Thus, the mass flux of this flow into the shell depends on the
pressure and temperature of the tube-side fluid and on the flow
path to the rupture location. That is, if the rupture occurs at the
tube sheet, one side of the break can be treated as isentropic flow
through a nozzle (or orifice) while the other side can be treated as
adiabatic frictional (Fanno) flow through a tube of length L
depending on the assumed location of the tube-rupture. API 520,
Part 1 (2014) and API 521 (2014) provide a good guideline and
necessary equations for single- and two-phase flowcalculation. The
mass flux is calculated under the assumption of a homogeneous
equilibrium model (HEM), which was justified by Henry (1970) and
Henry and Fauske (1971). The mass flux through a tube follows a
slightly more complex procedure due to the effects of friction and
the location along the tube where flashing may occur as described
by Leung and Grolmes (1988) and Leung and Ciolek (1994). The
flow models developed by DIERS (Design Institute for Emergency
Relief Systems) can also be used.