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Calibration-quality ab initio adiabatic potential energy surfaces (PES) have been determined for all isotopologues of the molecular ion H3+. The underlying Born-Oppenheimer electronic structure computations used optimized explicitly correlated shifted Gaussian functions. The surfaces include diagonal Born-Oppenheimer corrections computed from the accurate electronic wave functions. A fit to the 41 655 ab initio points is presented which gives a standard deviation better than 0.1 cm-1 when restricted to the points up to 6000 cm-1 above the first dissociation asymptote. Nuclear motion calculations utilizing this PES, called GLH3P, and an exact kinetic energy operator given in orthogonal internal coordinates are presented. The ro-vibrational transition frequencies for H3+, H2D+, and HD2+ are compared with high resolution measurements. The most sophisticated and complete procedure employed to compute ro-vibrational energy levels, which makes explicit allowance for the inclusion of non-adiabatic effects, reproduces all the known ro-vibrational levels of the H3+ isotopologues considered to better than 0.2 cm-1. This represents a significant (order-of-magnitude) improvement compared to previous studies of transitions in the visible. Careful treatment of linear geometries is important for high frequency transitions and leads to new assignments for some of the previously observed lines. Prospects for further investigations of non-adiabatic effects in the H3+ isotopologues are discussed. In short, the paper presents (a) an extremely accurate global potential energy surface of H3+ resulting from high accuracy ab initio computations and global fit, (b) very accurate nuclear motion calculations of all available experimental line data up to 16 000 cm-1, and (c) results suggest that we can predict accurately the lines of H3+ towards dissociation and thus facilitate their experimental observation. [ABSTRACT FROM AUTHOR]

The abstraction and addition reactions of H with trans-N2H2 are studied by high-level ab initio methods and density functional theory. Rate constants were calculated for these two reactions by multistructural variational transition state theory with multidimensional tunneling and including torsional anharmonicity by the multistructural torsion method. Rate constants of the abstraction reaction show large variational effects, that is, the variational transition state yields a smaller rate constant than the conventional transition state; this results from the fact that the variational transition state has a higher zero-point vibrational energy than the conventional transition state. The addition reaction has a classical barrier height that is about 1 kcal/mol lower than that of the abstraction reaction, but the addition rates are lower than the abstraction rates due to vibrational adiabaticity. The calculated branching ratio of abstraction to addition is 3.5 at 200 K and decreases to 1.2 at 1000 K and 1.06 at 1500 K. [ABSTRACT FROM AUTHOR]

Limiting high pressure rate constants for the recombination reaction H+O2→HO2 are modeled between 0 and 5000 K on an ab initio potential. Quantum capture theory is employed for the temperature range from 0 to about 1 K, while classical trajectory calculations are suitable for covering temperatures above about 200 K. The intermediate temperature range is analyzed by adiabatic channel capture theory. The system is characterized by transition-state switching from outer transition states in the long-range-C6/R6 potential to inner transition states in the range of a “shoulder” of the potential. The limiting high pressure rate constants from the trajectory calculations are sufficient for comparison with the experimental data which are available over the range from 300 to 900 K. Specific rate constants k(E,J) for HO2 dissociation are also given and analyzed with respect to internal consistency with capture cross sections. [ABSTRACT FROM AUTHOR]

In open quantum systems, decoherence occurs through interaction of a quantum subsystem with its environment. The computation of expectation values requires a knowledge of the quantum dynamics of operators and sampling from initial states of the density matrix describing the subsystem and bath. We consider situations where the quantum evolution can be approximated by quantum-classical Liouville dynamics and examine the circumstances under which the evolution can be reduced to surface-hopping dynamics, where the evolution consists of trajectory segments exclusively evolving on single adiabatic surfaces, with probabilistic hops between these surfaces. The justification for the reduction depends on the validity of a Markovian approximation on a bath averaged memory kernel that accounts for quantum coherence in the system. We show that such a reduction is often possible when initial sampling is from either the quantum or classical bath initial distributions. If the average is taken only over the quantum dispersion that broadens the classical distribution, then such a reduction is not always possible. [ABSTRACT FROM AUTHOR]

