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A method to estimate wax thickness inside petroleum pipes from the external pipe temperature measurements is proposed. When wax is deposited inside the pipe, the external pipe surface temperature decreases because the heat resistance of the wax reduces the heat flow from the fluid inside the pipe to the fluid outside the pipe. The decrease in the external pipe temperature can be calculated by solving a heat equation about the heat transfer from the pipe inner fluid to external ambient fluid, and thus the wax thickness can be estimated by measuring the pipe surface temperature. An experiment to validate the method was performed. Crude oil was passed through a pipe with an inner diameter of about 8 mm. Ten thermocouples were installed on the pipe. The pipe was covered by a heat-shrink tube as a substitute for an insulation material. The pipe was cooled by a coolant jacket, and wax about 0.8 mm thick was deposited in the pipe. The wax thickness estimated from the temperature measurements agreed well with the thickness estimated from the pressure rise because of the wax layer and from the final gross weight of the wax. The difference between wax thickness estimated from the temperature measurements and from the final gross weight was less than 0.2 mm.

Regarding a severe accident of supercritical water-cooled reactor (SCWR), phase change between subcritical and supercritical conditions is crucial since heat transfer rate changes massively causing a dryout accident. Fundamental knowledge on surface wettability and boiling heat transfer on metals at subcritical conditions under radiation are, thus, important in thermal-hydraulic design and safety analysis of reactor core in light water reactors including a supercritical water-cooled reactor. The radiation induced surface activation (RISA) which enhances wettability and anticorrosive effect on the metal surface was first revealed by authors in 1999. In the earlier studies, significant improvements of surface wettability and boiling heat transfer on oxide film coated-materials by the RISA were observed in a room temperature condition. The purpose of this study is to evaluate the effect of oxidized metal and γ-ray irradiation on metal surface wettability in high pressure and high temperature conditions. In this experiment, the test section was pressurized at 12 MPa with nitrogen gas using pressure vessel and was heated up to temperatures of 20, 150, 200, 250 and 290 centigrade. Two types of material; a stainless-304 and austenitic stainless steel named PNC1520, which is considered as a potential material of fuel-cladding tube of the SCWR, were used as specimens. The oxide film on the specimen was formed in supercritical water at 380 centigrade and 22 MPa. About 600 kGy Co-60 γ-ray source was used for irradiation. The results showed that the difference of oxidization on wettability was insignificant at room temperature before γ-ray irradiation while contact angles on the oxidized specimen decreased at high temperatures. The water growth rate on oxidized material slightly lower compare to non-oxidized material. This result suggests oxide film formation on metal surface plays an important role in surface wettability enhancement by the RISA.

In order to extend a precise database on local two-phase flow parameters in mini pipes, experiments were conducted for adiabatic gas–liquid bubbly flows flowing down in vertical mini pipes with inner diameters of 1.03, 3.00, and 5.00 mm. A stereo image-processing was applied to observe the phase distribution characteristics in pipe cross-section. The local flow parameters including profiles of void fraction, Sauter mean bubble diameter, and interfacial area concentration in pipe cross-section were obtained at three axial locations in the test pipes with various flow conditions: superficial gas velocity of 0.00508–0.0834 m/s and superficial liquid velocity of 0.208–3.00 m/s. The axial developments of the local flow parameters were discussed in detail based on the obtained data and the visual observation. It was confirmed that the core peak distributions were formed at low liquid flow rate conditions in which the buoyancy force dominated while the wall peak distributions were formed at high liquid flow rate conditions in which the body acceleration due to the frictional pressure gradient dominated. The result indicated the existence of lift force pushing the bubbles towards the pipe wall even in vertical downward flows. The database obtained through the present experiment is expected to be useful in modeling the interfacial area transport terms, the validation of the existing lift force models as well as the benchmarking of various CFD simulation codes.

