The movement of a single bubble in an extremely narrow channel whose size ranged from 40 μm to 200 μm in height and l0 mm to 30 mm in width was investigated experimentally. R113 and nitrogen were used as the test fluids. In the 40 μm channels, the velocity of the bubble approached about twice that of the liquid, which agreed with Tanveer's analysis of a single two-dimensional bubble in a Hele-Shaw cell with side walls where surface tension is small. However, in larger channels, inertial effect made the velocity ratio between the bubble and the liquid smaller. Simultaneously, the aspect ratio of the bubble also decreased, though it agreed well with Tanveer's analysis when the channel was narrower. The breakup condition of the bubble on account of the viscous instability was also examined.

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The turbulent state of superfluid helium at very low temperatures presents some important and unresolved problems. The turbulent state has a dense tangle of quantized vortex filaments that are characteristic in superfluid. Little is known, however, about their dynamics, particularly, interactive motion. The present paper studies three-dimensional dynamics of two interacting vortex filaments numerically. The equations of motion and the method of numerical calculation follow those of Schwarz. Two identical vortex rings which are initially placed far apart proceed toward the same direction. They gradually become close due to of their interaction, then suddenly collide. The critical distance where the collision occurs is determined by the competition between the local self-induced field of onering and the nonlocal field of the other. The critical distance is grearly influenced by an applied superflow.

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A new algorithm for particle tracking has been developed in order to improve its trackability for flows in which considerable acceleration acts locally. This algorithm consists of two main stages. At the first stage, the particle tracking method using the Kalman filter "type P" is applied in order to estimate individual particle states ; then the measuring region is divided into subregions for the purpose of evaluating local statistics of the particle velocity and acceleration. At the second stage, a new type of Kalman filter which can take account of the local acceleration statistics is applied to tracking particles. Numerical simulations using a 2-D cavity flow are performed for accuracy tests of the present algorithm. As a result, it is proved that the present method achieves measurements with sufficient precision even when the flow direction changes rapidly due to the effect of large acceleration.

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As a fundamental consideration in hydraulic valve dynamics, transient flow through a pipe orifice has been studied via numerical analysis. Steady axisymmetric viscous fluid flow was first investigated to confirm the present SIMPLER-based finite volume methodology. Time-dependent calculation for a suddenly imposed pressure gradient has shown two distinct characteristic time constants for the transient state. The first characteristic time constant is commonly considered corresponding to the flow rate change, while the second one concerning the variation of flow structure has not been investigated in earlier studies. The final settling of the flow is established through the second characteristic time which is almost ten times larger than the first one for the present condition.

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This paper describes deformation, collapse and interaction of two tandem liquid columns exposed to a shock wave and shock-induced high-speed airflow. Experiments are conducted in a shock tube for incident shock Mach number 1.47 in air. Shattering processes of two tandem water columns set in the airflow direction are observed using holographic interferometry. The shattering process is characterized by three stages ; however, the shattering mechanism is different in the last stage. Time variations of longitudinal and transverse diameters, and mass of the two shattering water columns are measured from the interferograms. Experimental results are compared with results for a single water column. It is revealed that a strong interference exists between the two tandem water columns.

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The capability of two-equation K-ε and K- T models to predict separated flows is investigated from the computational standpoint. The flow over a backward-facing step is chosen as a test problem. A method of lines approach is adopted as a numerical method. The spatial derivatives are discretized by the second order central and upwind difference approximations. As a time integration scheme a rational Runge-Kutta method is used. In the first place, a variety of low-Raynolds number K-ε and K-T (Launder-Sharma, Lam-Bremhorst, Speziale) models are tested. It is found that the Launder-Sharma model predicts the reattachment length more closely to the experimentally measured value than the other two models, and that the dumping function used in the Lam-Bremhorst or Speziale model is not appropriate for separated flows. In the next place, it is found that the use of the anisotropic eddy-viscosity models predicts normal stress better than the isotropic model, whereas the computed reattachment length and mean-velocity profile are not greatly improved by the use of the anisotropic models.

