scholarly journals Subcritical and Supercritical Droplet Evaporation within a Zero Gravity Environment; On the Discrepancies between Theoretical and Experimental Results

2009 ◽  
Vol 1 (3) ◽  
pp. 317-338 ◽  
Author(s):  
Hongtao Zhang ◽  
Vasudevan Raghavan ◽  
George Gogos
Keyword(s):  
High Pressure ◽  
Ambient Pressure ◽  
Local Maximum ◽  
Droplet Evaporation ◽  
Experimental Results ◽  
Spherically Symmetric ◽  
Transient Effects ◽  
Ambient Temperatures ◽  
Wide Range ◽  
Thermo Physical Properties

A comprehensive axisymmetric numerical model has been developed to study high pressure droplet evaporation. In this model, high pressure transient effects, variable thermo-physical properties and inert species solubility in the liquid-phase are considered. First, the axisymmetric model has been utilized to explain the discrepancy between theoretical and experimental results on microgravity droplet evaporation that has been reported in the literature [J.R. Yang and S.C. Wong, Ref. 35]. In addition, this effort led to a thorough validation of the model against the most extensive microgravity experimental data available in the literature on droplet evaporation. Second, the validated model has been utilized to investigate spherically symmetric droplet evaporation for a wide range of ambient pressures and temperatures. The predictions show that the average droplet evaporation constant decreases with ambient pressure at sub-critical ambient temperatures, becomes insensitive to pressure at ambient temperatures around the critical temperature of the fuel and presents a local maximum while increasing with the ambient pressure at super-critical ambient temperatures.

Fuel Droplet Evaporation in a Supercritical Environment

2002 ◽  
Vol 124 (4) ◽  
pp. 762-770 ◽  
Author(s):  
G. S. Zhu ◽  
S. K. Aggarwal
Keyword(s):  
Experimental Data ◽  
Phase Equilibrium ◽  
Ambient Pressure ◽  
Droplet Surface ◽  
Fuel Vapor ◽  
Phase Solubility ◽  
Liquid Density ◽  
Ambient Temperatures ◽  
Droplet Vaporization ◽  
Wide Range

This paper reports a numerical investigation of the transcritical droplet vaporization phenomena. The simulation is based on the time-dependent conservation equations for liquid and gas phases, pressure-dependent variable thermophysical properties, and a detailed treatment of liquid-vapor phase equilibrium at the droplet surface. The numerical solution of the two-phase equations employs an arbitrary Eulerian-Lagrangian, explicit-implicit method with a dynamically adaptive mesh. Three different equations of state (EOS), namely the Redlich-Kwong (RK), the Peng-Robinson (PR), and Soave-Redlich-Kwong (SRK) EOS, are employed to represent phase equilibrium at the droplet surface. In addition, two different methods are used to determine the liquid density. Results indicate that the predictions of RK-EOS are significantly different from those obtained by using the RK-EOS and SRK-EOS. For the phase-equilibrium of n-heptane-nitrogen system, the RK-EOS predicts higher liquid-phase solubility of nitrogen, higher fuel vapor concentration, lower critical-mixing-state temperature, and lower enthalpy of vaporization. As a consequence, it significantly overpredicts droplet vaporization rates, and underpredicts droplet lifetimes compared to those predicted by PR and SRK-EOS. In contrast, predictions using the PR-EOS and SRK-EOS show excellent agreement with each other and with experimental data over a wide range of conditions. A detailed investigation of the transcritical droplet vaporization phenomena indicates that at low to moderate ambient temperatures, the droplet lifetime first increases and then decreases as the ambient pressure is increased. At high ambient temperatures, however, the droplet lifetime decreases monotonically with pressure. This behavior is in accord with the reported experimental data.

Fuel Droplet Evaporation in a Supercritical Environment

1999 ◽  
Author(s):  
G. S. Zhu ◽  
S. K. Aggarwal
Keyword(s):  
Experimental Data ◽  
Phase Equilibrium ◽  
Ambient Pressure ◽  
Droplet Surface ◽  
Fuel Vapor ◽  
Phase Solubility ◽  
Liquid Density ◽  
Ambient Temperatures ◽  
Droplet Vaporization ◽  
Wide Range

