• Volume 4, Issue 2

      April 1982,   pages  53-192

    • Materials processing in space — A brief review

      S Ramaseshan

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    • Methods of low gravity simulation

      J M Haynes

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      The dependence on gravity forces of both static and dynamic fluid behaviour is explained, and dimensionless numbers are defined which express the relative influence of gravitational and various other forces. Methods of reducing gravitational effects are outlined, including neutral buoyancy, free fall and orbital flight and their relative merits, in studies of various types of fluid behaviour, are compared.

    • Capillary equilibrium and stability in liquids under microgravity

      J M Haynes

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      The conditions governing capillary equilibrium and stability of a fluid interface are stated. A distinction is drawn between hydrostatic (or Laplace) and diffusional (or Kelvin) equilibria, which is often of practical importance in the behaviour of real liquids. In the light of these principles, the fluid physics experiments proposed for the first Spacelab payload are discussed, with particular reference to the rotational stability of a fluid cylinder in microgravity and to processes used to grow large single crystals of pure materials.

    • TheSpacelab fluid physics module

      J M Haynes

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    • Convection phenomena at reduced gravity of importance in space processing of materials

      Simon Ostrach

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      The basic aspects of convection processes are delineated. It is shown that even in weak gravitational fields buoyancy can induce fluid motions. Furthermore, at reduced-gravity other non-gravity forces such as surface or interfacial tensions,g-jitter, thermal-volume expansions, density differences due to phase changes, and magnetic and electric fields can induce fluid motions.

      The various types of flow possible with these various driving forces are described and criteria for determining the extent and nature of the resulting flows and heat transfer are presented. The various physical mechanisms that can occur separately and in combination are indicated and the present state of knowledge of each of the phenomena is outlined.

    • Motion induced by surface-tension gradients

      Simon Ostrach

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      The physical mechanisms of flows generated by surface-tension gradients are clearly defined and the relevant dimensionless parameters are derived. These are used to indicate the qualitative nature of possible flows.

    • An experimental study of surface-tension induced convection at reduced gravity

      Simon Ostrach

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      Fluid motions are induced by surface-tension gradients on the free surface of a liquid in a cylindrical container which is in free fall in a drop tower. Identical experiments are conducted in a normal gravitational environment. The motion in that case is due to natural convection. The ratio of surface-tension to buoyancy forces in the tests is of the order of 104 at reduced gravity conditions and 0·13 under normal gravity. In each case a two way flow occurs throughout most of the liquid. Comparison of the results from the two types of experiments is made in order to indicate differences in the flow details.

    • Thermal convection induced byg-jitter in space environment

      Simon Ostrach

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      The article discusses thermal convection in an enclosure induced by spacecraft vibrations (g-jitter). Two theoretical investigations are described. The conclusions are that if theg-jitter is decomposed into a time-mean part and an oscillatory part, the mean part is more important than the oscillatory part, in determining the flow field and heat transfer rate. Under normal circumstances (no manoeuvres, no intentional spinning of the spacecraft) theg-jitter generates predominantly oscillatory velocity and temperature fields with zero time-mean values. Theg-jitter can also generate secondary flows with non-zero mean but they are of much smaller order. Some implications of theg-jitter on materials processing in space are also discussed.

    • Electrochemical experiments in space

      S R Rajagopalan

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      The probable effects of rarefied atmosphere and near-zero gravity conditions that prevail in space, in relation to electrochemical experiments, are briefly discussed. The various space electrophoresis experiments are reviewed and discussed. Some possible additional electrochemical experiments are suggested.

    • Possible studies on adhesion in space

      G Venkataraman

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      This paper reviews possible experiments on adhesion that can be carried out in a space lab environment. After introducing the basic concepts of adhesion physics, the proposed European experiment on surface energy measurement by dynamic methods in space environment is discussed and reviewed. It is concluded that as of now more studies on adhesion in terrestrial environment are desirable than space experiments.

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