| Budget Amount *help |
¥5,000,000 (Direct Cost: ¥5,000,000)
Fiscal Year 1991: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1990: ¥3,900,000 (Direct Cost: ¥3,900,000)
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| Research Abstract |
At present, good understanding of heat transfer of cryogenic liquids is needed to prepare for advent of superconducting magnets made of high Tc superconducting materials. In this research, first, boiling heat transfer of coolant in natural-convection cooling-channels in superconducting magnets was investigated experimentally for liquid nitrogen. As the result, an equation correlating critical heat flux (CHF) to the channel gap was derived, and it was shown that the equation predicted correctly the critical heat flux in rectangular, circular, and annular channels for both liquid nitrogen and helium. Second, as a base of the critical-current margin design criterion proposed by lwasa, a model predicting the take-off conditions of conductor temperature was developed, and it was shown that the model can predict correctly the take-off conditions for liquid helium and water. Coupling this model with the CHF correlation derived in the research, it became possible to predict approximately the take-off condition in cooling channels. Finally, to enhance the critical heat flux in a cooling channel, the effect of electric field applied between the channel walls was investigated. The results showed that the critical heat flux was increased by applying electric field between the channel walls. Based on the results stated above, a novel method to improve the stability of current-carrying superconductors was proposed. In the method, it was proposed that to suppress normal-zone propagation, heat transfer of coolant adjacent to normal zone was enhanced by imposing an electric field locally between the conductor and an electrode if the normal transition was detected by acoustic emission. The method proposed in the study is considered to be superior to conventional methods of stabilization, because this method makes possible to decrease the copper ratio.
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