小林 弘明

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 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.

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.

© 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.

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。

Systems analysis and evaluation of Mach 5 class hypersonic airplanes is performed. The airplane can fly across the Pacific Ocean in 2 hours. A multi-disciplinary optimization program with aerodynamic, thermal structure, propulsion and trajectory is used to define baseline shape. Pre-cooled turbojet engine is assumed as the propulsion system for the hypersonic airplane. The engine can be operated from takeoff to Mach 5, continuously. This engine has adopted pre-cooling cycle using cryogenic liquid hydrogen. The high temperature inlet air at the hypersonic flight will be cooled by liquid hydrogen for fuel. Surface flow of the airplane at hypersonic speed and low speed are evaluated using results of CFD analyses. The control characteristics with control wings and variation of aerodynamic characteristics by adding strakes are obtained by a low speed wind tunnel experiment. The heat flux distribution on the surface of the airframe at hypersonic cruise condition is evaluated by using the results of CFD analyses. The characteristics of heat shield materials for the surface of the fuselage at downstream of the exhaust gas is evaluated by an elemental experiment. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Heat transfer from a flat plate facing upward immersed in a liquid hydrogen pool was measured for the pressures from atmospheric to 1.1 MPa. The flat plate heater used was 10 mm in width, 100 mm in length and 0.1 mm in thickness. Critical heat fluxes (CHFs) in saturated boiling increased with the increase in pressure up to around 0.3 MPa and then decreased with further pressure increase. The CHFs under sub-cooled condition at each pressure increased with the increase in sub-cooling. Discussions were made on the experimental results by comparing with those of the other cryogenic liquids and also the Kutateladze's equations under saturated and subcooled conditions. The experimental CHFs were much smaller than the Kutateladze's equation for higher pressure up to critical. The heater surface temperature was found to reach the critical temperature before the occurrence of hydrodynamic instability and jump to the film boiling regime at the lower heat flux in the higher pressure range. It was suggested that the CHFs are determined not by the heat flux but by the temperature in the higher pressure range. (C) 2010 Elsevier Ltd. All rights reserved.

Numerical simulation on the Air Data Sensor System (ADS), which measures the flow angles and Mach number using the surface pressures on a nose cone, was conducted in this study. The effect of the half cone angle on the flow angle and Mach number measurement was investigated. As a result, we found that a large half cone angle achieves a high sensitivity at the flow angle measurement. It was also found that a small half cone angle achieves a high sensitivity at the Mach number measurement. To satisfy these conflicting requests, we proposed a new shape nose cone which has two different gradients. The high sensitivity was achieved at both the flow angle measurement and Mach number measurement by this new shape nose cone.

A precooled turbojet engine has been developed by JAXA used for the hypersonic airplane and spaceplane. The subscale engine named "S-engine" whose thrust and weight are about 1.2 kN and 100 kg was designed, fabricated and tested. The components and the system firing tests under the sea-level-static condition were successfully conducted. In the next phase, a flight test of the S-engine is planned using a stratospheric balloon in 2010 called balloon-based operation vehicle (BOV). The vehicle is dropped from an altitude of 40 km by a high altitude balloon. After 40 s free-fall, the vehicle is pulled up and the S-engine operates for 30 s at about Mach 2. High-altitude tests of the core-engine verified the performance and healthiness of the engine under the condition corresponding to the BOV flight trajectory. (C) 2009 Elsevier Ltd. All rights reserved.

A thermal-hydraulics experimental system of liquid hydrogen was developed in order to investigate the forced flow heat transfer characteristics in the various cooling channels for wide ranges of subcoolings, flow velocities, and pressures up to supercritical. A main tank is connected to a sub tank through a hydrogen transfer line with a control valve. A channel heater is located at one end of the transfer line in the main tank. Forced flow through the channel is produced by adjusting the pressure difference between the tanks and the valve opening. The mass flow rate is measured from the weight change of the main tank. For the explosion protection, electrical equipments are covered with a nitrogen gas blanket layer and a remote control system was established. The first cryogenic performance tests confirmed that the experimental system had satisfied with the required performances. The forced convection heat transfer characteristics was successfully measured at the pressure of 0.7 MPa for various flow velocities. © 2010 IOP Publishing Ltd.

Liquid hydrogen is expected as a coolant for a HTS superconducting magnet because of its excellent cooling properties. However, there has been a lack of an extensive heat transfer data of liquid hydrogen in forced flow condition for superconductor cooling. As a first step of the study, the experimental setup, which can be used for investigating heat transfer characteristics of liquid hydrogen in a pool and also in forced flow for wide range of sub-coolings, flow velocities and pressures up to supercritical condition, have been designed and fabricated. The mass flow rates during the forced flow tests were measured by the weight change of the main cryostat. All the control valves, the heating control and measuring system were remote-operated through optical fiber connected computer controls. It was confirmed that the control and measuring systems were operated well as designed. A basic test of heat transfer in liquid hydrogen was carried out by quasi-steadily increasing heat inputs to horizontal flat plate with pool cooling and vertical tubes with forced flow cooling. Outlines of the experimental set up and techniques and typical test results are shown. © 2010 American Institute of Physics.

The aim of this paper is to apply a multi-objective optimization generic algorithm (MOGA) to the conceptual design of the hypersonic/supersonic vehicles with different cruise Mach number. The pre-cooled turbojet engine is employed as a propulsion system and some engine parameters such as the precooler size, compressor size, compression ratio and fuel type are varied in the analysis. The result shows that the optimum cruise Mach number is about 4 if hydrogen fuel is used. Methane fuel instead of hydrogen reduces the vehicle gross weight by 33% in case of the Mach 2 vehicle.

For high temperature superconductor (HTS) applications such as a power cable, a motor, and a transformer, a refrigerator enough to cool them below liquid nitrogen temperature is required to attain the HTS system stable operation. Since no refrigerator matched for the HTS application both in temperature and in cooling power is available up to now, a neon turbo-Brayton cycle refrigerator of 2 kW at 70 K was developed. Neon gas was used as the working fluid in the refrigerator. Although hydrogen and helium could be selected as a working fluid for the refrigerator, neon is better energy carrier since it has higher heat capacity and larger molecular weight than hydrogen and helium at a temperature around 70 K in order to make a refrigerator smaller in size. Neon has an advantage in using a small turbo-expander with an impeller of 25 mm in diameter. The turbine rotated at a maximum speed of 100,000 rpm. The information for developing a suitable refrigerator for HTS applications was collected and a new type of neon refrigerator was proposed. © 2009 Elsevier B.V. All rights reserved.

JAXA では,マッハ5 クラスの極超音速機へ搭載するための極超音速ターボジェットエンジンの開発研究を進めている.このエンジンの特徴は,液体水素燃料の冷熱を利用して圧縮機入口の空気を冷却する空気予冷却サイクルを採用している点にあり,これによって従来のターボジェットエンジンでは動作不可能な極超音速飛行が可能になる.現在,推力100 kgf 級のサブスケールエンジンを製作し,飛行実験機搭載形態での地上燃焼試験を実施している.本稿では,極超音速ターボジェットエンジンの飛行実験用に開発した搭載型エンジン制御装置の設計と,地上実験による性能確認結果を示す.