In recent years, we can easily find the gas-liquid two-phase flow in narrow channel which has straight section and curved section in many industrial products. In order to improve the performance of these industrial products, it is important to clarify the effects of curved section on gas-liquid two-phase flow behavior in narrow channel. In this study, we have measured the pressure loss precisely on straight section and curved section in milli-channel respectively. From the measured pressure loss, we evaluated the mean pressure loss and its intensity. Flow visualization by using high-speed video camera was additionally performed to make clear the relation between modification of pressure loss and flow pattern in curved section. As a result, effects of curved section on gas-liquid two-phase flow in narrow channel were evaluated.

The phenomena of frosting and defrosting are quite important in evaluation of efficiency of various heat equipments such as heat pump etc. In this paper, hydrodynamic phenomena in frosting and defrosting were studied experimentally. Cooling surfaces were flat or artificially grooved with the size of several tens of microns in pitch and depth. In frosting process, super cooled small water droplets were formed on the cooling surface. In the flat surface, droplets are formed around the cavities which are small holes or scars on the surface. In the artificially grooved surface, droplets are formed in the groove or flat part between grooves. Maximum size of droplets on the artificially grooved surface was controlled by pitch and depth of the grooves. In the defrosting, larger water droplets or water films were formed on the cooling surface. On the flat surface, water droplets or films remained on the surface for long time. On the other hand, on the grooved surface, water droplets or films were drained rapidly through microgroove due to the capillary driven flow.

Accurate analyses of turbulence structure and void fraction distribution are quite important in designing and safety evaluation of various industrial equipments using gas-liquid two-phase flow such as nuclear reactor, etc. Using turbulence model of two-phase flow and models of bubble behaviors in bubble flow and slug flow, systematic analyses of distributions of void fraction, averaged velocity and turbulent velocity were carried out and compared with experimental data. In bubbly flow, diffusion of bubble and lift force are dominant in determining void fraction distribution. On the other hand, in slug flow, large scale turbulence eddies which convey bubbles into the center of flow passage are important in determining void fraction distribution. In turbulence model, one equation turbulence model is used with turbulence generation and turbulence dissipation due to bubbles. Mixing length due to bubble is also modeled. Using these bubble behavior models and turbulence models, systematic predictions were carried out for void distributions and turbulence distributions for wide range of flow conditions of two phase flow including bubbly and slug flow. The results of predictions were compared with experimental data in round straight tube with successful agreement. In particular, concave void distributions in bubbly flow and convex distribution in slug flow were well predicted based on the present model.

Unsteady numerical analyses were carried out for the PCCI combustion realization on the next generation diesel engine. The effects of intentional initial fuel concentration distribution on the ignition timing and the expansion of the operable range were focused. The numerical code was originally developed to analyze the unsteady combustion behavior of premixed gas with intentional initial fuel concentration distribution in the combustion chamber of PCCI engine. The fundamental equations for the numerical analysis are the Euler’s equations for compressible fluid, that consist of the conservation equation of mass, momentum, energy and chemical species. The equations are expressed in axisymmetric cylindrical (r-z) coordinate system. The time variation of the internal cylinder volume of the reciprocating crank-piston movement is expressed by the volume change rate, which is substituting the convection term in axial direction of the Euler’s equations. By using this technique, we can reduce the spatial dimension of the equations with keeping the consideration of volume change of the combustion chamber of reciprocating engine. The radial direction corresponds to the bore of the engine cylinder. By solving this equation system, we can consider the radial distribution in combustion chamber during the PCCI combustion such as temperature, mass fraction of chemical species, pressure, and so on. Detailed chemical kinetics with elementary reactions and multi-component diffusion for n-heptane system as fuel, ERC-mechanism, were considered. The NOx emission can be also considered by using the part of GRI-Mech3.0 for generation of thermal NOx. Totally, the 34 chemical species and 61 elementary reactions were considered. This code has a high resolution for time and space to capture the dynamic behavior in PCCI combustion such as a generation and propagation of shockwave causing detonation. A series of unsteady events on PCCI combustion can be simulated by considering the time variation of volume of combustion chamber varied with crank angle; such as the charged compression and auto-ignition of premixed gas, the flame propagation and the detonation with shockwave.