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A k-ε turbulence model is developed to calculate wall turbulent shear flows under various pressure gradient conditions. In the present model, we set the dissipation rate of turbulent energy at a wall equal to zero, though the wall limiting behavior of velocity fluctuations is reproduced exactly. Thus, the model assures computational expediency and convergence. The proposed model is constructed to properly take into account the effects of pressure gradients on shear layers. It was found by Nagano et al. (1992) that in adverse pressure gradient flows the Van Driest damping constant decreased with increasing dimensionless pressure gradient parameter P⁺. Therefore, the present model has introduced the modified Van Driest damping function which is a function of P⁺. The proposed model was tested by application to a turbulent channel flow and boundary layers with P⁺ < 0, P⁺=0 and P⁺ > 0. The model predictions indicate that agreement with the experiment and the direct simulation data is very good over a wide range of pressure variations.

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Two-dimensional flow problems of the Leslie-Ericksen theory for nematic liquid crystals are considered. As a concrete example, inlet flows between parallel plates are calculated using a finite difference method. The calculations are performed at low and intermediate Ericksen numbers for three patterns of surface alignment, and the effects of elasticity and viscosity in the nematic liquid crystals on the development in director orientation and velocity are examined. The validity of the numerical calculation is confirmed by making a comparison between the director orientation in the fully developed region in the present calculation and that obtained from the calculation in unidirectional flow. The director orientation in the inlet flow region depends on the Ericksen number and the surface alignment. Furthermore the velocity profile develops in a different manner from that for Newtonian fluids because of the effect of director orientation.

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Using the molecular beam method, scattering of argon and helium molecules from a stainless steel surface (SUS304) is studied experimentally. Time-of-flight (TOF) spectra corresponding to the velocity distribution of the scattered molecules are measured at various angles of reflection (15∼85°). Surface temperature is varied from 286 K to 723 K and angle of incidence from 45° to 75°. The TOF spectra are analyzed by means of superposition of two spectra : one corresponding to the elastic or inelastic scattering process and one to the adsorption and desorption process. Absence of the first process is verified for Ar beam, showing a large accommodation coefficient. On the other hand, the TOF spectrum of He beam at low temperature is analyzed adequately by the two processes. Accommodation coefficients, mean energy of the scattered molecules, and flux distributions are calculated from the TOF spectrum.

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The velocity distribution, turbulence shear-stress distribution and boundary-layer thickness for equilibrium turbulent boundary-layer were numerically calculated and compared with the measured data by Clauser. Numerical calculation was achieved by means of the momentum equation and the zero equation model for turbulence shear-stress. Boudary-layer thickness was also calculated with the momentum-integral equation. The results show the superior reliability of this method.

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Numerical stability of a one-dimensional one-pressure steady two-fluid model was analyzed under a wide range of flow conditions. The stability was evaluated by making use of a minimum relaxation distance, which was deduced from linearized differential equations of the two-fluid model. It was confirmed by numerical experiments that the obtained minimum relaxation distance corresponds to a maximum step size for stable numerical integration of the two-fluid model. Two types of constitutive equations for the interfacial drag force and three correlations for the virtual mass force were incorporated into the model to examine effects of interfacial momentum transfer on the numerical stability. It was found that the stability is improved not only by the virtual mass force but also by changing the functional form of the interfacial drag force. Furthermore, the effects of volumetric fluxes, pressure, pipe diameter and physical properties on the stability were also clarified by the stability analysis.

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Human aortic arch flow was regarded as an intermittent flow in a curved tube with large curvature ratio δ=1/3. The waveform of aortic flow was obtained by means of Doppler echocardiography from both resting and post-exercise conditions of healthy human adults (age : 22∼27). The result in the resting condition (Re=2300, α=13.34) shows that the transverse flow field is characterized by the appearance of three vertices (residue vortex from the previous cycle, one generated near the Stokes layer, and one induced by development of axial velocity boundary layer in the systole). In the post-exercise condition (Re=3400, α=16.7), a Lyne vortex appears in the end of systolic period and exists until the beginning of systolic phase, together with the vertices generated in the diastolic phase. Furthermore multiple period solutions were found numerically for several flow conditions. Our calculation indicates the aortic flow may have multiple period solutions, but its physiological significance is not yet clear.

