For preventing contamination, precise control of air pressure in rooms is important for biological clean rooms. And ventilation facilities need a function to control air pressure. To design air pressure control systems of ventilation facilities appopriately, an analytical method that can predict the change of air pressure in the rooms is demanded. In this paper, an analytical method of air pressure for ventilation systems is described. This method is baed on the Volume-Junction Method that is used for analysis of one-dimensional pipe flow. In ventilation facilities, the opening and closing of doors is one of the important and peculiar disturbances which cause a change of air pressure. For predicting the change of air pressure, the author proposed an analytical method that substitutes two kinds of equivalent mass flow rates of air for an opening/closing door. By experimental result, provided from a full sized experimental facility, it was demonstrated that the simulation method that combined Volume-Junction Method and the proposed analytical method for opening/closing doors could predict changes of air pressure in the rooms precisely.

抄録全体を表示

We have conducted the basic study on the lattice Boltzmann method from the viewpoint of applying it to many particle suspensions, by considering a uniform flow past a two-dimensional circular particle (i.e., cylinder). Successful application of the lattice Boltzmann method to particle dispersions is strongly dependent on what rough lattice system can be used, since the motion of suspended particles and the flow field have to be solved simultaneously; unless a rough lattice system is used, suspensions with sufficient number of particles cannot be treated in simulations. Hence, the present study mainly discusses the dependence of the flow field on the fineness of the lattice system, and the validity of several boundary models, including a revised boundary one presented here. Even if a significantly rough lattice system with the lattice unit width of one-fifth as long as the particle diameter is used, the results give rise to physically reasonable agreement with the Navier-Stokes solutions. We may, therefore, conclude that the lattice Boltzmann method is a promising tool as a micro-simulation technique with multi-body hydrodynamic interactions for many particle suspensions.

抄録全体を表示

A theoretical approach to the physical behaviors of a continuous media which is modeled by distinct particles has been constructed. The present study has focused on the particle system which expresses the mechanical behaviors of the continuous media by means of the computational mechanical simulation. The physical behaviors of the particles in the system have been investigated analytically in order to conduct the numerical analysis effectively. A basic equation which describes the motion of the particle is derived from the particle system. Since the basic equation is the nonlinear equation which contains the thermal effect, it is analyzed theoretically by using some mathematical techniques. As a result, it is shown that the behavior of the particles has the relation to that of the topological defects. It is found that the time-temperature superposition principle is derived from the particle system. Moreover, the energy conservation law of the particle system is formulated.

抄録全体を表示

A high efficiency small axial-flow fan was designed by using the design tool based on computational fluid dynamics and numerical optimization. For numerical optimization, a simulated annealing algorithm was applied to maximize fan efficiency. The optimized fan efficiency was increased by 17% compared to the initial fan. The initial fan was a conventional product designed by half vortex design. The differences in the blade shapes and the blade passage flow between the initial and optimized fans were investigated to analyze the causes of the fan efficiency improvement. The blade shape of the optimized fan had a different geometry to that of the initial fan in terms of the exit blade ange, solidity, and number of blades. By increasing the exit blade angle, the tip blade loading of the optimized fan was decreased compared to that of the initial fan. The decrease of the tip blade loading suppressed reverse flow and the increase of the deviation angle. The tip blade loading was found to have a great influence on the fan efficiency.

抄録全体を表示

In our previous study, a high efficiency small axial-flow fan was designed by using the design tool based on computational fluid dynamics (CFD) and numerical optimization. The optimized fan efficiency was increased by 17% compared to the initial fan. In this study, a detailed CFD simulation of the initial and optimized fans was carried out to investigate the dominant factors for designing a high efficiency fan. The detailed CFD simulation was conducted to capture the tip leakage vortex. Breakdown of the tip leakage vortex occurred in the initial fan, and the tip leakage vortex interacted with an adjacent blade. Therefore, a reverse flow region was expanded around the vortex core in the initial fan. On the contrary, the breakdown of the tip leakage vortex did not occur in the optimized fan. Therefore, a reverse flow region was not expanded around the vortex core in the optimized fan. The breakdown of the tip leakage vortex significantly affected static pressure and fan efficiency because it caused an increase in total pressure loss. As a result, suppressing the breakdown of the tip leakage vortex was found to improve static pressure and fan efficiency. Increasing the outlet angle at tip, increasing solidity at tip, and decreasing the number of blades were effective in suppressing the breakdown of the tip leakage vortex.

