Adiabatic Hypothesis Research Articles

Negative LIF Development For H2 Jet Characterization: Influence Of Tracers

This study focuses on the development of a new laser diagnostic based on Laser Induced Fluorescence by seeding the gas (N2) in which hydrogen is injected with fluorescent tracer. In this paper, three tracers were characterized, two aromatic compounds (toluene and difluorobenzene) and one ketone (acetone). The first part of this study compared the fluorescence of both aromatic compounds without injecting H2 . More particularly the influence of a temperature variation on the quantum yield and cross section absorption was regarded. It appeared that difluorobenzene was more suitable LIF measurement than toluene as it has a higher quantum yield that is less dependent to temperature variation. Then, Negative LIF was tested using two different tracers (difluorobenzene and acetone) and considering three different post-processing methods to consider the temperature variation inside the hydrogen jet: no temperature correction, temperature calculated based on a CFD RANS simulation, temperature calculated via an isentropic expansion and adiabatic mixture hypothesis. Results evidence that the first and the third methods presents respectively a lower and upper limit for the hydrogen mole fraction when the second method is biased by the presence of shock and expansion structures near the injector nozzle. Finally, it appears that, with the proper temperature correction, difluorobenzene and acetone yield similar results, despite the fact the acetone fluorescence needing more amplification to be captured, the signal to noise ratio is lower than for aromatic compounds.

Asymptotic States and S-Matrix Operator in de Sitter Ambient Space Formalism

Within the de Sitter ambient space framework, the two different bases of the one-particle Hilbert space of the de Sitter group algebra are presented for the scalar case. Using field operator algebra and its Fock space construction in this formalism, we discuss the existence of asymptotic states in de Sitter QFT under an extension of the adiabatic hypothesis and prove the Fock space completeness theorem for the massive scalar field. We define the quantum state in the limit of future and past infinity on the de Sitter hyperboloid in an observer-independent way. These results allow us to examine the existence of the S-matrix operator for de Sitter QFT in ambient space formalism, a question which is usually obscure in spacetime with a cosmological event horizon for a specific observer. Some similarities and differences between QFT in Minkowski and de Sitter spaces are discussed.

Flow characteristics and phase transition of subcritical to supercritical kerosene injections in a convergent nozzle

The internal flow characteristics of near- and supercritical RP-3 aviation kerosene injected into an atmospheric pressure environment were experimentally investigated. The internal flow structure was visualized in a two-dimensional transparent convergent nozzle using shadowgraph imaging. A series of images of the RP-3 flow inside a convergent nozzle varying from subcritical to supercritical injection conditions were obtained for the first time. Under subcritical, critical, and supercritical pressures, different RP-3 flow structure transitions with decreasing injection temperature were examined. In addition, the associated phase transition was analyzed using the thermodynamic phase diagram of a 10-component RP-3 surrogate based on the adiabatic isentropic expansion hypothesis. Six distinct phase state regions governing the flow structure were identified, considering the phase transitions and density variations of the fuel injection from different regions during their respective expansion processes. The experimentally observed phase transition boundary with respect to injection conditions was further determined, which can be utilized to predict the onset of a drastic change in mass flow rate. Furthermore, the axial length between the nozzle exit and the onset location of observable phase transition was detected, which initially increases and then decreases with decreasing injection temperature. Further analysis showed that the unique evolution behaviour of the specific heat ratio during injection process has a strong effect on flow characteristics near critical point.

Applicability of Temperature Discrete Equation to NMRF Boundary Layer Scheme in GRAPES Model

By deriving the discrete equation of the parameterized equation for the New Medium-Range Forecast (NMRF) boundary layer scheme in the GRAPES model, the adjusted discrete equation for temperature is obviously different from the original equation under the background of hydrostatic equilibrium and adiabatic hypothesis. In the present research, three discrete equations for temperature in the NMRF boundary layer scheme are applied, namely the original (hereafter NMRF), the adjustment (hereafter NMRF-gocp), and the one in the YSU boundary-layer scheme (hereafter NMRF-TZ). The results show that the deviations of height, temperature, U and V wind in the boundary layer in the NMRF-gocp and NMRF-TZ experiments are smaller than those in the NMRF experiment and the deviations in the NMRF-gocp experiment are the smallest. The deviations of humidity are complex for the different forecasting lead time in the three experiments. Moreover, there are obvious diurnal variations of deviations from these variables, where the diurnal variations of deviations from height and temperature are similar and those from U and V wind are also similar. However, the diurnal variation of humidity is relatively complicated. The root means square errors of 2m temperature (T2m) and 10m speed (V10m) from the three experiments show that the error of NMRF-gocp is the smallest and that of NMRF is the biggest. There is also a diurnal variation of T2m and V10m, where T2m has double peaks and V10m has only one peak. Comparison of the discrete equations between NMRF and NMRF-gocp experiments shows that the deviation of temperature is likely to be caused by the calculation of vertical eddy diffusive coefficients of heating, which also leads to the deviations of other elements.

