M. R. Smith

Observed drag crisis on a sphere in flowing He I and He II

The pressure distribution on the surface of a sphere has been measured in flowing He I and He II as a function of Reynolds number. The drag coefficient was extracted by integrating the pressure distribution, using some assumptions about symmetry of the flow field. Drag coefficients are plotted against Reynolds number for both He I and He II against classical data for both smooth and nonsmooth spheres. Latest results in He II suggest that the drag crisis occurs at a Reynolds number of approximately 2×105, in fair agreement with classical data.

A capacitive liquid helium level sensor instrument

The design, construction, and performance of a prototype capacitive liquid helium level sensor instrument with cold electronics is described.

Pressure drop measurements of prototype NET and CEA cable-in-conduit conductors (CICCs)

The pressure drop of two prototype cable-in-conduit conductors (CICCs) were measured. The NET conductor is a conventional type CICC, while the CEA conductor has a central flow channel to reduce hydraulic impedance. The pressure drop measurements were conducted with helium at temperatures ranging from 2 K to 4.7 K, and pressure from the saturated vapor pressure to in excess of 3 bar. Computer image analysis was used to estimate the flow cross sectional area and wetted perimeter of the conductors. The data are expressed in terms of a classical friction factor, and compared with previous experimental results.<<ETX>>

The Temperature Dependent Drag Crisis on a Sphere in Flowing Helium II

In a previous paper, we reported observing a drag crisis on a sphere in flowing He I and He II. Data in He II suggested a possible temperature dependence to the critical Reynolds number, as well as the magnitude of the crisis. In this paper, we explore temperature dependence more completely. Dynamical similarity arguments, which lead to Reynolds number scaling in the case of the Navier-Stokes equations, are applied to the two-fluid equations. The result is a modified Reynolds number involving the factor 1-β, where β ≡ ρs/ρ. The ramifications of this argument, together with other possible scaling relationships, are discussed. Data and critical Reynolds numbers are plotted for several temperatures between 1.6 K and 2.0 K. Results appear to agree well with the proposed scaling for He II.

Thin-Film Thermometer and Heater Design for the Detection and Generation of Second Sound Shock Pulses

Using a known heater design, and a common type of pencil lead graphite in a novel thermometer design, second sound shock (SSS) pulses comparable to those of previous researchers were successfully transmitted and received in a 1.7 K He II bath. Two sample traces of SSS pulses are presented. Extensive design requirements are outlined for highspeed thin-film thermometers and heaters used to transmit and receive SSS pulses. The heater and thermometer can be described by lumped parameter first order ordinary differential equations for the thermal case because their Biot numbers are less than 0.1 in the presented design. Also, their thermal time constants are minimized. However, the heater and thermometer can be described by lumped parameter first order ordinary differential equations also for the electrical case because they are embedded in an electronic instrumentation system. The time constants in both cases must be considered with respect to the required minimum pulse duration to arrive at a correct design for the heater and thermometer.

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.

A study on the temperature dependent drag coefficient on a sphere in flowing helium II

The drag coefficient on the surface of a sphere for temperatures between 1.6 K and 2.1 K has been measured in flowing He II. The measurement suggests a temperature dependence to the drag coefficient not seen in ordinary fluids and this dependence appears to correlate with the normal fluid density, ρn. The results scale with normal fluid Reynolds number, Ren=Re (ρn/ρ), based on non-dimensionalizing the He II two fluid equations. The drag coefficient has a minimum value at same normal fluid Reynolds number, Ren≈2.5×105 for each temperature. This is in reasonable agreement with the minimum in the classical sphere drag coefficient curve at approximately Re=3×105. The drag crisis is governed by the location of the boundary layer separation and this position may depend upon the normal fluid density. Recent He II measurements confirm that the drag coefficient has a temperature dependence possibly related to a variation of the turbulent transition within the boundary layer.

Measurement of the Pressure Distribution and Drag on a Sphere in Flowing Helium I and Helium II

We have designed and constructed an apparatus for measuring the pressure distribution around a sphere as a function of Reynolds number (mass flow rate) in both He I and He II. Liquid helium possesses kinematic viscosities nearly three orders of magnitude smaller than that of air. This offers the possibility of correspondingly higher Reynolds numbers to engineers carrying out dynamic similarity studies of modern high performance aircraft and marine vessels. Important questions remain however, about the fundamental nature of turbulence in liquid helium. Additionally, many techniques in common use for room temperature fluid dynamics experiments are not well developed for low temperatures. Our goal in this work was to demonstrate one technique for measuring the pressure distribution and drag on a sphere in flowing liquid helium. A further goal was to compare our findings with classical results in the hope of assessing the degree to which helium II and helium I behave classically within the context of a classical fluid dynamics experiment.

An experimental and numerical study of He II two-phase flow in the TESLA test facility

We report on measurements of the liquid level and temperature corresponding to different local heat loads at several sections of the He II two-phase flow channel in the TESLA (Tera-eV Energy Superconducting Linear Accelerator) Test Facility phase I (TTF1) during its operation. The measurements show that under normal operating conditions saturation between He II and its vapor can be maintained even in the transient process of heat transfer. A computer code for He II stratified two-phase flow analysis has been developed for the numerical simulation of the He II and vapor flow in the configuration of the cryogenic cooling channel in TTF1. Comparison with the measurement shows the prediction by the code agrees well with the experimental results. The code also predicts the maximum heat load under which the two-phase tube in TTF1 would locally dry out. In its application, the code is helpful to evaluate the impact on the flow behaviour resulting from changes to the TTF1 configuration.

Realization of a 10 7 Reynolds Number Helium Facility

We describe preliminary work directed toward the development of a flow facility capable of sphere Reynolds number of order 107. There are two components to this paper. First, results from a preliminary experiment to measure sphere drag to Re > 105 in He I and He II are presented and discussed in terms of current understanding of the problem. These results have encouraged the second part of the present work, which involves the conceptual design of a 107 Reynolds number facility. Comments on the feasibility of hydrodynamic testing with liquid helium are included.