Heat transfer was investigated for high pressure ratio air flow in square minichannels, which were machined on the oxygen free copper block. The size of the channels were 0.3, 0.6, 1.0 and 2.0 mm, and the length were 10, 20, 50 and 100 mm. The pressure ratio was changed widely up to the flow choked at the exit. It was found that the heat transfer coefficient was about 7.3 times greater than fully developed turbulent pipe flow. Experimental result showed that 75 percent of the total heat transfer was achieved in 10 percent inlet portion of the whole channel.

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A new reduced-order model accounting for a thermal damping effect on a radial motion of a spherical bubble is proposed. The present model is based on that developed by Preston et al. (2002). A temperature gradient at the bubble wall is approximated by use of an average bubble temperature and a thermal penetration length inside the bubble based on a linear theory (Prosperetti, 1991). A phase difference between the temperature gradient and the average temperature is taken into account. In the present report, a perturbation analysis of the bubble motion is performed. The result of the present model shows good agreement with the second order theory (Sugiyama et al., 2004), in which the temperature distribution inside the bubble is fully considered. The reason for the agreement is discussed.

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Flow structures around a hypersonic re-entry Mars Environmental Survey (MESUR) capsule traveling at supersonic/hypersonic speeds are investigated utilizing a new computational method based on the finite element method (FEM). In order to confirm the validity of the computational method, the results are compared with experimental ones obtained by the electrical discharge method for a hypersonic flow at Mach 10. From these results, it can be concluded that they were in good agreement. As an example of the numerical simulation, flowfields around the capsule traveling at speeds of Mach 5, 3, and 2 are investigated. By these simulations, differences between the flow structures for these Mach numbers are clarified. The result shows that the location of the separation behind the capsule is governed by the strength of the adverse pressure gradient. The reverse flow behind the capsule that determines the base pressure distribution is correlated to the strength of the re-circulation and the stability of the capsule.

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Pitched and skewed jets issuing through small holes in a wall into a freestream have proven effective regarding the control of boundary layer separation. Longitudinal vortices are produced by the interaction between the jets and the freestream. In this method, the fluid particles which have large energy of the freestream are supplied to decelerated fluid particles in the boundary layer by longitudinal vortices. In order to have a better understanding of the suppressing mechanism of longitudinal vortices, the velocity measurements were carried out in a region close to the wall for the various jet pitch angles. In the case of a large pitch angle (measured from lower wall), longitudinal vortices exist apart from the lower wall under influence of the velocity induced by the vortex pair. The flow in the boundary layer is affected by a pitch angle. Longitudinal vortices produced by the small jet pitch angle strongly disturb the flow in the boundary layer and therefore effective separation control is attained.

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Energy transfer mechanism of internal gravity waves in their transition process was experimentally investigated. Thermal regulation was conducted by giving small sinusoidal thermal disturbance satisfying the three-wave resonance condition at the initial stage of their streamwise development. For the excited case, the frequencies of their irregular eigen-modes became fixed and the phase difference between vertical velocity and temperature fluctuation components was locked up around -π. Increase in correlation between the velocity and the temperature fluctuations strengthened down-gradient heat flux and the energy of mean temperature gradient was efficiently transferred to encourage the wave motion. The internal gravity waves became to have larger potential energy as they developed downstream. The excited internal gravity waves produced stronger random velocity fluctuations through the cascade process and induced larger counter-gradient heat flux at their collapse.

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This paper deals with a flow of an aqueous surfactant solution due to a rotating disc in a cylindrical casing with aspect ratio H/R =1 and 2, where H and R is the height of the cylindrical casing and the radius of the rotating disc, respectively. The aqueous surfactant solution (C₁₄ TASal), whose concentration is 0.4, 0.8 and 1.2%, is consisted of n-tetradecyltrirnethylammonium bromide (C₁₄TABr) and sodium salicylate (NaSal). Rheological properties such as a first normal stress difference and a shear viscosity of the surfactant solution are measured with a rheometer and a viscometer. The behavior of the secondary flow has been investigated using a flow visualization technique and a two-component laser Doppler velocimetry (LDV) system. The patterns of the secondary flow are classified using the Reynolds and elastic numbers. We found the secondary flow which was moving up and down at a constant frequency near the rotating disc, as not seen in polymer solutions.