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In order to establish an accurate method for simultaneous measurements of flow rates Q and particle concentrations C_v in heterogeneous solid-liquid two-phase flows, the pressure-drop ratios were carefully investigated at the exit of a typical Hershel type Venturi in both horizontal and vertical pipe arrangements for six different kinds of solid-water two-phase flows with various Q and C_v, and the results were represented in a simple experimental formula, as in the previous report on throat measurements. These results at the exit, together with those at the throat, indicate the possibility of simultaneously measuring Q and C_v easily and accurately by means of only one Venturi.

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Flows in heated horizontal ducts and heated parallel rotating ducts include secondary flows due to buoyancy, which can cause increases in the friction factor and the heat transfer. Fundamental characteristics common to these two flows are given for the fully developed laminar flows by the similarity discussion and by numerical computation. A new similarity parameter is proposed and the characteristics are correlated with it. Empirical formulae for the friction factor and the Nusselt number are presented.

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The heat transfer characteristics of hot-wire sensors in rarefied gas flow have been investigated for Knudsen number K_n ranging from 0.01 to 10 while Mach number was kept constant below 0.075. The probe was mounted on a support arm which rotates in an evacuated chamber, so that the flow velocity is kept constant. The diameter of the sensor was changed from 1.25 to 10μm, covering the Reynolds number Re between 10^-2 and 10. The Nusselt number Nu was determined from the CTA output voltage transmitted via mercury slip-ring. It has been indicated that Nu is expressed by the unique function of Re for K_n &le; 0.06 ; the biasing effect due to the K_n-dependence of Nu can be successfully corrected using the Collis-Williams formula for 0.06 &le; K_n &le; 0.1. Nu is shown to be entirely independent of Re for K_n &le; 1.3. The results have been compared with the linear solution of B-G-K equation and its validity and limit have been discussed.

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We show that the compressible Navier-Stokes equations can be cast as a symmetric advective-diffusive system through the use of entropy variables. The explicit forms of homogeneous-type variables and related matrices are derived. We employ the Streamline-Upwind/Petrov-Galerkin method (SUPG) as the basis of our formulation. A SUPG and a discontinuity-capturing operator are included in the finite element variational form enabling a non-oscillatory yet crisp shock profile to be obtained. Numerical examples of high Mach number flows exhibit the suitability of the method.

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In order to make precise force measurements for supercavitating hydrofoils, behavior of the disc drag, as well as the effects of the gap between the test foil and the facing side-wall, is carefully investigated for three typical supercavitating hydrofoils whose nose shapes are modiffied slightly, in a wider range of cavitation number, for various incidences and gap distances. Unexpectedly from Numachi's disc-drag-experiments, the disc drag significantly decreases within the transient region from the subcavitating region to the supercavitating region. It is also very sensitive to foil shapes as well as incidences.

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Flows around a flat plate exhibiting a pitching motion in a uniform crossflow are studied numerically. Two cases of pitching motion, sinusoidal oscillation and oscillation with constant velocity, are analyzed and the effects on the flow of the position of the pivot, Reynolds number, angular velocity and maximum angle of attack are researched. Body-fitted grid generation with moving boundaries is used to obtain the numerical solution of the incompressible Navier-Stokes equations. The time-dependent curvilinear coordinate system which coincides with a contour of a moving boundary is transformed into a fixed rectangular coordinate system in a calculational plane. The changes in C_D and C_L during the pitching motion are obtained.

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This paper proposes a new numerical model expanding on the previous fundamental model, which aims at a more accurate representation of both surge and rotating stall for practical applications. The model deals with the full set of fluid equations for two-dimensional unsteady compressible flow in the axial and circumferential directions throughout the compressor. The blade rows are replaced by semiactuator disks, where the blade row characteristics are expressed by the total pressure loss versus the incidence angle. The basic function and validity of the proposed model are examined through numerical simulation of both surge and rotating stall in multiblade-row compressors.

