scholarly journals Effects of Ambient Pressure on the Instability of a Liquid Boiling Explosively at the Superheat Limit

1986 ◽  
Vol 108 (2) ◽  
pp. 418-424 ◽  
Author(s):  
D. Frost ◽  
B. Sturtevant
Keyword(s):  
Atmospheric Pressure ◽  
Bubble Growth ◽  
Absolute Stability ◽  
Pressure Field ◽  
Ambient Pressure ◽  
Small Temperature ◽  
Instability Theory ◽  
Two Stages ◽  
Single Droplets ◽  
Superheat Limit

The effect of ambient pressure on the intrinsic instability of rapid vaporization in single droplets boiling explosively at the limit of superheat has been studied experimentally and theoretically. The instability that distorts the evaporating interface and substantially enhances the mass flux at atmospheric pressure is suppressed at high pressure. The radiated pressure field is two orders of magnitude smaller from stabilized bubbles than from unstable. At intermediate pressures bubble growth occurs in two stages, first stable, then unstable. The Landau–Darrieus instability theory predicts absolute stability at atmospheric pressure for a spherical bubble, whereas the theory for planar interfaces yields results in general agreement with observation. The sensitivity of the instability to temperature suggests that small temperature nonuniformities may be responsible for quantitative departures of the behavior from predictions.

Effect of Ambient Pressure on Bubble Growth in Micro-Channel and Its Pumping Effect

2010 ◽  
Author(s):  
F. Mobadersani ◽  
M. Eskandarzade ◽  
S. Azizi ◽  
S. Abbasnezhad
Keyword(s):  
Atmospheric Pressure ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Stokes Equations ◽  
Ambient Pressure ◽  
Three Dimensional ◽  
Numerical Results ◽  
Micro Channel ◽  
Bubble Volume ◽  
Explosive Boiling

Over the last two decades, explosive boiling has been widely used in industry, many researches have been dedicated to study its aspects. Some applications of explosive boiling are in thermal bubble jet printers, micro-injectors and micro-medicine devices. In such applications ambient pressure is not usually the atmospheric pressure. To have a good design, there is a great need to simulate the bubble growth under non-atmospheric pressure. In this research a three dimensional numerical analysis of growth and collapse of a bubble in a micro-channel under four different ambient pressures is presented. Flow3D package which solves the Navier-Stokes equations with surface tension effects, is used to reach this aim. Leinhard’s equation is used to compute the temperature of explosive boiling in various pressures. It is considered that the internal pressure of the bubble has an exponential form. Bubble dynamics relations have been used to obtain time constant of the bubble. The bubble volume and the flow rates from both ends of the microchannel are obtained. It has been shown that increasing in the ambient pressure causes decreasing in the bubble volume. Numerical results for the growth and collapse of the bubble in the micro-channel are compared with those of experiments under similar conditions. Results of the growth and collapse of the bubble in the micro-channel of a printer, BJ-80, have been used to validation. Comparisons show that the bubble evolution is well predicted by the numerical results.

scholarly journals Interactive Effects in Two-Droplets Combustion of RP-3 Kerosene under Sub-Atmospheric Pressure

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1229
Author(s):  
Hongtao Zhang ◽  
Zhihua Wang ◽  
Yong He ◽  
Jie Huang ◽  
Kefa Cen
Keyword(s):  
Burning Rate ◽  
Atmospheric Pressure ◽  
High Speed ◽  
Ambient Pressure ◽  
Interactive Effects ◽  
Propagation Time ◽  
High Speed Camera ◽  
Single Droplet ◽  
Fuel Droplets ◽  
Spacing Distance

To improve our understanding of the interactive effects in combustion of binary multicomponent fuel droplets at sub-atmospheric pressure, combustion experiments were conducted on two fibre-supported RP-3 kerosene droplets at pressures from 0.2 to 1.0 bar. The burning life of the interactive droplets was recorded by a high-speed camera and a mirrorless camera. The results showed that the flame propagation time from burning droplet to unburned droplet was proportional to the normalised spacing distance between droplets and the ambient pressure. Meanwhile, the maximum normalised spacing distance from which the left droplet can be ignited has been investigated under different ambient pressure. The burning rate was evaluated and found to have the same trend as the single droplet combustion, which decreased with the reduction in the pressure. For every experiment, the interactive coefficient was less than one owing to the oxygen competition, except for the experiment at L/D0 = 2.5 and P = 1.0 bar. During the interactive combustion, puffing and microexplosion were found to have a significant impact on secondary atomization, ignition and extinction.