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An orifice flow meter is widely used to measure the flow rate in a pipe, where the accuracy of the measurement is acceptable when the flow is steady. It is desired that in order to develop an accurate method to measure the flow rate in a pipe under pulsating flow conditions a detailed flow pattern of the unsteady flow field should be sought. In the present paper, the velocity distributions and turbulent intensity were measured in the flow field downstream of the orifice in a pipe under pulsating flow conditions. The experimental results showed the following : velocity profiles have almost similarities in the potential core region, velocity profiles on the centerline of the pipe show hysteresis phenomena when opening area ratio of the rotary valve changes with time, and the peak of turbnlent intensity near the edge of the orifice moves downstream with time as the rotary valve opens.

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This paper is concerned with the dynamics of pulsating flow in pipes with an axisymmetric and asymmetric constriction, which are modeled as a stenosis of the human internal carotid artery. The flow is solved by a finite difference method with CIP and fractional step schemes in a general coordinate system. Obtained axial velocity distributions and thickness of separation region are confirmed with Ojha's experimental results. Resultant flow brings about large periodical changes of the wall shear stress in the downstream and of the pressure at the converging part of the constriction, respectively, suggesting that the flow behavior relates closely with arterial diseases.

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Experimental modal analysis, using an impact hammer and accelerometers, was conducted on a full-scale flap gate with a height of 0.963 m and a span of 14.8 m to determine its in-air natural frequencies, mode shapes and modal damping. Subsequently, the in-water self-excited vibration characteristics of the gate (without any spoilers) were recorded using the same accelerometers. This paper reports the major in-air vibration characteristics (the mode shape, frequency and damping ratio for the damped vibrations), as well as the major in-water self-excited vibration characteristics (the excitation ratio and frequency of the self-excited vibrations in water). In parallel with these experiments, calculations of the inherent in-water vibration frequency of the gate using a potential flow theory, and based on input from the in-air modal testing, are presented. Comparison of the calculated inherent in-water vibration frequency with the measured frequency of the in-water self-excited vibration confirms the validity of the present theoretical analysis.

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The present experiment demonstrated an omnidirectional reduction of drag and fluctuating forces of a circular cylinder to the cross-flow by attaching cylindrical rings, which were spaced several diameters along span. The Reynolds number based on the diameter of the base cylinder, Re_d, ranged from 3 000 to 38 000. For Re_d≥20 000, the drag force was markedly reduced by 15% although the projected area to the flow was increased. This is attributed to the formation of the separation bubbles on both sides of the ring due to the turbulent transition in the boundary layers. The fluctuating lift, which was estimated from the fluctuating surface pressures, was much reduced throughout the examined Reynolds numbers due to the suppression of the vortex shedding.

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Oscillatory flow in a loop channel consisting of a T-branch, two reservoirs and connecting pipes was experimentally investigated. It was found that the oscillatory flow including a constant circulation flow component is induced in the loop channel by a reciprocating flow given to a branch of the loop channel. Pressure differences between two exits of the T-branch and between inside and outside of the reservoirs cause the constant circulation flow component in the oscillatory flow. We investigated the relationship between the reciprocating flow given to the loop channel and the constant circulation flow component. We also investigated the relationship between the reciprocating flow and the pressure differences at the T-branch and at the reservoirs.

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We are under obligation to coexist with natural ecosystem, for the next leap in the hydroelectric power development. In such circumstances, the authors have proposed the new type hydraulic turbine, named “Gyro-Type Hydraulic Turbine”, composed of some blades with high aspect ratio and the rotor is submerged nearly parallel to the stream. The turbine is suitable for shallow streams with high velocity in mountain torrents and/or rivers. This paper, continuously, discusses the flow conditions around the rotating blade using the flow visualizations by PIV and the numerical simulations by CFD. The visualizations and the simulations proved that the self-motive power is generated by the drag force of the blade facing to the downstream. With the increase of the rotational speed, however, the rotational torque comes to be caused by the lift force of the blade not only facing to the upstream but also facing to the downstream, and the maximum torque/output is at the higher rotational speed.