In view of the quality assurance of two-phase flow simulations, CSAU (Code Scalability, Applicability, and Uncertainty) methodology and code V & V (Verification and Validation) have been proposed. The estimation of simulation uncertainty is indispensable in using best-estimate computational codes. A key of successful two-phase flow simulations is to use the state-of-the-art constitutive equations to close the mathematical system used in two-phase flow analyses. The advanced constitutive equations should be developed based on “physics” behind phenomena and should consider scaling parameters which enable their application beyond test conditions used for a code validation. Two-phase flow simulations in a rod bundle is important in various industrial apparatuses such as heat exchangers and nuclear reactors. Constitutive equations for two-phase flows in a vertical rod bundles have been advanced in recent five years. In view of this, this paper provides a comprehensive review of most advanced constitutive equations for two-phase flow analyses in a vertical rod bundle. The constitutive equations of two-phase flow parameters reviewed in this paper are flow regime map, void fraction, void fraction covariance and relative velocity covariance, interfacial area concentration and wall friction. In addition, an exact formulation of one-dimensional momentum equation in two-fluid model considering void fraction distribution is discussed.

From the viewpoint of the improvement of the air lubrication method for the ship's hull resistance reduction, an experimental study was conducted for two-phase flow in a horizontal rectangular channel with a length of 3.0 m, a gap of 0.05 m, and a width of 0.2 m, which simulates the external two-phase flow.The database on frictional drag and local two-phase flow parameters, including void fraction profile and gas chord length, was collected using a shear stress sensor and a double sensor probe. Measurement of two-phase flow structure was performed at three axial positions of z = 0.930, 1.43, and 1.93 m from the bubble injection port. The wall shear stress was obtained at z = 1.93 m. A total of 72 datasets are acquired a room temperature and at flow conditions of superficial liquid velocity ranging from 0.832 to 3.00 m/s and superficial gas velocity ranging from 0.0232 to 0.714 m/s. The effects of entry length, liquid and gas flow rates on the phase distribution characteristics beneath the wall were discussed. The bubble layer thickness was newly defined as the length scale. The bubble layer thickness was not so sensitive to the changes in the liquid flow rates and the entry length, and highly dependent on the gas flow rates in the present experimental conditions. The mean void fraction in the bubble layer was highly reliant on the liquid flow rate and decreased with the superficial liquid velocity.In contrast, the insignificant effect of gas flow rate on the mean void fraction was confirmed. A strong correlation between the drag reduction effect due to the air lubrication and the mean void fraction in the bubble layer was confirmed.The obtained data are expected to be used for the modeling of the interfacial area transport terms, development of the constitutive equations of the drift flux model, modeling of the drag reduction for the external two-phase flow and the benchmark tests of various CFD codes in the future study., 公開日: 2024-02-24

In view of the practical importance of the interfacial area transport equation in flow analysis based on the two-fluid model, especially for flow analysis in a reactor core which has a relatively small channel configuration, the dominant mechanism in the interfacial area transport in small diameter pipes was firstly identified by evaluating the experimental data obtained for pressurized bubbly flows under microgravity, where the source and sink terms of the interfacial area concentration due to bubble expansion and wake entrainment collision are negligible. The sink term of the interfacial area concentration of bubbly flow in small diameter pipe was modeled in terms of the shear collision mechanism. The one-dimensional interfacial area transport equation with the developed sink term was evaluated by using 74 datasets obtained for adiabatic gas-liquid bubbly flows, including upward flows and microgravity flows in pipes with inside diameters of 9.0, 5.0 and 3.0 mm. A detailed discussion was provided on the interfacial area transport mechanism in small-diameter pipe. The overall standard deviation of the absolute error between predicted and measured interfacial area concentrations was 11.8%. The present model will reproduce the interfacial area transport of bubbly two-phase flows in small-diameter pipes with inside diameters of 3.0–9.0 mm, at superficial liquid and gas velocities over the ranges 〈 j f 〉 = 0.073–0.949 m/s, and 〈 j g 〉 = 0.00434–0.0500 m/s, and also over a wide range of axial distances, z / D = 5–188.