The adiabatic potential energy surfaces for the lowest five electronic states of 3A″ symmetry for the H++O2 collision system have been obtained at the multireference configuration interaction level of accuracy using Dunning’s correlation consistent polarized valence triple zeta basis set. The radial nonadiabatic coupling terms and the mixing angle between the lowest two electronic states (1 3A″ and 2 3A″), which adiabatically correlate in the asymptotic limit to H(2S)+O2+(X 2Πg) and H++O2(X 3Σg-), respectively, have been computed using ab initio procedures at the same level of accuracy to yield the corresponding quasidiabatic potential energy matrix. The computed strengths of the vibrational coupling matrix elements reflect the trend observed for inelastic vibrational excitations of O2 in the experiments at collision energy of 9.5 eV. The quantum dynamics has been preformed on the newly obtained coupled quasidiabatic potential energy surfaces under the vibrational close-coupling rotational infinite-order sudden framework at the experimental collision energy of 9.5 eV. The present theoretical results for vibrational elastic/inelastic excitations of O2 are in overall good agreement with the available experimental data obtained from the proton energy-loss spectra in molecular beam experiments [F. A. Gianturco et al., J. Phys. B 14, 667 (1981)]. The results for the complementary charge transfer processes are also presented at this collision energy. [ABSTRACT FROM AUTHOR]

The state-to-state dynamics of the H+D2 reaction is studied by the reactant-product decoupling method using the double many-body expansion potential energy surface. Two approaches are compared: one uses only the lowest adiabatic sheet while the other employs both coupled diabatic sheets. Rotational distributions for the reaction H+D2 (υ=0,j=0)→HD(υ′=3,j′)+D are obtained at eight different collision energies between 1.49 and 1.85 eV; no significant difference are found between the two approaches. Initial state-selected total reaction probabilities and integral cross sections are also given for energies ranging from 0.25 up to 2.0 eV with extremely small differences being observed between the two sets of results, thus showing that the nonadiabatic effects in the title reaction are negligible at least for small energies below 2.0 eV. [ABSTRACT FROM AUTHOR]

The need of cryogenic hydrogenic fuels in inertial confinement fusion (ICF) ignition targets has been long been established. Efficient implosion of such targets has mandated keeping the adiabat of the main fuel layer at low levels to ensure drive energies are kept at reasonable minima. The use of cryogenic fuels helps meet this requirement and has therefore become the standard in most ICF ignition designs. To date most theoretical ICF ignition target designs have assumed a homogeneous layer of deuterium-tritium (DT) fuel kept slightly below the triple point. However, recent work has indicated that, as cryogenic fuel layers are formed inside an ICF capsule, isotopic dissociation of the tritium (T), deuterium (D), and DT takes place leading to a “fractionation” of the final ice layer. This paper will numerically investigate the effects that various scenarios of fractionation have on hot-spot formation, ignition, and burn in ICF ignition target designs. [ABSTRACT FROM AUTHOR]

The Drude model for treating the interaction of excess electrons with polar molecules is extended to calculate continuum functions and to evaluate photodetachment cross sections. The approach is applied to calculate the cross sections for photodetachment of dipole-bound electrons from HCN- and HNC-. In addition, an adiabatic model separating the angular and radial degrees of freedom of the excess electron is introduced and shown to account in a qualitative manner for the cross sections. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A study of equilibrium states of a thermodynamic system whose evolution is governed not only by the temperature, but also by the ordering field is carried out. It is found that an adiabatically insulated system may have a new type of nonuniform state of equilibrium which is inhomogeneous in temperature. The comparison is made of the stability conditions in isothermal and adiabatic systems. The steady motion of an interface boundary during a first-order phase transition is investigated. It is shown, that depending upon the values of the diffusion coefficients, different regimes can exist. For small thermal diffusivity, the temperature of the final phase after the exothermal transition can be above the equilibrium point. The kinetic problem is reformulated to a dynamical system, and a numerical procedure to solve the latter is presented. Numerical results are discussed in comparison with analytic ones. [ABSTRACT FROM AUTHOR]

