An experimental study of hydrogen solubility in liquid aluminium

Hydrogen solubility in molten aluminium at different temperatures from 973–1123 K, has been measured using Sieverts' method. Inert gas (helium or argon) was used as a reference gas to calibrate the measurement system of the Sieverts' apparatus. The measured hydrogen solubility was found to vary with the reference gases. Helium was detected to be soluble in liquid aluminium. When helium is used as the reference gas, its solubility resulted in lower measured hydrogen solubility than that when argon was used to calibrate the measurement system of the apparatus. Argon gas was therefore considered as an appropriate reference gas when Sieverts' method is used to measure the hydrogen solubility in liquid aluminium. The hydrogen solubility, S, in liquid aluminium as a function of melt temperature, T, determined in the present investigation is expressed as log S = (−2980/T) + 3.07.     

Trapped Bubble Dynamics in Cryogenic Fluids

Initial studies of the properties of helium bubbles acoustically trapped in liquid nitrogen at 66 K have been carried out. Laser scattering is used to monitor the dynamics of the bubble radius as a function of the acoustic driving field. In this apparatus, no sonoluminescence has yet been observed from helium bubbles in liquid nitrogen, although sonoluminescence was previously observed from xenon bubbles in ethanol cooled to 165 K. It is found that bubbles can be stably trapped at quite low acoustic drive levels, enabling the observation of new dynamical bubble behavior.     

Precise Measurements of the Vapor-Liquid Equilibria (VLE) of HFC-32/134a Mixtures Using a New Apparatus

A new apparatus for precise measurements of the vapor-liquid equilibria of mixtures by the circulation method has been developed. This apparatus has two special components: a high-stability temperature control system and a helium pressurization system. The temperature in the liquid bath surrounding the sample cell is kept constant within ±0.5mK. The helium pressurization system increases the pressure of the sampled mixture when measuring the compositions at low temperatures by gas chromatography. With these components, the uncertainty in measuring the vapor-liquid equilibria has been reduced. Using this apparatus, the vapor-liquid equilibria of HFC-32/134a mixtures were measured in a temperature range of 263.15 to 293.15K. These results are in good agreement with the calculated results from REFPROP (Ver. 6.01) with a relative pressure difference of about 2%.     

Cryogenic design and operation of liquid helium in an electron bubble chamber towards low energy solar neutrino detectors

We are developing a new cryogenic neutrino detector: electron bubble chamber, using liquid helium as the detecting medium, for the detection of low energy p-p reaction neutrinos (<420 keV), from the Sun. The program focuses in particular on the interactions of neutrinos scattering off atomic electrons in the detecting medium of liquid helium, resulting in recoil electrons which can be measured. We designed and constructed a small test chamber with 1.5 L active volume to start the detector R&D, and performed experimental proofs of the operation principle. The test chamber is a stainless steel cylinder equipped with five optical windows and ten high voltage cables. To shield the liquid helium chamber against the external heat loads, the chamber is made of double-walled jacket cooled by a pumped helium bath and is built into a LN₂/LHe cryostat, equipped with 80 K and 4 K radiation shields. A needle valve for vapor helium cooling was used to provide a 1.7-4.5 K low temperature environments. The cryogenic test chamber has been successfully operated to test the performance of Gas Electron Multipliers (GEMs) in He and He + H₂ at temperatures in the range of 3-293 K. This paper will give an introduction on the cryogenic solar neutrino detector using electron bubbles in liquid helium, then present the cryogenic design and operation of liquid helium in the small test chamber. The general principles of a full-scale electron bubble detector for the detection of low energy solar neutrinos are also proposed.     

Explosion of Electron Bubbles Trapped on Vortices in He-II

Electrons injected into liquid helium become trapped in a spherical cavity from which the liquid is almost completely excluded. When a negative pressure is applied to the liquid the size of the electron bubble increases, and at a critical negative pressure P _c the bubble explodes. We have observed these explosions and have measured P _c as a function of temperature. At low temperatures an electron bubble can become bound to a quantized vortex. The flow of the helium around the quantized vortex leads to a reduction in the magnitude of P _c. We will report measurements of this reduction in P _c and will make a comparison of the results with theoretical predictions.     

Liquid Helium and Liquid Neon-Sensitive, Low Background Scintillation Media for the Detection of Low Energy Neutrinos

The use of liquid helium and neon as scintillators for neutrino detection is investigated. Several unique properties of these cryogens make them promising candidates for real-time solar neutrino spectroscopy: large ultraviolet scintillation yields from ionizing radiation, transparency to their own scintillation light, and low levels of radioactive impurities. When neutrinos scatter from electrons in liquid helium or neon, ultraviolet light is emitted. The ultraviolet scintillation light can be efficiently converted to the visible with wavelength shifting films. In this way the neutrino-electron scattering events can be detected by photomultiplier tubes at room temperature. We conclude that the solar neutrino flux from the p+pe⁺+d+ _e reaction could be characterized and monitored versus time using a 10 ton mass of liquid helium or neon as a scintillation target.     

