小林 弘明

Forced flow heat transfer of hydrogen from a round wire in a vertically-mounted pipe was measured at pressure of 1.5 MPa and temperature of 21 K by applying electrical current to give an exponential heat input (Q=Q0exp(t/τ),τ=10 s) to the round wire. Two round wire heaters, which were made of Pt-Co alloy, with a diameter of 1.2 mm and lengths of 54.5 and 120 mm were set on the central axis of a flow channel made of FRP with inner diameter of 5.7 and 8.0 mm, respectively. Supercritical hydrogen flowed upward in the channel. Flow velocities were varied from 1 to 12.5 m/s. The heat transfer coefficients of supercritical hydrogen were compared with the conventional correlation presented by Shiotsu et al. It was confirmed that the heat transfer coefficients for a round wire were expressed well by the correlation using the hydraulic equivalent diameter.

Heat transfer from a horizontal wire immersed in both liquid and supercritical hydrogen was measured with a quasi-steady increase of the heat generation rate for a wide range of bath temperatures and pressures. The nucleate boiling heat transfer coefficient is higher for higher pressures. The critical heat flux (CHF) is highest in the vicinity of 0.4 MPa and is expressed by Kutateladze's equation. The CHFs become higher for higher degrees of subcooling. The heat transfer under supercritical pressures is the same as natural convection heat transfer in liquid hydrogen, but it deteriorates for heated surface temperautres higher than the pseudocritical temperature. The heat transfer correlation was derived based on the experimental data.

In this study, bypass door area for the Hypersonic Precooled Turbojet Engine to restart the variable intake is estimated. Total pressure recovery and mass capture ratio of the variable air intake is acquired by the supersonic wind tunnel testing of the half scale intake model. Pressure loss and temperature effectiveness of the precooler is acquired by direct connect firing tests of the engine. Using these results, area of the bypass door by which the intake can start is estimated. The bypass door area to restart the intake depends on the precooler’s cooling capability. If the engine runs on liquid hydrogen, area of the bypass door is 1800mm2~2000mm2(Abyp_eng/A0=0.26~0.29). If the liquid nitrogen is used for the coolant of the precooler, area of the bypass door is 2600mm2~2700mm2(Abyp_eng/A0=0.37~0.39).

Pre-cooled turbojet engine is investigated to realize Mach 5 class hypersonic transport aircraft. The engine has been demonstrated under sea level static and Mach 2 flight conditions using hydrogen as fuel. In this study, Mach 4 propulsion wind tunnel test is performed and the performance of air intake, pre-cooler, core engine and exhaust nozzle are obtained. Liquid nitrogen is supplied to the pre-cooler as a coolant in place of liquid hydrogen. Gaseous hydrogen is supplied to the main burner to drive the turbine with the combustion gas. A protective screen is placed in front of the pre-cooler to prevent damages of it from high-speed particles. Bypass door is placed in front of the core engine to start the mixed compression air intake at low speed operation of the core engine. As a result, the engine performance data is obtained without any damage of pre-cooler. Air intake is started by the effect of bypass door at low speed operation of the core engine.

In the present experiment, by using the sounding rocket’s sub-orbital ballistic flight, realized the gravitational environment similar to that of liquid-fueled rockets during its coasting flight. In the low-gravity state, the cryogenic test fluid, liquid nitrogen, was introduced into the test sections which had similar shapes to the flow channels in the cryogenic propulsion systems. The boiling of liquid nitrogen inside the test-sections and the transition of flow regimes from gas/liquid two-phase flow to liquid mono-phase flow were successfully visualized. The temperatures, pressures and void fractions in each channel were measured as well. The mechanisms enhancing heat transfer were discussed based on the visualization. In the present case, compared with the corresponding ground test, it was confirmed that the two-phase flow in the complex channel could wet the heat transfer surfaces more easily due to the absence of gravity, and that more uniform chill-down effect could been obtained.

