J. G. Weisend

Turbulent flow pressure drop in various He II transfer system components

Pressure drop experiments in highly turbulent He II flow were performed in flow loops driven by either a centrifugal pump or a single-stroke bellows pump. Pressure drops in straight tubing, coiled tubing, bellows sections, valves and Venturi flow meters were measured over a range of flow rates and temperatures. Our pressure drop data are in general agreement with classical fluid correlations when the He II normal component viscosity is used in calculating the Reynolds number. Cavitation and, in some cases, metastable superheating were observed in pressure drop measurements with Venturis in both centrifugal and bellows pump flow circuits.

Pressure drop from flow of cryogens in corrugated bellows

Abstract The pressure drop experienced by cryogenic fluids flowing through corrugated bellows is investigated up to Re = 4 × 10 6 . The measured pressure drop is seen to increase approximately as the square of the velocity. Comparison of N 2 gas, LN 2 and He II pressure drop results indicates that there is no fundamental difference between the behaviour of classical fluids and turbulent He II in bellows systems. The present results are analysed with only limited success in terms of existing correlations for pressure drop in bellows. One finding is that the classical friction factor appears to increase slightly with Reynolds number, which is consistent with the behaviour of the drag coefficient measured in similar geometrical configurations.

He II flowmetering

Abstract Flowmetering methods for He II are reviewed with emphasis on problems particular to this unique fluid. The flowmetering of He II is unusual because the fluid processes a number of special properties: a high rate of heat conductivity, a low temperature ( T

Characterization of a Centrifugal Pump in He II

As part of an effort to determine the feasibility of helium transfer in space a centrifugal pump was tested in He II at a variety of flow rates, pump speeds and fluid temperatures. The pump which has a straight bladed impeller 6.86 cm in diameter generated a maximum pressure rise of 15 kPa and a maximum flow rate of 22 g/s for the conditions of the test. Pump performance seems independent of fluid temperature and is good agreement with the values predicted by the manufacturer. Over the range of flow coefficients, measured maximum efficiency is around 50%. Cavitation is observed in the pump and is thought to be highly dependent on the local heating of the helium in the pump. Preliminary measurements of the noise spectra of the pump suggest a possible mechanism to predict the onset of cavitation.

DESIGN AND OPERATION OF A HORIZONTAL LIQUID HELIUM FLOW FACILITY

The University of Wisconsin horizontal liquid helium flow facility (LHFF) consists of a five meter long 20 cm ID horizontal dewar connected to two end boxes. Several heat exchanger inserts have been built to allow variable temperature operation of 1.6 K ≤ T ≤ 4.2 K. A centrifugal pump is installed at one end of the facility permitting experiments in forced flow liquid helium up to 100 gm/s. The horizontal design allows experimentation on long straight test sections which may be used either to study fundamental properties of heat and mass transfer in helium or prototype cryogenic components under realistic conditions. A detailed description of the design and operating experience of the LHFF is presented.

The TESLA 500 cryogenic system and He II two-phase flow: issues and planned experiments

Abstract The cooling system of the proposed TESLA 500 superconducting linac makes extensive use of He II two-phase flow. However, there remain a number of open questions about the expected performance of this unique two-phase flow system. One of the purposes of the TESLA Test Facility (TTF) currently under construction at DESY, is to test the planned cryogenic cooling system for TESLA 500. Towards this end, sensors will be installed in TTF to verify the stability and structure of the two-phase flow regime, and measure the vapour velocity, temperature and slip. These measurements will assist in predicting the performance of the TESLA cooling system as well as providing information on the basic behaviour of He II two-phase flow. These sensors include ones installed by DESY staff as well as an experiment designed and built by the National High Magnetic Field Laboratory in Tallahassee, FL, USA. This paper describes the proposed cooling system for TESLA 500 and its predicted performance. In addition, experiments designed to understand the behaviour of the He II two-phase flow system are described.

Numerical Study of Two-Phase Helium II Stratified Channel Flow

A key feature of the cryogenic system for the proposed TeV Superconducting Linear Accelerator (TESLA) is a He II two-phase flow line that provides cooling for the superconducting RF cavities. Understanding the behavior of this line is vital to the proper functioning of the accelerator. A numerical model has been developed that allows predictions of the pressure, temperature and mass flow rates of the components in the twophase line and in the connected gas return line. The model also predicts the helium level in the two-phase line. This is a rigorous model using the conservation laws of mass, momentum and energy for each phase and allowing for interactions between the phases and the walls as well as between each other. The model also takes into account the specific geometry of the TESLA cooling system. This paper describes the model and presents its predictions for two alternative cooling schemes.

T-S diagram for helium that extends below the lambda line

Abstract Temperature-entropy ( T-S ) phase diagrams for helium between 1 and 7 K have been generated from available numerical codes. These diagrams show isobaric and isenthalpic slope changes at the lambda (λ) point. In the He II regime, the entropy is an increasing function of pressure, which is exactly opposite to the behaviour of ordinary fluids. This effect is caused by the depression of the λ transition with applied pressure.

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.