Acta Polytechnica CTU Proceedings


doi:10.14311/AP.2016.4.0001
Acta Polytechnica CTU Proceedings 4:1–7, 2016 © Czech Technical University in Prague, 2016

available online at http://ojs.cvut.cz/ojs/index.php/app

STUDY OF IDENTIFICATION OF TWO-PHASE FLOW
PARAMETERS BY PRESSURE FLUCTUATION ANALYSIS

Ondrej Burian∗, Vaclav Dostal, Ladislav Vesely

Faculty of Mechanical Engineering, Czech Technical University in Prague, Technická 4, Praha 6, Czech Republic
∗ corresponding author: ondrej.burian@fs.cvut.cz

Abstract. This paper deals with an identification of a parameters of simple a pool boiling in a vertical
rectangular channel by analysis of pressure fluctuation. A small experimental facility about 9 kW
power, which was used for simulation of apool boiling phenomena and creation of steam-water volume
in this work is introduced. A several pressure fluctuations measurements and differential pressure
fluctuations measurements at various were carried out. Main changed parameters were a power of
heaters and a hydraulics resistance of a channel internals. A measured pressure data were statistically
analysed and compared with goal to find dependencies between parameters of a two-phase flow and
statistical properties of pressure fluctuation. At the end of this paper are summarized final results and
applicability of this method for parameters determination of two phase flow for pool boiling conditions
at ambient pressure is discused.

Keywords: two-phase flow, pressure fluctuation measurement, void fraction.

1. Introduction
Boiling of liquids is a high dynamic phenomena, which
is characterized as a phase change of a liquid phase
to a gaseous phase. The most common example of
that is boiling of water to water steam, which occurs
in many facilities in our life. It may exist in wide
range of parameters and regiments, which includes
pressure, temperature, heat flux, bulk temperature
etc. The one of the key parameters is a void fraction
which represents a share of steam fraction in overall
volume. The knowledge of this parameter is key for
identification other parameters of boiling and oper-
ational parameters of facilities which operate with
boiling phenomena like steam boilers, boiling water
reactors or steam generators.

One of a perspective method for identification a key
parameters of boiling and two-phase flow phenomena,
which is focused on analysis of measured differential
pressure and its a time fluctuation, is described in
this work. This method is based on fact that differ-
ential pressure between two measured locations in a
two-phase mixture located in some distance at above
is dependent on the void fraction. Void fraction in
volumetric form is defined as a ratio of a steam frac-
tion volume to overall a two-phase volume, see (1).
The density of a two-phase mixture can be expressed
by (2), where ρl is density of liquid fraction and ρg is
density of steam fraction.

α =
Vg
V

(1)

ρm = ρl(1 −〈α〉) + ρg〈α〉 (2)

Second assumption is that the value of this differ-
ential pressure is not stable in stable state, but it
fluctuated around some mean value. This dependency

is a result of influence of the void fraction on a hydro-
static pressure at measured locations – a measurement
points. Hydrostatic pressure of a two-phase volume
about some void fraction is value between hydrostatic
pressure of a liquid volume and a steam volume, which
decreases with increasing a void fraction. A pressure
fluctuation is a result of a process of a bubble genera-
tion and its flow throw the measured section.
If we find dependency between void fraction and

measured differential pressure, which is measured be-
tween two measurement points located at above in
some distance, we can use it like fundamental of a
method for determination of the void fraction. How-
ever more interesting may be an information about
boiling and two-phase flow parameters which we can
get from statistical analysis of fluctuation of measured
differential pressure. Research of this method, identifi-
cation advantages and disadvantages of this method is
subject of this research work which will be introduced
in this paper.
Due to a boiling and a two-phase flow are compli-

cated phenomenas, is impossible to determinate an
analytical solution with physical model of dependency
between void fraction and differential pressure. They
are complex phenomenas which are affected many
external and internal influences. From that reasons
as described at above was chose experimental way
which should give empirical view of scope to this prob-
lem. Using differential pressure as a parameter is
more useful than point pressure, because we do not
know position of a level of a two-phase mixture up
the measured points.
The beginning phase of this research project is fo-

cused on an experimental research at an ambient pres-
sure conditions. The aim of this phase is a verification
an initial assumptions, assessment a general values of

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