Convergence of metadynamics: Discussion of the adiabatic hypothesis

By drawing a parallel between metadynamics and self interacting models for polymers, we study the longtime convergence of the original metadynamics algorithm in the adiabatic setting, namely when the dynamics along the collective variables decouples from the dynamics along the other degrees of freedom. We also discuss the bias which is introduced when the adiabatic assumption does not hold.

Noether’s theorem, the Rund–Trautman function, and adiabatic invariance

This article focuses on the recognition of an important quantity that will be called the Rund–Trautman function. It already plays a central role in Noether’s theorem since its vanishing characterizes a symmetry and leads to a conservation law. The main aim of the paper will be to show how, in the realm of classical mechanics, an ‘almost’ vanishing Rund–Trautman function accompanying an ‘almost’ symmetry leads to an ‘almost’ constant of motion, especially within the adiabatic hypothesis for which the ‘almostness’ in question is in some sense measured by the slowness of time-dependent parameters. To this end, the Rund–Trautman function is first introduced and analyzed in detail, then it is implemented for the general one-dimensional problem. Finally, its relevance in the adiabatic context is examined through the example of the harmonic oscillator with a slowly varying frequency. Notably, for some frequency profiles, explicit expansions of adiabatic invariants are derived through it and an illustrative numerical test is realized.

Parametric influence study of cryogenic hydrogen dispersion on theoretical aspect

In this paper, we proposed a theoretical model to study the dispersion of hydrogen. The model given a correlation between the concentration and temperature for cryogenic gases. The model based on adiabatic mixing hypothesis and neglected exterior heat sources, and thought the gas mixture was always at quasi-steady state. Real-gas law was adopted, and thermal physical properties of the gases are obtained from NIST REFPROP database. The concentration curve approximately appears a decreasing straight line, and turns on dew point and ice point, since heat released from water vapor phase change. Compared with liquid hydrogen and liquid natural gas spill experimental data, the model obtained well agreement solutions.Effects of three typical weather conditions (atmospheric temperature, relative humidity and barometric pressure) on hydrogen dispersion were quantitatively studied. It is confirmed that the dispersion is excited in summer, and is depressed in winter and transition seasons with increased ambient temperature. With increased ambient temperature, the effect of increased enthalpy reduction of the dry air components and the effect of the water latent heat are respectively dominate in the 268.15–293.15 K and 293.15–308.15 K ranges. Compared to ambient temperature and barometric pressure, relative humidity has the strongest positive effect on hydrogen dispersion, and the slight dampening effect of barometric pressure could be neglected.

Effects of double parabolic profiles with groove textures on the hydrodynamic lubrication performance of journal bearing under steady operating conditions

The textures on the bushing surface have important effects on the performance of journal bearing. In this study, the effects of double parabolic profiles with groove textures on the hydrodynamic lubrication performance of journal bearing under steady operating conditions are investigated theoretically. The journal misalignment, asperity contact and thermal effects are considered, while the profile modifications due to running-in are neglected. The Winkler/Column model is used to calculate the elastic deformation of bushing surface and the adiabatic flow hypothesis is adopted to obtain the effective temperature of lubricating oil. The numerical solution is established by using finite difference and overrelaxation iterative methods, and the rupture zone of oil film is determined by Reynolds boundary conditions. The numerical results reveal that the double parabolic profiles with groove textures with proper location and geometric sizes can increase load carrying capacity and reduce friction loss under steady operating conditions, which effectively overcome the drawbacks of double parabolic profiles. This novel bushing profile may help to reduce the bushing edge wear and enhance the lubrication performance of journal bearing.

Adiabatic-Molecular Dynamics Generalized Vertical Hessian Approach: A Mixed Quantum Classical Method To Compute Electronic Spectra of Flexible Molecules in the Condensed Phase.