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While the use of WTGS expands over the world, complex terrain has become important candidate as the site proposed for a WTGS. In the complex terrain, contribution of local topographic effects to the wind energy resources is quite large and intensity of wind turbulence, which brings about complicated aerodynamics loads on the wind turbine, is much larger than that over the flat terrain. The purpose of the present work is to investigate the turbulence characteristics of the wind flow over complex terrain such as mountainous region. The wind measurements were carried out at Shitara-cho in Aichi during the period from November 19th to December 10th in 2003, using three meteorological masts and ten anemometers. The influence of the slope on the turbulence has been evaluated by examining the power spectrum of the wind fluctuation.

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The N₂ second positive bands observed in high-temperature air plasmas are considered to be useful to determine internal states of high-temperature plasmas. In the experiments with a micro-air plasma-jet, the N₂ second positive bands with higher vibrational levels (v′≥2) were found to show a characteristic intensity distribution. The intensity distribution could not be explained by a usual equilibrium radiation theory. In order to investigate the phenomenon, theoretical spectra were calculated by taking account of two effects, that is, predissociation of N₂ C ³Π_u state through C′³Π_u state and non-Boltzmann rotational population distribution. This calculated spectra with such effects agreed very well with the experiments.

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The paper investigates the flow characteristics of reactant gas on the silicon wafers in a vertical LPCVD (Low-Pressure Chemical Vapor Deposition) reactor by the flow visualization and the numerical simulation. The observation was made in a model reactor in a very low-pressure condition, which makes the observation quite difficult because of tracer seeding. The CFD code FLUENT was used for the numerical simulation. The results of the visualization and the numerical simulation showed that the gas flow was quite viscous and it received large resistance force from the wafers and the supporting lodes. Regardless of the low-pressure condition, the flow can be treated as continuous system and can be simulated well by the CFD code based on Navier-Stokes equation. It shows that the most of the field appeared to be laminar. For the establishment of the uniform flow pattern, twin counter-flow nozzles were better than a single nozzle. The flow was free from stagnant flow or re-circulating flow so that it appeared to be suited for the prevention of particle formations.

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Nongray analyses of radiative heat transfer in a 2-dimensional furnace of practical scale were carried out taking the narrow band nonuniformity of absorption coefficient into account. The results obtained from such numerical simulation were compared with those obtained from nongray analyses where the narrow band nonuniformity of absorption coefficient was neglected. Numerical simulations of radiative heat transfer were coupled with a numerical prediction of flow and combustion process in some cases and conducted based on the given distributions of temperature and species concentrations in other cases. These comparisons showed that disregard of narrow band nonuniformity led to an overestimation of wall heat flux due to radiative heat transfer when the distributions of temperature and species concentrations were fixed without linkage to radiative heat transfer.

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A high efficient co-generation system named “Neighboring Communities Co-generation System” is proposed to a multiple dwelling house. The key technology of this system is to connect home and home with one loop of heat transfer line of one-inch diameter, and to level the heat demand by a heat storage unit in each house. This system requires compact heat storage unit of quick response. In this study, a plate fin type brazing heat exchanger was built and tested as a heat storage unit. Sodium acetate trihydrate with a melting point of about 58°C and paraffin wax with a higher value of 74.8°C were used as the phase change material (PCM). As a result, it was shown that the heat transfer in the heat storage unit was dominated by thermal conductivity in PCM. Paraffin wax showed higher responsibility and higher heat output due to its higher melting point and quite lower super cooling in solidification.

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To elucidate the mechanism and characteristics of boiling heat transfer in a micro-channel vaporizer, the experimental investigation of the micro-layer thickness that formed between the heating surface and vapor generated was important. The micro-layer thickness was measured applying the laser extinction method for the channel gap sizes of 0.5, 0.3 and 0.15 mm. It was clarified that the gap size, the rate of bubble growth and the distance from the incipient bubble site have an effect on the micro-layer thickness in a micro-channel boiling system. The initial micro-layer thickness increased with increase of the velocity of bubble forefront to moderate value of the velocity. In the region of larger velocity, the thickness was constant for each gap. The distributions of the initial thickness of micro-layer on the heat transfer surface were shown.

