Book Description

Excerpt from Heat Transfer and Flow of Helium in Channels: Practical Limits for Applications in Superconductivity The development of large superconducting devices is intimately related to the fluid mechanics and heat transfer characteristics of cryogenic helium. In the earliest successfully developed magnets for bubble chambers and accelerator beam transport and focussing, the main function of the helium was to cool the conductor matrix down, to stabilize it against flux jumps, and to provide a heat sink for the relatively low losses which occur in charging. The success of this phase of development of superconducting technol ogy is attested to by the existence of several such devices with 1000 hours or more of routine operation behind them The wide range of applications under consideration for the future, however, demands much more of the helium as a heat transfer medium, and will exercise the ingenuity of designers to the full. The simple expedient of immersing a device in a bath of liquid helium at a temperature close to 4 K will not suffice or may simply be impractical. Our research philosophy at the National Bureau of Standards has been to explore as far as possible all modes of application of helium as a heat transfer medium in order to preserve as many options as possible for the designer. As a consequence we are interested in all phases of helium and we are particularly interested in exploring the possible boundaries of operation imposed by the thermodynamic and transport properties of helium. In this paper, after a brief discussion of the relevant properties of helium, we consider some important characteristics of helium flowing in channels, since we anticipate that this mode of cooling in some form or other will be preferred over natural convection in future large devices. First we discuss heat transport to helium I above the critical pressure, then heat transport to helium I below the critical pressure. We then discuss some possibilities for cooling to lower temperatures by means of helium II. In the final section we consider the problem of flow stability and oscillations in channels cooled by forced flow of helium. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.