The payload capacity of launch vehicles must be increased in order to allow the exploration and development of space to be extended from low-Earth orbit into the solar system. A propellant system using a cryogenic fluid such as liquid oxygen or liquid hydrogen must reduce the amount of unusable propellant due to evaporation and boiling. However, in the space exploration and development where safety and reliability of missions are critical, predictions of the boiling heat transfer of the present technology are not sufficiently reliable for thermal management design due to a lack of knowledge and relevant research. Therefore, the objective of this research is to understand and accurately predict boiling heat transfer by developing numerical simulation tool for two-phase flows that consider phase change. In this paper, some recent research activities toward the development of chill-down process simulation technology are presented.

© 2015 Published by Elsevier B.V. Film boiling heat transfer properties of LH2 for various pressures and subcooling conditions were measured by applying electric current to give an exponential heat input to a PtCo wire with a diameter of 1.2 mm submerged in LH2. The heated wire was set to be horizontal to the ground. The heat transfer coefficient in the film boiling region was higher for higher pressure and higher subcooling. The experimental results are compared with the equation of pool film boiling heat transfer. It is confirmed that the pool film boiling heat transfer coefficients in LH2 can be expressed by this equation.

Pressure drop and forced convection heat transfer were studied in the boiling nitrogen flow in a horizontal square pipe with a side of 12 mm at inlet pressure between 0.1 and 0.15 MPa with a mass flux between 70 and 2000 kg/m(2)-s and with a heat flux of 5, 10 and 20 kW/m(2). Accordingly, the flow and heat transfer mechanisms specific to square pipe were elucidated, and the applicability to cryogenic fluids of pressure drop and heat transfer models originally proposed for room temperature fluids was clarified. (C) 2014 The Authors. Published by Elsevier B.V.

© 2015 Published by Elsevier B.V. In this report, we show results on the forced flow boiling heat transfer experiments for manganin plate pasted on one side of a rectangular duct. Nucleate boiling heat transfer and its Departure from Nucleate Boiling (DNB) heat flux were measured for various pressures, subcooling and flow velocities. The DNB heat fluxes are higher for higher subcooling and higher flow velocity. The DNB heat fluxes were compared with the experimental data for round tube of nearly equal equivalent diameter. The DNB heat fluxes for the rectangular duct are lower than those for the round tube.

© 2015 The Authors. Hydrogen film boiling heat transfer coefficients were measured for the heater surface superheats up to 400 K under pressures from 400 to 1100 kPa, liquid subcoolings from 0 to 11 K and flow velocities up to 7 m/s. The test wire used was 1.2 mm in diameter and 120 mm in length made of PtCo (0.5 wt.%) alloy, which was located at the center of 8 mm diameter conduit made of FRP (Fiber Reinforced Plastics). The heat transfer coefficients were higher for higher pressure, higher subcooling and higher flow velocity. The heat transfer coefficients were about 1.6 times higher than those predicted by Shiotsu-Hama equation for forced flow film boiling in a wide channel. Discussions were made on the mechanism of difference between them.

© 2015 The Authors. The transient heat transfer from a Pt-Co wire heater inserted into a vertically mounted pipe, through which forced flow subcooled liquid hydrogen was passed, is measured by increasing the exponential heat input with various time periods at a pressure of 0.7 MPa and an inlet temperature of 21 K. The flow velocities range from 0.8 to 5.5 m/s. For shorter periods, the non-boiling heat transfer becomes higher than that given by the Dittus-Boelter equation due to the transient conductive heat transfer contribution. In addition, the transient critical heat flux (CHF) becomes higher than the steady-state CHF. The effect of the flow velocity and period on the transient CHF heat flux is also clarified.

In this paper is presented a microgravity experiment system utilizing a high altitude balloon. The feature is a double shell structure of a vehicle that is dropped off from the balloon and a microgravity experiment section that is attached to the inside of the vehicle with a liner slider. Control with cold gas jet thrusters of relative position of the experiment section to the vehicle and attitude of the vehicle maintains fine microgravity environment. The design strategy of the vehicle is explained, mainly referring to differences from the authors' previous design. The result of the flight experiment is also shown to evaluate the characteristics of the presented system.