Effect of Pressure on Bubble Growth Within Liquid Droplets at the Superheat Limit

1982 ◽  
Vol 104 (4) ◽  
pp. 750-757 ◽  
Author(s):  
C. T. Avedisian
Keyword(s):  
Vapor Bubble ◽  
Bubble Growth ◽  
High Speed ◽  
Ambient Pressure ◽  
Organic Liquid ◽  
Liquid Droplets ◽  
Growth Data ◽  
Two Phase ◽  
Photographic Evidence ◽  
Good Agreement

A study of high-pressure bubble growth within liquid droplets heated to their limits of superheat is reported. Droplets of an organic liquid (n-octane) were heated in an immiscible nonvolatile field liquid (glycerine) until they began to boil. High-speed cine photography was used for recording the qualitative aspects of boiling intensity and for obtaining some basic bubble growth data which have not been previously reported. The intensity of droplet boiling was found to be strongly dependent on ambient pressure. At atmospheric pressure the droplets boiled in a comparatively violent manner. At higher pressures photographic evidence revealed a two-phase droplet configuration consisting of an expanding vapor bubble beneath which was suspended a pool of the vaporizing liquid. A qualitative theory for growth of the two-phase droplet was based on assuming that heat for vaporizing the volatile liquid was transferred across a thin thermal boundary layer surrounding the vapor bubble. Measured droplet radii were found to be in relatively good agreement with predicted radii.

Collective Effects on the Growth of Vapor Bubbles in a Superheated Liquid

1984 ◽  
Vol 106 (4) ◽  
pp. 486-490 ◽  
Author(s):  
G. L. Chahine ◽  
H. L. Liu
Keyword(s):  
Collective Behavior ◽  
Bubble Growth ◽  
Theoretical Study ◽  
Pressure Field ◽  
Bubble Radius ◽  
Significant Inhibition ◽  
Collective Effects ◽  
Superheated Liquid ◽  
Vapor Bubbles ◽  
Bubble Interaction

The problem of the growth of a spherical isolated bubble in a superheated liquid has been extensively studied. However, very little work has been done for the case of a cloud of bubbles. The collective behavior of the bubbles departs considerably from that of a single isolated bubble, due to the cumulative modification of the pressure field from all other bubbles. This paper presents a theoretical study on bubble interaction in a superheated liquid during the growth stage. The solution is sought in terms of matched asymptotic expansions in powers of ε, the ratio between rb0, a characteristic bubble radius and l0, the interbubble distance. Numerical results show a significant inhibition of the bubble growth rate due to the presence of interacting bubbles. In addition, the temperature at the bubble wall decreases at a slower rate. Consequently, the overall heat exchange during the bubble growth is reduced.

scholarly journals Decoupling of ground level pressures observed in Italian volcanoes: are they driven by space weather geo-effectiveness?

2014 ◽  
Vol 57 (3) ◽  
Author(s):  
Paolo Madonia ◽  
Paolo Romano ◽  
Salvatore Inguaggiato
Keyword(s):  
Space Weather ◽  
Atmospheric Pressure ◽  
Pressure Field ◽  
Ground Level ◽  
Total Solar Irradiance ◽  
Weather Parameters ◽  
Sun Activity ◽  
Fft Analysis ◽  
Sunspot Groups

<p>Investigations on correlation drops between near-ground atmospheric pressures measured at sea level and at higher altitudes on Italian volcanoes have been carried out. We looked for perturbations of the atmospheric pressure field driven by volcanic activity, but not excluding possible external triggers for the observed anomalies. Decorrelations between atmospheric pressures measured at Stromboli Island in stations located at different altitudes (years 2002-10) have been analysed and compared with data from other volcanic (Vesuvius) and non volcanic (Mt. Soro) orographic structures. We investigated as their possible triggers volcanic, meteorological and space weather parameters, with particular attention to Total Solar Irradiance (TSI), Kp index and Forbush decreases. Pressure decorrelations seems to be driven by astronomic cycles, with maxima in summer and minima in winter. A further contribution was found, seemingly assignable to TSI anomalies, with correlation minima occurring 12 hours after these but only during phases of high Sun activity. Moreover, during the same phases a main periodicity of about 27 days in pressure decorrelations was revealed by FFT analysis. This period is the same of the Sun Carrington rotation, expressing the periodic reappearance of sunspot groups on Sun’s surface. The strong similarity between recurrences of sunspot number and atmospheric pressure anomalies further supports the role of the former as a possible trigger for the latter.</p>

