Boilers are frequently used in agricultural engineering. After micro cracks appear on the wall of the boiler for high
pressure saturated liquor, the containing liquid will be overheated, rapidly boiled and expanded, which may result in
explosion of the whole container. The evolving processes differ greatly by cracking conditions. In the experiment
conducted in the this article, we made a small sized experimental device and applied high speed photography technology
observing the simulated fierce boiling process of the high temperature and high pressure saturated water under overheat
condition when micro cracking appears on boiler wall. According to our study, lower depressurization rate will suppress
the boiling intensity of the overheated liquid and slow the growth of bubbles, decelerating the expansion of the
two-phase flow compared with the boiling liquid expanding vapor explosion. The magnitude of overpressure in the
container is also relatively smaller than overpressure in BLEVE.
Experiments of flame propagation in a small, closed rectangular duct with a 90° bend were performed for a propane-air
mixture. The high speed camera and Schlieren techniques were used to record images of flame propagation process in
the combustion pipe. Meanwhile, the fine thermocouples and ion current probes were applied to measure the temperature
distribution and reaction intensity of combustion. The characteristics of propane-air flame and its microstructure were
analyzed in detail by the experimental results. In the test, the special tulip flame formation was observed. Around the
bend, the flame tip proceeded more quickly at the lower side with the flame front elongated toward the axial direction.
And transition to turbulent flame occurred. It was suggested that fluctuations of velocity, ion current and temperature
were mainly due to the comprehensive effects of multi-wave and the intense of turbulent combustion.
In the study of boiling liquid expanding vapor explosion (BLEVE), the critical point to interpret the mechanism of the
disaster is to analyze the phase transition of the superheated liquid in the container and the motions of the medium during
the first several or several tens of milliseconds after the explosion from the microscopic angle of view. In the study
recorded in this paper, a BLEVE simulative device was made. Using high-speed camera, the instant explosive boiling in
the liquor phase space and the formation and development of the high speed two-phase flow were observed at the
moment of the container broken in explosion, the growing and moving speed of the bubble in the liquor phase space
were measured, and the influence of the energy released by blasted bubble nucleate in the early stages on the boiling
characteristics of the superheated liquid and the overpressure disciplines in the container were analyzed. The study shows
that in a BLEVE process, the boiling of superheated liquid does not present in the form of volume boiling, but presents
as a progressive process with several steps that starts from the surface and develops over time.
In order to explore the flame propagation characteristics and tulip flame formation mechanism of premixed methane/air
mixture in horizontal rectangular ducts, the techniques of Schlieren and high-speed video camera are used to study the
flame behaviors of the premixed gases in a closed duct and opened one respectively, and the propagation characteristics
in both cases and the formation mechanism of the tulip flame are analyzed. The results show that, the propagation flame
in a closed duct is prior to form a tulip flame structure than that in an opened duct, and the tulip flame structure
formation in a closed duct is related to the flame propagation velocity decrease. The sharp decrease of the flame
propagation velocity is one of the reasons to the tulip flame formation, and the decrease of the flame propagation
velocity is due to the decrease of the burned product flow velocity mainly.
KEYWORDS: Liquids, Sensors, High speed photography, Video, Cameras, High speed cameras, Video processing, Data acquisition, Water, Temperature metrology
The liquefied-petroleum gas tank in some failure situations may release its contents, and then a series of hazards with
different degrees of severity may occur. The most dangerous accident is the boiling liquid expanding vapor explosion
(BLEVE). In this paper, a small-scale experiment was established to experimentally investigate the possible processes
that could lead to a BLEVE. As there is some danger in using LPG in the experiments, water was used as the test fluid.
The change of pressure and temperature was measured during the experiment. The ejection of the vapor and the sequent
two-phase flow were recorded by a high-speed video camera. It was observed that two pressure peaks result after the
pressure is released. The vapor was first ejected at a high speed; there was a sudden pressure drop which made the liquid
superheated. The superheated liquid then boiled violently causing the liquid contents to swell, and also, the vapor
pressure in the tank increased rapidly. The second pressure peak was possibly due to the swell of this two-phase flow
which was likely to violently impact the wall of the tank with high speed. The whole evolution of the two-phase flow
was recorded through photos captured by the high-speed video camera, and the "two step" BLEVE process was
confirmed.
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