The purpose of this paper is to clarify the valve dimensions required to reduce the lateral flow force on the spool caused by inner flow. The flow path of the examined spool valve with the outlet port near the valve orifice is non-axisymmetric. Numerical simulations of three-dimensional flow, flow visualization and pressure measurement were performed to investigate the magnitude of the lateral force and the relation between the force and flow pattern. The lateral force is mainly caused by a flow pattern in which the jet at the opposite side of the outlet port turns along the spool toward the port. The lateral force depends on the magnitude of the circumferential velocity component as well as the jet impinging pattern and the flow pattern near the outlet port edge. It was found that increasing the axial spool length and the bucket depth effectively reduced the lateral flow force.

View full abstract

The compound choking by confluence of two subsonic and parallel streams through a converging duct is experimentally investigated for various ratios of the upstream stagnation pressure to the static pressure at the duct exit. The optical observations by schlieren method are carried out as well as the pressure measurements. The critical pressure ratio across the converging duct when the compound choking occurs at the duct exit is calculated by a simple flow model where the mixing of the two streams is taken into consideration. The calculated results agree well with the present experimental data.

View full abstract

A free-piston shock tunnel is the most capable facility to reproduce hypervelocity flows with chemical nonequilibrium around reentry vehicles. However, performance expected for the free-piston shock tunnel has not been achieved yet, mainly due to the lack of driver-gas volume after free-piston compression, which causes decay of shock wave strength and reduction in test time. In order to overcome this problem, the authors proposed the tuned operation method which enables safe overdriving of piston to maintain driver-gas pressure, and ensured its applicability by the tests in the middle-size pilot facility. Then, based on the tuned operation theory the largest free-piston shock tunnel HIEST was designed and built in the National Aerospace Laboratory. In the present study, the tuned operation of the HIEST was attempted and the effect on the performance of the free-piston driver was discussed.

View full abstract

A ring-type obstacle, which simulated a spacer in Light Water Reactor or a flow obstruction supporting heat exchanger tube, was set in an upward air-water two-phase flow within a vertical tube to investigate the effects of the obstacle on liquid film thickness in relation to the drypatch generation. We measured the axial distributions of time varying liquid film thickness near the obstacle in the range of the superficial water velocity of 0.06-1.6 m/s and the superficial air velocity of 0.5-36 m/s and discussed the effects of the length of the obstacle on the liquid film thickness. The results are summarized as follows: (1) The minimum film thickness and the mean film thickness near the obstacle become thinner as the length of the obstacle becomes shorter. (2) The length of the obstacle has stronger effects on both the minimum and the mean film thickness near the obstacle as the superficial water velocity becomes lower. (3) The generation of drypatch is possible under the flow conditions examined in the present experiment if heat is applied.

View full abstract

A horizontally placed Y-junction was used to separate gas and liquid in gas-liquid two-phase flows in a pipe of circular cross section. The original wettability of the Y-junction was good because it was made of acrylic resin. The wettability of one side of the Y-junction was changed to become poor by coating fluororesin. The motions of bubbles and slugs were observed with a high-speed video camera. The bubbles attached preferably to the wall of poor wettability, and accordingly, the separation of gas and liquid was satisfactorily achieved. The efficiency of the separation decreased as the air flow rate increased and it became zero when the gas flow rate exceeded a certain critical value.

View full abstract

Road tunnels in urban area tend to have diverging and merging roads and ventilation shafts. In such complex tunnels, the dynamics of air flow is so complicated that it is difficult to develop ventilation simulation and control systems by using traditional air flow velocity model based on equation of motion. In this paper, a general model of air flow velocity for complex tunnels is proposed. By using the proposed model, it is possible to simulate one-dimensional air flow velocity in any complex tunnels and shutdown operation without changing structure of the model.

View full abstract

A theoretical and experimental study has been made on the transient radial hydrodynamic forces on a diffuser pump impeller during its rapid acceleration from standstill to final speed. Instantaneous radial hydrodynamic forces, suction pressure, discharge pressure and flow rate were measured for various start-up schemes. Theoretical calculations were developed for the prediction of transient radial hydrodynamic forces and compared with the corresponding experimental results. As the results of this study, it becomes clear that the impulsive pressure and the lag in circulation formation around impeller vanes play predominant roles for the difference between transient and quasi-steady hydrodynamic forces of the diffuser pump during its starting period.