The supercritical water reactor (SCWR), which is one of the generation IV reactor concepts, has particular thermal hydraulics features. If a severe accident happens and pressure and mass flux in a reactor core are rapidly decreased, a film boiling on a fuel cladding tube surface may occur at subcritical conditions. Once the film boiling happens, heat transfer on the cladding tube surface drastically deteriorated and may result in serious damage to the reactor core. The cooling capability during the film boiling depends on the wetting phenomenon, therefore, experiments to clarify wettability phenomenon in subcritical condition are required. One of the experiments to clarify the wettability phenomenon is the capillary action experiment. In the closed system, the water level will elevate due to the injection of the water. The difference in water elevation is due to the capillary force in the different diameter of the pipes. Based on the different water levels with known surface tension, it is possible to quantify the contact angle. The challenge of the experiment is to measure the precise elevation of the water in small diameter metal pipes under high-temperature and high-pressure condition. Therefore, the neutron imaging was applied in this experiment. Neutron imaging is a structure visualization technique. The principle is the neutron flux captured after passing through the object for visualizing the structure of an object. Neutron flux which is captured using a scintillator plate thus can be seen as an image using CCD video camera. Our research group focuses on the radiation induced surface activation (RISA) effect. Significant improvements of surface wettability and boiling heat transfer on oxide film coatedmaterials by the RISA were confirmed especially under room temperature conditions. In this present research, we evaluate the RISA effect on capillary action in a subcritical condition using the various diameter of the pipe. Neutron imaging was used to visualize the water-gas interface in small diameter stainless steel pipes. The capillary pipes with various inside diameters such as 0.5, 0.8, 1.2, 1.4, and 1.8 mm were used as a test section which was heated up to a temperature of 320° C under a pressure of 21 MPa. The pipes irradiated by γ-ray with an integrated irradiation dose of approximately 500 kGy and non-irradiated pipes with various diameters are installed in parallel and water levels in each pipe were compared to evaluate capillary action differences.

The radiation induced surface activation (RISA) effect which occurs at the bilayer of metal and oxide due to irradiation contributes to improving the materials surface wettability and enhancing electrothermal characteristics and corrosion resistance. The purpose of the present study is to reveal the correlation between the wettability recovery behavior and the microstructural features of the adsorbed water and/or hydroxyl species on the surfaces. The wettability change due to the RISA effect was investigated in the oxidized austenitic stainless steel with various holding times under darkness after UV irradiation. The microstructure features of the adsorbed water and/or hydroxyl species on the surfaces were characterized by Raman spectroscopy and scanning probe microscopy (SPM). Results show that the contact angle of the specimen after UV irradiation parabolically increased with increasing holding time, regardless of the chemical composition within these two steels. The absorbed water layer was observed in both specimens by Raman analysis, and its intensity decreased with increasing holding time. From the force-distance curves of SPM analysis, the hydrophilic component was rapidly decreased at a holding time below 200 h, then gradually saturated when the holding time increased above 200 h from the SPM analysis. These results reveal that the wettability recovery behavior in oxidized austenitic stainless steels after UV irradiation can be ascribed to two kinds of mechanisms. One is the desorption of the hydrophilic components which are predominant when the contact angle is less than 30°, and the other is the absorption of the hydrophobic components which works mainly when the contact angle is above 30°.

Fundamental knowledge of electrochemical characteristics of metals under high temperature and radiation conditions is important in development of reactor core materials for light water reactors including a supercritical water-cooled reactor (SCWR). In the past studies, however, the majority of electrochemical measurements of the metals have been conducted at temperatures less than 290 °C and under a non-radiation condition. On the other hand, the radiation induced surface activation (RISA) which enhances of wettability and anticorrosive effect on metal surfaces was first revealed by authors in 1999. This study is aimed to confirm the RISA effect experimentally under high temperature conditions. The electrochemical characteristics measurement of a specimen immersed in pure water in an autoclave were performed at temperatures up to 300 °C. A normal 304 stainless-steel and a radioactivated 304 stainless-steel were used as the specimen. The radioactivated specimen was made by 140 MeV irradiation of C4+ ion beam at a cyclotron accelerator of Tohoku University in Japan. The experimental results showed that the corrosion potential of specimen was lowered due to radioactivation.

