Technical Reports

An Experimental Investigation of the Discharge of a Flashing Liquid from a Finite Reservoir: A Fundamental Study of the Two-Phase Flow Phenomena Occurring During Venting from Rail Tank Cars

  • 01
  • Jan
  • 1985
AUTHOR: Federal Railroad Administration
OFFICE: RPD
SUBOFFICE: RPD-30
REPORT NUMBER: DOT/FRA/ORD-85/05
SUBJECT: Hazardous Materials
KEYWORDS: Two-Phase Flow; Pressure Vessel; Blowdown; Rail-Tank Car Venting; Two-Phase Boiling; Flashing Flow; Venting of Compressed Liquified Vapor
ABSTRACT: The design of pressure relief valves for railroad tank cars containing pressurized liquid commodities is dependent on knowledge of venting rates during accidents. In turn, development of an appropriate theoretical model requires knowledge of many properties which affect the venting rates of vapor, liquid and two-phase mixtures. Previous reports and technical papers on this phenomenon published by members of the Mechanical Engineering Department of the University of Maryland as part of the D.O.T. sponsored project have described experimental investigations of the blowdown of flashing liquids from finite vessels. In these studies the system mass, pressure, vertical temperature profile and mass flow rate were measured. This report describes experiments which expand upon previous studies to include measurements of horizontal temperature variations, quality of the two-phase mixture, bubble rise velocities and growth rates, fluid flow patterns and boiling phenomena during the blowdown. Venting tests were conducted with three different orifice sizes, four liquid fill fractions and two wall materials of different thermal conductivity. From this new data a detailed description of the two-phase blowdown is presented, including boiling and heat transfer effects. The essential visual features of the two phase flow and boiling were recorded with a high speed 16 mm movie camera. An edited film was produced and is available for future review of the phenomena described in this report.
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