The Japan Aerospace Exploration Agency launched the S-310-43 sounding rocket from the Uchinoura Space Center on Aug.04, 2014 for the purpose of investigating such behavior as boiling and flow of cryogenic liquid rocket propellant in an environment simulating coasting flight on orbit by using the sounding rocket's sub-orbital ballistic flight. In the low-gravity state, the cryogenic fluid (liquid nitrogen) was introduced into the test sections of similar shapes to the flow channels in the cryogenic propulsion systems. The boiling of liquid nitrogen inside the test-sections and the transition of flow regimes from gas/liquid two-phase flow to liquid mono-phase flow were visualized. The temperatures, pressures and void fractions of each channels were measured as well. Development of the experimental equipment for S-310-43 sounding rocket is described in this paper.

The transient heat transfer from a Pt-Co wire heater inserted into a vertically mounted pipe, through which forced flow subcooled liquid hydrogen was passed, is measured by increasing the exponential heat input with various time periods at a pressure of 0.7 MPa and an inlet temperature of 21 K. The flow velocities range from 0.8 to 5.5 m/s. For shorter periods, the non-boiling heat transfer becomes higher than that given by the Dittus-Boelter equation due to the transient conductive heat transfer contribution. In addition, the transient critical heat flux (CHF) becomes higher than the steady-state CHF. The effect of the flow velocity and period on the transient CHF heat flux is also clarified. (C) 2014 The Authors. Published by Elsevier B.V.

Pre-cooled turbojet engine is investigated to realize Mach 5 class hypersonic transport aircraft. The engine has been demonstrated under sea level static and Mach 2 flight conditions using hydrogen as fuel. Presently, Mach 5 propulsion wind tunnel test using liquid hydrogen is planned and the engine components such as pre-cooler, core engine, afterburner and exhaust nozzle are under development. The engine components were tested under Mach 4 simulating condition by connecting the pre-cooler inlet to an air supply facility. The engine was tested in a propulsion wind tunnel with Mach 4 flight condition. Liquid nitogen was supplied to the pre-cooler as a coolant in place of liquid hydrogen. Gaseous hydrogen was supplied to the main burner to drive the turbine with the combustion gas. As a result, high temperature structure and cooling system was proved to endure Mach 4 high temperature airstream. Wind-mill starting sequence of the core engine under Mach 4 flight condition was confirmed. Gross thrust of the core engine was obtained as an initial evaluation of elemental performance.

This paper describes altitude ignition experiment results for a scaled hydrogen-fueled turbojet engine model applied for Balloon-Based Operational Vehicle in-flight testing. Although hydrogen has remarkable combustion characteristics among the combustion fuels, at low pressures, the hydrogen-fueled combustor showed difficulty in the originally planned altitude ignition conditions. The follow-up step-by-step refinement of the ignition sequence is explained using experimental data. A similar situation might occur for future hydrogen-fueled High Altitude Long Endurance (HALE) flights. These limited but still wide combustion capabilities of the hydrogen fuel might facilitate the introduction of gas-turbine power plants in the HALE flights.

This paper describes altitude ignition experiment results for a scaled hydrogen-fueled turbojet engine model applied for Balloon-Based Operational Vehicle in-flight testing. Although hydrogen has remarkable combustion characteristics among the combustion fuels, at low pressures, the hydrogen-fueled combustor showed difficulty in the originally planned altitude ignition conditions. The follow-up step-by-step refinement of the ignition sequence is explained using experimental data. A similar situation might occur for future hydrogen-fueled High Altitude Long Endurance (HALE) flights. These limited but still wide combustion capabilities of the hydrogen fuel might facilitate the introduction of gas-turbine power plants in the HALE flights.

© 2014 AIP Publishing LLC. Heat transfer from inner side of a vertical tube to forced flow of hydrogen was measured at the pressure of 1.5 MPa. The test tubes were made of stainless steel 316L with the inner diameters from 3 mm to 9 mm and lengths from 100 mm to 250 mm. Heat transfer curves were obtained by gradually increasing the heating current to the test tube and raising the surface temperature up to around 200 K. Inlet fluid temperature and flow velocity were varied from 21 to 30 K and 0.5 to 12 m/s, respectively. Effects of inlet temperature, flow velocity and tube dimension were clearly observed. The heat transfer curve for each flow velocity consists of a lower temperature region with a higher gradient and higher temperature region with a lower gradient. The experimental results were compared with the authors' correlation presented formerly. It was confirmed that this correlation can describe the experimental results obtained here.