We present a general mixed quantum classical method that couples classical molecular dynamics (MD) and vibronic models to compute the shape of electronic spectra of flexible molecules in the condensed phase without, in principle, any phenomenological broadening. It is based on a partition of the nuclear motions of the solute + solvent system in "soft" and "stiff" vibrational modes and an adiabatic hypothesis that assumes that stiff modes are much faster than soft ones. In this framework, the spectrum is rigorously expressed as a conformational integral of quantum vibronic spectra along the stiff coordinates only. Soft modes enter at the classical level through the conformational distribution that is sampled with classical MD runs. In each configuration, reduced-dimensionality quadratic Hamiltonians are built in the space of the stiff coordinates only, thanks to a generalization of the Vertical Hessian harmonic model and an iterative application of projectors in internal coordinates to remove soft modes. Quantum vibronic spectra, specific for each sampled configuration of the soft coordinates, are then computed at the desired temperature with efficient time-dependent techniques, and the global spectrum simply arises from their average. For consistency of the whole procedure, classical MD runs are performed with quantum-mechanically derived force fields, parameterized at the same level of theory selected for generating the quadratic Hamiltonians along the stiff coordinates. Application to N-methyl-6-oxyquinolinium betaine in water, dithiophene in ethanol, and cyanidine in water is presented to show the performance of the method.

Thermal effects on the diesel injector performance through adiabatic 1D modelling. Part I: Model description and assessment of the adiabatic flow hypothesis

The fuel flow along common-rail injectors is usually treated as isothermal, although the expansions across the injector orifices lead to variations in the fuel temperature that in turn modify the fuel properties influencing injector dynamics. This investigation introduces the hypothesis of adiabatic flow to account for local temperature variations in the computational model of a solenoid injector previously introduced by the authors in its isothermal variant. The main contribution of the study consists on the assessment of the validity of this hypothesis by qualitatively estimating the relative importance of the heat transfer processes during the injection event and in the time lapse among injections. Results of this tentative assessment for engine-like conditions imply that heat transfer is usually still occurring by the time of a new injection, meaning any initial temperature difference among the fuel and the injector wall is not expected to be completely mitigated before each injection event. The magnitude of reduction of this temperature difference depends on the injection frequency through engine speed and load. Anyway, the assumption of adiabatic flow seems to hold once the steady conditions of the injection are reached, meaning that any temperature change predictions considered with the adiabatic hypothesis may be valid as long as a certain temperature change is accounted for at the injector inlet. In a second part of the paper, the capabilities of this new model are validated against experimental data, allowing the use of the model to explore the influence of the thermal effects on the injection event.

Thermal effects on the diesel injector performance through adiabatic 1D modelling. Part II: Model validation, results of the simulations and discussion

In this paper, a one-dimensional computational model of the flow in a common-rail injector is used to compute local variations of fuel temperature (including the temperature change produced upon expansion across the nozzle) and analyse their effect on injector dynamics. These variations are accounted through the adiabatic flow hypothesis, assessed in a first part of the paper where the model features are also described. They imply variations in the fuel properties and the flow regime established across the injector internal restrictions driving the solenoid valve. An extensive validation of the model against experimental results is presented for a wide range of conditions. Multiple injection strategies are also explored, analysing the influence of the inlet fuel temperature and its variations on the mass injected by successive injections and the critical dwell time below which they cannot be separated. Results show significant changes in fuel temperature across some injector restrictions. These changes are greater the higher the rail pressure and lower the fuel temperature at the injector inlet. In the case of the flow across nozzle orifices, the fuel can be either heated or subcooled depending on the operating conditions, the heating being especially relevant for cold-start-like fuel temperatures at the inlet. Thermal effects also influence the injection rate and duration. This influence on injector dynamics is particularly accused in the injector of study due to its ballistic nature. In this regard, the time needed to effectively separate two successive injections is greater the higher the fuel temperature and the injection pressure.