View full abstract

In the present paper, the change of flow structure such as the wall shear stress at the apex of the anterior communicating artery with the initiation of aneurysm is described in steady flow. The anterior communicating artery composing the circle of Willis is one of the predilection sites where the cerebral aneurysm occurs frequently. The flow field around the anterior communicating artery is simulated by two confluent tubes joining at the angle of 60 degrees, two parallel bifurcating tubes, and the junctional tube, bypass, connecting four tubes at normal condition. Once the small aneurysm initiates at the apex in one confluent tube with much flow rate, the distribution of wall shear stress abruptly changes around the initial aneurysm. This change may induce the progressive development of aneurysm. The relation between the initiation and the development of aneurysm is physiologically discussed from the viewpoint of hemodynamics.

View full abstract

In order to analyze the effect of flows on nematic defect nucleation, the isotropic-nematic phase transition processes under shear flows are simulated using second order tensor type theory. The theory includes three major effects of the nematic flows, which are the short and long range order elasticity effects, and viscous flow effect. The point defect structures emerge during the phase transition, as a result of the macroscopic disorder in the molecular orientation field. From the simulation results, it is found that the nucleation of the nematic defect structures is suppressed by the shear flows. The shear flows introduce the extension direction to the nematic liquid crystal materials, and thus the materials evolve to macroscopically ordered systems. Above a certain Ericksen number, no defect structure appears in the materials. Finally, the way to produce defect-free liquid crystal materials is proposed.

View full abstract

Various direct numerical simulations (DNS) of turbulence are performed hitherto. In most of those DNS's, the mean flow is assumed to be steady. This is because the DNS of the turbulence with an unsteady mean flow requires more computational effort to obtain a stable statistical average. In the present study, DNS of turbulent channel flow driven by temporally-changing pressure gradient is performed. The pressure gradient is so determined that the bulk mean velocity averaged over one cycle is approximately equal to the one with a steady state Reynolds number of Re_τs= 180. The each period is divided into twenty phases and statistical average is obtained for various turbulence statistics. Obtained turbulence statistics are compared with steady ones. Number of streamwise vortices decreases in the acceleration period while it increases in the deceleration one.

View full abstract

Present paper deals with viscous drag reduction research in the case of bypass transition on a flat plate with textile surface. Special boundary layers such as one over a swimsuit, sail wing, or ski wear, where certain boundary layer trip structure like folded edges, or mast of the yacht exist, contain limited turbulence level in the boundary layer even in laminar condition. Turbulent transition delay in such typical boundary layers is observed in the case of the textile surface.

View full abstract

A measurement technique for a flow field in a microchannel was developed using sub-micron fluorescent particles. The present study focused on a novel measurement technique so called Spatial Averaged Time-resolved Particle Tracking Velocimetry (SAT-PTV) which is able to detect the temporal variation of a fluid flow eliminating the effect of Brownian motion of the sub-micron tracer particles. Velocity vectors of individual tracer particles were averaged within a local small area, instead of temporal aerage, to realize higher time resolution. SAT-PTV method was evaluated by synthetic particle images in both a uniform flow and a flow with linear velocity gradient and the method confirmed the reduction of the measurement errors associated with Brownian motion. The validation of the present technique was performed in a microchannel flow with the time resolution of 37 ms.

View full abstract

The relation between the vortex shedding phenomena and the resonant noise caused by tube banks was experimentally investigated. We measured the spectrum, the coherence, the phase delay of velocity fluctuations, the gap velocity in the tube banks and the sound pressure level near the duct exit in the case of tube banks that has the same pitch ratio as that of a heat exchanger of a power station. When acoustic resonance occurred at the natural frequency of the duct 343 Hz, we found several peaks with different frequencies, the main peaks being at 343 Hz and 263 Hz of the velocity fluctuation of the flow inside of the tube banks. The coherence of the velocity fluctuations due to vortex shedding in the transverse direction is large in the case with resonance. The Strouhal number 0.22 calculated by vortex shedding frequency 263 Hz and mean gap flow velocity agrees approximately with Strouhal number 0.23 determined by the Fitz-hugh's map. However, the other Strouhal number for 343 Hz is about 0.29, which controls the resonant frequency and is not predicted by Fitz-hugh's map.