The axial development of the void fraction, interfacial area concentration and Sauter mean bubble diameter profiles of adiabatic air-water bubbly flows in 5.0 and 3.0 mm-diameter pipes were measured using a stereo image processing method under two gravity conditions, vertical upward (normal gravity) and microgravity. The flow measurements were performed at four axial locations. The axial distances from the pipe inlet (z) normalized by the pipe diameter (D) were z/D = 5.5, 34, 72 and 110 for 5.0 mm-diameter pipe and z/D = 15, 62, 120 and 188 for 3.0 mm-diameter pipe. Data were collected for superficial gas and liquid velocities respectively in the ranges of 0.00434–0.0500 m/s and 0.205–0.754 m/s. The effect of gravity on the radial distribution of bubbles and the axial development of two-phase flow parameters is discussed in detail, based on the obtained database. The phase distributions in pipe cross-sections were classified into 3 basic patterns: core peak, intermediate peak and wall peak distributions, based on two normalized parameters: a normalized void peak position and a normalized void peak intensity. Phase distribution pattern maps under normal and microgravity conditions were generated for bubbly flows in 5.0 and 3.0 mm-diameter pipes. The data obtained in the current experiment are expected to contribute to the benchmarking of CFD simulation of void fraction and interfacial area concentration distribution patterns in forced convective pipe flow under microgravity conditions.

The axial development of the void fraction profile, interfacial area concentration and Sauter mean bubble diameter of adiabatic nitrogen–water bubbly flows in a 9 mm-diameter pipe were measured using stereo image processing under normal and microgravity conditions. The flow measurements were performed at four axial locations (axial distance from the inlet, z normalized by the pipe diameter, D, z/D = 5, 20, 40 and 60) and with various flows: superficial gas velocity of 0.00840–0.0298 m/s, and superficial liquid velocity of 0.138–0.914 m/s. The effect of gravity on radial distribution of bubbles and the axial development of two-phase flow parameters is discussed in detail based on the obtained database and visual observation. Following Serizawa–Kataoka’s phase distribution pattern criteria under normal gravity conditions, the phase distribution pattern map was developed. Similar to normal gravity two-phase flows, wall, core and intermediate void peak patterns are observed under microgravity conditions but a transition void distribution pattern is not observed in the current experimental conditions. The data obtained in the current experiment are expected to contribute to the benchmarking of CFD simulation of phase distribution pattern and interfacial area concentration in forced convective pipe flow under microgravity conditions.

Flow regime transition criteria are of practical importance for two-phase flow analyses at reduced gravity conditions. Here, flow regime transition criteria which take the frictional pressure loss effect into account were studied in detail. Criteria at reduced gravity conditions were developed by extending an existing model from normal gravity to reduced gravity conditions. A comparison of the newly developed flow regime transition criteria model with various experimental datasets taken at microgravity conditions showed satisfactory agreement. Sample computations of the model were performed at various gravity conditions, such as 0.196, 1.62, 3.71 and 9.81 m/s2 corresponding to micro-gravity and lunar, Martian and Earth surface gravity, respectively. It was found that the effect of gravity on bubbly–slug and slug–annular (churn) transitions in a two-phase flow system was more pronounced at low liquid flow conditions, whereas the gravity effect could be ignored at high mixture volumetric flux conditions. While for the annular flow transitions due to flow reversal and onset of droplet entrainment, higher superficial gas velocity was obtained at higher gravity level.

The interfacial-area transport equation is of practical importance for two-phase flow analyses at reduced-gravity conditions. In view of this, the interfacial-area transport equation, which takes the gravity effect into account, is studied in detail. The constitutive equation for the sink term of the interfacial-area concentration due to wake entrainment has been developed by considering the body acceleration due to frictional pressure loss. A comparison of the newly developed interfacial-area transport equation with various experimental data taken at normal-gravity and microgravity conditions shows a satisfactory agreement. An example computation of the newly developed interfacial-area transport equation has been performed at various gravity conditions such as 0, 1.62, 3.71, and 9.80 m/s 2 , which correspond to zero-gravity and the lunar, Martian, and Earth surface gravities, respectively. It has been revealed that the effect of the gravity on the interfacial-area transport in a two-phase flow system is more pronounced for low-liquid-flow and low-void-fraction conditions, whereas the gravity effect can be ignored for high-mixture-volumetric-flux conditions.