In order to predict the critical power or void fraction in BWR fuel bundles and the DNB heat flux of PWR fuel assemblies, the boiling transition analysis code called “CAPE” with mechanistic models has been developed in the IMPACT project by NUPEC. The objective of the CAPE code development is to perform with good accuracy the safety evaluation for a new type or improved fuel bundle design of BWR and PWR without full-scale experiments or any tuning parameters in the analysis code. In the present study dryout heat fluxes of BWR fuel assembly were analyzed by the CAPE code and compared with experimental data of BFBT benchmark test carried out by NUPEC. In the CAPE code, mechanistic model of liquid film dryout in annular flow is used considering entrainment and deposition of droplet. In such mechanistic prediction of dryout, the correlations of entrainment and deposition rates play quite important roles and many correlations have been developed. In addition to the original correlations in the CAPE code, several typical correlations, which are widely used in the analysis of annular dispersed flow, were tested for the prediction of dryout. The results indicated that the CAPE code satisfactorily predicted dryout heat fluxes of fuel assembly for wide range of pressure, mass flux, subcooling and bundle geometries obtained in BFBT benchmark test. The accuracy of prediction depends upon the combination of correlations of entrainment and deposition rates. The evaluation of correlations of entrainment and deposition rates was carried out.

In order to predict the critical power or void fraction in BWR fuel bundles and the DNB heat flux of PWR fuel assemblies, the boiling transition analysis code called “CAPE” with mechanistic models has been developed in the IMPACT project by NUPEC. The objective of the CAPE code development is to perform with good accuracy the safety evaluation for a new type or improved fuel bundle design of BWR and PWR without full-scale experiments or any tuning parameters in the analysis code. In the present study void fraction distribution of BWR fuel assembly were analyzed by the CAPE code and compared with experimental data of BFBT benchmark test carried out by NUPEC. The analyses were carried out by changing the operational parameter such as the inlet subcooling, mass flow rate and the power output of the fuel bundles. Resultantly, the thermal equilibrium quality at the outlet ranges 2% ∼25%. Averaged and local void fractions were compared between experiment and analysis. The results indicated that the CAPE code satisfactorily predicted void fraction distribution of fuel assembly for wide range of pressure, mass flux, subcooling and bundle geometries obtained in BFBT benchmark test. However, the detailed analysis showed that in some subchannels, which was surrounded by the heated fuel rods and partially unheated wall such as an unheated rod, a water rod and a separation wall of the channel box, certain difference between experiment and prediction appeared. In the CAPE code, the drift flux model is used for predicting void behavior in fuel assembly. In drift flux model, correlations of drift velocity and distribution parameters are quite important in predictive accuracy of void fraction. In particular, it is considered that distribution parameter plays important role in void distributions in subchannel surrounded by unheated rods. In addition to the original correlations in the CAPE, some typical correlations of drift velocity and distribution parameter were tested for the prediction of void fraction distribution. The evaluations of correlations of drift velocity and distribution parameter were carried out, and some recommendations for improvement of predictive capability of the CAPE code were made.

Water jet is utilized in various industrial application such as cutting carious materials and soil. In particular, jet grouting for soil improvement is one of the most important application of water jet under high pressure and high liquid flow rate. Such technology is already in practical use in civil engineering. In order to improve the efficiency and performance of jet grouting, it is quite important to clarify the hydrodynamic structure of water jet under high pressure and high flow rate. However, basic researches on this subject are quite insufficient both experimentally and analytically. Water jet utilized in jet grouting is usually very high speed ( up to 500 m/s) two-phase dispersed flow. Therefore, it is quite difficult to make visual observation of such water jet using conventional optical methods. In the present work, the authors utilized high sensitive CCD camera with image intensifier of which gate speed is 10 ns. Using this optical device, the authors obtained still image of high speed water jet for the first time. Visual observation revealed that high speed water jet is composed of very fine droplets and has complicated structures such as swirl and cluster of droplets. Velocity of water jet was also measured using two consecutive images taken between 10 microsecond. Such direct measurement of jet velocity of high speed water jet has not been carried out so far. The result indicated that jet speed (droplet speed) is even very high even at the boundary of water jet. Measure water jet velocity was reasonably correlated with jet velocity at the exit of nozzle.

In the present investigation, detailed observations on the flow patterns and measurements for pressure drop characteristics affected by the curvature effect in a micro-channel were carried out. The test channel has a square cross section that has 2.0mm on a side, and the radii of the curvature were 1.0mm and 3.0mm. It was cleared that the pressure fluctuation intensity became larger in the case of the curvature 1.0mm compared with the case of the curvature 3.0mm. Furthermore, in order to investigate the influence of the wall wettabirity, we applied the water repellent channel. In the case of the water repellent micro-channel, the flow pattern tended to easily transit to Annular flow side compared with the normal micro-channel without the water repellent, and we can see a new flow regime like Rivulet flow due to applying water repellent.