One of us has previously developed a technique for obtaining the leading terms in a perturbation expansion of the Born–Oppenheimer energies and derivative couplings for the X3 system near the conical intersection at a C3v configuration. In a preceding paper, these leading terms have been utilized to study various aspects of the adiabatic approximation for both model and real systems of this type. In the present article, this technique is generalized and extended to all orders, yielding rigorous functional forms for both energies and derivative couplings. In particular, the ‘‘nonremovable’’ part of the derivative coupling, which cannot be transformed away by going to a diabatic basis, is explicitly exhibited. Convenient approximations for both removable and nonremovable couplings are also obtained. These should facilitate the estimation of the effect of the different couplings in various situations. [ABSTRACT FROM AUTHOR]

Detailed experimental data are presented on the n-heptane isobaric heat capacity obtained by a modernized adiabatic running calorimeter with the calorimetric measurement of the flow rate in the liquid, gaseous, and supercritical domains, within a temperature range of 300-620 K and a pressure range of 0.5-60 MPa. A thorough consideration of errors made it possible to obtain an error of 0.4% within a wide range of the state parameters. According to the experimental data on the heat capacity, using the known thermodynamics relations, the tables of the n-heptane enthalpy, entropy, and Gibbs energy were calculated (estimated against the accuracy) on the basis of the reliable state equations and the available literature data. The obtained results can be applied directly in the design of chemical processes and the processes in the bedded systems of the hydrocarbon deposits and for development and testing of the equations of state and the methods of the thermodynamic similarity. [ABSTRACT FROM AUTHOR]

In this study, simulation and optimization of ammonia synthesis reactor based on the implemented cooling methods was presented in three cases: internal direct cooling reactor (IDCR), adiabatic quench cooling reactor (AQCR), and adiabatic indirect cooling reactor (AICR). A one-dimensional pseudo-homogeneous model was developed to investigate the effect of various parameters on maximum N 2 conversion at the outlet of IDCR, 2-bed AQCR and 2-bed AICR. Differential evolution algorithm was applied to optimize three types of ammonia synthesis reactor, considering N 2 conversion as the main objective. A comparison between IDCR, 2/3/4-bed AQCR and 2/3/4-bed AICR was carried out under the optimal operating conditions by considering the same catalyst volume, operating pressure and feed mass flow rate for all three types of reactor. The optimization results show that a maximum conversion of 0.26 was achieved in 3-bed AQCR, in which the temperature of feed gas to the first bed was 635 K, dimensionless lengths of each bed were 0.13, 0.25 and 0.62, and fractions of total feed flow rate quenching from the first to end bed were 0.2, 0.26 and 0.54, respectively. The optimum value of N 2 conversion was found 0.3 in IDCR at the gas temperature to the cooling tube of 495 K. In 3-bed AICR, the highest conversion of 0.3 was determined at temperature of inlet gas to each bed, 696 K, and dimensionless length of each bed, 0.33. Generally, IDCR, 3-bed AICR and 3-bed AQCR were suggested as ammonia synthesis reactor configurations from the most favorable to the least favorable. [ABSTRACT FROM AUTHOR]

An adjoint-response surface method is developed to provide efficient surrogate model in a parametrized design space for aerodynamic optimization of turbomachinery blades. Our goal is to improve the adiabatic efficiency or equivalently reduce the entropy generation through blade row with a mass flow rate constraint. Firstly, an aerodynamic sensitivity analysis is conducted with a viscous adjoint method to find the suitable number of control points on the suction surface of the transonic NASA rotor 67. Then quadratic polynomial (QP) based response surfaces of 4, 6 and 8 parameters are examined to validate the advantages of the gradient-enhanced model. In the following 24-parameter aerodynamic design optimization case, a steepest descent optimization (SDO) based on adjoint gradient is conducted, then QP based response surface model is constructed using both the values of cost function and its adjoint gradients with respect to geometry control parameters. We present the geometric features, overall aerodynamic improvements and flow details of optimal designs given by SDO and gradient-enhanced response surface model (GERSM). The effects of blade reshaping on shock system, tip clearance flow and flow separation at hub are examined. Also, off-design performances are analyzed regarding both adiabatic efficiency and stall margin. [ABSTRACT FROM AUTHOR]

