Helium Mass Flow Rate Research Articles

Mass flow rate measurements in a microchannel, from hydrodynamic to near free molecular regimes

Helium mass flow rates in a microchannel were measured, for a wide Knudsen-number range, in isothermal steady conditions. The flow Knudsen numbers, considered here, cover the range from continuum slip regime to the near free molecular regime. We used a single-channel system involved in an experimental platform more powerful than those previously used. The experimental errors and uncertainties were accurately investigated and estimated. In the continuum slip regime, it was found that the first-order approach is pertinent for Knudsen number between 0.03 and 0.3. Moreover, the slip coefficient was deduced by comparing the experiments with the theoretical first-order slip continuum approach. For Knudsen number between 0.03 and 0.7, a polynomial second-power form is proposed for the mass flow rate expression. Otherwise, the experimental results on the mass flow rate were compared with theoretical values calculated from kinetic approaches over the 0.03–50 Knudsen number range, and an overall agreement appears through the comparison. It was also found, when the Knudsen number increased, that the wall influence on measurement occurred first through the accommodation process in the transition regime followed by the wall influence through the aspect ratio in the free molecular regime.

Design of high-temperature superconductor current leads for ITER

In the framework of the European Fusion Programme, the Forschungszentrum Karlsruhe and the Centre de Recherches en Physique des Plasmas (CRPP) have successfully developed and tested a 70 kA high-temperature superconductor (HTS) current lead demonstrator. In the present work, the optimisation of the cooling conditions with respect to the cooling power consumption and the required amount of HTS material is described for a binary current lead consisting of a conduction-cooled HTS part and a gas-cooled heat exchanger. The refrigerator input power, required to cool a binary HTS current lead, is determined by the heat load at the 4.5 K level, the helium mass flow rate necessary to cool the heat exchanger part and the helium inlet temperature ( T He,in). For a range of copper ( T Cu) and helium inlet ( T He,in) temperatures at the cold end of the heat exchanger, the optimum values of the length of the heat exchanger and the required helium mass flow rate have been calculated. Furthermore, the main results of the pulsed operation of the 70 kA HTS current lead demonstrator are presented. The possibility of pulsed operation of HTS current leads for the CS and PF coils is discussed.

Experimental study of DEMO helium cooled divertor target mock-ups to estimate their thermal and pumping efficiencies

Abstract The helium cooled divertor for the DEMO fusion reactor is designed for removal of surface high-heat-flux up to 15 MW/m 2 during normal operation. To reduce thermal stresses in divertor plates finger-like array structure was chosen, where each tungsten finger is cooled by helium at inlet parameters of 10 MPa, 634 °C. The gas puffing facility (GPF) was developed for measurement of mock-ups performance at the reversed high heat flux, when the plasma-facing surface of finger-like mock-up was intensively cooled by water. The goals of these experiments are: (1) to compare heat removal performance for different design mock-ups and (2) to adjust computational fluids dynamics (CFD) codes for accurate simulations. Long helium pulses (∼100 s duration) and sufficient capability (1–2 kg of He per pulse) facilitate attainment of the steady-state regime in experiments, when 5–15 g/s mass flow rate of helium was scanned. Results of last experimental campaign carried on in December 2004 revealed that all helium distributing cartridge options demonstrate optimistic performance (as compared to CFD simulations) and capability to transfer 10–25 MW/m 2 in the helium mass flow rate (MFR) range of 5–15 g/s.

A New Method for Measurement of Helium Mass Flow Rate in the Cryogenic System of TORE SUPRA

The TORE SUPRA Tokamak was built by EURATOM-CEA association. The NbTi conductor of superconducting coils is inserted in a tight enclosure filled with pressurized superfluid helium of 0.125 MPa at 1.8 K. The thick casing is cooled to 4.5 K by 1.8 MPa in 4.5 K supercritical helium circulation. Around this thick casing, a 80 K thermal shield protects the parts at very low temperatures from the thermal radiation, which is cooled by pressurized helium at 80 K and 1.8 MPa. A new measurement method for helium mass flow rate of 80 K shield and 4.5 K casing is described in this paper. The commissioning was done on the two helium loops of the cryoplant: The supercritical 4.5 K thick casing and 80 K shields. The purpose is to improve control of the 4.5 K and 80 K refrigeration loops.

