T h e influence of inert gas on performance characteristics of liquid metal heat pipe was experimentally studied over a wide range of gas loading. In this experiment, potassium was used as a working fluid and argon was loaded in the heat pipe. T h e loading amount of argon ranged in initial pressure 10-2-102Torr a t room temperature. As the results, the followings became evident.During a start-up, an axial heat flux of the heat pipe is reduced from that corresponding to the sonic vapor flow by the presence of inert gas accumulating in the condenser section. In the region of high initial gas pressure, an over-all thermal conductance of the heat pipe can be described with the model due to "flat-front", but, with decreasing initial gas pressure, the over-all thermal conductance deviates from the theoretical values obtained from the flat-front model and approaches to that corresponding to the sonic vapor flow. Also, the over-all thermal conductance is influenced by the effect of the gravitational force on the wick pcmping ability of the heat pipe and the decrease of the thermal conductance depends on the initial gas pressure.

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The experimental study was conducted to examine the applicability of boiling potassium two-phase flow to the blanket cooling of fusion power reactors. A high flux heater pin of 44 mm heating length and 6.5 mm 0. D. with eight thermocouples of 0.5 mm 0. D. was inserted from the bottom of a vertical channel which was made of a 4 m long, 14.9 mm I. D. and 17.5 mm 0. D. stainless steel tube and placed in a D. C. magnet of 50 em long poles. The experimental conditions were the heat flux: 0-67 W /cm 2 , the magnetic field strength: 0-1.8 T, the Ar cover gas pressure: 1.0 bar, the potassium level above heater: 1.8 m, and the temperature of upper unheated section: 400'C.In the absence of magnetic field, boiling occurred intermittently, repeating the cycles between superheating with moderate temperature fluctuation and desuperheating with condensing shock pulses. When a weak magnetic field was applied, the temperature fluctuation was enhanced by natural convection, the incipient boiling superheat was reduced, and the boiling pattern became continuous. With increasing the magnetic field strength, the fluctuation was suppressed and the incipient boiling superheat increased but tended to level off around 1.5 T. Violent incipient boiling caused by a large superheat inherent in liquid metals was mitigated by magnetohydrodynamic interaction under a transverse magnetic field of 1.0 T or larger, and subsequently followed by continuous saturation boiling with small fluctuation. No burn-out of the heater pin occurred in spite of symptom of dryout within the experimental range: q=67 W /cm 2 and B=l.5 T.

The experimental study was conducted to examine the applicability of boiling potassium two-phase flow to the blanket cooling of fusion power reactors. A high flux heater pin of 44 mm heating length and 6.5 mm 0. D. with eight thermocouples of 0.5 mm 0. D. was inserted from the bottom of a vertical channel which was made of a 4 m long, 14.9 mm I. D. and 17.5 mm 0. D. stainless steel tube and placed in a D. C. magnet of 50 em long poles. The experimental conditions were the heat flux: 0-67 W /cm 2 , the magnetic field strength: 0-1.8 T, the Ar cover gas pressure: 1.0 bar, the potassium level above heater: 1.8 m, and the temperature of upper unheated section: 400'C.In the absence of magnetic field, boiling occurred intermittently, repeating the cycles between superheating with moderate temperature fluctuation and desuperheating with condensing shock pulses. When a weak magnetic field was applied, the temperature fluctuation was enhanced by natural convection, the incipient boiling superheat was reduced, and the boiling pattern became continuous. With increasing the magnetic field strength, the fluctuation was suppressed and the incipient boiling superheat increased but tended to level off around 1.5 T. Violent incipient boiling caused by a large superheat inherent in liquid metals was mitigated by magnetohydrodynamic interaction under a transverse magnetic field of 1.0 T or larger, and subsequently followed by continuous saturation boiling with small fluctuation. No burn-out of the heater pin occurred in spite of symptom of dryout within the experimental range: q=67 W /cm 2 and B=l.5 T.

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