This paper reports a numerical investigation of the transcritical and supercritical droplet vaporization phenomena. The simulation is based on the time-dependent conservation equations for liquid and gas phases, pressure-dependent variable thermophysical properties, and a detailed treatment of liquid-vapor phase equilibrium at the droplet surface. The numerical solution of the two-phase equations employs an arbitrary Eulerian-Lagrangian, explicit-implicit method with a dynamically adaptive mesh. Three different equations of state (EOS), namely the Redlich-Kwong (RK), the Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) EOS, are employed to represent phase equilibrium at the droplet surface. In addition, two different methods are used to determine the liquid density. Results indicate that the predictions of RK-EOS are significantly different from those obtained by using the RK-EOS and SRK-EOS. For the phase-equilibrium of n-heptane-nitrogen system, the RK-EOS predicts higher liquid-phase solubility of nitrogen, higher fuel vapor concentration, lower critical-mixing-state temperature, and lower enthalpy of vaporization. As a consequence, it significantly overpredicts droplet vaporization rates, and underpredicts droplet lifetimes compared to those predicted by PR- and SRK-EOS. In contrast, predictions using the PR-EOS and SRK-EOS show excellent agreement with each other and with experimental data over a wide range of conditions. A detailed investigation of the transcritical droplet vaporization phenomena indicates that at low to moderate ambient temperatures, the droplet lifetime first increases and then decreases as the ambient pressure is increased. At high ambient temperatures, however, the droplet lifetime decreases monotonically with pressure. This behavior is in accord with the reported experimental data.

An Accurate and Simple Approach to Allow for the Transient Temperature Gradient in a Vaporizing Droplet

2012 ◽  
Author(s):  
Alexander Snegirev ◽  
Victor Talalov
Keyword(s):  
Temperature Gradient ◽  
Life Time ◽  
Droplet Evaporation ◽  
Transient Temperature ◽  
Internal Temperature ◽  
Ambient Temperatures ◽  
Wide Range ◽  
Order Polynomial ◽  
Volatile Liquid ◽  
Evaporation Dynamics

The purpose of this work is to analyze the importance of considering internal temperature gradient in modeling droplet evaporation, and to demonstrate performance of simplified methods in which the temperature gradient is approximately taken into account. Based on three characteristic time scales, two dimensionless criteria have been identified which determine magnitude of the internal temperature gradient and its effect on the evaporation dynamics. Numerical values of these criteria in a wide range of ambient temperatures show that the effect of the internal temperature gradient is more pronounced in more volatile liquid at higher ambient temperatures. Although droplet life time predictions are not sensitive to the internal temperature gradient, its effect might be strong at the initial stages of droplet evaporation, and this substantiates the need in robust and computationally inexpensive methods to take it into account. Two simple and yet accurate approaches (quasi-steady higher order polynomial approximation and the integral balance method) have been favourably tested and recommended for use in CFD spray modeling.

Mechanical Behavior of a Metal Matrix Nanocomposite Synthesized by High-Pressure Torsion via Diffusion Bonding

2016 ◽  
Vol 879 ◽  
pp. 1068-1073
Author(s):  
Han Joo Lee ◽  
Jae Kyung Han ◽  
Byung Min Ahn ◽  
Megumi Kawasaki ◽  
Terence G. Langdon
Keyword(s):  
Mechanical Properties ◽  
High Pressure ◽  
Metal Matrix ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Ambient Temperatures ◽  
Metal Matrix Nanocomposite ◽  
Wide Range ◽  
Zk60 Magnesium Alloy ◽  
Matrix Nanocomposite

High-pressure torsion (HPT) is one of the major severe plastic deformation (SPD) procedures where disk metals generally achieve exceptional grain refinement at ambient temperatures. HPT has been applied for the consolidation of metallic powders and bonding of machining chips whereas very limited reports examined the application of HPT for the fabrication of nanocomposites. An investigation was initiated to evaluate the potential for the formation of a metal matrix nanocomposite (MMNC) by processing two commercial metal disks of Al-1050 and ZK60 magnesium alloy through HPT at room temperature. Evolutions in microstructure and mechanical properties including hardness and plasticity were examined in the processed disks with increasing numbers of HPT turns up to 5. This study demonstrates the promising possibility for using HPT to fabricate a wide range of hybrid MMNCs from simple metals.

scholarly journals Lichtabsorption von oxidischen Silber(I)-Verbindungen / Light Absorption of Silver(I)-oxides

1984 ◽  
Vol 39 (6) ◽  
pp. 739-743 ◽  
Author(s):  
Claus Friebel ◽  
Martin Jansen
Keyword(s):  
High Pressure ◽  
Charge Transfer ◽  
Low Temperature ◽  
Absorption Edge ◽  
Diffuse Reflectance ◽  
Static Pressure ◽  
Ambient Pressure ◽  
Partial Structures ◽  
Wide Range ◽  
Charge Transfer Transitions