View full abstract

Experiments on swirling flows through conical diffusers have been carried out. Mean and fluctuating velocities, and static pressure in three diffusers of different included angle were measured under the various swirl intensity. In addition, relationships between static pressure recovery and flow characteristics were investigated. In the case of weak swirl that the static pressure recovery is improved, it is shown that the separation of the flow from the wall is prevented and the velocity is made rapidly uniform, and additionally that the turbulence is suppressed. In the meantime, the vibration of the pipe is observed in the flow with strong swirl and it is clarified that this vibration is induced by eccentricity of the center of the swirling flow, its center circulating about the pipe axis, from the results of the velocity measurement.

View full abstract

Values of added mass of a vibrating centrifugal impeller were analyzed by using unsteady potential theory. Impeller operating in diffusers with one and two vanes was modeled and the fluid forces were calculated for vibrations in the x and y directions covering various frequencies. Results of fluid forces were converted to mass, damping, stiffness matrices by the Fourier integral and the method of least squares. Mean values of added mass of the impeller in the diffusers which were obtained from mass matrix were larger than those in vaneless diffuser and different for vibrations of x and y directions. It was clarified that the prediction of radial force as the sum the circulation induced lift on the orbiting impeller, and the centrifugal forces on the apparent mass of the impeller was available for the unsymmetrical boundary conditions.

View full abstract

We have been investigating a new cycle concept for advanced propulsion system, in which hydrogen gas is directly injected from turbine blade surfaces and combusted within turbine blade passages. However, in the previous studies, we found that the aerodynamic performance of the blade is largely decreased due to the fuel injection. For the purpose of realizing our concept, turbine blade is required to have the adequate performance even with the hydrogen injection. In the present study, we develop the shape optimization procedure for turbine blade with air injection. Our procedure is based on the gradient method, and composed of some elements, including CFD, geometry modification and design point arrangement, in which design points are automatically clustered around the complicated surface. The validity of our approach is demonstrated by applying the geometry optimization to 2 types of turbine blade with different injection.

View full abstract

Development of the turbine last stage long blades and increase of the turbine generator capacity are very important to increase the unit capacity of the tandem compound units. The 45 inch titanium blades have been developed which are applicable to the unit above 1000 MW and also the large turbine generators above 1000 MW have been developed. This paper describes how to realize the large tandem compound units above 1000 MW.

View full abstract

Cavitation erosion tests were performed in deaerated and aerated water, in water at various temperatures, in water/ethanol mixtures and in various kinds of organic liquids, the impact loads by collapsing bubbles were measured with the pressure detector. The volume loss curves do not change with the type of water such as deaerated and aerated water, and a similar trend was observed for the results of the pressure distribution. A further increase in the air content decreases the volume loss causing a cushioning effect of bubble collapses. The cavitation erosion increases with increased vapor pressure and reaches a peak, followed by a decrease. The initial increase is due to the increased number of bubbles. Thus, cavitation erosion is mainly affected by both air content a and vapor pressure P_υ of liquid properties. The volume loss rate can be described as P_υ^-0.38·e^-0.49a. A critical rate air content is found to be 1.6, below which the air content does no longer affect the volume loss rate. It was found that the volume loss rate shows a good correlation with ∑F²₁/(pc), where F₁ is the impact load, p the density and c the sound velocity in the liquid.

View full abstract

The formation mechanism of single-walled carbon nanotubes (SWNTs) was studied with the molecular dynamics simulation. Starting from randomly distributed carbon and nickel atoms, random cage structures of carbon atoms with a few nickel atoms were obtained after 6 ns simulation. Nickel atoms on the random cage prohibited the complete closure and anneal of the cage structure into the fullerene structure. In the next stage the simulation cell size was artificially shrunk for realization of proceeding collisions of precursor clusters within the computational time limit. Collisions of such imperfect random-cage clusters lead to an elongated tubular cage structure, which could be regarded as an imperfect SWNTs. Furthermore, we compared simulation results with the FT-ICR mass spectra of the positive clusters generated by the laser-vaporization supersonic-expansion cluster beam source.

View full abstract

This paper presents discussions on predicting turbulence and heat transfer in complicated flow fields by recent low-Reynolds-number (LRN) second moment closures. The flow fields discussed are two types of square sectioned U-bend duct flows with mild and strong curvature. The strain fields are complex and thus so are the heat transfer characteristics. A version of the Two-Component-Limit (TCL) second moment closure and Shima's "wall-reflection free" model are presently focused on. They are LRN models totally free from geometrical parameters. For turbulent heat flux, the higher order version of the generalized gradient diffusion hypothesis is applied along with the TCL model. The results are compared with those of the nonlinear cubic κ-ε-A₂ eddy viscosity model. It is concluded that in the case of mild curvature, both second moment closures are generally good enough for predicting flow and heat transfer though they are not more attractive than the κ-ε-A₂ model. However, in the strong curvature case, only the TCL model gives reliable heat transfer prediction.