Impact of thermodynamic properties and heat loss on ignition of transportation fuels in rapid compression machines

Rapid compression machines (RCM) are extensively used to study autoignition of a wide variety of fuels at engine relevant conditions. Fuels ranging from pure species to full boiling range gasoline and diesel can be studied in an RCM to develop a better understanding of autoignition kinetics in low to intermediate temperature ranges. In an RCM, autoignition is achieved by compressing a fuel/oxidizer mixture to higher pressure and temperature, thereby initiating chemical reactions promoting ignition. During these experiments, the pressure is continuously monitored and is used to deduce significant events such as the end of compression and the onset of ignition. The pressure profile is also used to assess the temperature evolution of the gas mixture with time using the adiabatic core hypothesis and the heat capacity ratio of the gas mixture. In such RCM studies, real transportation fuels containing many components are often represented by simpler surrogate fuels. While simpler surrogates such as primary reference fuels (PRFs) and ternary primary reference fuel (TPRFs) can match research and motor octane number of transportation fuels, they may not accurately replicate thermodynamic properties (including heat capacity ratio). This non-conformity could exhibit significant discrepancies in the end of compression temperature, thereby affecting ignition delay (τign) measurements. Another aspect of RCMs that can affect τign measurement is post compression heat loss, which depends on various RCM parameters including geometry, extent of insulation, pre-heating temperature etc. To, better understand the effects of these non-chemical kinetic parameters on τign, thermodynamic properties of a number of FACE G gasoline surrogates were calculated and simulated in a multi-zone RCM model. The problem was further investigated using a variance based analysis and individual sensitivities were calculated. This study highlights the effects on τign due to thermodynamic properties of various surrogate fuels and differences in post compression heat loss over low, intermediate and high temperature region.

The puzzle of half-integral quanta in the application of the adiabatic hypothesis to rotational motion

We present and discuss an interesting and puzzling problem Ehrenfest found in his first application of the adiabatic hypothesis, in 1913. It arose when trying to extend Planck׳s quantization of the energy of harmonic oscillators to a rotating dipole within the frame of the old quantum theory. Such an extension seemed to lead unavoidably to half-integral values for the rotational angular momentum of a system (in units of ℏ). We present the problem in its original form along with the (few) responses we have found to Ehrenfest׳s treatment. After giving a brief account of the classical and quantum adiabatic theorem, we also describe how Quantum Mechanics provides an explanation for this difficulty.

Cloud and Aerosol Interaction Observed in SKYNET Hefei Site in China

The interaction relationship between cloud and aerosol is studied via their optical depth and cloud effective radius based on ground-based remote sensors. By attenuated backscatter obtained by lidar the optical depth of cloud and aerosol is retrieved. Combing with liquid water path observed by microwave radiometer, the cloud number concentration and cloud effective radius is also retrieved based on the adiabatic hypothesis Cases studies shows that during the stable stratocumulus with interval precipitation period and aerosol with vertical motion, the cloud effective radius shows both negative and positive relationship with aerosol optical depth. It may be due to the difference of liquid water path of the cloud properties and shows complex interaction with aerosol.

On the uncertainty of temperature estimation in a rapid compression machine

Rapid compression machines (RCMs) have been widely used in the combustion literature to study the low-to-intermediate temperature ignition of many fuels. In a typical RCM, the pressure during and after the compression stroke is measured. However, measurement of the temperature history in the RCM reaction chamber is challenging. Thus, the temperature is generally calculated by the isentropic relations between pressure and temperature, assuming that the adiabatic core hypothesis holds. To estimate the uncertainty in the calculated temperature, an uncertainty propagation analysis must be carried out. Our previous analyses assumed that the uncertainties of the parameters in the equation to calculate the temperature were normally distributed and independent, but these assumptions do not hold for typical RCM operating procedures. In this work, a Monte Carlo method is developed to estimate the uncertainty in the calculated temperature, while taking into account the correlation between parameters and the possibility of non-normal probability distributions. In addition, the Monte Carlo method is compared to an analysis that assumes normally distributed, independent parameters. Both analysis methods show that the magnitude of the initial pressure and the uncertainty of the initial temperature have strong influences on the magnitude of the uncertainty. Finally, the uncertainty estimation methods studied here provide a reference value for the uncertainty of the reference temperature in an RCM and can be generalized to other similar facilities.

The Centrifugation Casting of Nd:YAG Ceramics Melt by Combustion Synthesis

In this paper, Nd:YAG ceramic was prepared by combustion synthesis with centrifugation casting. Combustion temperature and pressure were calculated under adiabatic hypothesis, and measured experimentally by W/Re thermocouple and piezometer, respectively. The combustion temperature and pressure decreased with increase of the content of diluents (Y2O3 and A12O3). The YAG could be obtained as the ratio between the Y2O3 and A12O3 reached 3:5. Phase composition and microstructures of the derived products were analyzed by XRD, SEM and EDS. The results show that the other reaction product TiN and a small quantity of gas and oxide impurity were not completely separated from YAG melt under centrifugal force so that transparent YAG ceramic was not obtained in this work.