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Steam flow disturbance and the resultant tube metal temperature excursion have been experienced in heated downflow tubes in large capacity utility boilers during low load operation. In order to solve the problem, analysis has been made by studying the hydraulic characteristics of steady and unsteady conditions. The analysis results showed good agreement with the phenomena experienced at existing boilers. It is diagnosed that the stability of flow is improved by additional flow resistance to the tubes. The countermeasure to install thicker tubes has been applied to the boilers and it is demonstrated that the flow stability is acquired through the field operation and measurement.

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Mass-selected silicon cluster ions were levitated in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer and monitored during chemisorption reaction with ethylene (C₂H₄). Through measurements of “time-dependency” of this reaction process, large change of the reactivity depending on the number of absorbed ethylene was observed, in addition to the strong dependency to silicon cluster size. From Si⁺₁₅ to Si⁺₁₈ shows a special stability of Si_xE⁺_y when x+y=19, such as Si₁₅E⁺₄. The large decrease in the reactivity of Si⁺_n was observed due to the contamination of hydrogen atom to Si⁺_n. Rate constants for the adsorption of the first C₂H₄ molecules on Si⁺_n were estimated. The reaction kinetics data suggest that structural isomers are present for all clusters except Si⁺₁₄ in the size range investigated.

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The solubility of CO₂ in pure water was investigated at high-pressure conditions, from 7 to 12 MPa, and at temperatures between 2.5-20°C. CO₂ clathrate hydrate film formed at temperatures below approximately 10°C. The CO₂ solubility was estimated by expanding the dissolved gas. The solubility decreased with decreasing temperature and with decreasing pressure, although some researchers reported it decreased with increasing pressure at 7°C, in the presence of the hydrate. Many other researchers reported that the pressure conditions did not affect the solubility in the presence of the hydrate. Although this seemed to be mostly correct, we did confirm a small difference of the solubility at pressures ranging 7-12 MPa.

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Any strategy of CO₂ sequestration needs to clear the CO₂ solubility into water and the dissolution behavior. We measured the pH distribution around a dissolving CO₂ droplet in a high pressure vessel by using a 2 color LIF method. Qunine and sulforhodamine were used as fluorescence dyes. Molar absorption coefficient and emission intensity of quinine depends on pH of aqueous solution, while those of sulforhodamine are not affected by pH. The ratio of these fluorescence intensities represents pH at each point of image. The map of pH around the dissolving droplet gives also a map of CO₂ concentration, from which the solubility can be estimated.

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Route planning program of hot water piping of a fuel cell energy network for central system and distributed system was developed. City area model of 74 buildings of Sapporo was applied to the route planning program, and quantity of heat loss of hot water piping and piping route was investigated. Consequently, compared with a central system, quantity of piping heat loss in annual year of the distributed system is 75%. When there is less than ±30% of load fluctuations, compared with the case where there is no load fluctuation, quantity of cut of heat loss is 6% on an average. Moreover, compared with the case where solar generation device are not connected as output of the solar generation device linked to the network is less than ±50% of fluctuations, quantity of heat loss is cut of 2% on an average.

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Effect of hydrogen addition to hydrocarbon fuels on combustion characteristics were investigated using chemical full kinetics. The changes of ignition delay time and laminar flame velocity when hydrogen is added to methane or propane fuels were calculated. The result shows that for ambient pressure condition, ignition delay time decreases corresponding to the amount of hydrogen addition. However for high pressure condition, when 10% hydrogen is added to hydrocarbon fuel, ignition delay time decreases as short as that of hydrogen itself. Laminar flame velocity increases gradually with adding hydrogen, and when more than 70% hydrogen is added, laminar flame velocity rapidly increases. Furthermore, the production rate of OH is an important factor for the change of ignition delay time and laminar flame velocity, when hydrogen is added.

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In designing advanced combustion systems with methane fuel toward reducing the pollutants and improving the thermal efficiency, the laminar burning velocities under wider range of pressure and temperature than ever are indispensable. Measurements under adiabatic processes were conducted using a spherical combustion bomb equipped with heaters which can raise the initial premixed gases up to 700 K, and therefore obtained were the results which should cover the operation condition for the most up-to-date industrial combustion facilities. From the analytical examination of the results, an equation for laminar burning velocities was proposed in terms of a product of equivalence ratio dependent distribution function in addition to ordinary pressure and temperature exponent terms, where the exponents were -0.32 for the pressure and 2.33 for the temperature. The value of the pressure exponent seems smaller than that reported elsewhere, typically -0.5, which is presumed to be due to the behavior of the pressure dependence on the relation between adiabatic flame temperatures and equivalence rations.

