the gas-liquid interface. Also, the definition of the values for ghost cells has been improved. The improved GFM is applied to one-dimensional shock tube problems, the interaction between a water shock wave and a cylindrical gas bubble, and the interaction between an air shock wave and a water column. It is shown that the correction with the Riemann solutions is effective in diminishing the numerical oscillations near the interface. We have succeeded in capturing the sharp interface for the shock-air bubble interaction with good mass conservation. The present numerical result for the interaction between an air shock wave and a water column is in good agreement with the experiment by Igra and Takayama.

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A new reconstruction method called Generalized Vector Sampled Pattern Matching (GVSPM) was applied to the image reconstruction of an electrical capacitance computed tomography (ECT) in freely falling particles in a vertical pipe. This new method is able to achieve stable convergence without the use of an empirical value. Experiments were carried out using three particle types with various electric charges and four particle flow rates to measure the capacitance of a pipe cross section. The three particle types were polyethylene pellets (PP), silica sand (SS) and polyvinyl chloride (PVC). Four flow rate settings were used resulting in a volume flow rate ranging from3.08×10^-5 to 1.04×10^-3 [m³/s]. The GVSPM method is compared with conventional methods in terms of volume fraction, residual capacitance, and capacitance correlation. Overall, the GVSPM method proved superior to conventional methods in the case of polyethylene pellets with high electric charge. GVSPM achieves accurate reconstruction by using an objective function that is calculated as the inner product calculation between the experimental capacitance and the reconstructed image capacitance.

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The difference of the influence of numerical viscosity between the Navier-Stokes based finite difference method and the finite difference lattice Boltzmann mathod is shown. In order to stabilize calculation, upwind schemes with numerical viscosity is generally used in the finite difference lattice Boltzmann method. The influence of numerical viscosity is dependent on a Mach number. The dependence to the direction of the flow of numerical viscosity is small as compared with the Navier-Stokes based finite difference method.

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The smoothed particle hydrodynamics (SPH) method developed by Lucy, Benz, Gingold, Monaghan and Liversky has a problem of numerical disorder at the boundary of 2 phase flow as gas and liquid. In this paper, new formulas of SPH method, named Relaxation equations, suited for treating 2 phase flow of non-viscous fluid are proposed. The Relaxation equations are constructed based on the mass conservation equation and the momentum conservation equation. By using the formulas, it is possible to suppress numerical disorder around the boundary of 2 fluids.

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This paper deals with a flow of an aqueous polymer solution due to a rotating disc in a cylindrical casing with aspect ratio H/R=2, where H and R are the height of the cylindrical casing and the radius of the rotating disc, respectively. As the aqueous polymer solution, polyacrylamide (PAA) solutions whose concentration was 0.025, 0.1, 0.2, 0.5, 0.8 and 1.0 wt% were used. The unsteady behavior of the flow has been investigated using sectional and three-dimensional flow visualization techniques. The unsteady flow patterns were classified using the Reynolds and elastic numbers. It was revealed that a ring vortex formed near the center of rotating disc was periodically shed away from near the rotating disc.

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Numerical methods for predicting heterogeneous bubbly flows in bubble columns are indispensable in the design of bubble column reactors. The objectives of the present study are (1) to experimentally investigate the effects of a bubble size distribution on heterogeneous bubbly flows in an open vessel and (2) to examine the applicability of the NP 2 model ((N+2) -field model) to heterogeneous bubbly flows. Distributions of void fraction and liquid velocity in air-water bubble plumes in the vessel were measured using an experimental setup with a bubble injection device by which the ratio of the volume flow rate of large bubbles to that of small bubbles was controlled to a desired value. The main conclusions obtained were as follows : (1) experimental data on the effects of bubble size distribution on air-water bubble plume were obtained, and (2) the NP 2 model gave good predictions for heterogeneous bubbly plumes.