Improved pressure–volume–temperature method for estimation of cryogenic liquid volume

One of the most important issues in a liquid propellant rocket is to measure the amount of remaining liquid propellant under low gravity environment during space mission. This paper presents the results of experiment and analysis of a pressure–volume–temperature (PVT) method which is a gauging method for low gravity environment. The experiment is conducted using 7.4 l tank for liquid nitrogen with various liquid-fill levels. To maximize the accuracy of a PVT method with minimum hardware, the technique of a helium injection with low mass flow rate is applied to maintain stable temperature profile in the ullage volume. The PVT analysis considering both pressurant and cryogen as a binary mixture is suggested. At high liquid-fill levels of 72–80%, the accuracy from the conventional PVT analysis is within 4.6%. At low fill levels of 27–30%, the gauging error is within 3.4% by mixture analysis of a PVT method with specific low mass flow rate of a helium injection. It is concluded that the proper mass flow rate of a helium injection and PVT analyses are crucial to enhance the accuracy of the PVT method with regard to various liquid-fill levels.     

Emerging issues in helium turbulence

It has been appreciated recently that because helium has the lowest viscosity of any known material, it can be used in reaching the very highest Reynolds numbers and Rayleigh numbers. Critical helium gas, helium I and helium II are all candidates for such uses. Helium gas and helium I are classical fluids and the advantage stems solely from their low kinematic viscosity. Helium II obeys two-fluid equations and their use in turbulence investigations is under study. This article provides a brief introduction and review of this topic, outlining some of the progress already made and questions which need to be resolved as this relatively new field of investigation evolves. A summary of instrumentation available is included.     

Linear Electron Chains on the Liquid Helium Surface: Carrier Transport

The unique system - linear electron chains on the liquid helium surface was realized experimentally for the first time. The system was realized using curvature of the liquid helium surface film covering a profiled substrate with a small dielectric constant and a pressing electric field holding electrons in the liquid channels. The conductivity of carriers in linear electron chains and magnetoresistance of a quasi-one-dimensional system have been measured in the temperature range 0.5 - 1.8 K in holding electric fields up to 1 kV/cm. The transport properties of the system depend on the substrate cleanness. For a clean system the electron mobility increases with decreasing temperature, the data are in good agreement with the existing theory which describes transport properties in a one-dimensional electron system without localization. Charging of substrate leads to the localization process in electron chains. It has been shown that in the absence of localization magnetoresistance of a quasi-one-dimensional system on liquid helium in the region of ripplon scattering increases with increasing magnetic field.     

New calculation of the acoustical mismatch in the Kapitza conductance of bulk helium

Elastic wave transmission at the interface between a substrate and liquid helium has been calculated using a model that takes into account the inhomogeneous character of the acoustical impedance in helium and in particular the existence of a solid helium layer intermediate between the substrate and bulk liquid helium. The properties of this layer (width, velocity, and attenuation of elastic waves) have a great influence on the calculated transmission. A width of about 10 Å seems to fit many quoted experimental results. The Kapitza conductanceh _k derived from this model and the temperature variation ofh _k agree with experimental results obtained from clean copper samples.Associated with the Centre National de la Recherche Scientifique.     

The measurement of specific heats at low temperatures by an adiabatic technique

An apparatus is described for the measurement of specific heats, by an adiabatic technique, from liquid helium to room temperature. The method is particularly applicable to radio-active samples where the heat generation due to decay within the specimen may be very large.The adiabatic shield, which surrounds the sample, is automatically regulated to the same temperature as the specimen, which may be heating at 20K min^?1. The apparatus is automated such that all data is read out in a form suitable for computer handling.     

液氦流动速度对温度测量的影响

当测量液体或气体流动时的温度时,温度计所测得的温度为流体的滞止温度,而不是流体的真实温度。为提高测量精度,需对所测量的温度进行修正才能得到流体的真实温度。通过液氦泵获得不同的液氦流速,来研究它对液氦测量温度的影响。描叙了实验的结果及其理论分析,并给出了如何修正测量温度而得到液氦的真实温度。     

Measurement of the surface tensions and the interfacial tensions of n-pentane-water and R 113-water systems

The surface and the interfacial tensions of mutually immiscible liquid systems were experimentally studied. The measured systems are n-pentane-water and R 113-water, which are proposed as heat transfer fluids for a direct-contact heat exchanger to be used for geothermal and waste heat recovery plants. The experimental apparatus was constructed based on the principle of the pendant drop method. Measurements were performed in the temperature range from 20 to 150°C. Based on the correlation of the surface and the interfacial tensions, the temperature dependences of the spreading coefficient, the film pressure, and the work of adhesion in each system were calculated.     

