The thermosyphon is a type of heat exchanger that has been widely used in
many applications. The use of thermosyphons has been intensified in recent
years, mainly in the manufacture of solar collectors and various industrial
activities. A thermosyphon is a vertical sealed tube filled with a working
fluid, consisting of, from bottom to top, by an evaporator, an adiabatic
section, and a condenser. The study of geyser-boiling phenomena, which
occurs inside the thermosyphon is of extreme importance, therefore the
experimental analysis of the parameters related to the two-phase flow
(liquid-steam), such as void fraction, bubble frequency, bubble velocity,
and bubble length are necessary, since these parameters have a significant
influence on heat transfer. In this work, a pair of wire mesh sensors was
used, a relative innovative technology to obtain experimental values of the
reported quantities for measuring these parameters of slug flow in
thermosyphons. An experimental setup is assembled and the sensors are
coupled to the thermosyphon enabling the development of the experimental
procedure. Here is presented an experimental study of a glass thermosyphon
instrumented with two Wire-Mesh Sensors, in which the aforementioned slug
flow hydrodynamic parameters inherent to the geyser type boiling process are
measured. It was measured successfully, as a function of the heat load (110,
120, 130, 140, and 150W), the void fraction (instantly and average), liquid
film thickness, translation velocity of the elongated bubbles, lengths of
the bubbles, and the liquid slug (displaced by the bubble rise up). It was
observed that the higher the heat load, the lower is the bubble translation
velocity. For all heat loads, based on the measured length of liquid slug
(consequent displacement of liquid volume), caused by bubbles rise from
evaporator to condenser, it could be affirmed to some extent that both
boiling regime (pool and film) exist in the evaporator. The measured average
void fraction (80%) and liquid film thickness (around 2.5mm) during the
elongated bubble passages were approximately constant and independent of the
heat load.
Numerical Study of Hydrodynamic Characteristics of Gas–Liquid Slug Flow in Vertical Pipes