An experimental system has been developed to investigate electro-magnetic properties of high-Tc superconductors cooled by liquid hydrogen under the external magnetic field of up to 7 T. A LH2 cryostat is concentrically mounted on the inside of a LHe cryostat to cool a NbTi superconducting magnet. The experimental system is installed in an explosion-proof room. Explosion proof electrical devices are used and current leads are covered with an enclosure filled with nitrogen gas. A remote control system has been developed. Furthermore, the effects of stray magnetic field on the existing and the new devices are investigated and electro-magnetic shielding panels and enclosure made of iron were designed. It is confirmed through the cryogenic test that the experimental system meets the design requirements.

© 2014 AIP Publishing LLC. Liquid hydrogen (LH2) is a key issue in a carbon-free energy infrastructure at the energy storage and transportation stage. The typical features of LH2 are low viscosity, large latent heat and small density, compared with other general liquids. It is necessary to measure a mass flow of liquid hydrogen with a simple and compact method, especially in a two phase separate flow condition. We have proposed applying a hot-wire type flow meter, which is usually used a for gas flow meter, to LH2 flow due to the quite low viscosity and density. A test model of a compact LH2 hot-wire flow meter to measure local flow velocities near and around an inside perimeter of a horizontal tube by resistance thermometry was designed and made. The model flow meter consists of two thin heater wires made of manganin fixed in a 10 mm-diameter and 40 mm-length tube flow path made of GFRP. Each rigid heater wire was set twisted by 90 degrees from the inlet to the outlet along the inner wall. In other words, the wires were aslant with regard to the LH2 stream line. The heated wire was cooled by flowing LH2, and the flow velocity was obtained by means of the difference of the cooling characteristic in response to the flow velocity. In this report, we show results on the basic experiments with the model LH2 hot-wire flow meter. First, the heat transfer characteristics of the two heater wires for several LH2 flow velocities were measured. Second, the heating current was controlled to keep the wire temperature constant for various flow velocities. The relations between the flow velocity and the heating current were measured. The feasibility of the proposed model was confirmed.

© Published under licence by IOP Publishing Ltd. Forced convection heat transfer from a PtCo wire with a length of 120 mm and a diameter of 1.2 mm that was inserted into a vertically-mounted pipe with a diameter of 8.0 mm to liquid hydrogen flowing upward was measured with a quasi-steady increase of a heat generation rate for wide ranges of flow rate under saturated conditions. The pressures were varied from 0.4 MPa to 1.1 MPa. The non-boiling heat transfer characteristic agrees with that predicted by Dittus-Boelter correlation. The critical heat fluxes are higher for higher flow rates and lower pressures. Effect of Weber number on the CHF was clarified and a CHF correlation that can describe the experimental data is derived based on our correlation for a pipe.

Liquid hydrogen (LH2), which has large latent heat, low viscosity coefficient, is expected to be a candidate for a cryogen for superconducting wires, not only MgB2 but also other HTC superconductors. LH2 cooled superconducting wires are expected to have excellent electro-magnetic characteristics, which is necessary to be clear for cooling stability design of LH2 cooled superconducting device, however, due to handling difficulties of LH2, there are only few papers on the properties of LH2 cooled superconductors, especially under external magnetic field. We designed and made an experimental setup which can energize superconducting wires immersed in LH2 with the current of up to 500A under the condition of external magnetic field up to 7 T and pressure up to 1.5 MPa. In order to confirm experimental method and safety operation of the setup, over current tests were carried out using MgB2 superconducting wires under various external magnetic field conditions. Critical current of the test wire at the temperature 21, 24, 27, 29 K under external magnetic fields up to 1.2 T was successfully measured. The resistance of the wire also was measured, while the transport current exceeded the critical current of the wire.

Stator windings for a superconducting motor with MgB2 wires are fabricated and tested. The stator windings are composed of 12 element coils in the form of a racetrack, and located in iron core slots to generate a rotating magnetic field of three phases and four poles. Preliminary estimations by means of numerical calculations with a finite element method indicate that the magnetic-flux distribution in a gap between the stator and rotor cores contains relatively significant components of fifth and seventh harmonics compared with a fundamental component. An MgB2 rotor prepared in the previous work can be rotated at a synchronous speed successfully by energizing the fabricated stator windings with a pulse width modulation inverter and compensating for the higher harmonics with a torque boost voltage.