Disturbance waves play an important role in interfacial transfer of mass, momentum and energy in annular two-phase flow. In spite of their importance, majority of the experimental data available in literature on disturbance wave properties such as velocity, frequency, wavelength and amplitude are limited to near atmospheric conditions (Azzopardi, B.J., 1997. Drops in annular two-phase flow. International Journal of Multiphase Flow, 23, 1–53). In view of this, air–water annular flow experiments have been conducted at three pressure conditions (1.2, 4.0 and 5.8 bar) in a tubular test section having an inside diameter 9.4 mm. At each pressure condition liquid and gas phase flow rates are varied over a large range so that the effects of density ratio, liquid flow rate and gas flow rate on disturbance wave properties can be studied systematically. A liquid film thickness is measured by two flush mounted ring shaped conductance probes located 38.1 mm apart. Disturbance wave velocity, frequency, amplitude and wavelength are estimated from the liquid film thickness measurements by following the statistical analysis methods. Parametric trends in variations of disturbance wave properties are analyzed using the non-dimensional numbers; liquid phase Reynolds number ( Re f ), gas phase Reynolds number ( Re g ), Weber number ( We ) and Strouhal number ( Sr ). Finally, the existing correlations available for the prediction of disturbance wave velocity and frequency are analyzed and a new, improved correlation is proposed for the prediction of disturbance wave frequency. The new correlation satisfactorily predicted the current data and the data available in literature.

In this study, reflooding experiments were performed on a vertical rod surface before and after γ-ray irradiation to see the effect of Radiation-Induced Surface Activation (RISA) on the quenching speed. The test section was an annular channel with a concentric inner rod made of stainless steel SUS304 and an outer tube made of quartz glass. The inner rod was irradiated by 60Co γ-rays with predetermined radiation intensity and period to improve the surface wettability based on the radiation-induced surface activation phenomenon. Prior to the reflooding experiments, the contact angle of a droplet on the inner rod surface was measured using a CCD camera. It was indicated that the irradiated surface wettability was clearly improved and the quenching speed was enhanced after γ-ray irradiation.

Accurate measurements of the interfacial wave structure of upward annular two-phase flow in a vertical pipe were performed using a laser focus displacement meter (LFD). The purpose of this study was to clarify the effectiveness of the LFD for obtaining detailed information on the interfacial displacement of a liquid film in annular two-phase flow and to investigate the effect of axial distance from the air–water inlet on the phenomena. Adiabatic upward annular air–water flow experiments were conducted using a 3 m long, 11 mm ID pipe. Measurements of interfacial waves were conducted at 21 axial locations, spaced 110 mm apart in the pipe. The axial distances from the inlet (z) normalized by the pipe diameter (D) varied over z/D = 50–250. Data were collected for predetermined gas and liquid flow conditions and for Reynolds numbers ranging from ReG = 31,800 to 98,300 for the gas phase and ReL = 1050 to 9430 for the liquid phase. Using the LFD, we obtained such local properties as the minimum thickness, maximum thickness, and passing frequency of the waves. The maximum film thickness and passing frequency of disturbance waves decreased gradually, with some oscillations, as flow developed. The flow development, i.e., decreasing film thickness and passing frequency, persisted until the end of the pipe, which means that the flow might never reach the fully developed state. The minimum film thickness decreased with flow development and with increasing gas flow rate. These results are discussed, taking into account the buffer layer calculated from Karman’s three-layer model. A correlation is proposed between the minimum film thickness obtained in relation to the interfacial shear stress and the Reynolds number of the liquid.

In relation to the development of the interfacial area transport equation, axial developments of void fraction profile, interfacial area concentration and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured by using a stereo image-processing method at normal-and micro-gravity conditions. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D=5, 20, 40 and 60) at various flow conditions of superficial gas velocity (0.008 40-0.029 8 m/s) and superficial liquid velocity (0.138-0.914 m/s). The effect of gravity on radial distribution of bubbles and the axial developments of two-phase flow parameter was discussed in detail based on the obtained data and the visual observation.