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Experimental study was made on the multu-dimensional behavior of upward gas-liquid two-phase flow through a vartical pipe with an axisymmetric sudden expansion. In this study, the liquid velocity and turbulent intensity along the flow direction in the sudden expansion channel were measured by using a hot-film anemometer for various turbulent flow conditions. The development of the liquid velocity and the turbulent intensity profiles of the sudden expansion showed quite complicated behaviors depending upon the flow rates of gas and liquid phases as well as the bubble size. Especially, it was noted that the turbulent intensity was enhanced near wall region, otherwise suppressed near central axis region due to the void blanket staying at the shear layer in the sudden expansion. These results would become useful data for the development of multi-dimensional analysis in two-phase flow.

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The flow past the ring-type manipulator with permeability was investigated by measuring the mean flow field. The manipulator used in this study has a rectangular cross section with a height of 0.14 times the pipe radius. Main parameter was the ring open-area ratio (β) with values of 0, 0.1, 0.2, 0.3 and 0.4. The experiments were conducted for Reynolds number of Re=4 × 10⁴ to 10 × 10⁴. The results indicate that as the ring open-area raito is increased, the separated shear layer arising from the ring top becomes weaker and the pressure loss reduces by increasing fluid flow through the manipulator ring. The critical ranges of a were identified, which provides useful references of engineering applications. When a is less than 0.2, the velocity gradient is steeper over the ring and in the shear layer near the reattachment region. When β is greater than 0.3, the width of the shear layer shows a relatively large augmentation and the back pressure in the separating region increases. There is no re-circulation flow behind the manipulator ring due to the large bleed flow through it in the case of β =0.4.

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In this paper, we investigate the velocity-scalar joint statistics and their Reynolds number dependence in an axisymmetric turbulent jet diffusion field of high Schmidt-number matter. The diffusing fluid is a water solution of a commercial dye (Sc≅3800), and three different issuing Reynolds numbers are chosen, i. e., 6.3×10³, 9.5×10³ and 1.3×10⁴. Simultaneous measurements of the longitudinal velocity and concentration have been made by a combined probe of an I-type hotfilm and a fiber-optic concentration sensor. It is found that the distribution of the axial-flux probability density function (PDF) has a positive skewness, and its slope of negative tail tends to become gentle as the Reynolds number increases. The axial mean velocity conditioned by the concentration shows a good linearity to the concentration on the jet centerline. The derivative PDFs of the velocity and concentration have the exponential tails. The derivative skewness of the velocity is negative. On the other hand, the PDF of the derivative concentration shows almost symmetric distribution in the present case.

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A new idea has been proposed to deaerate liquid flowing in a channel on an on-line basis, utilizing a near-vacuum cavity formed on the wall downstream of the point of separation in most vigorous cavitation. The idea has been materialized such a concrete method as connecting a vacuum pump to the cavity formed in a cylindrical constriction and sucking out gas coming out successively from the surrounding liquid. When the method was tested in a hydraulic unit with 25 L of oil in the tank, the gas solubility in the oil was lowered by 40% in 30 minutes. The two experimental factors such as a flow rate through the constriction and air dissolution from atmosphere were examined in the same test unit in terms of their effects on the method's capacity, showing that a larger flow rate results in a better deaseration capacity and a float covering the free surface of oil in a tank works to improve the capacity by preventing air dissolution into the oil. When the critical flow rate at which an incipient cavity emerged on the entrance edge of the cylindrical constriction was measured for oils with different air solubilities, it turned out a 60% reduction of gas solubility increased it by 33%. Moreover oil cloudy with cavitation bubbles after a start of deaeration became more and more translucent as the deaeration proceeded.

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The objective of the present paper is to investigate Reynolds number dependence of separation and reattachment process over a backward facing step in a low Reynolds number range. A study on low Reynolds number flow such as the flow around the micro device is strongly required in MEMS development. The Reynolds number based on step height is set at 133 to 3690 in a micro sensing wind tunnel. The reattachment and separation points are determined from the detailed measurement on forward flow fraction by Micro Flow Sensor, and the vortex structure is visualized with a high speed video camera. The results show a strong dependence of Reynolds number on the flow behavior on the step and opposite-side wall downstream of the step.

