An experimental study has been conducted to examine the boiling instabilities of convective flow in a vertical channel. A test section is made of stainless steel tube of 1.8m-length with inner diameter of 4.4mm. It is connected to the upper and the lower plenums in parallel with a bypass line. The liquid flows through the bypass line with the mass flow rate about 20 times lager than through the test section. R-113 is used as the working fluid. Variation of the oscillating phenomena was examined by changing the mass flow rate, inlet subcooling, inlet and exit flow restrictions, and the heat flux.
Different types of oscillations were observed depending on the heat flux conditions. Here, the oscillation with the high heat-flux condition was named as Mode II while that with the low heat-flux condition being called as Mode I.
Mode II is characterized by the sinusoidal shape with a regular period. There is a phase difference of 180˚between the oscillations of the inlet mass flow rate and the pressure drop in a heated channel. The flow becomes stable with increasing of the inlet flow restriction and/or decreasing of the exit flow restriction. Mode II oscillation is judged to be the Type II density wave oscillation, reported in the previous works, since it occurs at high heat-flux conditions.
On the other hand, Mode I oscillation appears at low heat-flux conditions; however it is not observed when the inlet flow restriction becomes very large. This mode is characterized by the irregular wave with a shorter period and transits to a stable mode as the heat flux is increased.