This study examines a corrosion control technique for corrosion-resistant materials or of stainless steel. This employs an effect of Radiation Induced Surface Activation (RISA) . The experimental results revealed: (1) The mechanism behind the corrosion control proposed by the previous report was confirmed to be appropriate. This via tests that measured the amount of dissolved oxygen and iron ions, in the solution. (2) The corrosion control technique was confirmed to be useful for stainless steel with any kind of metal oxide film coating on the surface. (3) It was also shown to be useful even in actual seawater, due to biological effects, which is a far more severe environment for corrosion control than simple salt water. The corrosion control technique for corrosion-resistant material using RISA in seawater has therefore been shown to offer a significant potential for practical applications in naval architecture and marine structures.

Accurate prediction of the interfacial area concentration is essential to successful development of the interfacial transfer terms in the two-fluid model. The interfacial area concentration in annular flow and annular-mist flow is especially relevant to the transition process to the liquid film dryout, which might lead to fatal problem in the safety and efficient operation of boiling heat transfer system. However, very few experimental and theoretical studies focusing on the interfacial area concentration in annular flow region have been conducted. From this point of view, measurements of annular flow parameters such as one-dimensional interfacial area concentration of liquid film and local interfacial area concentration profile of liquid film were performed by a laser focus displacement meter at 21 axial locations in vertical upward annular two-phase flow using a 3-m-long and 11-mm-diameter pipe. The axial distances from the inlet ( z ) normalized by the pipe diameter ( D ) varied over z / D = 50–250. Data were collected for preset gas and liquid flow conditions and for Reynolds numbers ranging from 31,800 to 98,300 for the gas phase and 1050 to 9430 for the liquid phase. Axial development of the one-dimensional interfacial area concentration and the non-dimensional local interfacial area concentration profile of liquid film were examined with the data obtained in the experiment. Total interfacial area concentration including liquid film and droplets was also discussed with help of the existing drift-flux model, entrainment correlation, and droplet size correlation.

In relation to the development of the interfacial area transport equation, axial developments of void fraction profile, bubble number density, interfacial area concentration and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured by using a stereo image-processing method under normal- and micro-gravity environment. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter, z/D = 5, 20, 40 and 60) at various flow conditions of superficial gas velocity (0.00823-0.0303 m/s) and superficial liquid velocity (0.147-0.907 m/s). The effect of gravity on radial distribution of bubbles and axial developments of two-phase flow parameter was discussed in detail based on the obtained data and the visual observation.

A corrosion mitigation technique based on radiation induced surface activation (RISA) from the gamma ray irradiation on a metal surface is reported in this paper. This study aimed to develop a RISA method to prevent crevice corrosion in SUS304 stainless steel using low-intensity radioactive material. Experiment showed that an electrode potential of -100 mV vs. Ag/AgCl was produced and maintained on TiO2-coated SUS304 stainless steel specimens immersed in artificial seawater and in close contact with a small, sealed60Co source or activated by spontaneous neutron irradiation, with no corrosion observed for more than 7 days. On the contrary, the potential of the specimen without a radiation source decreased less than-280 mV vs. Ag/AgCl and crevice corrosion occurred beneath the O-ring within few days. The RISA effect of low-intensity radioactive material has the potential to prevent crevice corrosion of SUS304 stainless steel in actual seawater.

In thermohydraulic safety analysis for heating pipe in boilers and nuclear reactors, inverted-churn flow is commonly formulated due to high-temperature wall. In such flow, liquid ligaments fly upward and downward in the gas core flow and the cooling liquid cannot contact with the wall so that severe wall damage might occur by its low heat transfer. In this study, an inverted-churn flow was formulated in vertical 20-mm diameter pipe coated with water-shedding material. The basic flow characteristics of ligaments in the floww were measured and discussed using the stereo image-processing method and the optical flow method.