scholarly journals Vertical Field Emission Air-Channel Diodes and Transistors

Micromachines ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 858 ◽  
Author(s):  
Wen-Teng Chang ◽  
Hsu-Jung Hsu ◽  
Po-Heng Pao
Keyword(s):  
Metal Oxide ◽  
Atmospheric Pressure ◽  
High Speed ◽  
Ambient Pressure ◽  
Electron Flow ◽  
Mean Free Path ◽  
Oxide Semiconductor ◽  
Radiation Environment ◽  
Reduced Pressure ◽  
Transport Distance

Vacuum channel transistors are potential candidates for low-loss and high-speed electronic devices beyond complementary metal-oxide-semiconductors (CMOS). When the nanoscale transport distance is smaller than the mean free path (MFP) in atmospheric pressure, a transistor can work in air owing to the immunity of carrier collision. The nature of a vacuum channel allows devices to function in a high-temperature radiation environment. This research intended to investigate gate location in a vertical vacuum channel transistor. The influence of scattering under different ambient pressure levels was evaluated using a transport distance of about 60 nm, around the range of MFP in air. The finite element model suggests that gate electrodes should be near emitters in vertical vacuum channel transistors because the electrodes exhibit high-drive currents and low-subthreshold swings. The particle trajectory model indicates that collected electron flow (electric current) performs like a typical metal oxide semiconductor field effect-transistor (MOSFET), and that gate voltage plays a role in enhancing emission electrons. The results of the measurement on vertical diodes show that current and voltage under reduced pressure and filled with CO2 are different from those under atmospheric pressure. This result implies that this design can be used for gas and pressure sensing.

Inflammability and Electrical Studies of Foams Which may Occur at Altitude by De-Aeration of Aviation Turbine Fuels

1959 ◽  
Vol 63 (586) ◽  
pp. 581-588 ◽  
Author(s):  
B. V. Poulston ◽  
A. Thomas
Keyword(s):  
High Altitude ◽  
Sea Level ◽  
Atmospheric Pressure ◽  
Ambient Pressure ◽  
Electrical Charge ◽  
Air Bubbles ◽  
Electrical Studies ◽  
To Come ◽  
Short Time

Air dissolves in aircraft fuels to an extent directly proportional to the ambient pressure, so that when fuel which has been stored at sea-level atmospheric pressure is taken up to a high altitude, there is a tendency for air to come out of solution. In certain circumstances, which are later described in detail, air bubbles can be liberated very violently from fuels in aircraft tanks at high altitude and a thick foam can form on the surface for a short time.The production of fuel foams by degassing has posed a certain problem; foams, being intimate mixtures of air and fuel, may well be inflammable; furthermore, the rising of air bubbles through fuel can result in the accumulation of electrical charge in the foam giving rise to the possibility of a source of ignition.

scholarly journals Polymer track membranes for atmospheric pressure field extraction of ions from liquid solutions

2010 ◽  
Vol 68 (1) ◽  
pp. 96-100
Author(s):  
A.A. Balakin ◽  
E.A. Buido ◽  
M.I. Markin ◽  
L.I. Novikova ◽  
M.A. Baldwin
Keyword(s):  
Atmospheric Pressure ◽  
Pressure Field ◽  
Track Membranes ◽  
Liquid Solutions

Problems related to the tests of resistance and strength of military equipment in reduced atmospheric pressure conditions

2019 ◽  
Vol 124 ◽  
pp. 151-159
Author(s):  
Patryk Płochocki ◽  
Mateusz Makarewicz ◽  
Przemysław Simiński
Keyword(s):  
High Altitude ◽  
Working Conditions ◽  
Atmospheric Pressure ◽  
Ambient Pressure ◽  
Air Transport ◽  
Normative Documents ◽  
Military Equipment ◽  
The Subject

This article is about military equipment research in conditions of reduced atmospheric pressure. Reported cases of equipment damage during work at high altitude or air transport show the need to perform research on phenomena occurring during storage, transport and operation of equipment at a reduced ambient pressure. One of the fragments of the article is devoted to the records contained in normative documents regarding the subject of the study. In addition, an exemplary experiment was made, the purpose of which was to illustrate some of the effects associated with the use of the equipment in the above-mentioned working conditions.

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