Two-Phase critical flow from pipes: a difficult accident to assess

The two-phase release of substances stored or conveyed as pressure liquefied gases in an accident of great interest in chemical and process industries and in transportation and its consequences can be also extremely serious owing to the quality (toxic or inflammable) of the accidentally released substance. As much interest is devoted to have reliable tools allowing to make a correct evaluation of the consequences, this study presents a new model which assumes different velocities for liquid and gas and evaluates the release by taking into consideration the flow pattern inside the pipe and the mixture quality too. A comparison between experimental data referring to critical discharges of freon 12, available in the open literature, and the predicted results obtained with the models most largely used in risk analysis, shows how big expected errors are