View full abstract

Experimental study on the heat transfer mechanism from a horizontal fine platinum wire to particles was carried out in a riser of a circulating fluidized bed(CFB). As an experimental apparatus, the riser duct consisted of 33.7mm squared cross sectional area and 1620mm in a height. The test section was installed at the suitable height (0.9 m) from a distributor. Both the particle diameters (d_p) and the wire diameters (d_w) were 100, 200 and 400 μm. As the results, it was found the significant relationship between the particle behavior and the characteristics of heat transfer around a horizontal fine wire in CFB was found. It was found out that the heat transfer coefficient for the case of d_p<d_w was larger than that for the case of d_p>d_w in the turbulent fluidization region. It was also found that there were some relationships between the gas velocity and the characteristics of the heat transfer around a horizontal fine wire in the dilute fluidization region.

View full abstract

Alternative turbine cooling schemes should be applied for future aero-engine to increase turbine inlet temperature. To estimate feasibility of this new cooling system, several experiments were conducted with some kind of heat pipes. Although sodium heat pipe with sintered powder metal wick assisted argon gas showed good performance, the highest heat flux on the evaporator was insufficient because of the temperature limit of the heat pipe shell material. To increase heat transport, heat pipe length is reduced and heat pipe shell is changed into heat resistance material. In the result, large amount of heat transport were demonstrated, with 38 W/cm² as the heat flux, however start-up time was increased slightly. Since the results show a 46% decrease in cooling air and a 5.4% increase in specific thrust with this heat pipe as the turbine cooling system, this advanced cooling system is practical to apply.

View full abstract

Pressure loss of a rectangular block on the wall of parallel channel was measured. The height of the channel B was constant 30 mm. The side length and height, C and H, of the rectangular block were varied from 30 to 180 mm and from 3 to 20 mm, respectively. The mean velocity of the channel ranged from 6 to 10 m/s. The effects of the opening ratio β=1-H/B and the side/height ratio C/H on the pressure loss coefficient ζwere measured. The pressure loss coefficient can be formulated by introducing the governing factor δ=(1-β)/β² as follows: ζ=1.2δ¹.25 (C/H)⁰.09 for β<2/3 and ζ=1.1δ⁰.8 (C/H)⁰.09 for β≥2/3. And the recommended equation agrees with the experimental data within 8%. The pressure drop on the sudden contraction and the pressure rise on the sudden expansion agree with those of ordinary data for double steps.

View full abstract

An experimental study was performed to investigate the heat transfer in separated flow behind a circular cylinder. The Reynolds number ranged from 120 to 30000. The temperature distribution around the cylinder was measured by an infrared camera under the condition of constant heat flux. From the results of the present study, it was found that the heat transfer in the separated flow region is strongly affected by the vortex formation length behind the cylinder. The value of heat transfer coefficient at the rear stagnation, Nu_r/Re⁰.5, has a maximum at Re&ap;200, and has a minimum at Re=1500-3000, corresponding to the change of the vortex formation length.

View full abstract

Homogeneous heat conduction analysis can be easily solved by means of the boundary-element method. However, domain integrals are generally necessary to solve the heat conduction problem in the functionally gradient materials. This paper shows that the heat conduction problem in the functionally gradient materials can be solved approximately without a domain integral by the triple-reciprocity boundary element method. In this method, the distribution of domain effects is interpolated by integral equations. A new computer program is developed and applied to several problems.

View full abstract

An experimental study to synthesize diamond films has been conducted under a well-defined flow field to make clear the mechanism of combustion synthesis of diamond films. Using a flat flame burner, the homogeneous diamond films are synthesized on substrates, above which flat, premixed acetylene/hydrogen/oxygen flames are established. The effect of equivalence ratio and velocity gradient is examined on the growth rates of diamond films, crystal sizes, and their morphology. It is found that not only the maximum growth rate but also the maximum crystal size can be obtained when the equivalence ratio is about 2.50, and that the growth rate, crystal size, and/or morphology are nearly the same when the velocity gradient is kept constant. These results are confirmed by a conical flame with a welding torch. In addition, the scratching treatment for the substrates by diamond powder is unnecessary, the maximum growth rate of diamond films can be obtained when the surface roughness is about 0.11 μm, and the nuclei of diamond appear in scratches on the substrates.