Adiabatic potential energy curves of the 28 low-lying doublet and quartet electronic states in the representation 2s+1Λ(±) of the zinc monofluoride molecule are investigated using the complete active space self-consistent field (CASSCF) with multi-reference configuration interaction (MRCI) method including single and double excitations with the Davidson correction (+Q). The internuclear distance Re, the harmonic frequency ωe, the static and transition dipole moment μ, the rotational constant Be, and the electronic transition energy with respect to the ground state Te are calculated for the bound states. The transition dipole moment between some doublet states is used to determine the Einstein spontaneous A21 and induced emission coefficients, as well as the spontaneous radiative lifetime τspon, emission wavelength λ21, and oscillator strength f21. The ground state ionicity qionicity and equilibrium dissociation energy DE,e are also computed. The comparison between the values of the present work and those available in the literature for several electronic states shows very good agreement. Twenty-three new electronic states have been studied in the present work for the first time. [ABSTRACT FROM AUTHOR]

The difference between quantum isoenergetic process and quantum isothermal process comes from the violation of the law of equipartition of energy in the quantum regime. To reveal an important physical meaning of this fact, here we study a special type of quantum heat engine consisting of three processes: isoenergetic, isothermal and adiabatic processes. Therefore, this engine works between the energy and heat baths. Combining two engines of this kind, it is possible to realize the quantum Carnot engine. Furthermore, considering finite velocity of change of the potential shape, here an infinite square well with moving walls, the power output of the engine is discussed. It is found that the efficiency and power output are both closely dependent on the initial and final states of the quantum isothermal process. The performance of the engine cycle is shown to be optimized by control of the occupation probability of the ground state, which is determined by the temperature and the potential width. The relation between the efficiency and power output is also discussed. [ABSTRACT FROM AUTHOR]

The finite-time operation of a quantum heat engine that uses a single particle as a working medium generally increases the output power at the expense of inducing friction that lowers the cycle efficiency. We propose to scale up a quantum heat engine utilizing a many-particle working medium in combination with the use of shortcuts to adiabaticity to boost the nonadiabatic performance by eliminating quantum friction and reducing the cycle time. To this end, we first analyze the finite-time thermodynamics of a quantum Otto cycle implemented with a quantum fluid confined in a time-dependent harmonic trap. We show that nonadiabatic effects can be controlled and tailored to match the adiabatic performance using a variety of shortcuts to adiabaticity. As a result, the nonadiabatic dynamics of the scaled-up many-particle quantum heat engine exhibits no friction, and the cycle can be run at maximum efficiency with a tunable output power. We demonstrate our results with a working medium consisting of particles with inverse-square pairwise interactions that includes non-interacting and hard-core bosons as limiting cases. [ABSTRACT FROM AUTHOR]

The assumptions of second order Stirling engine models were reviewed. An ideal adiabatic plus simple heat exchanger model was developed. The model included the external components such as the fan, combustor, and preheater. The external heat transfer to the engine heater was modeled using a log-mean-temperature difference for a constant tube surface temperature. The performance of the model of the external components compared reasonably well to experimental data. The performance of the complete engine model was also compared to experimental data of the GPU-3. By adjusting the flow dissipation to better account for unsteady flow conditions and compressibility effects, the complete engine model was able to predict engine power and brake specific fuel consumption to within ±14% over a wide range of engine speeds and mean pressures. This analysis and others suggest that second order models of Stirling engines need to account for the gradient of the divergence of velocity term in the compressible momentum equation if the mean engine pressure is low enough (less than 3.0 MPa) and the engine speed is high enough (above 30 Hz). [ABSTRACT FROM AUTHOR]

The practical untenability of the quasi-static assumption makes any realistic engine intrinsically irreversible and its operating time finite, thus implying friction effects at short cycle times. An important technological goal is thus the design of maximally efficient engines working at the maximum possible power. We show that, by utilising shortcuts to adiabaticity in a quantum engine cycle, one can engineer a thermodynamic cycle working at finite power and zero friction. Our findings are illustrated using a harmonic oscillator undergoing a quantum Otto cycle. [ABSTRACT FROM AUTHOR]