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Annular two phase flow is encountered in many industries which use steam generators in power plants and boilers. Especially, disturbance wave flow which large water lumps move with faster velocity on the thin water film in annular flow region is an important flow regime, since dryout of water-film always occurs at the thin base film between two successive disturbance waves in the case that the interval of the disturbance waves become large accidentally. Therefore, it is important to clarify the behavior of disturbance waves and base film. However, mont of the studies with respect to the behavior limited to the adiabatic flow, that is, air/water system, and even in the boiling flow limited to the behavior of only disturbance waves (frequency, velocity, and spacing). Therefore in this paper we focused on not only the behavior of the disturbance wave but also the base film in the boiling upward annular two phase flow. The results are summarized as follows : (1) Liquid film thickness in steam-water system fluctuates at random compared with air-water system. This is because the flow in steam-water system is always developing toward downstream side due to the heating. In particular, liquid film thickness in steam-water system does change largely with low frequency in the case the flow is accelerated rapidly due to the high heat flux. These large liquid lumps seem to be the traces of the liquid slug in the froth flow region. (2) Liquid film thickness fluctuation in steam-water system is influenced by the heating length clearly. However, statistical film thickness characteristics, i.e., minimum, average, and maximum film thickness, are almost the same even in the different heating length. (3) The dryout always occurs at the thin liquid film between large liquid lumps which are the traces of liquid slug in froth flow region.

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An NO-LIF imaging spectroscopy of A²Σ+→X²Π (0, 0) excitation (225-226 nm) and A²Σ+→X²Π (0, 2) emission (246-248 nm) was applied to methane-air flames with equivalence ratio of 0.8, 1.0, 1.2, and a methane diffusion flame for measuring mole fractions of nitrogen monoxide (NO) and temperature. The mole fractions were determined comparing the NO-LIF intensities of non NO-seeded and NO-seeded cases. Temperatures in flames were also obtained using two-line method. Nitrogen monoxide was doped in both burner nozzle flow and surrounding air co-flow to enable two-dimensional measurements of mole fraction in the flanges. The results of NO mole fraction images which should be closely correlated to the obtained temperature distributions showed good agreement with the well known NO formation mechanisms. Narrow-band filters for removing non-resonant lights were not enough to remove the strong Mie scattering of laser light by soot in the diffusion flame. Introduction of an imaging spectrometer provided high signal-to-noise ratio of NO-LIF imaging. The NO-LIF acquisition technique for the diffusion flame also revealed that NO A²Σ+←X²Π (0, 0) excitation was a good choice to capture strong NO-LIF while avoiding non-resonant lights such as LIF of soot precursors and Laser Induced Incandescence (LII) of soot.

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For the development of a better thermophotovoltaic (TPV) power generation system, it is important to develop a spectrally-selective functional emitter which emits an infrared radiation spectrum to match the spectrally-selective absorption spectrum of the adopted photovoltaic element. In this work, we first present an idea of a coefficient for evaluating the matching performance of such an emitter. The index compares the electric power gain for the case of the functional emitter with that for the case of a gray surface to which the same thermal energy as that to the functional surface is input. The ratio is noted as (COP) _spec. Second, we choose a high-temperature air-oxidized nickel surface as an emitter candidate. This film system has a spectrally-selective emission function based on the radiation interference. We present a spectral experiment technique to determine the condition for fabricating the optimum film system. Third, we make the optimum film system experimentally to clarify the reality of the excellent result of (COP) _spec= 6. It is concluded that this film system is excellent in spectral performance, and that the system has a simple structure for the spectral characteristics to be controlled easily. This surface can be produced in a m²-scale large area, and it is prospective for the thermal energy engineering application.

