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Technical Briefs

Circulation in Blowdown Flows

[+] Author and Article Information
Jonathan I. Katz

 MITRE Corporation, 7515 Colshire Drive, McLean, VA 22102; and Department of Physics and McDonnell Center for the Space Sciences, Washington University, 1 Brookings Drive, St. Louis, MO 63130katz@wuphys.wustl.edu

This paper concerns pressure vessels that initially contain only gas. Blowdown of vessels that initially contain liquid or solid that flashes into vapor upon pressure release involves different phenomena.

J. Pressure Vessel Technol. 131(3), 034501 (Apr 07, 2009) (2 pages) doi:10.1115/1.3110038 History: Received April 30, 2008; Revised November 12, 2008; Published April 07, 2009

The blowdown (rapid release) of high pressure gas from a pressure vessel adiabatically cools the gas remaining in the vessel. The gas near the wall is warmed by conduction from the wall, producing radial temperature and density gradients that affect the flow, the mass efflux rate, and the thermodynamic states of both the outflowing and the contained gas. The resulting buoyancy-driven flow circulates the gas through the vessel and reduces, but does not eliminate, these gradients. The purpose of this technical brief is to estimate when blowdown cooling is rapid enough that the gas in the pressure vessel is neither isothermal nor isopycnic, though it remains isobaric. I define a dimensionless number, the buoyancy circulation number, that parametrizes these effects.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Flow during blowdown of a pressure vessel in which the boundary layer is warmed by thermal conduction from the wall. The adiabatically cooled gas in the interior of the vessel sinks, while the buoyant warmer gas in the boundary layer rises, some of it escaping through the exit orifice.

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