Low Temperature Mobility of Steps on the 4He Crystal Facets: Effects of 3He Impurities

At low temperatures, the dissipation due to scattering of thermal phonons by elementary steps on the facets of helium crystals is very small; ³ He impurities may dominate in dissipative processes even at low concentrations. We calculate the step mobility determined by collisions of the step with impurities in bulk liquid and impurities absorbed on the liquid-solid interface, in different temperature and concentration regions.     

Top loading cryogen-free apparatus for low temperature thermophysical properties measurement

The thermophysical properties of matter, especially properties at low temperature, are extremely important for engineering and materials science. Traditional liquid helium based cryostats are in many cases no longer affordable to operate due to the high liquid helium cost. This paper describes the design and test results of a cryogen-free cryostat, based on a GM cryocooler, with 50 mm diameter top loading sample facilities for thermophysical properties measurement at low temperature. The sample temperature range is tuned between 2.6 K and 300 K and it can be continuously controlled with a high resolution. Moreover, the modular sample holder can be adapted to multiple properties measurement.     

Optical Observation of Atomic Hydrogen on the Surface of Liquid Helium

We have optically detected hydrogen atoms adsorbed on the surface of liquid helium, a system relevant for the study of Base degeneracy in two dimensions. The atoms are excited by 121.6 nm light and detected both in fluorescence and in absorption. The optical spectrum of the adsorbed hydrogen atoms was not known a priori. It shows a resonance that is much broader than that of a hydrogen atom in vacuo, and it is shifted to lower frequencies. From the fluorescence intensity we determine that we have reached a surface density corresponding to one atom per square De Broglie wavelength. This means that our experiments take place at the edge of quantum degeneracy. In the regime where the adsorption isotherm is known we can use the measured hydrogen densities to infer the temperature of the helium surface. We use this information to determine the thermal conductance between the surface and the bulk of liquid helium. We find quantitative agreement between the measured temperature drops and the prediction of ripplon-phonon coupling theory.     

Apparatus for Optical Study of Atomic Hydrogen on the Surface of Liquid Helium

Spin-polarized atomic hydrogen adsorbed on the surface of liquid helium is the most promising candidate for the observation of quantum degeneracy in a two-dimensional Base gas. In this article we describe our experimental apparatus which is being used to realize this goal. The apparatus employs a system of superconducting and iron magnets to supply electron and proton spin-polarized hydrogen to a cold cell (T 0.1K) at sufficient flux to compensate recombination losses and attain the regime of two-dimensional quantum degeneracy. The gas in the cell is probed using light resonant with the Lyman- atomic transition.     

Temperature Dependence of the Surface Tension between Liquid Helium-4 and Cesium

Pricaupenko and Treiner ¹ predicted a small but non-negligible temperature dependence of the surface tension between liquid helium and cesium. However, when the effects of bulk phonons in both liquid and solid are taken into account, the temperature dependence is found to be significantly weaker. The effect of surface adsorption, surface stress and surface elasticity are also considered, and found to be negligible. Experimental results have so far been contradictory.     

Near-Critical-Point Thermodynamics from Shock Experiments with Porous Ni Samples

Results of experiments on the expansion of shock-compressed nickel samples into helium are presented. An isentrope with an initial pressure of 170 GPa was studied. The radiance temperature of the nickel sample and the velocity of the shock wave, generated in helium, were measured by a fast multichannel optical pyrometer; other parameters, such as the particle velocity, the pressure on the He-Ni interface, and the temperature of He were calculated using He Hugoniot (chemical plasma model). To increase the shock entropy up to a near-critical value and to intensify the process of heat-mass transfer, porous samples were used. Final states with pressures below 1.5 GPa, determined by the initial He pressure, were generated. The isobaric overheat of nickel by hot shocked helium provided an information about the nickel liquid spinodal. The change in slope of an isentrope in the pressure-particle velocity plane allowed an estimate of the point of its entrance in the two-phase region. Estimates of the critical temperature and pressure were made from peculiarities of P-T path, using various models of the nickel liquid spinodal to represent experimental data.     

A Low Power Photoemission Source for Electrons on Liquid Helium

Electrons on the surface of liquid helium are a widely studied system that may also provide a promising method to implement a quantum computer. One experimental challenge in these studies is to generate electrons on the helium surface in a reliable manner without heating the cryo-system. An electron source relying on photoemission from a zinc film has been previously described using a high power continuous light source that heated the low temperature system. This work has been reproduced more compactly by using a low power pulsed lamp that avoids any heating. About 5×10³ electrons are collected on 1 cm² of helium surface for every pulse of light. A time-resolved experiment suggests that electrons are either emitted over or tunnel through the 1 eV barrier formed by the thin superfluid helium film on the zinc surface. No evidence of trapping or bubble formation is seen.