This paper presents a new method for measuring the interfacial displacement of a liquid film in microchannels using a laser focus displacement meter (LFD). The purpose of the study is to clarify the effectiveness of the new method for obtaining detailed information concerning interfacial displacement, especially in the case of a thin liquid film, in microchannels and minichannels. To prevent the tube wall signal from disturbing that of the gas–liquid interface, a fluorocarbon tube with a water box was used; the refraction index of this device is the same as that for water. With this method, accurate instantaneous measurements of the interfacial displacement of the liquid film were achieved. The error caused by refraction of the laser beam passing through the acrylic water box and fluorocarbon tube was estimated analytically and experimentally. The formulated analytical equation can estimate the real interface displacement by using the measured displacement in a fluorocarbon tube of 25 μm to 2.0 mm I.D. A preliminary test using fluorocarbon tubes of 1 mm and 2 mm I.D. showed that the corrected interface displacement calculated by the equation agreed with the real displacement to within a 1% margin of error. It was also confirmed that the LFD in the system could measure a liquid film of 0.25 μm at the thinnest. We made simultaneous measurements of the interface in fluorocarbon tubes of 0.5 mm and 1 mm I.D. using the LFD and a high-speed video camera with a microscope. These showed that the LFD could measure the interface of a liquid film with high spatial and temporal resolution during annular, slug, and piston flow regimes. The data also clarified the existence of a thin liquid film of less than 1 μm in thickness in the slug and annular flow regimes.

Improving the limit of boiling heat transfer or critical heat flux requires that the cooling liquid can contact the heating surface, or a high wettability, highly hydrophilic heating surface, even if a vapor bubble layer is generated on the surface. In our previous study, contact angle, an indicator of macroscopic wettability, of a water droplet on metal oxide at room temperature was measured by image processing of the images obtained by a CCD video camera. The results showed that the surface wettability on metal oxide pieces of titanium, zircaloy No. 4, SUS-304, and copper was improved significantly by the radiation induced surface activation (RISA) phenomenon. To delineate the effect of RISA on heat transferring phenomena, the Leidenfrost condition and quenching of metal oxides irradiated by γ-rays were investigated in this study. In the Leidenfrost experiment, when the temperature of the heating surface reached the wetting limit temperature, water–solid contact vanished because a stable vapor film existed between the droplet and the metal surface; i.e., a Leidenfrost condition obtained. The wetting limit temperature increased with integrated irradiation dose. After irradiation, the wet length and the duration of contact increased, and the contact angle decreased. In the quenching test, high surface wettability, or a highly hydrophilic condition, of a simulated fuel rod made of SUS was achieved, and the quenching velocities were increased up to 20–30% after 300 kGy 60 Co γ-ray irradiation.

Accurate prediction of the interfacial area concentration is essential to successful development of the interfacial transfer terms in the two-fluid model. Mechanistic modeling of the interfacial area concentration entirely relies on accurate local flow measurements over extensive flow conditions and channel geometries. From this point of view, accurate measurements of flow parameters such as void fraction, interfacial area concentration, gas velocity, bubble Sauter mean diameter, and bubble number density were performed by the image processing method at five axial locations in vertical upward bubbly flows using 0.55 mm and 1.02 mm-diameter pipes. The frictional pressure loss was also measured by a differential pressure cell. In the experiments, the obtained data give near complete information on the time-averaged local hydrodynamic parameters of two-phase flow. These data can be used for the development of reliable constitutive relations which reflect the true transfer mechanisms in two-phase flow. As the first step to understand the flow characteristics in micro- and mini-channels, the applicability of the existing drift-flux model, interfacial area correlation, and frictional pressure correlation was examined by the data obtained in the mini-channel.

In this study, a precise database of microscopic interfacil wave-structure was obtained for annular two-phase flow developing in a vertical pipe. Using a laser focus displacement meter (LFD), measurements of such local properties as the minimum film thickness and passing frequency of the waves along the pipe were conducted. The results showed that the passing frequency of disturbance waves decreased gradually with some oscillations in the pipe axial direction, whose phenomena had a similarity with those of maximum film thickness reported in the 1st report. These unique phenomena were also discussed from a view of pressure resonant interactions based on the experimental results of pressure propagation in the pipe. Minimum thickness of the film decreased with flow development and with increasing gas flow rate. These results were discussed taking into account the buffer layer calculated from Karman's three-layer model. Correlation was proposed for obtained minimum film thickness in regarding to interfacial shear stress and the Reynolds number of the liquid. This correlation expressed the minimum film thickness obtained from the experiment withis 5% deviation.