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A new type of pump with a water-type stirling engine using the water-hammer principle is developed, and its characteristics are studied experimentally. The output oscillation of the engine is utilized for pumping water. Another type of pump with an ordinary water-piston engine, the so-called liquid piston stirling engine, is also tested to compare with the performance of the newly designed pump. The characteristic curves of the pumps indicate that the new pump has a relatively higher delivery pressure at the same low discharge flow than the other type. Conversely, the new pump has a relatively lower delivery pressure at the same high discharge flow. Moreover, the delivery pressure in the new pump is directly related to the pressure in the water hammer. The test results indicate the potential of the new design for the improvement of the pumping head.

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In order to predict pump erosion practically, severe erosion is systematically and precisely observed in a typical centrifugal pump of specific speed N_s=150(m, m³/min, rpm) in various test conditions in relation to types of cavitation, by means of erosion-depth measurements, noise detections, and cavitation-pressure pulse measurements through the paint method as well as the pressure-sensitive film method. The severe erosion directly result from the vortex cavitation, and the erosion rates are closely related to the size and the occurrence frequency of the vortex cavitation.

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A new method of Scaling-up efficiency of a hydraulic turbine is established with theoretical considerations. Two kinds of scale-up formulae are given. One is a precise conversion formula, and the other is a practical one. The former can obtain prototype efficiency from model tests that consider both Reynolds number and surface roughness of individual flow passages in the turbine. The latter can be calculated by using the constant dimensionless friction loss irrespective of specific speed. The scaling-up efficiencies calculated from the formulae are compared with the ones obtained from theoretical performances calculated numerically for model Francis turbines and pump turbines, and also with the ones calculated from the conventional scale effect formulae.

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Laser Doppler Velocimeter (LDV) measurements of velocity fields and determination of static pressure distributions in the rotors of cross flow fans with good geometrical similarity but different dimensions have been made, and the clear scale effects appearing in the flow details have been shown. As the fan dimensions become larger, the internal flow fields tend to be more active, i. e., nondimensional velocity, vorticity, velocity fluctuations and pressure drops in the eccentric vortex increase. The mechanisms of generation and dissipation of the eccentric vortex in the rotor have been discussed, and it is suggested that the scale effects are attributed to differences in the rate of diffusion of the circulation vortices in the recirculatory region. A new procedure to represent the characteristics of cross flow fans in a universal form has been proposed by analyzing the influences of Reynolds number and fan dimensions on performance curves.

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In this paper, compression waves produced by hooded trains which enter a tunnel at high speed were numerically investigated. The equations of the one-dimensional, unsteady and compressible flow in which the area of a tube is dependent on the time and the distance were numerically solved by the method of characteristics. The calculations were performed for tunnels with various hoods of different shapes in cases in which the speed of the train was 200 km/h or 300 km/h, and the effects of the shape of the hood on the shape and the strength of compression waves were quantitatively clarified. The results show that the pressure gradient of compression waves is greatly affected by the shape of the hood.

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In this study, compression waves produced by high-speed trains which enter a tunnel with the perforated hood of which the cross-sectional area equals the tunnel were numerically investigated. The equations of the one-dimensional, unsteady and compressible flow with the mass removal in which the area of a tube is dependent on the time and the distance were numerically solved by the method of characteristics. The calculations were performed for tunnels with various hoods of which porosities are different in the cases in which the speeds of the train are 200km/h and 300km/h, and the effects of the porosity of the hood for the shape and the pressure gradient of compression waves were quantitatively clarified. The results show that the pressure gradient with time of compression waves is affected largely by the porosity of the hood.

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For application to spectroscopic seed fraction measurement in a closed-cycle MHD (magnetohydro-dynamics) power generation system, the relation between the total absorption of second resonance doublets and atomic number density was determined experimentally for K-He (potassium 5p-4s lines : 404.4, 404.7 nm) and Cs-Ar (cesium 7p-6s lines : 455.5, 459.3 nm) mixtures. Atomic number density of alkali metal was precisely measured by a modified hook method which is not affected by the profile and width of the absorption coefficient. The results were compared with the total absorption calculated using the previous experimental data on collision broadening and the applicability of these data to quantitative measurement of atomic number density was investigated.

