Boiling of Potassium in Vertical Tube under Transverse Magnetic Field

Abstract

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.