In this paper we present a novel method for the numerical simulation of flow in a hydro-dynamic thrust bearing with floating disk. Floating disks are commonly employed in turbochargers and are situated between the thrust collar, which is rotating at turbocharger speed, and the static casing. A floating disk reduces wear, improves the skew compensating capacity of the bearing, and is freely movable in the axial direction. The simulation model presented combines a commercial flow solver (ANSYS CFX) with a control unit. Based on physical principles and a predefined axial thrust, the control unit automatically sets the rotational speed of the floating disk, the mass flow of the oil supply, and the oil film thickness between the rotating disk and the casing wall and collar, respectively. The only additional inputs required are the temperature and the pressure of the oil at the oil feed and the turbocharger speed. The width of the computational grid of the thin lubricating oil film in the gaps is adjusted using a mesh-morphing approach. The temperature- dependent variation in viscosity is included in the model. The calculated solution of the flow field in the domain, the oil film thickness, and the resulting rotational velocity of the floating disk are validated against experimental data and demonstrate favorable agreement. The influence of uncertainties in the measurements and the behavior of the systems are thoroughly investigated in parametric studies that reveal the key influencing factors. These are the temperature-dependent viscosity of the oil, the axial thrust, and turbulence effects in the supply grooves and ducts of the floating disk. Using the model presented here, it is now possible to predict design variants for this type of bearing. [ABSTRACT FROM AUTHOR]

Engine development requires accurate estimates of the heat loads. Estimates of the convective heat fluxes are particularly vital to assess the thermomechanical integrity of the turbomachinery components. This paper reports an experimental heat transfer research in a one and a half turbine stage, composed of a high-pressure turbine and a low-pressure vane. Measurements were petformed in a compression tube facility at the von Karman Institute, able to reproduce engine representative Reynolds and Mach numbers. Double-layered thin film gauges were used to monitor the time-dependent temperature distribution around the airfoil. Several tests at different metal temperatures were performed to derive the adiabatic wall temperature. This research allowed quantifying the independent effects on the unsteady heat flux of the gas temperature fluctuations and boundary layer unsteadiness. [ABSTRACT FROM AUTHOR]

In this paper we find a full connection between the long lasting macroscopic classical laws of gases and the quantum mechanical description of non-interacting particles confined in a box, thus constituting an ideal gas. In such a gas, the motion of each individual molecule can be considered to be independent of all other molecules, and the macroscopic parameters of an ideal gas, mainly, pressure P and temperature T, can be defined as simple average quantities based on individual motions of all molecules in consideration. It is shown that for an ideal gas enclosed in a macroscopic cubic box of volume V, an alphanumeric expression for the Constant appearing in the classical law of adiabatic expansion law, i.e. PV=5/3 Constant, can be derived based on quantum mechanics. Note that this constant has otherwise remained for centuries, as just an abstract quantity in the form of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. written for different thermodynamic states, delineated through an adiabatic transformation. No one even seems to have thought that it may eventually have a particular expression. Physical implications of the result we disclose are discussed. [ABSTRACT FROM AUTHOR]

The clustering instability in granular matter manifests in many physical situations. Here we present an analysis of a set of adiabatic pistons that separate different granular gases. It is shown, by means of a linear stability analysis, that the symmetric state is unstable against small perturbations, leading to a collapse of all the pistons to the outer walls. [ABSTRACT FROM AUTHOR]

We study the efficiency at maximum power, &eegr;m, of irreversible quantum Camot engines (QCEs) that perform finite-time cycles between a hot and a cold reservoir at temperatures Th and Tc., respectively. For QCEs in the reversible limit (long cycle period, zero dissipation), &eegr;m becomes identical to the Carnot efficiency &eegr;c = 1 -- Tc/Th- For QCE cycles in which nonadiabatic dissipation and the time spent on two adiabais are included, the efficiency &eegr;m at maximum power output is bounded from above by &eegr;c/(2 -- &eegr;c) and from below by &eegr;c/2. In the case of symmetric dissipation, the Curzon-Ahlbom efficiency &eegr;CA = 1 - √Tc/Th is recovered under the condition that the time allocation between the adiabais and the contact time with the reservoir satisfy a certain relation. [ABSTRACT FROM AUTHOR]

