The flow patterns of liquid inside nozzles have great effect on spray characteristics in flashing spray. A transparent nozzle was manufactured to investigate the flow characteristic inside nozzles during flashing spray and its effects on spray characteristics. The flow patterns of R134a inside the nozzle and spray outside the nozzle were recorded by a high-speed CCD camera under different injection pressure of 0.77

0.8

0.9 and 1.5 MPa. The relationship between the internal flow inside the nozzle and external flashing spray were analyzed. It was found that spray patterns will expand immediately around the exit of the nozzle when vaporization occurred inside the nozzle

while the further development of spray radius could be restricted in the same condition. The spray cone angle caused by internal flashing spray was smaller than that caused by external flashing spray in the same condition for the flashing spray of R134a which had high superheated degree at room temperature and atmospheric pressure. The internal flow pattern was extremely unstable under a certain scope of injection pressure

and it was helpful to form stabilized spray patterns when homogeneous bubble flow was formed inside the nozzle.