Discussion of the adiabatic hypothesis in control schemes using exceptional points

We present calculations for the action of laser pulses on vibrational transfer within the H and Na2 molecules in the presence of dissipation due to photodissociation of the molecule. The laser fields perform closed loops surrounding exceptional points in the laser parameter plane of intensity and wavelength. In principle the process should produce controlled vibrational transfers due to an adiabatic flip of the dressed eigenstates. We directly solve the Schrödinger equation with the complete time-dependent field instead of using the adiabatic Floquet formalism which initially suggested the design of the laser pulses. Results given by wavepacket propagations disagree with predictions obtained using the adiabatic hypothesis. Thus we show that there are large non-adiabatic exchanges and that the dissipative character of the dynamics renders the adiabatic flip very difficult to obtain. Using much longer durations than expected from previous studies, the adiabatic flip is only obtained for the Na2 molecule and with strong dissociation.

Mesoscale Eddy Buoyancy Flux and Eddy-Induced Circulation in Eastern Boundary Currents

Abstract A dynamical interpretation is made of the mesoscale eddy buoyancy fluxes in the Eastern Boundary Currents off California and Peru–Chile, based on regional equilibrium simulations. The eddy fluxes are primarily shoreward and upward across a swath several hundred kilometers wide in the upper ocean; as such they serve to balance mean offshore air–sea heating and coastal upwelling. In the stratified interior the eddy fluxes are consistent with the adiabatic hypothesis associated with a mean eddy-induced velocity advecting mean buoyancy and tracers. Furthermore, with a suitable gauge choice, the horizontal fluxes are almost entirely aligned with the mean horizontal buoyancy gradient, consistent with the advective parameterization scheme of Gent and McWilliams. The associated diffusivity κ is surface intensified, matching the vertical stratification profile. The fluxes span the across-shore band of high eddy energy, but their alongshore structure is unresolved because of sampling limitations. In the surface layer the eddy flux is significantly diabatic with a shallow eddy-induced circulation cell and downgradient lateral diapycnal flux. The dominant eddy generation process is baroclinic instability, but there are significant regional differences between the upwelling systems in the flux and κ that are not consistent with simple instability theory.

A Finite Element Study of Chip Formation Process in Orthogonal Machining

This paper examines the plane strain 2D Finite Element (FE) modeling of segmented, as well as continuous chip formation while machining AISI 4340 with a negative rake carbide tool. The main objective is to simulate both the continuous and segmented chips from the same FE model based on FE code ABAQUS/Explicit. Both the adiabatic and coupled temperature displacement analysis has been performed to simulate the right kind of chip formation. It is observed that adiabatic hypothesis plays a critical role in the simulation of segmented chip formation based on adiabatic shearing. The numerical results dealing with distribution of stress, strain and temperature for segmented and continuous chip formations were compared and found to vary considerably from each other. The simulation results were also compared with other published results; thus validating the developed model.

Microscopic transport theory of nuclear processes

We formulate a microscopic theory of the decay of a compound nucleus through fission which generalizes earlier microscopic approaches of fission dynamics performed in the framework of the adiabatic hypothesis. It is based on the constrained Hartree–Fock–Bogoliubov procedure and the Generator Coordinate Method, and requires an effective nucleon–nucleon interaction as the only input quantity. The basic assumption is that the slow evolution of the nuclear shape must be treated explicitly, whereas the rapidly time-dependent intrinsic excitations can be treated by statistical approximations. More precisely, we introduce a “reference density” ρ P which represents the slow evolution of the nuclear shape by a reduced density matrix and the state of intrinsic excitations by a canonical distribution at each given shape of the nucleus. The shape of the nuclear density distribution is described by parameters (“generator coordinates” q), not by “superabundant” degrees of freedom introduced in addition to the complete set of nucleonic degrees of freedom. We first derive a rigorous equation of motion for the reference density ρ P and, subsequently, simplify this equation on the basis of the “Markov approximation”. The temperature T which appears in the canonical distribution is determined by the requirement that, at each time t, the reference density should correctly reproduce the mean excitation energy at given values of the shape parameters q. The resulting equation for the “local” temperature T ( q , t ) must be solved together with the equations of motion obtained for the reduced density matrix R ( q 1 , q 2 ; t ) .