View full abstract

A gas engine heat pump (GHP) system, which could make use of the heat exhausted from its gas engine, was designed and set in a model house as a trial. This GHP system has a hot water supply, a bath for 24 hours, a dryer in bathroom, a floor heater, and room air conditioning units. The coefficient of performance of this system was measured for various life styles and the availability of this system has been proved.

View full abstract

The critical heat flux of the counter-current flow in narrow-annular flow passages (δ=0.5∼10.0 mm) was examined by using R-113 vapor and liquid at 0.1 MP_a for the bottom closed and the open system. When the clearance δ≤2.0 mm, the falling liquid flow rate was restricted by the upward vapor flow in the bottom open system, which was expressed with the Wallis type flooding correlation. The heat flux at the initiation of the temperature excursion (EXC) was well predicted for both the bottom closed and the open system by considering that the EXC occurs when the falling flow rate becomes equal to the evaporation rate under the liquid falling limiting. In the case of δ=5.0 mm, the liquid penetration was also restricted, however it was much lower than the Wallis flooding velocity. It was rather predicted with the flooding by the level swell of the two-phase mixture with the falling film. After the penetration limiting, the falling flow rate became equal to the evaporation rate, and then the EXC was initiated after a further increase in the heat flux. In the case of δ= 10.0 mm, the EXC started like the pool boiling without any penetration limiting. The EXC heat flux correlation for δ=2.0∼10.0 mm was derived by considering that the EXC occurs when the mixture void fraction exceeds a critical value.

View full abstract

The influence of stack position on the performance of thermoacoustic sound wave generators is examined. Two types of experiments are performed for various values of sound wave frequency f of 66, 74, 100, 125 and 134 Hz. When a sound wave generator is independently operated, regardless of f, a maximum amount of heat is transferred by sound waves when the stack is at 30-40% of the resonance tube length, L, from the closed end, and the highest pressure amplitude is obtained when the stack position is approximately 20% of L. The third harmonic is generated when the resonance tube is long and the stack is positioned at 10% of L. When two sound wave generators are connected to each other at the closed ends, the transferred heat values are different, but their distributions are symmetrical. The lowest temperature of the hot heat exchanger, T_H, is lower than that of an independently operated generator. The difference between the lowest T_H values changes from 40°C to 70°C. Maximum pressure amplitude at the central region is confirmed when the stacks are positioned symmetrically. Both pressure and velocity waveforms at each point of the resonance tube showed tendencies similar to those of an independently operated generator.

View full abstract

A new type of plate heat exchanger for water-refrigerant systems such as chillers has been developed. Plates embossed with pyramid-like structures are stacked up to form the heat exchanger. Measured heat-transfer coefficients (for convective vaporization) of the heat exchanger are about one and a half to two times higher than those of commercial herringbone-type plate heat exchangers. Moreover, its measured heat-transfer coefficients for water convection are generally in the higher range of values for conventional plate heat exchangers. It was found that the developed plate surface reduces the volume of the plate heat exchanger by nearly half, under equivalent heat-transfer rate and water-side pressure drop, compared to conventional plate heat exchangers.

View full abstract

A Detailed analytical model to explain the vapor film collapse was developed to evaluate the occurrence conditions of self-triggering vapor explosions. The following conclusions were drawn based on linear stability analysis using the thermo-dynamic property of water, by linearizing and perturbing basic equations (Rayleigh-Lamb-Plesset's bubble momentum equation, the mass conservation equation, the state equation for ideal gas, and the Clausius-Clapeyron equation). The vapor film stabilizes with the reduction of the hot-liquid diameter, decreasing the condensation heat transfer coefficient, and increasing the thermal radiation coefficient. The cold-liquid viscosity and surface tension have a stabilizing effect, though this effect is negligibly small where the hot-liquid diameter is over 1 mm. The analysis predicts the vapor explosion occurrence limits obtained experimentally by other researchers to within approximately 10 K.

View full abstract

Regenerator losses of two 3-kW two-piston type Stirling engines are analyzed in detail to optimize their regenerators. A fifty-percent indicated efficiency and a lower regenerator loss were obtained by adopting a unique cylinder arrangement and a well-designed heat exchanger system. To clarify the regenerator performance, the losses are adequately evaluated by using experimental data and are analyzed by a mathematical model. Based on these analysis results and optimizing processes, a design method for regenerators of practical engine was established and was introduced in this paper. Mixed-screen mesh and calender-type matrixes were tested to clarify their effects to the engine performances. Also, the relation between the regenerator loss and operating time during an engine durability test is shown.

