DEVELOPMENT OF A NEW COOLING DESIGN DATABASE FOR SUPERCONDUCTING MAGNETS OF FUSION EXPERIMENTAL FACILITY

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Steady and unsteady heat transfer characteristics on single horizontal wires with the diameters ranged over 0.08 to 1.2 mm were studied experimentally and theoretically for wide ranges of experimental conditions to develop a new two dimensional cooling design database. Major results are as follows :1.Development of Test Cylinders Made of Special AlloyTest cylinders made of special alloys (Au-Mn, 0.9 atomic % ; Pt-Co, 0.5 atomic %) were developed to use the iestcylinder as well as the resistance thermometer. Steady-state heat transfer and unsteady heat tranfer caused by step heat input under saturated and subcooled conditions were obtained systematically by using these cylinders with the diameters ranged over 0.08 to 1.2 mm.2.Steady-state Heat Transfer Resultsa)Critical Heat Flux (CHF)The CHF in He II under saturated conditions are dependent on bulk liquid temperature and liquid head, H : for a fixed liquid temperature, CHF is higher for higher liquid, head, and that for a fixed liquid … More head increases with decreasing liuqid temperature from lambda point. It has a maximum at liquid tempreture of around 2 K and gradually decreases with further decreasing liquid temperature. The authors have presented the CHF correlation based on the solution for Gorter-Mellink equations. This correlation was based on the assumptions that the critical heat flux was determined by the condition that liquid in the vicintiy of the wire which was initially under a subcooled conditon due to pressure P_L(=P+rhogH) at the wire surface had reached the saturation temperature of lambda temperature. It was confirmed that this correlation predicts the CHF under wide range of conditions (pressure, liquid subcooling and cylinder diameter).b)Film Boiling Heat TransferTheoretical film boiling heat transfer correlation for horizontal cylinder was presented. Not only the experimental data by the authors but also the data by other workers for different cylinder diameters are in agreement with the theoretical values.3.Unsteady Heat Tranfer caused by Step Heat InputIt was first clarified by the authors that, when the stepwise heat input with the height higher than that corresponding to the steady-state critical heat flux is given to the test cylinder, quasi-steady state last a period of time on the extrapolation of steady-state Kapitza conductance curve and then jumps to film boiling. A general correlation which can evaluate the lifetime of the quasi-steady state for various wave for of the heat inputs was presented based on the experimental results for wide ranges of pressure, liquid subcooling and cylinder diameter. An absolute stability limit for magnet windings was given based on the correlation. Less