Experiments have been performed for steam-air mixture injected from a circle nozzle fixed at the bottom of a cool water tank. Acoustic sound characteristic and gas volume fraction distribution around the nozzle exit have been measured. For this purpose, a waterproof microphone and a high speed camera have been employed. Fast Fourier Transform (FFT) of detected sound waves proves the existence of a few dominant frequencies whose strength are affected by both water subcooling and air content. Gas volume fraction in the whole fluid field was obtained through MATLAB image processing technique, which mainly contains image binaryzation and adding of a thousand of image matrixes. With the increase of air content as well as tank water temperature, the gas volume fraction decreases more slowly, in both axial and radial directions. The gas volume fraction profiles studied at three different transverse positions were able to be fitted into one single cure, suggesting the self-similarity of the gas volume fraction distribution. The air content and water temperature covered the range 1-10% and 310-340 K, respectively. All the measurements were carried out by varying steam flow rate in the range of 0.30-0.32 g/s and 0.42-0.44 g/s with the nozzle diameter of 1.6 mm. (C) 2015 Elsevier Ltd. All rights reserved.