View full abstract

Many studies of diesel engine operation by vegetable oils have been carried out as vegetable oils are renewable and offer reductions in carbon dioxide emissions. This paper investigates gas oil blended with rapeseed oil as a diesel fuel substitute. Prior to the engine experiments, the evaporation behavior of the blended fuel was examined with single droplet evaporation on a hot plate, and the spray characteristics such as spray angle and penetration are discuseed using spray images in photos taken with single injections into air at high pressure and room temperature (1.57 MPa and 298 K). The performance and emissions of two types of small single cylinder DI diesel engines (engine A equipped with a bowl in piston type combustion chamber and a throttle nozzle, and engine B a toronidal type with a multi hole nozzle of 4-φ 0.2) were also examined. As a result, the blended fuels with equal proportions of gas oil and rapeseed oil or higher gas oil ratios showed good engine performance and emission characteristics, like those of gas oil operation.

View full abstract

Combustion experiments were carried out for four kinds of single droplet emulsified fuels; Asphalt/Water (As100), Pitch/Water(Pi100) and their mixing emulsions (As50 and As70). It was observed As100 had intensive microexplosion phenomena, however, it could never be seen in Pi100. The As70 and As50 also induced microexplosion and their combustion times were shorter than a half value of Pi100, so that the mixed fuels are efficient for using pitch as a thermal energy resource. The experiments of thermal analysis (TG/DTA) were carried out for making clear the cause of microexplosion. It could be seen in As70 and As50 as well as As100 that the water phase was drained in the emulsion at the specific point of decreasing TG curve before the saturation temperature (100°C) like Ref.(5), however, the TG curve of Pi100 showed only gradual decrease curve without the specific point. The occurrence of microexplosion can be explained by the facts and it may depend on the distillation property of neat mother oil playing an important role to microexplosion.

View full abstract

A stirred reactor was newly designed and the structure of the low Damkohler number flame was investigated. The visual observation by schlieren photography does not indicate the occurrence of the thin flame under low Damkohler number as proposed by Peters. Further investigation is carried out by concentration measurement of the reacting species. Ion current was also measured in the reaction zone. Ion current has no sharp peaks, which are typical feature of te thin laminar flame. In the vicinity of the injector, ion current ws low but mean ion current increases with the radal distance and shows the wavy form. This indicates that in one region, the chemical reaction is active and in another, the chemical reaction is inactive. The power spectra of the ion current show no peaks. The distributed reaction zone regime was confirmed to exist. From the cross-correlation of the ion current, it was found that the reaction zone conjectured to be reacting eddies or thick reaction zones of the order of 4∼5 mm. These reacting eddies or zones are transported by the mean convection velocity of the flow field. From these experimental results, it can be concluded that the mechanism of reactions are quite different from that of the wrinkled laminar flame.

View full abstract

This paper presents experimental results for effects of electric field on combustion of single droplets for sooting and non-sooting fuels in microgravity. The ambient gas was air at atmospheric temperature and pressure, and ethyl alcohol, n-octane, and toluene were used as fuels. The distance between electrodes is 50 mm and applied electric voltages ranged between 0 and 7 kV. The deformation of flame occurred and the burning rate constant increased with an increase in the electric field intensity for all of the fuels tested. It is supposed that the deformation of flame and the increase in the burning rate constant can be explained due to the movement of ions and soot particles which are charged positively and the flow induced by the movement. In consideration of not only the movement and induced flow but also behavior of soots, the experimental results of sooty flames can be explained.

View full abstract

Forced oscillating combustion can reduce nitrogen oxides (NO_χ) emission, as described previous researches. In this paper, in order to estimate the effect on NO_χ reduction, the concept is applied to two kinds of commercial burners for use in industrial furnaces. Natural gas is supplied through a set of solenoid valves, which are alternately made open and close at several times a second with various duty ratios, whereas preheated air from a recuperator is supplied at a fixed rate. Combustion products are sampled at the exit of recuperator and analyzed using a series of analyzers. It is found that about 30% reduction of NO_χ emission is realized by introducing forced oscillation combustion into two kinds of industrial burners, exclusive of an operation of long turbulent jet flame.

View full abstract