Experimental studies were made on the multi-dimensional behavior of upward gas-liquid two-phase flow through the vertical round tube with an axisymmetric sudden expansion, which is one of the typical multi-dimensional channel geometry. The aims of this study are to clarify the multi-dimensional behavior of bubbly or slug flow affected by sudden expansion channel geometry, and to accumulate the experimental data for two-phase flow analysis, which is applicable to predict with appropriate accuracy the multi-dimensional its behavior. The direct observation using high-speed video camera was performed and revealed the multi-dimensional dynamic flow behavior with bubbles and gas-slug affected by the sudden expansion part (20 mm-tube to 50 mm-tube). The characteristic phenomena were observed such as bubble break-up, deformation due to the strong shear of liquid flow, or liquid micro jet penetration through the gas-slug, and so on. From these results, the flow regime map and the flow patterns at the below and above of the sudden expansion part were classified in relation to the bubble diameter. Additionally, the measurement of the void fraction profiles in the tube cross sections of sudden expansion were conducted at the different axial positions. The void fraction was measured using a point-electrode resistivity probe. The void fraction measurements in this study showed in detail that how the two phase flow develops along the direction of the downstream of the sudden expansion. In just above the sudden expansion, the void fraction distribution appeared the wall peak or the core peak in void fraction in the upstream of the sudden expansion. In the downstream of the sudden expansion, the void fraction distribution changes from a saddle shape or power-low shape into finally the saddle shape as the bubbly flow develops along the downstream of the sudden expansion. These experimental data in the sudden expansion of a vertical upward bubbly flow would become benchmark with respect to the multi-dimensional behavior of the two-phase flow analysis.

Experimental and analytical studies have been carried out on the hydrodynamic behavior of swirling liquid film flow on a rotating disc. Film flow formation and swirling waves on the liquid film were analyzed through observation using high speed video. Liquid film thickness was measured using the Laser refraction method and compared with prediction. The rotating disc is 200 mm in diameter and was made of Silicon (Silicon wafer in industrial use). The rotating speed is up to 100 rad/sec (2000 rotations per min.) Water is supplied to the center of the disc at a flow rate of 8.3 × 10 −6 m 3 /s (500 cc/min). The film flow is divided into three regimes depending upon rotating speed. For the lower rotating speed (up to 10 rad/sec), formation of liquid film flow is incomplete and some part of the peripheral region of the disc is not completely covered by liquid film. For the intermediate rotating speed (15–25 rad/sec), laminar film flow covered the whole disc. Furthermore, there are swirling waves on the liquid film. This wave is considered to be a continuity wave arising at the center portion of disc due to the water flow rate variation form the nozzle. Wave propagation speed and behavior of these swirling waves were well explained by the theory of continuity wave. For the high rotating speed (more than 30 rad/sec), the liquid film flow changed its flow regime from laminar flow to turbulent flow. The estimated film Reynolds number at transition is about 1200 which is consistent with turbulent flow transition for pipe flow and film flow on non-rotating surface. Three dimensional turbulent waves were observed on this turbulent liquid film. The behavior of such three dimensional turbulent waves were quite random in time and space. Measured film thicknesses ranged from 50 to 300 micron. Film thickness and its fluctuation decreased as the rotation speed of disc increased and distance from disc center increased. The analysis was made on the film thickness based on the force balance between shear stress and centrifugal force acting on the film. The predicted film thickness agreed well with the measured value.

Experimental studies were made on the multi-dimensional behavior of upward gas-liquid two-phase flow through a vertical pipe with an axisymmetric sudden expansion, which is one of the typical multi-dimensional channel geometries. The aims of this study are to clarify the multi-dimensional behavior of bubbly and slug flow affected by the sudden expansion channel geometry and to accumulate the experimental data for two-phase flow analysis, which is applicable to predict appropriate accuracy the multi-dimensional behavior. In this report, the first, the observation using high-speed video camera was performed and revealed the multi-dimensional dynamic flow behavior with bubbles and gas-slug affected by the sudden expansion point. From these results, the flow regime map at the below and above of the sudden expansion point were classified with bubble diameter. The second, the variation of the phase distribution in the sudden expansion was measured at the different axial positions using a point-electrode resistivity probe for various gas and liquid flow conditions. Thirdly, the cross-sectional averaged void fractions along the flow direction were calculated by using the one-dimensional two-fluid model considering the phase distribution parameter to confirm the applicability of the computations. As a result, they concretely pointed out that some multi-dimensional modeling or modifications for numerical simulation would be needed for more accurate prediction of two-phase flow. Such radial phase distributions in this study are significant for the multi-dimensional two-phase flow analysis.