Abstract: In this work we carry out calculations of the long-range interactions between a ground state O atom and a hydrogen molecule at C s geometries in order to describe the diabatic and adiabatic surfaces that connect the 3Π and 3Σ states at collinear geometries with the 3 B 1, 3 B 2 and 3 A 2 states at C 2v configurations. We show that the usual procedure to correct the basis set superposition error gives inconsistent results for the diabatic potentials and their coupling terms. Consistent results can only be obtained using high quality basis sets for which this error can be negligible. [Copyright &y& Elsevier]

Abstract: This experimental study was conducted to investigate the effect of a flame holder on multi-slot film cooling in a ramjet combustor. A prediffuser-type ramjet combustor equipped with a flame holder was utilized in this study. The change in adiabatic film cooling effectiveness on the downstream wall was measured using thermochromic liquid crystals. Experiments were conducted using five different blowing ratios, ranging from 0.5 to 1.5. The effect of the flame holder on heat transfer shows different characteristics between the first and second slots. In the first slot, the accelerated flows by blockage effect suppress the ejected secondary flows resulting in better cooling performance in case with the flame holder. However, the second slot represents the low cooling performance over all the regions by the disturbed flows with the flame holder compared to that without the flame holder. And the difference in cooling performance is enlarged with the increase of blowing ratio. The results reveal that it is essential to consider the effect of a wake behind the flame holder. Therefore, it should be considered in the design of film cooling systems for a practical application in ramjet combustors. [Copyright &y& Elsevier]

Abstract: The objective of this work was to study the effect of dilution with carbon dioxide on the adiabatic burning velocity of syngas fuel (with various H2/CO ratios)-air(21% O2–79% N2 by volume) mixtures along with detailed understanding of cellular flame structures. Heat flux method with a setup similar to that of de Goey and co-workers was used for measurement of burning velocities. Validation experiments were done for H2 (5%)–CO (95%)–air and H2 (5%)–CO (45%)–CO2 (50%)–air mixtures at various equivalence ratios and the results were in good agreement with published data in the literature. The mixtures considered in this work had 1:4, 1:1 and 4:1 H2/CO ratio in the fuel and 40%, 50% and 60% CO2 dilution. The burning velocity increased significantly with the increase in H2 content in mixture of H2–CO with fixed CO2 dilution. The burning velocity reduced remarkably with carbon dioxide dilution in H2–CO mixture due to reduction in heat release, flame temperature and thermal diffusivity of the mixture. The location of peak adiabatic burning velocity shifted from ϕ =1.6 for 40% CO2 to ϕ =1.2 for 60% CO2, whereas it remained unchanged with variation of H2:CO ratio (4:1, 1:1 and 1:4) at a given CO2 dilution. A comparison of experiments and simulations indicated that the Davis et al. mechanism predicted burning velocities well for the most of experimental operating conditions except for rich conditions. For some lean mixtures, flames exhibited cellular structures. In order to explain the structures and generate profiles of various field variables of interest, computations of three dimensional porous burner stabilized cellular flames were performed using commercial CFD software FLUENT. Simulations for lean H2 (25%)–CO (25%)–CO2 (50%)–air mixtures (ϕ =0.6 and 0.8) produced cellular flame structures very similar to those observed in the experiments. It was found that the in the core region of a typical cell, stretch rate was positive, the volumetric heat release rate was high and the net reaction rate for the reaction O+H2 ⇄H+OH and the net consumption rate of H2 were both high. [Copyright &y& Elsevier]