Liquid hydrogen (LH2) has excellent properties as a coolant, such as large latent heat, low viscosity coefficient, etc. Not only MgB2 but also other high-Tc superconductors are expected to have excellent properties when cooled by LH2. It is necessary for a stability design of a high-Tc superconductor cooled by LH2 to make an electro-magnetic characteristic clear. However, due to the handling difficulties of LH2, there are only few papers on the properties of LH2-cooled superconductors, especially under the external magnetic field. In this paper, an experimental set-up is described, which was designed and fabricated for the evaluation of the electro-magnetic characteristics of high-Tc superconductors cooled by LH2. The LH2 cryostat of 309 mm inner diameter was set co-axially with vacuum layer in the LHe cryostat in which the LHe-cooled superconducting magnet for external magnetic field (up to 7 T) was set. The LH2 cryostat has three power leads for feeding up to 500 A to the test high-Tc superconductors.

An electric pump composed of an MgB2 motor is combined with superconducting level sensors using thin CuNi-sheathed MgB2 wires to transfer liquid hydrogen. An impeller is attached to the lower end of a rotating shaft on the MgB2 motor and covered with an outer casing to form a centrifugal pump. Then, the MgB2 motor and impeller are placed vertically inside a cryostat with an infill of liquid hydrogen. A glass Dewar vessel is prepared to receive the liquid hydrogen transferred from the cryostat containing the MgB2 motor. The MgB2 sensors are used not only to detect the level of liquid hydrogen but also to control the electric pump on the basis of their pre-estimated calibration curves. By using the assembled pump system, the liquid hydrogen is successfully transferred from the cryostat to the glass Dewar vessel via a transfer tube. (C) 2012 Elsevier Ltd. All rights reserved.

Systems analysis of a Mach 5 class hypersonic aircraft is performed. The aircraft can fly across the Pacific Ocean in 2 h. A multidisciplinary optimization program for aerodynamics, structure, propulsion, and trajectory is used in the analysis. The result of each element model is improved using higher accuracy analysis tools. The aerodynamic performance of the hypersonic aircraft is examined through hypersonic wind tunnel tests. A thermal management system based on the data of the wind tunnel tests is proposed. A pre-cooled turbojet engine is adopted as the propulsion system for the hypersonic aircraft. The engine can be operated continuously from take-off to Mach 5. This engine uses a pre-cooling cycle using cryogenic liquid hydrogen. The high temperature inlet air of hypersonic flight would be cooled by the same liquid hydrogen used as fuel. The engine is tested under sea level static conditions. The engine is installed on a flight test vehicle. Both liquid hydrogen fuel and gaseous hydrogen fuel are supplied to the engine from a tank and cylinders installed within the vehicle. The designed operation of major components of the engine is confirmed. A large amount of liquid hydrogen is supplied to the pre-cooler in order to make its performance sufficient for Mach 5 flight. Thus, fuel rich combustion is adopted at the afterburner. The experiments are carried out under the conditions that the engine is mounted upon an experimental airframe with both set up either horizontally or vertically. As a result, the operating procedure of the pre-cooled turbojet engine is demonstrated. (C) 2011 Elsevier Ltd. All rights reserved.

Numerical simulation of the flow around an air data sensor (ADS), which measures flow angles and Mach numbers using surface pressures on a nose cone, was conducted in this study. Effects of the half-cone angle on the flow angle and Mach number measurements were investigated. Results show that a large half-cone angle achieves high sensitivity of flow angle measurements. Results further demonstrated that a small half-cone angle achieves high-sensitivity of Mach number measurements. To satisfy these conflicting requests, we proposed the use of bi-conic nose cones with two gradients. High sensitivity was achieved for both flow angle measurements and Mach number measurements using this bi-conic nose cone. © 2012 The Japan Society for Aeronautical and Space Sciences.

