| Summary: | The thesis describes the expansion process in a cylinder
and the accompanying transient flow through an orifice when compressed
air is discharged from the cylinder. The orifice which is
located at one end of the cylinder is small enough to prevent the
development of significant wave action.
The aim of the investigation is to study the behaviour of
flows through circular orifices under transient upstream conditions
and to compare such flows with those through similar orifices under
steady state conditions.
A critical review of previous work is included from which
it is evident that further experimental work is necessary both for
a better understanding of the nature of transient flow and to obtain
results of practical value. The experiments in the present investigation
have been designed from-dimensional considerations. The main
conclusions that have been made are as follows:
The expansion of the air in the cylinder is not reversible.
Gradients of temperature in the radial and axial directions are
quickly established after the commencement of discharge and heat is
transferred from the cylinder wall to the residual air. In practice
it is impossible to achieve a truly adiabatic wall.
An experimental correlation between the pressure
The expansion of the air in the cylinder is not reversible.
Gradients of temperature in the radial and axial directions are
quickly established after the commencement of discharge and heat is
transferred from the cylinder wall to the residual air. In practice
it is impossible to achieve a truly adiabatic wall.
An experimental correlation between the pressure and
weighted average temperature of the air in the cylinder during expansion
has been obtained. This relationship can be used to predict
the transient average temperature of the air from the instantaneous
pressure in the cylinder.
The transient mass flow through a given orifice, and the
corresponding discharge coefficient, have been found to be functions
of the length-diameter ratio of the orifice, the pressure ratio
across it and the heat transferred to the residual air. The latter
involves a consideration of the temporal sequence of the discharge
which makes it impossible to obtain general statements about
transient flows.
From dimensional considerations, and from experiments, it
has been possible to obtain hypothetical transient mass flows without
heat transfer. These flows are consistently lower than those
under steady state conditions when geometrical and physical
similarity is preserved.
Heat transfer to the residual air in the cylinder during
discharge increases the instantaneous mass flow through the orifice.
Its effect on the mass flow may be quite pronounced for relatively
slow discharges.
The effect on the transient mass flow of the lengthdiameter
ratio of an orifice has been found to be similar to that
for steady state conditions.
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