Experimental and numerical studies were made to investigate the effects of wavy interface on the liquid film to gas-phase turbulence modification of air-water annular flow in a vertically arranged round tube. By using the constant temperature hotwire anemometer, time-averaged axial velocity profiles, turbulence fluctuation profiles, energy spectrum and auto-correlation coefficient for fluctuation velocity component of gas-phase axial velocity were precisely measured. The liquid film thickness was also measured by using point-electrode resistivity probe to make clear the time-averaged liquid film thickness and wave height moving on the liquid film. Direct observations using high speed video camera were also added to make clear the dynamic behavior and propergating velocity of ripple or disturbance waves on liquid film flow. Numerical simulations for gas-phase turbulence in annular flow considering the effect of wavy interface of liquid film flow were also carried out. Liquid film flow was modeled to be the wall surface roughness of interfacial wave height moving with the interfacial velocity. The roughness and moving velocity of the modeled liquid film for computational condition were provided by the present experimental results. Time-averaged velocity profiles and fluctuation velocity profiles were calculated with standard k -ε model. Numerical results were generally consistent with the experimental results obtained in the present study.

Analyses of water jet based on two-fluid model of two-phase dispersed flow have been carried out for single water jet and cross water jet in relation to the water jet technology in civil engineering. Mass and momentum conservation equations for liquid phase (droplet) gas phase (air) were formulated separately (two-fluid model formulation). Physical modeling of diffusion of droplets, drag coefficient of droplet in dispersed flow, shear stress at jet interface, etc has been carried out in detail and constitutive equations for these physical phenomena have been developed. Based on the two-fluid model basic equations and constitutive equations, one-dimensional analysis has been carried out considering simplified model. In the practical application of present analyses, some preliminary analyses on cross jet where two water jets collide with certain collision angles have been carried out and the predicted results reasonably explain the experimental results.

Experimental studies were made on the gas-core turbulence structure in vertical upward annular two-phase flow passing through a round tube with a throat section. The gas-core turbulence is affected and modified by the dynamic interaction between gas-core flow and liquid film flow through the wavy interface. The test channel has a throat section, which consist of nozzle, throat and diffuser part, where the cross sectional area of the channel is changed along the flow direction. In the throat section, the flow is in transient state because the flow is accelerated or decelerated along the flow direction as the cross sectional area of the channel is changes. The gas-phase turbulence structure such as the time-averaged velocity profiles and fluctuation velocity profiles were precisely measured by using the constant temperature hot-wire anemometer. For the liquid film flow, the time-averaged film thickness, base-film thickness and interfacial wave height were obtained by using the point electrode resistivity probe. Direct observations for the interfacial waves on liquid film flow such as disturbance waves and ripple were also carried out by using the high-performance camera system to make clear the interfacial wave structure.

Analyses of water jet based on two-fluid model of two-phase dispersed flow have been carried out for single water jet and cross water jet in relation to the water jet technology in civil engineering. Mass and momentum conservation equations for liquid phase (droplet) gas phase (air) were formulated separately (two-fluid model formulation). Physical modeling of diffusion of droplets, drag coefficient of droplet in dispersed flow, shear stress at jet interface, etc has been carried out in detail and constitutive equations for these physical phenomena have been developed. Based on the two-fluid model basic equations and constitutive equations, one-dimensional analysis has been carried out considering simplified mode and hydrodynamic structure of water jet was well predicted. In the practical application of present analyses, some preliminary analyses on cross jet where two water jets collide with certain collision angles have been carried out and the predicted results reasonably explain the experimental results.

In order to predict the critical power or void fraction in BWR fuel bundles and the DNB heat flux of PWR fuel assemblies, the boiling transition analysis code called “CAPE” with mechanistic models has been developed in the IMPACT project by NUPEC. The objective of the CAPE code development is to perform with good accuracy the safety evaluation for a new type or improved fuel bundle design of BWR and PWR without full-scale experiments or any tuning parameters in the analysis code. In this study, the CAPE for BWR was validated by the test analysis for 8 × 8 fuel bundles comparing with the void distribution data of the experimental data, which was carried out under several operational conditions in a BWR. The computations were carried out by changing the operational parameter such as the inlet subcooling, mass flow rate and the power output of the fuel bundles. Resultantly, the thermal equilibrium quality at the outlet ranges from 2% to 25%. From these results, though the predictive accuracy of the analytical results are in close agreement with the experimental data, it was noted that the errors were relatively outstanding in some subchannels, which was surrounded by the heated fuel rods and partially unheated walls, such as an unheated rod, a water rod and a separation wall of the channel box. The reason for this error is thought to be that the cross sectional void distribution was partially distributed in such subchannels surrounded partially by unheated wall, so the multidimensional void distribution structure might be formed in these subchannels. Under such conditions, it is very important to take into consideration the multidimensional structure of the two-phase flow in subchannel, and perhaps improve the estimation or correlations for the distribution parameter, as well as the amount of void exchange between neighboring subchannels.