S.W. Van Sciver

Transient heat transport in He II

Abstract Experimental and theoretical investigations of time dependent heat transport in He II have identified several new phenomena not previously reported. For heat fluxes greater than the steady state peak value, there is an observed time delay between the initiation of heating and the onset of film boiling. The time delay is seen to be nearly equal to the enthalpy rise in the helium divided by the applied heat flux. A well defined relationship is shown to exist between the time delay and the applied heat flux. Simple theoretical analysis of heat conductivity in He II is shown to predict the functional dependence and give approximately the correct proportionality factor. Experimental results are reported over a range of temperatures, 1.6 K to 2.1 K and for two external pressures, near saturated vapour pressure and at 0.125 MPa.

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.

An overview of the 45-T hybrid magnet system for the new National High Magnetic Field Laboratory

The new National High Magnetic Field Laboratory (NHMFL) at Tallahassee, Florida is committed to putting into operation in 1995 a 45-T Hybrid Magnet System to support research in steady, high magnetic fields. This facility will be accessible by qualified users world-wide on the basis of proposal and review. The more prominent components of this system will be a 24-MW resistive insert and a 120-MJ superconducting outsert. But successful achievement of the performance goals for the 45-T Hybrid System will depend on a number of unique, state-of-the-art subsystems and components. This paper describes the requirements and specifications on the individual subsystems and components in the context of the overall performance gears and reviews the plan for putting the whole together. >

Kapitza conductance of aluminium and heat transport through subcooled He II

Abstract Heat transport measurements in a large diameter tube containing He II are reported. The range of temperatures investigated are from 1.7 K to 2.1 K with applied pressures up to the critical pressure, 0.23 MPa. Temperature gradients established in the liquid are compared with previous experimental work and the theory of mutual friction. The Gorter-Mellink mutual friction constant, A, is observed to increase with applied pressure. At 2.01 K, a 0.1 MPa increase in pressure results in a 13.5 ± 4% enhancement of A. The results are used to predict the pressure and temperature dependence of the peak heat flux. Simultaneous measurements of the surface heat transfer from high purity aluminum to He II are reported. Kapitza conductance, film boiling and recovery heat flux data are analyzed and compared to other results on similar systems. A correlation is observed between the recovery heat flux and the film boiling heat transfer coefficient.

Heat Transport in Forced Flow He II: Analytic Solution

There is considerable interest in the problem of forced flow He II particularly as it relates to the cooling of large magnet systems. The potential advantages of forced flow He II are an improved heat transport in the direction of flow and an ability to sweep away regions of He I created by major disturbances. There have been several experimental investigations of forced flow He II reported in the literature.1–3 In addition there has been one experiment4 which reported the induction of flow in a natural circulation cooling loop containing He II.

High heat flux Kapitza conductance of technical copper with several different surface preparations

Abstract Kapitza conductance values of technical copper with different surface treatments and for heat fluxes of up to 6 W cm −2 are reported. Five different surface preparations were studied: a, polished with 0.3 μm alumina powder; b, oxidized at room temperature in air for a period of one month; c, oxidized in air at 200°C for 40 min; d, coated with 50-50 PbSn solder; e, coated with a layer of GE7031 varnish. The variation of surface temperature with heat flux as well as the limiting values of Kapitza conductance for small temperature difference are determined. Relative to the polished samples, it is observed that the baked and solder coated samples have higher conductances and that the samples oxidized in the atmosphere show lower conductances. The surface temperature of the varnished samples is controlled mostly by the low thermal conductivity of the varnish.

Steady State Forced Convection Heat Transfer in He II

A study of forced convection heat transfer in superfluid helium (He II) is initiated to better understand the physical behavior of this process and to compare it with the more familiar He II heat transfer mechanism of internal convection. An experimental assembly is designed to achieve fluid flow by a motor-driven hydraulic pump which utilizes two stainless steel bellows. Each bellows is connected to one end of a copper tube, 3 mm in diameter and 2 m long. The system allows measurements of one dimensional heat and mass transfer where the measured quantities include: temperature profile and pressure drop. The variable quantities are the helium bath temperature, flow velocity and heat input. The helium bath is held at 1.8 K and under saturation pressure. The flow tube is heated at the middle and the flow velocity is varied up to 97 cm/s. The helium pressure is monitored at both ends of the tube and a friction factor is estimated for He II. Temperature measurements are made at seven evenly spaced locations along the tube. The experimental temperature profile is compared with a numerical solution of an analytical model developed for the problem under study.

NUMERICAL SOLUTION OF FORCED CONVECTION HEAT TRANSFER IN He II

A theoretical investigation of one-dimensional forced convection heat transfer in He II is conducted. The problem of interest involves a flow tube containing He II, which is heated at its midpoint along its length. Two modes of heating are analyzed: step function and square pulse. The one-dimensional He II energy equation is used to find the temperature distribution along the tube for both steady-state and transient situations. For the steady-state case, a numerical integration routine is used to obtain a solution, whereas for the solution of the transient case, a finite-difference scheme is developed. The numerical temperature profiles are then shown to compare well with the results of an experiment.

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.

Channel heat transfer in He II — steady state orientation dependence

Abstract Heat transfer measurements of a channel configuration containing He II are reported. The configuration is a rectangular cross-section channel heated uniformly over its length and open at both ends so that natural circulation can occur. The gap dimension and the angular orientation of the channel are variable. Enhanced heat transfer occurs in the lower portion were all obtained at a nominal bath temperature of 1.9 K and atmospheric pressure (p ≈1 bar † ).