Arcjet Plasma Neutralization of Hall Thrusters, Part 2: Experimental Demonstration

Arcjet Plasma Neutralization of Hall Thrusters, Part 2: Experimental Demonstration

Stability Study on the HT-7U TF and PF Superconducting Magnets

The HT-7U device is a large fully Superconducting TOKAMAK Experimental Facility which is a National Large Scientific Project in China. The large fusion experimental device is being fabricated in the Institute of Plasma Physics, Chinese Academy of Sciences. In order to check the stability, a thermohydraulic analysis on the HT-7U TF and PF superconducting magnets was carried out using finite element method with adding the artificial viscosity and refined mesh in the disturbance region. The external heating is assumed as uniformly distributed over the conductor cross-section. The stability margin and quench are calculated under the various disturbance scenarios. Several simulation scenarios are assumed such as the disturbance spectrum, mass flow rate of supercritical helium. In the paper, numerical analysis on stability margin and quench characteristics is presented.

Modeling Techniques for Correcting Measured Data on the ITER Toroidal Field Insert Coil

The ITER TFIC (toroidal field insert coil), consisting of a titanium jacketed, 40 m long superconducting CICC (cable-in-conduit conductor) wound on a steel mandrel, was tested at the JAERI facility, Naka Japan in 2001. The tested coil is fully equipped with voltage taps and thermometers distributed in the high field region. As the thermometer responses showed some inconsistency, a re-assessment of the performance of the ITER TFIC CICC has been carried out based on a new thermo-hydraulic model allowing the reconstruction of the cable temperature during T/sub cs/ (current sharing temperature) tests. This model is a time dependent model using pressure, temperature and helium mass flow rates measured by reliable sensors attached to the facility. It includes special features such as heat exchange to the cold busbars at the electrical joints and heat exchange to the steel mandrel. A detailed description of the model is given together with the results of the conductor performance analysis carried out on T/sub cs/ runs. The impact of the TFIC conductor performance assessment on the ITER TF conductor design is then derived.

Investigation on the Relation of CICC Stability Margin to Mass Flow Rate and Operating Temperature of Helium

To circulate supercritical helium, a differential pressure between inlet and outlet has to be applied. A differential pressure can be generated by a refrigerating compressor which forces the coolant through cooling channels. A differential pressure corresponds to a constant flow rate in a constant length. The coolant flow rate was set at different values from 0.2 to 2.8 g/s. The numerical simulation was performed using the 1-D mathematical model (Gandalf). The results of the experiment and simulation show that the larger the coolant flow rate, the higher the stability margin is. It is also showed that the shorter the cooling channel, the higher the stability margin is with the same coolant flow rate. Meanwhile, we also introduce the influence of temperature and pressure on the stability margin of CICC.

Analysis on stability margin of Nb/sub 3/Sn Cable-in-Conduit-Conductor

The stability margin of Nb/sub 3/Sn Cable-in-Conduit Conductor (CICC) has been analyzed by a numerical model. The numerical code is based on the finite volume method to discretize the one-dimensional conservation equations on the staggered mesh. The algebraic method is used to transform the non-uniform mesh in the physical plane to the uniform mesh in the computational plane. The numerical simulation shows that the faster supercritical helium mass flow rate can improve the stability and increase the limiting current. The stability and limiting current are decreased with the increasing the operating temperature and background field. The shorter disturbance duration time allows the higher stability in the well-cooled region and the lower stability in the ill-cooled region.

Use of Nb3Sn inserts in a forced flow cooled 30 kA current lead

Abstract The reduction of the helium mass flow rate of a 30 kA current lead by inserting Nb3Sn wires in the low temperature part of the copper conductor is investigated. The technical realisation is described and the experimental results are presented. The mass flow rate normalized to the current has been measured to be 0.053 g/(s-kA) to 0.063 g/(s-kA) for operational currents of 15 to 30 kA respectively.