抄録全体を表示

Temperature estimation approach is examined for a heated jet in cross flow using velocity data by PIV and analytical results by CFD. A heated jet form transforms in crosswind since the buoyancy is caused by the difference of the density with fluid surrounding a heated jet. Centered streamline, velocity profile, and exit velocity of a heated jet at nozzle were experimentally measured by PIV, and this parameter is substituted for a numerical calculation as initial condition. The centered streamline obtained from PIV is compared with a numerical simulation by CFD, and the exit temperature at the nozzle is iteratedly replaced with the estimated exit temperature in order to converge with itself, and then the approach of which enables us to evaluate velocity and temperature fields of a heated jet by CFD.

抄録全体を表示

A supersonic jet is utilized in industries to cool a heated material, to blow the dust away from the product and so on, and also used as propulsion of space vehicle in aviation field. The jet is usually underexpanded or overexpanded, having a cell structure. When the jet impinges on materials, the jet oscillates itself and a noise radiates from it. In this paper, the underexpanded jet impinges normally on a thin plate, and oscillation of the jet and vibration of the plate were analyzed at different nozzle-plate spacings. The flow fields between the nozzle and the plate with various thicknesses were compared with each other. As a result, an effect of the flow pattern of the impinging jet was found on the vibration of the elastic plate.

抄録全体を表示

Applying micro spray of electrostatic inkjet to precision film coating was examined experimentally. High quality coating could by expected by drops-on-drops of super fine and mono-diameter droplets. At first, the most preferable jetting condition was determined through experiments with dilute dispersion of photo-sensitive pigment. Then, with those parameters examined, the surface quality of the coated films was evaluated through several coating tests. According to the increment of applied voltage, jetting mode was varied from Mode 1, dripping, to Mode 2, jetting. Most favorable condition for coating was found to be cone-jet mode in Mode 2, where well-oriented thread was jetted from the stable Taylor Cone at the nozzle tip and broken up into spray state during flight. Uniform and submicron film could be demonstrated by piling up the droplets several times, whose diameters were less than 10 micrometers, although unknown processes such as drying during flight, leveling phenomena on a coating substrate should be elucidated to meet industrial needs.

抄録全体を表示

The mechanism of bubble coalescence and repulsion is difficult and unresolved. This problem is one of key issues of the numerical research on multiphase flows. In experimental studies, it is revealed that not only a concentration of electrolyte solved in water but also ino-pair specificity are important for bubble coalescence. In our previous study, we qualitatively evaluated the multi-scale multiphase flow equations by simple numerical simulation of 2-dimensional bubble behaviors. In our simulation, a liquid film was observed between two microbubbles. The results indicated the importance of the effect of the contamination at the interface for the bubble interaction. In the present study, the coalescence model is newly developed which is based on the conventional nucleation theory correlated with an electric conductivity due to a contamination in the liquid. A simple 3-dimensional microbubble interaction is simulated with the coalescence model. As a result, we realize the duration of contact before the coalescence of two microbubbles in this numerical simulation.

抄録全体を表示

The effect of a spanwise traveling-wave motion on a zero-pressure-gradient turbulent boundary layer over a flexible sheet was investigated. The test plate placed in wind tunnel consisted of a flexible sheet section, where the traveling wave motion was generated by the vibration device with a crank, and the upstream and downstream smooth rigid wall sections. Velocity profiles were measured by single and cross hot-wire anemometry. Amplitude and frequency of the traveling wave motion were measured using two laser displacement sensors. The drag reduction ratio was estimated from the friction coefficients through the growth rate of the momentum thickness of the turbulent boundary layer over the flexible sheet section. The maximum drag reduction of up to 13% was obtained. The quadrant analysis of streamwise and wall-normal velocity fluctuations revealed that the drag reduction was attributed to the reduction in the sweep event and the increase in the negative contribution of the inward-interaction event to the Reynolds shear stress due to the sheet displacement fluctuation.