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Mass transfer has been numerically studied in a laminar flow through a circular graphite tube at high temperature. Homogeneous (carbon monoxide combustion) and heterogeneous (graphite oxidation) chemical reactions occur in the multicomponent gas mixture : helium, oxygen, carbon monoxide and carbon dioxide. The effects of carbon monoxide combustion and graphite oxidation on the mass transfer coefficients were quantitatively and qualitatively clarified in the range of 50 to 1000 of inlet Reynolds number, 0 to 0.5 of inlet oxygen mass fraction and 800 to 1600°C of temperature.

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A new apparatus to simultaneously measure surface tension and kinematic viscosity based on the surface laser-light scattering method has been developed. In this method, we can obtain the surface properties by heterodyne detection of the scattering light from thermally excited capillary waves (ripplon), which are typically of small amplitude (∼1 nm) and have a characteristic wavelength (∼100 μm). A diffraction grating is used in order to select the wave number of capillary waves and to produce a reference beam for heterodyne detection. The purpose of the present study is to establish surface laser-light scattering as a reliable technique for the measurement of thermophysical properties. It was found through the experimental study on water that this contact-free method has considerable potential for application to measurements under extreme conditions such as high temperature and high pressure.

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Heat transfer and pressure drop measurements were performed in a forced convection of air flow through a rectangular duct packed with spherical particles, which had upper cooled and lower heated surfaces. Four kinds of particles with different diameters and thermal conductivities were used as the packing materials. The effects of solid boundaries on fluid motion and heat transfer were discussed. The heat transfer rate from the surfaces was promoted by a thermal dispersion effect caused by a fluid mixing motion. However, it was decreased in the vicinity of the near-wall region due to low effective thermal conductivity and weak fluid mixing motion. It was clarified that the ratio of the thermal boundary layer thickness developed from the heat transfer surfacec to the size of the near-wall region was important in order to reduce the heat transfer data. Nondimensional heat transfer correlation equations were derived, using parameters expressing the average characteristics of the porous bed packed with spherical particles.

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Supercooling characteristics on still bulk water and several kinds of water solutions were investigated experimentally. The test fluids, which were sandwiched in between two immiscible liquids in a glass tube, were set in a constant low-temperature room, and its freezing temperature was measured. It was found that the critical degree of supercooling for the water increased with decreasing test fluid volume, V, and was proportional to the logarithm of V. However, the critical degree of supercooling for the water solutions varied with the type of solute, and for each solute, it increased with increasing solute concentration. The critical degree of supercooling for the water solution was larger than that for the water by about 0∼4 K. The increment supercooling, which depended on the type of solute, could be explained by the equilibrium freezing point depression, an increase in the viscosity and solute/water interactions. In addition, the present data for the water solutions were correlated with dimensionless parameters which expressed these effects.

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In order to obtain useful information to assess the feasibility of CO₂ confinement in the deep sea, a few experiments were conducted using a facility which can simulate the pressure and temperature condition of deep sea areas shallower than 3000 meters. The characteristics of CO₂ clathrate, such as the effect of the mixing process of injected CO₂ on the clathrate formation, and the stability of clathrate film formed at the CO₂-water interface, were carefully examined. The unexpectedly high permeability of CO₂ through clathrate film, which was determined from the observation of the shrinking process of a CO₂ droplet and the rate of pressure decrease after CO₂ injection, is an undesirable factor for the realization of CO₂ confinement in the deep sea.

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Following a study of liquid film flow, experimental results are presented on the variation of the liquid drop flow rate along the axis of a bend tube, the profile of the liquid drop flow rate at the bend exit, and the mean diameter and the distribution of liquid drops entrained in the gas core in an air-mixture flowing upward in an annular drop flow regime through a C-shaped bend of 144-mm radius of curvature with a 24-mm-inside-diameter tube lying in a vertical plane. In orer to study the effect of gravity on flow direction, some experiments are also carried out on downward and horizontal flows in the bend, and on a straight horizontal flow. The flow of liquid drops is greatly influenced by the secondary flow caused by centrifugal force within the gas core, and exhibits some notable features as well as liquid film flow.