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This paper describes the heat transfer and flow characteristics of a heat exchanger tube filled with a high porous material. Fine copper wire (diameter : 0.5 mm) was inserted in a circular tube dominated by thermal conduction and forced convection. The porosity was from 0.98 to 1.0. Working fluid was air. Hydraulic equivalent diameter was cited as the characteristic length in Nusselt number and Reynolds number. Nusselt number and friction factor were expressed as functions of Reynolds number and porosity. Thermal performance was evaluated by the ratio of Nusselt number with and without a high porous material and the entropy generation. It was recognized that the high porous material was effective in low Reynolds number and the Reynolds number which minimized the entropy generation, existed.

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An experimental study has been conducted to elucidate characteristics of transient heat transfer during quenching a vertical hot surface with a falling liquid film. The experiment was done at atmospheric pressure for the following conditions : an initial surface temperature from 200 to 400°C, a subcooling of 20-80 K, average velocity of 0.52-1.24 m/s, the block material is copper and carbon steel. The surface temperature and heat flux are estimated from the measured temperatures in the block during the quench by two-dimensional inverse solution. It follows that as the position of wetting advances downward, the position at which the heat flux becomes a maximum also advances downward. The time at which the position of maximum heat flux begins to move is one of the most important parameters and can be predicted by a proposed correlation. In addition, it is revealed that the maximum heat flux depends on the length to which it occurs from the leading edge.

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We present a novel microwave drying as an effective drying method for seafood. Microwave is irradiated in pulse or intermittently so as to keep the temperature of material at around room temperature in a reduced pressure system. Energy of microwave is supplied just for the latent heat for evaporation. Also, by introducing a small amount of external air into the system, water vapor can be effectively carried out of the drying system. We made several experiments using the scallop as seafood. The drying time was successfully shortened as compared with the warm-air drying and the drying at room-temperature results in good quality for dried seafood. Microphotographs of scallop indicate us that the morphological change of the muscular fiber-cells has an important role in water transport. The present drying method prevent from the cell shrink at the scallop surface observed in the warm-air drying, but keep the channel for water transportation to the outside. The new method is proved to be an effective and applicable way of seafood drying.

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In the present paper, experimental studies were performed on a mini-heat transport device incorporating a thermosensitive magnetic fluid. Heat transport systems using magnetic fluids have already been proposed by several researchers, but micro-sized devices of this type have not yet been developed. The device under discussion is made of a Teflon tube of 2 mm inner diameter and is formed in the shape of a loop. The operation of the device is based on the thermo-magnetic characteristics of the fluid, a suspension of Mn-Zn ferrite particles in kerosence, the magnetization of which is known to decrease with increasing temperature. The experimental parameters were magnetic force, the position of the magnet, and the temperature of the magnetic fluid. It was found that the velocity of the thermosensitive fluid could be controlled by changing the magnetic force and the position of the magnet. When there is a temperature difference in the magnetic fluid, the fluid flows automatically in the direction that reduces the non-equilibrium of the magnetic force. Furthermore, it was found that the maximum velocity of the thermosensitive magnetic fluid, without the use of a pump, was about 20 mm/s.

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A nonivasive technique was developed to measure the thermal conductivity and the thermal diffusivity of biological materials. This technique involves laser heating and infrared thermometry of target surface. The thermophysical properties are determined by comparing measured temperatures with those calculated analytically using an appropriate model. In this paper, heat transfer models that incorporate heat loss from the surface and laser absorption within the material were discussed. The accuracy of measurement was then examined using simulated experimental data that were generated by adding perturbation to a theoretical temperature response. The thermal conductivity and the thermal diffusivity of biomaterials, which are similar to those of water, are expected to be determined within an error of 1%and 6%, respectively.

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PEFC was simulated to the equivalent circuit with four resistances and three capacitances, and accuracy of these estimated value were investigated in AC impedance method. Results show that the estimation reliability of these characteristics can be quantitatively evaluated by coherence function value, and improved by nonlinear least squares technique. Integral calculus by current density i of the R₃ and R₄ (∫ (R₃+R₄) di) shows very good correlation to cathode overvoltage (OV) at lower current density region where cathode concentration OV is negligible small. The ∫R₃di suggests cathode activation OV and corresponds with Butler·Volmer's equation.The ∫R₄di suggests cathode concentration OV and increases with current density increase. Sum of the OVs (∫ΣR_idi) and output voltage is lower than Nernstian potential, which shows unknown OV is more than 20%. Analysis and improvement of the unknown OV will make big performance increase in PEFC.