抄録全体を表示

The reduction of aerodynamic drag for vehicle is an important item in vehicle engineering. However, as an automobile is strongly oriented to denign, aerodynamic drag coefficient C_D must be reduced maintaining the flexibility of design. In order to do so, it is necessary to clarify the characteristic flow structure around vehicle that increases C_D. As a secondary report, this study focuses on the flows in lateral side and under-floor of vehicle to clarify the characteristic flow structure that increases C_D using a sedan type vehicle, which has greater freedom of design. As a result, the flow from front bumper and the flow blowing out from wheelhouse in lateral side were clarified to have an impact on increase of C_D. The vortices under the floor generated by a flow blowing out from engine compartment were also identified to have an impact on C_D. It was clarified that the vehicle's trailing vortices dominant against C_D enhanced as those flows/vortices enhanced and front pillar vortices above trunk deck also enhanced (clarified in the initial report).

抄録全体を表示

Condensate drop moves spontaneously in Marangoni dropwise condensation due to the surface tension distribution along the condensate surface which is determined by a bulk temperature gradient on the condensing surface. The objective of this study is to investigate experimentally the mechanisms which decide the velocity of drop movement. The velocity of drop movement is considered to be affected by surface tension gradient, concentration of vapor mixture and the shape of condensate drop. In this study, the initial drop distance of condensate drops, which was considered to be related to the shape of condensate droplets, was measured in Marangoni dropwise condensation of water-ethanol binary vapor mixture, and its effect on condensate drops movement was investigated. It is shown that the velocities of drop movement are not only affected by the vapor concentration and surface tension gradient, but also have a strong relationship with the initial drop distance of condensate drops. The velocity of drop movement has maximum value against the initial drop distance.

抄録全体を表示

The mass transfer characteristics of gas diffusion layer (GDL) are closely related to cell performance in polymer electrolyte fuel cell (PEFC). In this study, the oxygen diffusivity of the paper type porous media used generally as GDL with respect to its liquid water content were measured by using an experimental apparatus consist of oxygen sensor based on Galvanic battery. Experimental results indicate that paper type GDLs have a relationship where the relative oxygen diffusivity increases nonlinearly as the water saturation decreases.

抄録全体を表示

We investigate experimentally flow and heat transfer characteristics of a turbulent natural convection flow with sub-millimeter bubbles along a vertical heated plate. Thermocouples and a particle tracking velocimetry technique are used for temperature and velocity measurements, respectively. The heat transfer deterioration occurs at a low bubble flow rate (33mm^3/s), while the heat transfer enhancement occurs at another bubble flow rate (56mm^3/s). For higher bubble flow rate, the ratio of the heat transfer coefficient with bubble injection to that without injection ranges from 1.2 to 1.3. It is considered from velocity measurements that this heat transfer enhancement originates from both the activation of large-scale eddies due to bubbles and the advection effect due to bubbles.

抄録全体を表示

In this study, a prediction model for condensation heat transfer on a vertical dispersed finned surface was proposed, utilizing Adamek-Webb model for the condensation heat transfer outside a horizontal finned tube. The prediction model was based on two main experimental observation results. One is the phenomena of the condensate retention at the bottom of each row of the dispersed fin. Another is the offset phenomena of the condensate flow between each row of the dispersed fin. As the results by the present model, it is predicted that the dependence of the condensation heat transfer coefficient for the dispersed fin on the fin pitch is controlled mainly by the dispersed fin length, not the total fin length. On the contrary, for a different fin pitch, the effect to the condensation heat transfer by dispersing is different. From comparison with the experiment results, it is confirmed that the present model was able to predict the condensation with extremely good precision when the fin pitch was larger. Further, when fin pitch was smaller, the predicted value was higher than the experimental value, but the tendency of the condensation heat transfer with dispersing was nearly predicted. In addition, this condensation model can predict experimental value with an error of 25% at the maximum in a range of fin pitch 0.6mm-1mm.