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Experimental study was made to investigate the flame propagating through a methane/air mixture flow with periodic concentration fluctuation by using a stagnation flow type burner. Three kinds of fluctuations different in the range of fluctuation expressed as (φ_m, a) = (0.85, 0.06), (1.07, 0.17) and (1.30, 0.06), where φ_m is the mean equivalence ratio and a is the fluctuation amplitude, were examined for the frequency f ranging from 3 Hz to 50 Hz, and fluctuating burning velocity and burnt gas temperature were estimated or measured. The dependences of their fluctuation widths on f were compared among the three kinds of fluctuations and discussed on the basis of the apparent equivalence ratio φ_a evaluated for the mixture flowing into the flame front using the relationship between mixture equivalence ratio and burnt gas temperature for the stationary flame. The results obtained were : (1) For a certain range of f, the maximum and minimum burning velocities of the flame are, respectively, higher and lower than those estimated for the mixture equivalence ratio fluctuation at the burner exit, irrespective of the kind of fluctuation. (2) The fluctuation width of φ_a, 2A, becomes maximum at the some value of f for every kind of fluctuation. This value of f for the fluctuation (1.07, 0.17) which includes the stoichiometric condition is approximately half of the values for other fluctuations. (3) The width 2A for the lean side fluctuation (0.85, 0.06) is larger than that for the rich side fluctuation (1.30, 0.06) in spite of the same value of a.

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For the purpose to develop advanced hydrogen combustors for micro gas turbines with low NO_x emission at high temperatures up to T_it=1700°C, single coaxial injectors with the two-staged (RQL; rich-quench-lean) combustion method were built based on the excellent combustion features of hydrogen. The injector was consisted of the inner pipe issuing rich premixed gases and the outer concentric annular port injecting secondary air with high velocity. The combustion characteristics of the small test combustors of 30 mm dia. installed the injector concerning NO_x emissions, temperature distributions, combustion efficiencies, total pressure losses and flame stability limits were measured at room temperature and atmospheric pressure. The optimum equivalence ratio of the rich premixed inner flame was confirmed to be about 2.0 in the viewpoint of decreasing NO_x emission and total pressure loss. The NO_x concentrations were reduced with decreasing the area of the coaxial-air port and were in inverse proportion to the ratio of the momentum of the coaxial-air to the premixed gas. For the injector with the smallest area of air-port, having the pressure loss of below 4%, NO_x emission levels were low enough and high combustion efficiencies over 99.95% were attained in the range from 0.3 to 0.6 of overall equivalence ratio since the mixing in the second stage was so rapid. It was confirmed that this type of the injector was suitable for two-staged of RQL combustion.

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Measures such as low air-ratio combustion have become the subject of a great deal of attention with a view to reducing the amount of environment impacting substances from the waste incineration process, and also to making the most effective use of energy. However, it has been understood there would be considerable difficulty utilizing low air-ratio combustion on the classic grate furnace due to fundamental problems in its process resulting from the wide range and heterogeneity of waste materials. The application of high-temperature air combustion technology for enhancing sound combustibility could provide solutions to these problems. In practice, a mixture of high-temperature air and flue gas is injected at high velocity from both sides of the furnace walls to form a stable high-temperature zone in the combustion initiation region above the waste. This prevents fluctuations or localized extinguishing of the flame, while at the same time heating the waste directly with the flame to promote gasification. A practical study was conducted at a 105 t/day municipal solid waste stoker type incineration plant. The test demonstrated that stable low excess-air combustion operation is possible at a combustion air stoichiometry of 1.3 with EGR (Exhaust Gas Recirculation) and high temperature air combustion technology resulting in a 17% decrease in flue gas flow, an energy efficiency improvement of 10%, and more than 50% reduction in NO_x emissions when compared with an air stoichiometry of 1.6.

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