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A new analytical method which divides the cathodic overvoltage (OV) in PEFC into the activation and concentration OVs has been developed. In this method, PEFC is simulated with an equivalent electric circuit consisting of resistances and capacitances, whose characteristic values are estimated by FFT (Fast Fourier Transform) impedance method. When oxygen gas is supplied into the cathode, the activation OV can be regarded as dominant since the cathodic OV obeys the Butler-Volmer equation. This is due to the negligibly small concentration OV. On the other hand, when air is supplied into the cathode, the cathodic concentration OV can be calculated by subtracting the cathodic activation OV from the cathodic OV. This concentration OV is larger than that measured with conventional method in high and limiting current density region. In addition, unknown OV which is obtained by subtracting the cell voltage, cathodic, anodic and ohomic OVs from the Nernstian potential (E) is investigated. Although the unknown OV is almost constant for the current density and in good agreement with the difference between E and OCV (Open Circuit Voltage) in the case of the oxygen operation, it decreases in large current density region in the case of the air operation. This suggests that the unknown OV decreases with decrease in side reactions such as H2O2 formation, which may be due to the smaller oxgen concentration in the supplied gas.

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This paper examines the effects of energy exchange between droplets and the gaseous phase as well as latent heat on evaporative cooling effects due to droplet group combustion. In addition, a parcel model on numerical simulations of spray combustion is investigated. Two-dimensional direct numerical simulations of spray flames in a laminar counterflow are employed. The results show that the contribution of evaporated vapor enthalpy has the strongest influence on the energy exchange and the latent heat causes the reduction of gaseous temperature in the droplet group flame. Furthermore, the use of the parcel model has the risk of causing a delay in the combustion reaction since the partial fuel vapor pressure increases at limited locations, which suppresses the global droplet evaporation rate.

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In this study, numerical simulation on fluid flow and secondary combustion reaction in a converter has been conducted, where CO formed from the high-temperature molten steel is reacted with oxygen. With top blowing lance, the oxygen jet impinges on liquid metal to produce a cavity under gravity. To consider two phases, molten steel and mixture of O₂, CO, CO₂, the Lattice Boltzmann method is used. As for the combustion reaction, the flameter model and finite reaction model are used to discuss the mass and heat transport in the conveter. Results show that the time-averaged cavity shape corresponds to the empirical model derived from the experiments and theoretical consideration. Then, the fluctuated liquid surface with the oxygen jet impingement is well simulated. By increasing the oxygen injection velocity, the surface of molten steel is largely wrinkled. The convection and reaction of CO are affected, with smaller secondary combustion ratio.

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In order to clarify the mechanism of heat loss in DI diesel engines, total amount of heat loss to the combustion chamber and local heat flux at various locations on the piston head were measured by using a rapid compression and expansion machine. High-speed direct photography of spray flame was carried out and flame temperature was obtained by two-color method. In order to investigate the effects of the flow induced by the spray and its impingement on the chamber wall on heat loss, swirl ratio was varied from 0 to 5 and two different fuel injection nozzles (φ0.15 mm ×4 and φ0.10mm × 10) were used. The measured local heat flux exhibited more uniform distribution with theφ0.10mm×10 nozzle than with the φ0.15 mm ×4 nozzle, and at higher swirl ratio. The heat loss amount during the single cycle increased with the increase in swirl ratio due to the increased heat loss after the combustion period. The heat loss amount during the combustion period was almost constant regardless of the swirl ratio. The heat loss amount during the single cycle and the combustion period were not very different between the two different nozzle cases. The magnitude of heat flux at flame impinging point did not significantly vary with the nozzle orifice diameter. This is because the effect of the reduced impinging velocity is cancelled out by the effect of the increased flame temperature in the case of smaller orifice diameter on the heat flux.

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