抄録全体を表示

The aim of this study is to inhibit the natural convection heat transfer on a perpendicular cooling plate. The heat transfer coefficients at several points on the cooling plate were obtained by using multi-type thermocouple method. In the experiment, one plate with periodic grooves in a zigzag state and another with a flat plate surface were used. Each heat transfer characteristic along the plate was compared. Furthermore, a grooved plate a deeper depth was tried in the experiment. The heat transfer coefficient of the plate with the grooves became smaller than that of the flat cooling plate as the thermal boundary layer developed in the grooves.

抄録全体を表示

To conventionaly extend heat transfer area in shell-and-tube heat exchangers, a method is proposed where sheet materials with high thermal conductivities are stretched among tubes. The numerical simulations are carried out to predict the performance of heat exchanger with or without the sheets. As a result, it is found that thermal contact resistances between the sheet and tubes rather than thickness and thermal conductivity of the sheet influence overall heat transfer coefficient. In the experiments, the carbon fibers clothes (27Wm^<-1>K^<-1>) are pass zigzag though the tubes whose pitch is 20mm. The heat transfer rate between hot water flowing in the tube side and air in the shell side are measured. No substantial improvement of heat transfer is unfortunately observed experimentally due to contact thermal resistance. The method proposed in this study conclusively has a potential that the heat transfer rate improves no less than a few ten percents.

抄録全体を表示

The measurement technique using a planar surface coil has advantages of acquiring a local Nuclear Magnetic Resonance (NMR) signal in short time from near the coil. The detection area of the coil depends on the inside diameter of the coil and the number of spin excitations. In this paper, the detection area and measurement depth of the coil in the case of measuring Free Induction decay (FID) signal and spin-echo signal were analyzed theoretically. In acquiring FID signal, the measurement depth of the coil is 0.38 time the inside diameter of the coil. On the other hand, in acquiring spin echo signal, the measurement depth decreases by 0.32 time the inside diameter of the coil. In order to verify the theoretical result, the surface coil with an inside diameter of 0.6mm was used, and the ratio of the intensity of FID signal and spin-echo signal was compared. The theoretical result agrees with the experimental result. Furthermore, the method to adjust the excitation angle of magnetization vector on the surface of a sample to 90 degress is described in this paper.

抄録全体を表示

For the high temperature air combustion (HiTAC), fuel nozzles are commonly located away from an air nozzle. The emission of NO_x from the HiTAC furnace is thought to be related to the distance between these nozzles (ΔL). Objectives of present study are to clarify the effect of ΔL on the NO_x emission. Measurements of the NO_x emission are made in the cylindrical furnace. Propane is issued from the two nozzles located at three different distances from the air nozzle. Preheated temperature of air is up to 1263K. The emission index of NO_x (EINO_x) decreases as an increase in ΔL. The large ΔL enhances the dilution by the burned gas, which leads to a decrease in flame temperature. The decrease of EINO_x is attributed to the decrease in flame temperature. The EINO_x characteristic is evaluated by the residence time and flame temperature. Dilution ratio is introduced to quantify the magnitude of dilution by the burned gas. The flame temperature is predicted by the modified flamelet model with the dilution ratio. The residence time and the dilution ratio are as a function of ΔL. The overall NO_x production rate is found to scale with the flame temperature predicted by the modified flamelet model.

抄録全体を表示

The purpose of this study is to develop high-efficiency Diesel injection nozzle, which is able to obtain the spray with high-dispersion and high-penetration. In this paper, the effects of the atomization enhancement nozzle, which the excellent spray characteristics with short breakup length, large spray angle and small Sauter mean diameter were obtained at low injection pressure, on atomization of intermittent spray at high-ambient pressure condition and application to the actual Diesel injector were investigated. As a result, it was cleared that the spray tip penetration of the atomization enhancement nozzle corresponds to a single hole nozzle for a D. I. Diesel injector, spread of the spray becomes large compared with a single hole nozzle and high-dispersion spray was obtained at the intermittent injection under high-ambient pressure.

抄録全体を表示