JAXA has been promoting research and development for hypersonic transports (HST) since 2004, following its long-term vision to demonstrate technologies for aircraft that can cruise at Mach 5. A precooled turbojet engine and Mach 5 flight experimental vehicle called Hypersonic Technology Experimental vehicle (HYTEX) are under development. Liquid hydrogen is the best fuel and coolant for the hypersonic turbojet, however safety standard in flight experiment tends to prohibit using hydrogen. Consequently we conducted the first flight experiment (Mach 2) of the hypersonic turbojet in September 2010 with gaseous hydrogen as a fuel and liquid nitrogen as a coolant. In this paper performance analysis of hypersonic turbojet engine using alternative fuel (methane and kerosene) and alternative coolant (liquid helium, liquid nitrogen, and other safe refrigerants) for the air-precooler during Mach 5 flight is discussed. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.

Hypersonic technology experimental vehicle for flight experiment of pre-cooled turbojet engine is investigated. The vehicle is assumed to mount two pre-cooled turbojet engines at the bottom. The vehicle will be accelerated up to Mach 5 flight speed by an external booster rocket. The vehicle aims at demonstrating Mach 5 cruise capability for a short period. Aerodynamic performance, engine thrust and structure mass are analyzed for the baseline system. Lift to drag ratio has improved by adding a strake in front of the main wing. Engine thrust is estimated without considering the additional thrust at the external nozzle. Structure mass is estimated using an optimization program using finite element method. Force balance around the vehicle is summarized and it is confirmed that the vehicle will slightly descend and decelerate at Mach 5 flight condition, without considering the external thrust. Component tests of pre-cooled turbojet engine with simulated flight condition are conducted toward the flight experiment. Pre-cooler is tested with high temperature condition simulating Mach 4 flight condition. Core engine starting sequence is confirmed with low pressure condition. Fuel supply system for hydrogen fuel with super-critical condition is tested to attain precise fuel flow control for the core engine. High temperature tests and propulsion wind tunnel tests of the engine with simulating Mach 5 condition is planned. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Conceptual study of thermo protection structure of the hypersonic aircraft was carried out. Cruising speed of the reference aircraft is Mach 5 at the altitude of 24 km and liquid hydrogen is used as propellant of the engine and vehicle coolant. Precooled turbojet engines and ramjet engines are used as main propulsion system of the aircraft. Heating rate around HST which flies at Mach 5 was from 5kW/m2 to 30kW/m2. For these heating rate vehicles, most suitable TPS was selected by 1-dimensional heating analysis. For heating rate of 5kW/m2, 10kW/m2 and 20kW/m2, Titanium multiwall TPS become the lightest. For heating rate of 30kW/m2 and 40kW/m2, SA honeycomb TPS became the lightest. To estimate the heating rate on lower and aft side of the vehicle where engine fuel rich combustion gas flows, engine combustion test was carried out. Heating rate on the vehicle was measured by two ways that is to estimate by history of wall thermocouples, and to estimate by flame temperature measured by radiation two-color method. Heating rates of both measurement agreed with accuracy of 15%. Assuming the TPS wall temperature of 1350K, heating rate on the vehicle is predicted from 350 kW/m2 to 1190 kW/m2.© 2012 by the American Institute of Aeronautics and Astronautics, Inc.

© 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. Knowledge of departure from nucleate boiling (DNB) heat flux is important for design of superconducting systems cooled by cryogenic liquids. We have already presented the equation of DNB heat flux that can describe the experimental data of liquid hydrogen. To see the applicability of the equation to other cryogenic liquids, similar heat transfer tests in forced flow of liquid nitrogen are performed for wide ranges of conditions in this work. It was confirmed that the DNB heat flux equation derived by the authors can express not only the data for liquid hydrogen but also those for liquid nitrogen.

Transient heat transfer caused by exponentially increasing heat input (Q = Q 0exp(t/τ)) to a flat plate in a pool of liquid hydrogen was measured under saturated and subcooled conditions at pressures from 104 to 700 kPa. The exponential period τ was varied from 8 ms to 8 s and the liquid subcoolings from 0 to 8 K. The flat plate heater used was 5 mm in width, 60 mm in length and 0.5 mm in thickness. Transient heat transfer before the inception of boiling for the exponential period shorter than 100 ms was expressed well by the transient conduction heat transfer with no movement of liquid. Incipient boiling heat flux and temperature were higher for shorter period. Transient critical heat flux was higher for shorter exponential period and higher subcooling. No direct transition from non-boiling to nucleate boiling such as first found by some of the authors for transient heat transfer in a pool of liquid nitrogen was observed for liquid hydrogen. An equation for transient critical heat flux was given. © 2012 American Institute of Physics.