In view of the great importance of two geometrical parameters such as void fraction and interfacial area concentration to the accurate two-phase flow analysis at microgravity conditions, axial developments of flow parameters such as void fraction, interfacial area concentration, bubble Sauter mean diameter, and bubble number density were measured in bubbly flow at microgravity and low liquid Reynolds number conditions where the gravity effect on the flow parameters were pronounced. A total of seven data sets were acquired in the flow range of the void fraction from 1.01% to 3.36% and the liquid Reynolds number from 1,400 to 4,750. The measurements were also performed in the similar flow range at normal gravity conditions. The transport mechanisms of the flow parameters are discussed in detail based on the data measured at normal and microgravity conditions, and the drift-flux model developed at microgravity conditions are compared with the measured data.

In view of the great importance of two geometrical parameters such as void fraction and interfacial area concentration to the accurate two-phase flow analysis at microgravity conditions, axial developments of flow parameters such as void fraction, interfacial area concentration, bubble Sauter mean diameter, and bubble number density were measured by image-processing in bubbly flow at microgravity and low liquid Reynolds number conditions where the gravity effect on the flow parameters were pronounced. Negligible bubble breakup was observed because of weak turbulence under tested flow conditions. The velocity profile entrainment effect under microgravity was likely to be comparable to the wake entrainment effect under normal gravity in the tested flow conditions.

In order to predict the free surface phenomena in a pool, the interaction between the liquid flow field and free surface should be evaluated. In this study, we aimed at developing a new three-dimensional measurement system for surface elevation and liquid velocity profiles in pool water using an image-processing technique and a laser focus displacement meter. The purpose of the experiments was to confirm the effectiveness of this new technique for obtaining temporal and spatial information on surface elevation and inclination as well as three-dimensional liquid velocity distribution. We confirmed that the free surface position and inclination were measured by this technique within 0.1 mm and 0.7° deviation. A data set for free surface and three-dimensional liquid velocity distribution was obtained through this study.

Waves on a film flowing down a vertical wall appear in many processes. The resulting interfacial waves show fascinating nonlinear phenomena, including solitary waves and complex disordered patterns. Measurements have often been made of these phenomena using electrical resistance or electrical capacitance methods, optical methods, and laser beam methods. This paper presents a new way of measuring the interfacial waves on a film flowing down a vertical plate wall in an entry region, using two laser focus displacement meters. The purpose of the study was to clarify the effectiveness of the new method for obtaining detailed information on the waves, and to investigate the effect of the entry length on the phenomena. With this method, accurate measurements of film thickness were achieved in real time with a sensitivity of 2 μm and 1 kHz. The error caused by refraction of the laser beam passing through a transparent wall was clarified. The present results for wave velocity and maximum film thickness agreed well with past experimental and theoretical studies. In short entry length conditions, the average measured film thickness and wave velocity agreed with those calculated using Nusselt’s Law, indicating that the flow is laminar even at a high flow rate. As a result of this study, an empirical equation expressing wave frequency in the entry region was formulated.

The university has created a new type of electric boat "RAICHO-S" in 2011. The craft has some special and unique features that set it apart from existing electric boats or battery-powered boats. "RAICHO-S" utilizes a lithium-ion battery with a rapid charging system and a water jet propulsion system driven by electric motor. In addition, "RAICHO-S" has a waterproof wired remote control system with a control knob that can be moved through 360 degrees to steer the boat in any direction. Its special features and advantages such as low noise, low vibration, high environmental advantages, highly-safe and highly-functional operation are expected to be useful in a wide range of areas which require underwater works. In order to evaluate the effectiveness of "RAICHO-S", measurement of an underwater noise and an underwater test for the waterproof wired remote control system were performed. The paper briefly introduces the design features of “RAICHO-S”, and presents the results of the measurement of underwater noise and the underwater operation test.

A new type of quick charging plug-in electric boat named "RAICHO-I" has been created by Tokyo University of Marine Science and Technology. "RAICHO-I" is the first electric boat adopted CHAdeMO standard which is the standard of quick charging method for electric vehicles in Japan. However, the operational time, speed and distance of electric boats are restricted since the loaded battery is limited because of cost, weight, etc. A Navigation Support System (NSS), which gives the remaining operational time, a possible cruising distance etc, is one of important technologies of electric boats from the view point of the operational safety. In this paper, algorithms to estimate the state of charge, the remaining operational time etc for NSS is proposed. The algorithm to obtain the recommended speed in order to cruise the desired distance is also proposed.