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The flow visualization and the measurement of velocity fluctuations in the streamwise and the spanwise directions were carried out for in-line fin arrays. It was observed that the streakline becomes unstable and bends in the wake of a fin in the middle range of the Reynolds number and that the streakline bend exhibits a hook-shaped pattern in the neighbourhood of the leading edge of the downstream fin. The destabilized flow suggested by the presence of these unstable streaklines was estimated to cause the velocity fluctuation of fluid near the fins. The same flow visualization was performed for 5-row offset fin arrays. However, it was found that wake flow instability is promoted as the fin pitch becomes narrower and that the flow near a fin interacts and is synchronized with those of neighbouring fins. The frequency of appearance of the bend of a streakline is found to depend mainly on the fin pitch .

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The similarity rule states that a similarity curve representing the relationship between a similarity function and frozen fraction is indpendent of the Biot number under four specified conditions, including uniform distribution of heat flux over a heat transfer surface of a latent heat storage unit. A storage unit with straight fins, which has the nature of losing such spatial uniformity of heat flux inherently, has been analyzed numerically. The effects of thickness, thermal conductivity and the number of fins on the formation of the similarity rule have been examined, following the 2nd report describing the effect of the heat transfer tube. The results show that a relative difference between similarity curves for different Biot numbers is reduced with decreases in ( ; that is, the similarity rule becomes more and more applicable with a reduction in the thermal conductance of the fin. thickness and/or thermal conductivity of the fin) The distributions of both temperature inside the storage unit and surface heat flux have been shown for the purpose of discussing the results.

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Dye transfer thermal printing systems are becoming increasingly important as a high quality color printing method. The fundamental mechanisms of the dye transfer process must be understood better in order to further develop the system. To understand the dye transfer mechanisms, several experiments were conducted using a test printer and printing materials which were specially prepared for the purpose of the present study. It was disclosed that the mechanism of the dye transfer from the dye donor ribbon to the dye receiving sheet is caused by diffusion in the layers of the dye donor ribbon and dye receiving sheet. Among the various properties of the printing materials, the polymer T_g (glass transition temperature) has a dominant effect on the initiation of the transfer process and the amount of transferred dye.

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Experimental investigation was performed to study the pressure drop characteristics of parallel-plate channels where model packages of various sizes are mounted. The ratio of channel height to package height and placement pitch to package height are 1.3∼2.7 and 1.8∼5.6 for packages without fins, and 1.2∼2.0 and 2.1∼3.4 for finned packages, respectively. A new flow model is proposed which incorporates the three-dimensional nature of wakes behind the packages. The predicted values of pressure drop based on this model correlate with the experimental results within ±20∼30%.

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Thermal radiation characteristics of real surfaces of metallic materials are strongly affected by the surface roughness and the existing surface film. In actual industrial environments, the surface state is not stable, and the radiation characteristics change from time to time. In this paper, we present an idea for modelling such dynamic change in the surface state in an air-oxidation process at high temperatures. Transient behavior of reflection characteristics of the surface is described on the basis of an electromagnetic theory of interference and diffraction of radiation. Numerical computation is performed to reproduce the notable phenomenon of spectrum transition which was found in the preceding experimental investigations.

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An analytical study has been made of critical heat flux of a two-phase thermosyphon, in which a liquid film and a vapor flow in a manner of countercurrent annular flow. An equation governing the flow of the liquid film and other equations for mass and energy balance in the thermosyphon are solved together under two conditions ; first, the critical heat flux takes place when liquid supply to the thermosyphon is just equal to the evaporation of the liquid due to the heat input into it, and second, thickness of the liquid flow is determined such that interface of the annular flow is kept stable. Thereby, two correlations are derived for both limiting conditions of 2/(C²_ik²N_k) and then one of them for 2/(C²_ik²N_k)»1 is in good agreement with the existing CHF data in a closed two-phase thermosyphon as well as a generalized correlation derived from dimensional analysis.