Forced flow heat transfers of liquid hydrogen through a vertical tube with the diameter, d, of 6.0 mm and length of 100 mm were measured at pressures of 0.4, 0.7 and 1.1 MPa for various inlet temperatures and flow velocities. The heat fluxes at the inception of boiling and the departure from nucleate boiling (DNB) heat fluxes were higher for higher flow velocity and subcooling. The DNB heat fluxes under subcooled condition were lower for higher pressure. The effects of tube diameter and subcooling on the DNB heat flux were investigated. A new correlation of saturated and subcooled DNB heat flux is established based on these data and the data for 3 mm diameter tube already reported by the authors. © 2012 American Institute of Physics.

Forced flow heat transfers of liquid hydrogen through horizontally-mounted tubes with the diameter of 3.0 mm and 6.0 mm were measured at the pressure of 0.7 MPa for various inlet temperatures and flow velocities. The measured non-boiling heat transfer coefficients agree with those by the Dittus-Boelter correlation. The heat fluxes at the onset of nucleate boiling and the departure from nucleate boiling (DNB) heat fluxes, where the heat transfer continuously changes to film boiling regime, are higher for higher flow velocity, larger subcooling and larger tube diameter. The DNB heat fluxes for the horizontally-mounted tube are slightly lower than those for the vertically-mounted tube, although the effect of the tube attitude direction disappears for a small tube diameter. The measured DNB heat fluxes agree with the correlation for vertically-mounted tubes. © 2012 American Institute of Physics.

© 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. An experimental setup which can energize superconducting wires immersed in LH2 was designed and made. Over current tests were carried out using MgB2 wire. Critical current and resistivity of a test MgB2 wire submerged in liquid hydrogen were measured for exponentially increasing heat input, while the transport current exceeded the critical current. The resistivity of the conductor was obtained as a function of current and the temperature of the conductor by using the transient heating method. The distribution ratio of the current through the superconductor and the sheath, and the resistivity of the MgB2 conductor itself were estimated.

© 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. The heat transfer from the inner side of a vertically- mounted heated tube with a length of 200.0 mm and a diameter of 6.0 mm to a forced flow of liquid hydrogen was measured for wide ranges of flow rate and liquid temperature. The non-boiling heat transfer coefficients agreed well with the Dittus -Boelter equation. The heat fluxes at departure from nucleate boiling (DNB) were higher for higher flow velocities and greater subcooling. The effect of the tube length on the DNB heat flux was clarified through comparison with our previous data. It was confirmed that the experimental data agreed well with the authors' DNB correlation.

The heat transfer from the inner side of a vertically-mounted heated tube with a length of 200.0 mm and a diameter of 6.0 mm to a forced flow of liquid hydrogen was measured for wide ranges of flow rate and liquid temperature. The non-boiling heat transfer coefficients agreed well with the Dittus -Boelter equation. The heat fluxes at departure from nucleate boiling (DNB) were higher for higher flow velocities and greater subcooling. The effect of the tube length on the DNB heat flux was clarified through comparison with our previous data. It was confirmed that the experimental data agreed well with the authors' DNB correlation. (C) 2012 Published by Elsevier B. V. Selection and/or peer-review under responsibility of the Guest Editors.

An experimental setup which can energize superconducting wires immersed in LH2 was designed and made. Over current tests were carried out using MgB2 wire. Critical current and resistivity of a test MgB2 wire submerged in liquid hydrogen were measured for exponentially increasing heat input, while the transport current exceeded the critical current. The resistivity of the conductor was obtained as a function of current and the temperature of the conductor by using the transient heating method. The distribution ratio of the current through the superconductor and the sheath, and the resistivity of the MgB2 conductor itself were estimated. (C) 2012 Published by Elsevier B. V. Selection and/or peer-review under responsibility of the Guest Editors.

