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Cryogenic engineering conference — International Cryogenic materials conference
Conferencereports Cryogenic engineering conferenceInternational Cryogenic materials conference San Diego, CA USA August 1981 The 1981 Cryogenic Engineering Conference jointly held with the International Cryogenic Materials Conference in San Diego attracted an exceptional attendance with over 300 contributed papers indicating a growing interest in cryogenic applications and materials. CEC Chairman, Dr T. Flynn opened the meeting with a dedication to Dr K. Timmerhaus for his 25 years of continuous and unrelenting service as editor of Advances in Cryogenics. Dr R. Fast will take up the editor's tasks to continue in the high quality tradition established. ICMC Chairman Dr W. Morris introduced the first of several outstanding plenary speakers, Dr S. Dean of Fusion Power Associates. Dr Dean discussed the prospects for fusion power as one of the candidates for providing the bulk of the world's long term energy needs. Several examples of cryogenic applications to fusion energy were cited such as large superconducting magnets, cryopumping and materials. An informative plenary talk was given by Dr A. Sherman on space cryogenic systems including passive radiators, solid cryogens, mechanical and magnetic coolers, and adsorption systems. Recent advancements included a 65 K Stifling cycle cooler with no rubbing parts, a one-year-lifetime liquid helium Dewar, and testing of solid hydrogen systems. Future applications were envisioned for gamma-ray and high energy astronomy, infrared astronomy, and space surveillance. Dr S. Van Sciver presented new and exciting research in super fluid helium. The basic heat transfer phenomenon was related to applications in superconducting magnets, as were the relative merits of saturated versus subcooled operations of Helium II. In a final plenary talk Dr F. Fickett covered an historical perspective on low temperature materials research. Structural and thermal components of cryogenic systems were the main topic, with practical superconductors included as well. In addition to the exceptional technical programme, a number of entertaining events were enjoyed by family and guests such as the world-famous Balboa Park, the San Diego Zoo and an evening dinner in the town of the Wild Animal Park. Overall the conference was one of our most successful, informative and enjoyable. Carl Henning CEC Programme Chairman
Superfluid helium research Presented were aspects of helium-II heat transfer in both steady-state and transient time domains, using geometries which ranged from microscopic 10/am capillaries and submillimeter slits up to tubes several mm in diameter. It seems
CRYOGENICS
. APRIL
1982
that counterflow convection of the normal and superfluid components leads to enhanced heat transfer below 2 K, which is now particularly interesting to designers of superconducting magnets. Several rather large scale facilities for investigating performance of magnets in superfluid helium were described in various papers. One group reported that a bath cooled magnet showed higher quench current in subcooled superfluid at 1 atm than under saturated conditions. Several authors reported good agreement between experimental results and calculations based on the Gorter-Mellink (GM) theory of mutual friction between the two fluid components. Transient measurements on bath cooled heaters indicate that when an intense heat flux is suddenly applied, the non-boiling superfluid state can persist for several seconds before transitions to nucleate and film boiling occur. Similarly, at the end of a heat pulse, a temporary recovery from film boiling in a channel can occur, even in the presence of a steady-state flux above the critical value. Vertical channels can tolerate greater initial pulse energy and steady-state post-heating than horizontal channels. One group noted thermal instabilities and oscillations at a constriction in a helium-lI filled channel with axial heat flow. Steady state observations on heat transfer through 1 atm helium-II in a narrow gap ( ~ 0.2 ram) between a heated surface and an insulator revealed that as the gap is increased, the film boiling critical heat flux is reduced, the critical temperature rise is increased, and a new regime of subcooled heat transfer appears between the GM convection and nucleate boiling states. On the other hand, other measurements on axial heat flow in 40 t~m microbore tubing show a peak heat flux over 10 W cm -2 in the liquid. It seems that a restricted geometry can inhibit heat transfer at the heater surface, but improve it through the liquid due to hydrodynamic effects. Several authors noted that in both steady state and transient time frames, heat transfer in helium-II becomes limited when the temperature of the heated surface approaches the lambda-point. S.W. Schwenterly
Helium refrigeration There were three separate sessions on refrigeration with some twenty seven papers programmed in this field. In the first session a number of papers dealt with design considerations of large helium refrigeration systems for superconducting facilities such as the Isabelle Ring at Brookhaven, the large Coil Test Facility at Oak Ridge, and the MFTF (Mirror Fusion Test Facility) at Livermore. This latter unit, built by CVI Corporation, is now on test and is designed to give 300 W at liquid helium temperature. For the Isabelle unit, an output of 24.8 kW below 4.2 K is needed indicating the scale of operation now needed in such projects.
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Superfluid helium research Presented were aspects of helium-II heat transfer in both steady-state and transient time domains, using geometries which ranged from microscopic 10/am capillaries and submillimeter slits up to tubes several mm in diameter. It seems
CRYOGENICS
. APRIL
1982
that counterflow convection of the normal and superfluid components leads to enhanced heat transfer below 2 K, which is now particularly interesting to designers of superconducting magnets. Several rather large scale facilities for investigating performance of magnets in superfluid helium were described in various papers. One group reported that a bath cooled magnet showed higher quench current in subcooled superfluid at 1 atm than under saturated conditions. Several authors reported good agreement between experimental results and calculations based on the Gorter-Mellink (GM) theory of mutual friction between the two fluid components. Transient measurements on bath cooled heaters indicate that when an intense heat flux is suddenly applied, the non-boiling superfluid state can persist for several seconds before transitions to nucleate and film boiling occur. Similarly, at the end of a heat pulse, a temporary recovery from film boiling in a channel can occur, even in the presence of a steady-state flux above the critical value. Vertical channels can tolerate greater initial pulse energy and steady-state post-heating than horizontal channels. One group noted thermal instabilities and oscillations at a constriction in a helium-lI filled channel with axial heat flow. Steady state observations on heat transfer through 1 atm helium-II in a narrow gap ( ~ 0.2 ram) between a heated surface and an insulator revealed that as the gap is increased, the film boiling critical heat flux is reduced, the critical temperature rise is increased, and a new regime of subcooled heat transfer appears between the GM convection and nucleate boiling states. On the other hand, other measurements on axial heat flow in 40 t~m microbore tubing show a peak heat flux over 10 W cm -2 in the liquid. It seems that a restricted geometry can inhibit heat transfer at the heater surface, but improve it through the liquid due to hydrodynamic effects. Several authors noted that in both steady state and transient time frames, heat transfer in helium-II becomes limited when the temperature of the heated surface approaches the lambda-point. S.W. Schwenterly
Helium refrigeration There were three separate sessions on refrigeration with some twenty seven papers programmed in this field. In the first session a number of papers dealt with design considerations of large helium refrigeration systems for superconducting facilities such as the Isabelle Ring at Brookhaven, the large Coil Test Facility at Oak Ridge, and the MFTF (Mirror Fusion Test Facility) at Livermore. This latter unit, built by CVI Corporation, is now on test and is designed to give 300 W at liquid helium temperature. For the Isabelle unit, an output of 24.8 kW below 4.2 K is needed indicating the scale of operation now needed in such projects.
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