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An acceleration method is developed for radiative heat transfer analysis in nongray media by the Monte Carlo method. Instead of deciding all the parameters of each energy particle used in the Monte Carlo procedure by stochastic method, the wave number assigned to each energy particle is determined by deterministic method in the present study. This change in the Monte Carlo algorithm reduces the computation time to 1/9 of the original time. To reduce the amount of iteration required to converge the temperature profile in a nongray media layer, an acceleration factor is incorporated to determine the new values of temperature in each iterational loop. The value of the acceleration factor is found to be related to the optical thickness of each media element. By using an appropriate acceleration factor, the amount of iteration is reduced to 1/4 of the original . Moreover, the total computation time becomes 1/36 of the original by the two improvements.

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Saturated pool boiling heat transfer of a toluene-solvent magnetic fluid containing magnetite particles of 0∼36.5 wt% was investigated on a horizontal surface in a vertical magnetic field and field gradient at the pressure of 0.021∼0.061MPa. In the absence of a magnetic field gradient, the heat transfer was enhanced significantly for magnetic fluid with dilute magnetite particles, while it was reduced for that with dense particles. As the magnetic field gradient was increased up to 3.9 x 10⁵ A/m², the heat transfer of the dense magnetic fluid was enhanced significantly in a low heat flux region, although it returned to the reduced heat transfer curve slowly at a certain transition heat flux. The transition heat flux increased, as the magnetic field gradient became higher, the magnetite concentration lower, and the pressure higher.

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An experimental investigation was conducted to determine the heat transfer characteristics of HCFC-22 for a two-phase double tube connected to a heat pump. This study focussed on the forced convection boiling heat transfer of small flow rate in a double tube. It was clarified that the quality at the dry-out point increases as mass velocity increases, and that the heat transfer coefficient of two-phase flow is about 30 times as large as that of the liquid single-phase laminar flow. Furthermore, it was found that the heat transfer performance of the double tube is superior to that of a single tube.

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An experiment was performed to investigate the enhancement of local heat transfer to a boiling or evaporating non-azeotropic refrigerant mixture of HCFC22 and CFC114 in a horizontal, spirally grooved tube. There was no notable difference in the enhancement among the mixture and the pure refrigerants at a high flow rate. At a low flow rate, the heat transfer to the mixture in the high quality region was found to be enhanced over the smooth tube as effectively as to the pure refrigerants ; therefore, no features of the mixture were recognized. In the low quality region where the effective enhancement was also achieved for the pure refrigerants, however, the enhancement for the mixture was greatly degraded. This degradation was theoretically explained by taking account of the variation of composition in the meniscus liquid film formed in the grooves on the upper part of the tube perimeter.

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The unsteady characteristics of heat transfer and particle behavior around a horizontal tube bundle near the expansion surface of a gas fluidized bed were experimentally studied. The instantaneous local heat transfer coefficient and the number of particles making contact with the heat transfer surface were measured simultaneously at the same location on the tube surface. The distributions of the local average heat transfer coefficient in the period during no particle contact were qualitatively similar to those for the gas single-phase flow, but were 2∼5 times larger than those for the corresponding gas single-phase flow. The relation between the local average heat transfer coefficient in the period during the particle contacts and the average number of the contacting particles were quantitatively evaluated.

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To attain a high enhancement rate in convective heat transfer, deformation or destruction of the boundary layer is a necessary condition. For example, injection or suction is one of the most fundamental methods. Although several attempts of heat transfer enhancement have been made in forced convection, in turbulent natural convection, we have not discussed an effective technique sufficiently. Especially, when only natural convection is applicable to cooling, it is important to analyze its enhancement mechanism. In this paper (the 1st report), therefore, injection and suction were added to turbulent natural convection along a vertical flat plate, and the possibility of heat transfer enhancement was discussed at first. It was realized that local Nusselt numbers affected by injection and suction were 1.5∼1.6 times as much as those for pure turbulent natural convection.

