The above parameters are accounted for by the pertinent governing
equations which will be described in the next sub-Sections.
When the pressure on the shell-side is relieved via a relief device,
typically the pressure drops quickly depending on the combination
of fluids in the shell at the time of relief and on the bulk modulus of
the liquid on the shell-side. The main assumption in the treatment
to follow is that the effluent fluid from the ruptured tube(s) into the
shell side of the heat exchanger undergoes adiabatic expansion
(with increase in entropy) from the condition in the tube (high
pressure) to the prevailing condition in the shell (generally lower
pressure) at any given time during the rupture event. This adiabatic
expansion may entail flashing of the effluent fluid into vapour and
multiple liquid phases, where the contribution of each ought to be
considered in the formulation of the physical dynamic equations