Second law analysis of active magnetic regenerative hydrogen liquefiers

Recent published work in the area of magnetic refrigeration reports on its potential for greater efficiency and high reliability. This paper presents an exergy analysis of a three-stage active magnetic regenerative (AMR) hydrogen liquefier which cools a hydrogen gas stream at 77 K and 1 atm to hydrogen liquid at 20 K. Ortho - para conversion of hydrogen is accomplished in a heat exchanger employing a 10 atm helium fluid that cycles in the refrigerator. The performance of the system is described in terms of the cooling capacity and exergy losses as functions of the magnetic material type, magnetic bed size and temperature, helium mass flow rate, ratio of isofield and adiabatic process times, and the operating frequency.

Influence of mass flow rate and hydraulic perimeter on the transient stability margin of a forced flow cooled superconductor

A numerical analysis has been carried out of the stability and thermal performance of internally cooled superconductors. The analysis of the system in question was performed using a one-dimensional computer code developed by Arp 1 based on a program for non-linear partial differential equations developed by Sinovec 2 and slightly modified by the present author. The effects of helium mass flow rate and hydraulic perimeter on the stability margin have been studied. The computer simulation results are presented in this paper. These results indicate that the thermally induced pressure gradients and fluid velocity caused by rapid perturbations are responsible for the stability margin, and both mass flow rate and hydraulic perimeter are quite significant factors for achieving high stability margins. A forced flow cooled superconductor with dual composite cooling channels is suggested from these results.

Stability of 10 T-(Nb-Ti) 3Sn forced flow cooled superconducting coil

Samples of 10 T-2.5 kA (Nb-Ti) 3Sn cable-in-conduit type superconductors with a void fraction in cable space 39.9% and 46.6% were developed and two small one-layer solenoid coils (10 turns, 7.5 m conductor length) were manufactured by a wind and react method. Several verification tests were performed under the condition of 10.8 T uniform backup field and mass flow rate of the supercritical helium m ̇ = 0 g s −1 ≈ 4 g s −1 at 4.2 K, 0.45 MPa. Quench simulations were also made with one-dimensional transient analysis code. It was found that the stability margins of these coils were proved to be large enough to apply for the fusion magnets and the experimental data such as stability margin and normal zone propagation velocity were in good agreement with the calculation results.

Transient stability analysis of a forced cooled superconductor

A numerical analysis of stability and thermal performance of internally cooled superconductors has been investigated. An analysis of this system has been performed using one dimensional computer code developed by Arp based on a program for nonliner partially differential equations by Sinovec and slightly modified by the author. The effects of helium mass flow rate and also hydraulic perimeter upon the stability margin has been studied. The computer simulation results will be presented. These results of computer analyses indicate that the thermally induced pressure gradients and fluid velocity caused by rapid perturbations are responsible for the stability margin, and both of mass flow rate and hydraulic perimeter are quite significant for high stability margins. A composite cooling channeled forced cooled superconductor will be suggested from these results.

Report upon the use of anthracite coal in locomotive engines on the reading railroad, made to the president of the Reading Railroad Company

A new variant of the void fraction RF-sensor of the round cross-section with ID = 38 mm is presented. Its sensitive part is made of the ceramic pipe with a meander line on the outer surface. This technique does not disturb the flow moving in the metal pipe of the same diameter. The technical solutions to provide rather high uniformity of the electric field within the sensitive volume and excellent stability of the readings are described. Irregular steps of the meander line are chosen after computer calculations and experimental checking. Some disadvantages of the previous modifications are shown as well. A new calibration procedure is discussed: it takes into account the dependence of the resonant frequency of the empty RF-sensor on the temperature of the sensor body. The method to find a mass flow rate of the two-phase helium and hydrogen flows in the range of void fractions from 0% to 100% is demonstrated with the new RF-sensor.