D. Celik

Tracer Particles for Application to PIV Studies of Liquid Helium

Material selection and methods for introduction of tracer particles into liquid helium are reviewed for application in particle image velocimetry experiments. The combination of low temperature environment and low-density fluid place unique requirements on particle selection. Options discussed include a variety of commercially available solid particles of different size and density as well as solid particles generated by freezing liquids or gases. Recommendations are presented based on the dynamic behavior of the particles. Also, methods for introducing the particles into liquid helium are discussed.

Tracer particle generation in superfluid helium through cryogenic liquid injection for particle image velocimetry (PIV) applications

Abstract This paper reports the first experimental study of liquid neon injection into superfluid helium (He II) through a plain orifice atomizer to explore different means of introducing micron-size tracer particles into a He II bath for particle image velocimetry (PIV) applications. The obtained results verify that the direct injection of liquid neon into He II introduces seed particles into the He II bath. It is also demonstrated that the particle sizes can be controlled by changing the pressure above the injected liquid. Additionally, the size distribution of the particles is calculated from the PIV results through the use of the correlations to the standard drag curve.

Helium II level measurement techniques

In this paper, a survey of cryogenic liquid level measurement techniques applicable to superfluid helium (He II) is given. The survey includes both continuous and discrete measurement techniques. A number of different probes and controlling circuits for this purpose have been described in the literature. They fall into one of the following categories: capacitive liquid level gauges, superconducting wire liquid level gauges, thermodynamic (heat transfer-based) liquid level gauges, resistive gauges, ultrasound and transmission line-based level detectors. The present paper reviews these techniques and their suitability for He II service. In addition to these methods, techniques for measuring the total liquid volume and mass gauging are also discussed.

Application of PIV to counterflow in He II

This study reports the first application of the Particle Image Velocimetry (PIV) technique to the counterflow heat transport in He II. Counterflow in He II is created by heating the bottom of a vertical channel contained in a He II reservoir. In order to make the flow visible, hollow glass spheres of diameter approximately 70 micrometers are used. These seeding particles, as they follow the motion of the normal component, are illuminated with a pulsed Nd:YAG laser sheet and instantaneous position of the particles are recorded using a high speed Charge Coupled Device (CCD) camera. The velocity field in the He II is deduced from two successive images using cross-correlation techniques.

SUBCOOLED LIQUID OXYGEN CRYOSTAT FOR MAGNETO-ARCHIMEDES PARTICLE SEPARATION BY DENSITY

An instrument for the separation of particles by density (sorting) is being developed that uses the magneto-archimedes effect in liquid oxygen. With liquid oxygen strongly paramagnetic, the magneto-archimedes effect is an extension of diamagnetic levitation in the sense of increasing the effective buoyancy of a particle. The instrument will be able to separate ensembles of particles from 100 μm to 100 nm in size, and vertically map or mechanically deliver the separated particles. The instrument requires a column of liquid oxygen that is nearly isothermal, free of thermal convection, subcooled to prevent nucleate boiling, and supported against the strong magnetic field used. Thus, the unique cryostat design that meets these requirements is described in the present article. It consists in part of a column of liquid nitrogen below for cooling the liquid oxygen, with the liquid oxygen pressurized by helium gas to prevent nucleate boiling.

An apparatus to measure the apparent thermal conductivity of multilayer insulation (MLI)

The design of a concentric cylinder calorimeter for measuring the apparent thermal conductivity of MLI blankets is presented. Unlike similar devices where a liquid cryogen is used to control the cold boundary temperature and the cryogen boil-off rate is used to obtain the heat transfer through blanket, the design presented in this paper utilizes mechanical refrigerators to control the boundary temperatures and a heat rate meter to determine the heat load. This approach ensures two unique features of the apparatus. First, the use of cryocoolers enables the user to set the boundary temperatures anywhere within the operating range of the refrigerators and therefore permits a wide range of temperature and temperature differences with the measurement. The other unique feature is that the total heat transfer through the blanket is obtained by measuring the heat conducted along a cold cylinder support rod of known thermal conductivity. To determine the absolute thermal conductivity, a calibration is needed to el...

Numerical study of liquid-hydrogen droplet generation from a vibrating orifice

Atomic hydrogen propellant feed systems for far-future spacecraft may utilize solid-hydrogen particle carriers for atomic species that undergo recombination to create hot rocket exhaust. Such technology will require the development of particle generation techniques. One such technique could involve the production of hydrogen droplets from a vibrating orifice that would then freeze in cryogenic helium vapor. Among other quantities, the shape and size of the droplet are of particular interest. The present paper addresses this problem within the framework of the incompressible Navier–Stokes equations for multiphase flows, in order to unravel the basic mechanisms of droplet formation with a view to control them. Surface tension, one of the most important mechanisms to determine droplet shape, is modeled as the source term in the momentum equation. Droplet shape is tracked using a volume-of-fluid approach. A dynamic meshing technique is employed to accommodate the vibration of the generator orifice. Numericall...

A Particle Seeding Apparatus for Cryogenic Flow Visualization

A particle seeding apparatus to create neutrally buoyant solid particles in liquid helium (He I and He II) has been developed and successfully tested as part of a flow visualization experiment. The apparatus consists of a liquid cavity to hold the hydrogendeuterium mixture, a vacuum jacket, a plain orifice atomizer, a needle valve, a solenoid valve, heaters and temperature sensors. During the condensation process, the vacuum jacket around the hydrogen cavity was filled temporarily with helium gas. The needle valve, which is coated with indium to prevent any leaks, closes the gate between liquid mixture and helium, and operates via a solenoid. Heaters in the can control the temperature of the liquid mixture. Temperature is monitored by silicon diode temperature sensors placed on the can. Tests have been performed inside a glass cryostat for visual inspection, and have been recorded using a black and white video camera and a camera equipped with a macro lens. Depending on the flow velocity inside the nozzle, atomization with different particle sizes has been observed.

Ortho and Para Hydrogen Concentration Determination Based on Vapor Pressure

We have constructed a simple ortho‐para hydrogen converter to generate para‐hydrogen for our ongoing transport property measurement efforts. The apparatus utilizes hydrous ferric oxide as the catalyst. Conversion from normal hydrogen to para‐hydrogen takes places at the boiling point of hydrogen. The heat due to condensation and conversion is removed by a liquid helium bath surrounding the vacuum jacketed apparatus. The temperature and the vapor pressure of the hydrogen inside the converter are used to determine the amount of the para content based on existing vapor pressure data. For verification purposes, we have also taken the more traditional approach to determine the para‐hydrogen concentration by measuring the thermal conductivity of the converted gas in a flat plate calorimeter. The results from the thermal conductivity measurements have demonstrated that the composition of the gas can change significantly over the period of time needed to make the measurement.

Thermal Conductivity Measurements of Subcooled Oxygen below 80 K

The first thermal conductivity measurements of liquid oxygen at temperatures below 80 K, and at pressures up to 1 MPa are reported. The measurements were conducted in a horizontal, guarded, flat plate calorimeter, and are based on the steady‐state approach. The cooling power to the calorimeter is provided by a Gifford‐McMahon type cryocooler. The temperature difference between the plates of the calorimeter and the absolute temperature are measured using calibrated platinum thermometers. One dimensional heat transfer between the hot and cold plates of the calorimeter is achieved by placing two thermal guards, instrumented with heaters and platinum thermometers, around the hot plate. Although used exclusively for measurements with oxygen, this apparatus is capable of measuring the thermal conductivity of other fluids including liquid hydrogen down to about 15 K.