Hideki Tatsumoto

Operational characteristics of the J-PARC cryogenic hydrogen system for a spallation neutron source

The J-PARC cryogenic hydrogen system provides supercritical hydrogen with the para-hydrogen concentration of more than 99 % and the temperature of less than 20 K to three moderators so as to provide cold pulsed neutron beams of a higher neutronic performance. Furthermore, the temperature fluctuation of the feed hydrogen stream is required to be within ± 0.25 K. A stable 300-kW proton beam operation has been carried out since November 2012. The para-hydrogen concentrations were measured during the cool-down process. It is confirmed that para-hydrogen always exists in the equilibrium concentration because of the installation of an ortho-para hydrogen convertor. Propagation characteristics of temperature fluctuation were measured by temporarily changing the heater power under off-beam condition to clarify the effects of a heater control for thermal compensation on the feed temperature fluctuation. The experimental data gave an allowable temperature fluctuation of ± 1.05 K. It is clarified through a 286-kW and a 524-kW proton beam operations that the heater control would be applicable for the 1-MW proton beam operation by extrapolating from the experimental data.

Forced convection heat transfer of subcooled liquid hydrogen in horizontal tubes

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.

PRELIMINARY STUDY ON HEAT TRANSFER CHARACTERISTICS OF LIQUID HYDROGEN FOR COOLANT OF HTC SUPERCONDUCTORS

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 wi...

Development of a thermal-hydraulics experimental system for high Tc superconductors cooled by liquid hydrogen

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.

Design Result of the Cryogenic Hydrogen Circulation System for 1 MW Pulse Spallation Neutron Source (JSNS) in J‐PARC

A cryogenic hydrogen circulation system to cool cryogenic hydrogen moderators for the spallation neutron source in J‐PARC has been designed. This system consists of a helium refrigerator system and a hydrogen circulation system. The refrigeration capacity required for the cryogenic system is specified to be around 6 kW at 17 K. The hydrogen circulation system is composed of a hydrogen‐helium heat exchanger, two circulation pumps, multiple transfer lines, three moderator vessels, an Ortho‐Para hydrogen converter, an accumulator, a heater and others. The system adopts a centrifugal‐type hydrogen pump that can circulate the cryogenic hydrogen (20 K, 0.5 to 1.5 MPa) with the mass flow up to 162 g/s through the three moderators. This forced‐flow circulation can remove the nuclear heating from the moderators and can keep the temperature difference through the moderators within 3 K. The Ortho‐Para hydrogen converter will be installed to maintain the Para‐hydrogen concentration of more than 99% at the inlet of th...

Forced convection heat transfer of saturated liquid hydrogen in vertically-mounted heated pipes

Heat transfer from the inner side of vertically-mounted heated pipes to forced flow of saturated liquid hydrogen was measured with a quasi-steady increase of a heat generation rate for wide ranges of flow rate and saturated pressure. The tube heaters have lengths L of 100 mm and 167 mm with the diameter D of 4 mm and lengths of 150 mm and 250 mm with the diameter of 6 mm. The heat fluxes at departure from nucleate boiling (DNB) were higher for higher flow velocity, lower pressures and shorter L/D. The effect of L/D on the DNB heat flux was clarified. It is confirmed that our DNB correlation can describe the experimental data.

Transient heat transfer from a horizontal flat plate in a pool of liquid hydrogen

Transient heat transfer caused by exponentially increasing heat input (Q=Q0exp(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.

PRESSURE FLUCTUATION BEHAVIOR IN THE CRYOGENIC HYDROGEN SYSTEM CAUSED BY A 100 kW PROTON BEAM INJECTION

Supercritical hydrogen (1.5 MPa and around 20 K) has been selected as a moderator material for the intense spallation neutron source (JSNS) in J‐PARC. The cryogenic hydrogen system provides the supercritical hydrogen for the moderators and removes the nuclear heating at the moderators, which is estimated to be 3.8 kW for a proton beam power of 1 MW. The pressure control system was designed to mitigate pressure fluctuation caused by suddenly turning a proton beam on and off, which is composed of a heater as an active controller for thermal compensation and an accumulator as a passive volume controller. A 109 kW proton beam was injected to the JSNS in December 2007. The pressure fluctuation behaviors were studied for the 109 kW proton beam operation. As soon as the proton beam was injected, the accumulator spontaneously started to constrict. The heater control succeeded in maintaining a constant heat load applied to the cryogenic hydrogen system. The pressure control system successfully reduced the pressure...

Over-Current Properties of MgB2 Wire Cooled by Liquid Hydrogen under Magnetic Field

Liquid hydrogen (LH2) has excellent properties such as large latent heat, low viscosity, and so on. Because of these properties, LH2 is expected to be used as a coolant for a high-critical-temperature superconductor (HTS), including MgB2. The over-critical-current properties of an HTS are important for the stable designs of HTS devices cooled by LH2; however, the temperature change of a sheathed superconducting wire cannot be revealed only by current-voltage properties beyond critical current, since the current-sharing ratio among MgB2 and sheath materials is not unknown. In this study, transient over-critical-current tests were performed on a short MgB2 sample cooled by LH2 under magnetic field, and the sample temperatures were calculated from test data. In addition, the test sample temperature based on the test was compared with that of the computer simulation result. It was found that the temperature change of the wire just after the transport current exceeds the critical current is affected by external magnetic fields.

Forced convection heat transfer from a wire inserted into a vertically-mounted pipe to liquid hydrogen flowing upward

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.