A new configuration of superconducting level sensor for liquid hydrogen is proposed. The proposed sensor has an advantage that it is difficult to be affected by various conditions of gas such as temperature, pressure and object, so that it is expected that the reproducibility of sensor output becomes very good. The operation of the proposed sensor is numerically simulated with a one-dimensional heat balance equation to evaluate the time evolution of temperature distribution for an ideal MgB2 wire. The proposed configuration of sensor with an MgB2 wire with stainless-steel sheath is also fabricated, and its operation is experimentally evaluated with the liquid hydrogen. (C) 2012 Published by Elsevier B. V. Selection and/or peer-review under responsibility of the Guest Editors.

Heat transfer from inner side of a heated vertical pipe to liquid hydrogen flowing upward was first measured at the pressure of 0.7 MPa for wide ranges of flow rates and liquid temperatures. The heat transfer coefficients in non-boiling regime for each flow velocity were well in agreement with the Dittus-Boelter equation. The heat fluxes at the inception of boiling and the departure from nucleate boiling (DNB) heat fluxes are higher for higher flow velocity and subcooling. It was found that the trend of dependence of the DNB heat flux on flow velocity was expressed by the correlation derived by Hata et al. based on their data for subcooled flow boiling of water, although it has different propensity to subcooling. (C) 2010 Elsevier Ltd. All rights reserved.

Conceptual study of thermo protection structure of the hypersonic aircraft was carried out. Cruising speed of the reference aircraft is Mach 5 at the altitude of 24 km and liquid hydrogen is used as propellant of the engine and vehicle coolant. Precooled turbojet engines and ramjet engines are used as main propulsion system of the aircraft. CFRP is applied to the main structure of the fuselage. Ceramic tiles are glued to the surface of the vehicle to prevent the CFRP structure from high temperature free stream. Liquid hydrogen tanks and cabin are cooled by the liquid hydrogen fuel. Thermal protection and vehicle cooling structure of the reference hypersonic vehicle was carried out in this study. Weight of the ceramic tile is 2.3ton and weight of the vehicle cooling system was 2.4 ton. Furthermore main structure of the vehicle was optimized using Hypersizer program. The lightest structure was 24.7 ton. As a result, total weight of structure and thermal protection became 29.4 ton, whereas that of reference vehicle estimated by MDO study in 2008 was 32.4 ton. © 2011 by Takayuki Kojima.

Japan Aerospace Exploration Agency (JAXA) is currently developing the pre-cooled turbo jet engine (PCTJ) for hypersonic flight. This engine features air pre-cooling using liquid hydrogen fuel in advance of the compression. The cryogenic hydrogen fuel changes drastically in density when it evaporates while passing the fuel tubing at the engine start-up. Presently, the inadequacy of the physical property data of two-phase hydrogen flow pertaining to evaporation hinders the construction of the fuel flow simulator required in establishing high accuracy fuel flow control. In the present study, a device for the void fraction measurement is developed, that is a key parameter of the characteristics of the two-phase flow. It uses the difference of the electric permittivity between the liquid and gas. Validation tests comparing with the optical method were conducted by oil/air, nitrogen and hydrogen. The electrical heater produces various evaporation modes such as bubbly flow, slug flow and churn flow. The void fraction meter could successfully acquire the physical property even in a cryogenic condition. We also measured the heat transfer coefficient of the cryogenic two phase flow. The data of the nitrogen flow arranged by well-known Lockhart-Martinelli parameter shows the agreement with the analytical value.

現在、液体水素の残量を外部から高精度、高信頼度を持って判断できる技術は確立されていない。そこで、我々のグループでは、超電導線と非超電導線を用いた新構造液体水素用液面計を提案している。この液面計は従来構造液面計に非超電導線を回路的に直列に配置したもので、超電導の発生電圧と非超電導線の差分を取ることで、高精度に液面を計測することが可能である。非超電導線は線引き加工後の未熱処理線を用いた。そして、SUSシースMgB₂線とこの未熱処理線を用いて液面計を試作し、液体水素中で動作模擬試験を行った。また、数値解析により実験結果の再現を試みた。