With deionized water as working fluid

ultrasonic particle detection system is applied to two-phase heat transfer process. The ultrasonic attenuation spectrum method is used to measure flow boiling in vertical narrow rectangular channel. The ultrasonic attenuation spectrum

the bubble size distribution and export rate of gas (dryness) under different mass flux of 2.22 kg/(m2?s)，2.86 kg/(m2?s) and 3.49 kg/(m2?s) in the narrow rectangular are obtained by theoretical model and inversion algorithm

respectively. The experiment results show that when the mass flow rate is constant

with an increase of the heating power

ultrasonic attenuation coefficient will increase under the same ultrasonic frequency

the value of D50 will increase and the distribution of dimensions will broaden. Under the same operating conditions

with an increase of the mass flow rate

the value of D50 will decrease and the distribution of dimensions will heighten and narrow. The degree of dryness measured by ultrasonic testing system is higher than the theoretical value

and the measurement are closed to the theoretical values when the dryness is small. The error increases when the dryness increases and the theoretical model should be adjusted in this case.