Incipient Boiling Pressure Pulse of Sodium under Forced Convection by Direct Heating

Abstract

An account is given of experiments on incipient boiling pressure pulses imparted by liquid sodium, performed in a forced convection loop. The sodium is heated by direct current applied to the liquid metal itself in a vertical tube of 14.9mm inner diameter through which the medium pumped. The experiments were carried out with the following ranges:
Input power: 6∼12kW, Pressure at condenser: 0.6∼1.0kg/cm²,
Inlet temperature: 780°∼850°C, Flow rate: 1.0∼3.5l/min
Typical pressure pulses registered during incipient boiling presented the form of damped oscillation. The initial pressure pulses were dependent on the location of boiling inception along the test section, the incipient boiling pattern and the degree of superheat. The initial pressure pulses observed were in the range of 0∼3.5kg/cm². The pressure pulses increased with the degree of superheat, which ranged 0°∼150°C.
The magnitudes of pressure pulses exceeded the saturation vapor pressure corresponding to the temperature of superheated liquid. Consideration of a simplified model indicated that, during incipient boiling, the pressure in the vapor phase oscillates while approaching asymptotically the saturation pressure.