AbstractDiffuse reflectance spectra of Ag2SO4, Ag3PO4, Ag2CO3, Ag2Ge2O5, AgBO2, Ag3BO3-II, Ag6Si2O7, Ag10Si4O13 and Ag10Ge4O13 in the region ν̄ = 10000-40000 cm-1 and generally at 298 K and ambient pressure were measured. Additional spectra were recorded at 5 K for Ag3BO3 and Ag3PO4, and under application of a static pressure of 80 kbar for Ag10Si4O13. As a common feature all spectra show a steep absorption edge, which is only structured in singular cases. The edges appear in the remarkably wide range from 33100 cm-1 (Ag2SO4) to 13500 cm-1 (Ag10Ge4O13). As the shifts correlate with the dimensions of the cluster-like silver partial structures, the absorptions have been attributed to 4d→5s band-band transitions, an interpretation, which is in agreement with the low temperature and high pressure spectra. However, effects originating from charge-transfer transitions cannot be absolutely excluded.

scholarly journals Deviations from classical droplet evaporation theory

2021 ◽  
Vol 477 (2251) ◽  
pp. 20210078
Author(s):  
Joshua Finneran ◽  
Colin P. Garner ◽  
François Nadal
Keyword(s):  
Droplet Evaporation ◽  
Transient Effects ◽  
Predictive Tool ◽  
Transient Regimes ◽  
Wide Range ◽  
Classical Models ◽  
Cold Vapour ◽  
Input Domain ◽  
Steady Temperature Field ◽  
Transient Models

In this article, we show that significant deviations from the classical quasi-steady models of droplet evaporation can arise solely due to transient effects in the gas phase. The problem of fully transient evaporation of a single droplet in an infinite atmosphere is solved in a generalized, dimensionless framework with explicitly stated assumptions. The differences between the classical quasi-steady and fully transient models are quantified for a wide range of the 10-dimensional input domain and a robust predictive tool to rapidly quantify this difference is reported. In extreme cases, the classical quasi-steady model can overpredict the droplet lifetime by 80%. This overprediction increases when the energy required to bring the droplet into equilibrium with its environment becomes small compared with the energy required to cool the space around the droplet and therefore establish the quasi-steady temperature field. In the general case, it is shown that two transient regimes emerge when a droplet is suddenly immersed into an atmosphere. Initially, the droplet vaporizes faster than classical models predict since the surrounding gas takes time to cool and to saturate with vapour. Towards the end of its life, the droplet vaporizes slower than expected since the region of cold vapour established in the early stages of evaporation remains and insulates the droplet.

Pressure Influence on the Flame Transfer Function of a Premixed Swirling Flame

2006 ◽  
Author(s):  
E. Freitag ◽  
H. Konle ◽  
M. Lauer ◽  
C. Hirsch ◽  
T. Sattelmayer
Keyword(s):  
High Pressure ◽  
Transfer Function ◽  
High Speed ◽  
Transfer Functions ◽  
Ambient Pressure ◽  
Operating Conditions ◽  
Phase Lag ◽  
Operating Pressure ◽  
Common Procedure ◽  
Wide Range

In order to assess the stability of gas turbine combustors measured flame transfer functions are frequently used in thermoacoustic network models. Although many combustion systems operate at high pressure, the measurement of flame transfer functions was essentially limited to atmospheric conditions in the past. With the test rig employed in the study presented in the paper transfer function measurements were made for a wide range of combustor pressures. The results show similarities of the amplitude response in the entire pressure range investigated. However, the increase of the pressure leads to a considerable amplitude gain at higher frequencies. In the low frequency regime the phase is also independent of pressure, whereas above this region the pressure increase results in a considerably smaller phase lag. These observations are particularly important when evaluating Rayleigh’s criterion: Interestingly, the choice of the operating pressure can render a system stable or unstable, so that the common procedure of applying flame transfer functions measured at ambient pressure for the high pressure engine case may not always be appropriate. The detailed analysis of high speed camera images, which were recorded to get locally resolved information on the flame response reveal different regions of activity within the flame that change in strength, size and location with changing operating conditions. The observed transfer function phase behavior is explained by the interaction of those regions and it is shown that the region of highest dynamic activity dominates the phase.

Ignition and Combustion of Magnesium Particles in Carbon Dioxide

2012 ◽  
Vol 152-154 ◽  
pp. 220-225 ◽  
Author(s):  
Sheng Min Zhang ◽  
Chun Bo Hu ◽  
Sheng Yong Xia ◽  
Lin Li ◽  
Xiang Geng Wei
Keyword(s):  
Carbon Dioxide ◽  
Resource Utilization ◽  
Surface Film ◽  
Ambient Pressure ◽  
Rocket Engines ◽  
Pulsation Frequency ◽  
Ambient Temperatures ◽  
Wide Range ◽  
Co2 Atmosphere