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Analytical study of the ice formation process associated with heat conductor plates located perpendicularly to isothermally heated and cooled surfaces with some clearance is presented. It is proposed that the onset conditions, which describe whether the ice volume fraction in a steady state is greater or less than that without heat conductor plates, are defined by dimensionless distances between the heated/cooled walls and the heat conductor plates. It is shown that the onset values are dependent on the pitch and the thickness of the heat conductor plates, and are less dependent on the thermal conductivity.

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The heat-transfer mechanism of a fine-tube heat exchanger developed by the authors has been studied on the basis of flow and heat-transfer experiments. To clarify the effect of the woven threads on turbulence promotion, a test section scaled up 30 times as large as the actual heat-transfer element was made of transparent Pyrex glass, and the flow field around fine tubes was measured by laser Doppler velocimeter using castor oil as a working fluid. The distributions of Nusselt number around the fine tube were measured as well, using silicon oil. The heat-transfer enhancement and its mechanism were discussed in light of the turbulence behavior which was highly augmented by the threads.

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Unsteady flow and heat transfer characteristics were studied numerically for an in-line array of fins located in a channel. The results were found to be in reasonably good agreement with the results of flow visualization and velocity measurements. This validates the numerical scheme developed in this study. The numerical results showed that the flow and thermal fields are destabilized in the wakes but are stabilized in the boundary layers developing on the downstream fins. It is also found that -μυ and υθ take nonzero values in the wake and even in the regions near the downstream fins. Another interesting feature found in the present study is that the value of -μυ was found to be negative but the value of υθ was positive around the downstream fins. This suggests, from a statistical viewpoint, that there exists a dissimilarity between the momentum. transfer and heat transfer. This dissimilarity was found also to be related to the negative production of the intensity of fluctuating velocity.

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Unsteady flow and heat transfer characteristics were studied numerically using the numerical scheme validated in the previous study for an in-line array of fins located in a channel. It is found that there exists at least one peak in the streamwise distribution of the instantaneous local Nusselt number, Nu_H, on the surfaces of fins located downstream from the destabilized wakes of other fins. The peak of Nu_H distribution appears at the minimum position of the instantaneous local skin friction. Thus, heat transfer enhancement of fin arrays is accompanied by the local and instantaneous dissimilarity between momentum transfer and heat transfer. The dissimilarity is related to the fluid motion corresponding to the outward and wallward interactions of near-wall turbulence. These fluid motions are caused by the rotating fluid motion induced by intermittently appearing vortices. These vortices are formed from the tips of protruding parts of the interface between the pcsitive and negative vortex layers in the wake. This rotating fluid motion pumps the hot fluid from the fin surface region to the main flow region and entrains the fresh fluid from the main flow region into the near-wall region from its downstream side.

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Radiation heat transfer from a solid plane surface is directionally controllable by means of a grating composed of circular cylinders. An analysis of the radiation heat transfer is made for a physical model in which a grating of parallel cylinders is placed in front of a black heat-transfer surface, and the cylinder surfaces have both specular and diffuse reflectivity components ( ρ_c=ρ^s_c+ρ^d_c). Numerical solutions are obtained. The apparent directional emissivities and the limiting angles expressing a degree of energy concentration are calculated for parameters such as ρ^s_c/ρ_c and center-to-center distance of cylinders. It is clarified that the grating of cylinders is useful for concentrating the radiation energy emitted from the heat-transfer surface in the direction normal to the grating surface.

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The objective of this paper is to clarify the effect of heat release and density difference in mean flow on the development of mixing layers. To achieve this purpose, we have performed a direct numerical simulation of a two-dimensional chemically reacting mixing layer by means of a spectral method. Low Mach number approximation was used to take into account the effect of density change. From these results, we have obtained the following conclusions. (1) Heat release causes baloclinic torque in the outside region of the coherent structure. Because of this baloclinic torque, the growth of the mixing layer and chemical reaction are suppressed. (2) The density difference of mean flow suppresses the growth of the mixing layer and chemical reaction because of the baloclinic torque and expansion. (3) The growth of the mixing layer and chemical reaction are further suppressed by the coexistence of heat release and density difference.

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