Metal-CO2 propulsion is less known than in-situ resource utilization (ISRU) technologies. This concept, based on using Martian carbon dioxide as an oxidizer in jet or rocket engines, offers the advantage of no chemical processing for CO2 and thus requires less power consumption than ISRU alternatives. In this paper, we study the burning behavior of the Mg in a CO2 atmosphere to assess the feasibility of using Mg/CO2 reactions as an in situ resource utilization technology for rocket propulsion and energy generation on other planets. From the experimental results, we can see that the critical ignition temperature increases with increasing the particle size and decreases with increasing the ambient pressure. In the CO2 atmosphere, we found the complicated sequence of interaction modes including pulsating combustion in a wide range of ambient temperatures. The pulsation frequency is determined by the sample temperature at the phases of slow heterogeneous combustion between the flashes. The combustion mechanisms are discussed with consideration of processes in both a surface film and gas phase.

scholarly journals Spray and Combustion Characterizations of Acetone-Butanol-Ethanol (ABE) blend at High-Pressure and High-Temperature Conditions

2017 ◽  
Author(s):  
Nilaphai Ob ◽  
Ajrouche Hugo ◽  
Hespel Camille ◽  
Moreau Bruno ◽  
Chanchaona Somchai ◽  
...  
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Ambient Pressure ◽  
Chemical Properties ◽  
Volume Ratio ◽  
Spray Combustion ◽  
Pure Nitrogen ◽  
Ambient Temperatures ◽  
Lift Off ◽  
Ci Engines

The intermediate fermentation mixture of butanol production, Acetone, Butanol and Ethanol (ABE), is increasinglyconsidered as a new alternative fuel in CI engines due to its physical and chemical properties, which are similar to those of butanol, and its advantages of no additional cost or energy consumption due to butanol separation. In a previous study, the High-Pressure and High-Temperature (HPHT) chamber, called ‘New One Shot Engine” (NOSE), was used to investigate macroscopic spray-combustion parameters by validating Spray-A conditions of the Engine Combustion Network. The present study concerns the spray-combustion characteristics of the ABE mixture (volume ratio 3:6:1), blended with n-dodecane at a volumetric ratio of 20% (ABE20), compared to n-dodecane as reference fuel. The macroscopic spray and combustion parameters were investigated, for non-reactive conditions, in pure Nitrogen and for reactive conditions, in 15% oxygen, at ambient pressure (60 bar), ambient density (22.8 kg/m3) and different ambient temperatures (800 K, 850 K and 900 K). The liquid and vapor spray penetrations were investigated by the Diffused Back Illumination (DBI) and Schlieren techniques in non-reactive conditions. In reactive conditions, the lift-off length was measured by OH* chemiluminescence images at 310 nm. The Schlieren technique was also used to verify the choice of detection criterion. The ignition delay results of the two fuels were compared. It was found that the behavior of the two fuels as a function of temperature was similar even if the liquid length of ABE20 was shorter than that of n-dodecane at all ambient temperatures. On the other hand, no real difference in vapor spray penetration between the two fuels was observed. The vaporization properties and the lower auto-ignition ability of ABE20 led to longer ignition delays and lift-off length.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4852

Characterisation of a Novel Pulsating Heat Pipe Cooler for Power Electronics at Extreme Ambient Temperatures

2015 ◽  
Author(s):  
Daniele Torresin ◽  
Mathieu Habert ◽  
Violette Mounier ◽  
Francesco Agostini ◽  
Bruno Agostini
Keyword(s):  
Heat Pipe ◽  
Low Cost ◽  
Saturation Temperature ◽  
Open Loop ◽  
Experimental Results ◽  
Fluid Distribution ◽  
Pulsating Heat Pipe ◽  
Ambient Temperatures ◽  
Air Temperatures ◽  
Thermo Physical Properties

A compact and low cost pulsating heat pipe cooler (PHP) based on automotive technology is presented. This technology uses numerous aluminium MultiPort Extruded (MPE) tubes with capillary sized channels disposed in parallel to achieve the desired compactness. The sub-channels of the MPEs are connected in a serpentine manner by means of fluid distribution elements integrated in the evaporator and condenser manifolds. This configuration enables the oscillation of liquid slugs and elongated bubbles between the evaporator and the condenser areas. In the present paper the experimental results of an open loop type PHP with refrigerants fluids R134a and R245fa are presented. Tests have been carried out for air temperatures ranging between −60 and 60 °C at a fixed air flow rate of 480 m3/h and heat loads from 3 to 13 W/cm2. The experimental results show the different thermo-physical properties effect of the two tested fluids on the cooler performances: R134a is more adapted to low saturation temperature than R245fa and the contrary has been observed at high saturation temperatures. This is due to the fact that R245fa reaches its viscous limit at low temperatures while at high temperatures R134a reaches its critical temperature.

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