Abstract: Tesla-type check valves were integrated into a flat-plate oscillating heat pipe (FP-OHP) in order to promote and sustain a desired circulatory flow to increase overall thermal performance. Using neutron radiography, gray-scale images capturing the internal flow behavior within two bottom-heated copper FP-OHPs – one with Tesla-type valves (TV FP-OHP) and one without – both charged with water at a filling ratio of 70% – were collected. With the Tesla-type valves installed in the adiabatic section of the TV FP-OHP, it was found that circulation in the desired direction was promoted and that this promotion increased with heat input. The TV FP-OHP consistently possessed a lower thermal resistance than its counterpart without check valves. The percent-reduction in thermal resistance was on-the-order of 15–25% depending on the power input. Implementation of Tesla-type check valves is a promising means for circulatory flow rectification within an OHP, but future research is needed to further optimize valve design, quantity, and alignment. [Copyright &y& Elsevier]

Abstract: Storage devices can provide several grid services, however it is challenging to quantify the value of providing several services and to optimally allocate storage resources to maximize value. We develop a co-optimized Compressed Air Energy Storage (CAES) dispatch model to characterize the value of providing operating reserves in addition to energy arbitrage in several U.S. markets. We use the model to: (1) quantify the added value of providing operating reserves in addition to energy arbitrage; (2) evaluate the dynamic nature of optimally allocating storage resources into energy and reserve markets; and (3) quantify the sensitivity of CAES net revenues to several design and performance parameters. We find that conventional CAES systems could earn an additional $23 ± 10/kW-yr by providing operating reserves, and adiabatic CAES systems could earn an additional $28 ± 13/kW-yr. We find that arbitrage-only revenues are unlikely to support a CAES investment in most market locations, but the addition of reserve revenues could support a conventional CAES investment in several markets. Adiabatic CAES revenues are not likely to support an investment in most regions studied. Modifying CAES design and performance parameters primarily impacts arbitrage revenues, and optimizing CAES design will be nearly independent of dispatch strategy. [Copyright &y& Elsevier]

Abstract: Laminar mixed convection heat transfer in a top and bottom heated rectangular channel with protruded discrete heat sources has been investigated experimentally for air. The lower and upper surfaces of the channel were equipped with 8×4 protruded heat sources subjected to uniform heat flux. Side walls, the lower and upper walls were insulated and adiabatic. An experimental study was made for Height/Width (H/W) ratios of (1/2), (1/4), (3/20) at various Reynolds (Re) and modified Grashof (Gr *) numbers. From experimental measurements, row-average surface temperature and Nusselt (Nu) number distributions of the discrete heat sources were obtained and effects of Reynolds and modified Grashof numbers on these distributions were investigated. The results show that the buoyancy affected secondary flow is more effective at the greater values of H/W ratios. [Copyright &y& Elsevier]

Abstract: In the current context of global warming due to CO2 (carbon dioxide) emissions, mainly produced by power plants and road transportation, it is imperative to optimize the operation of thermal engines in general and of gas turbines in particular. This requires accurate knowledge of their performance. In the case of turbomachines, performance is usually estimated by assuming an adiabatic flow. This assumption is inappropriate, however, for small-scale machines such as turbochargers and micro gas turbines. This study presents the influence of heat transfer on their performance. The concept of entropic temperature is developed and a general exergy analysis conducted in order to quantify accurately the available energy dissipation. Both a turbocharger and a gas turbine with internal heat transfer are investigated. Under the adiabatic assumption, the model results are overestimated. New gas turbine maps have therefore been generated and new operating points defined. The trends of the modeling results thus obtained are compared with the performance measured on a micro gas turbine with and without insulation. Fuel consumption is higher with internal heat transfer. [Copyright &y& Elsevier]

To analyze the formation of multiple shear bands in HY-100 steel, we consider an infinitely extended layer of finite thickness subjected to shear loading. The perturbation approach, associated with numerical methods, is used to determine the instability modes. The criteria of Wright-Ockendon and Molinari are used to determine the shear band spacing. The hypothesis consisting in considering the proportion of plastic work dissipated as heat (quantified by the Taylor-Quinney coefficient ) as independent of the loading path is now recognized as highly simplistic. The present study attempts to provide a systematic approach to the inelastic heat fraction evolution for a general loading within the framework of thermoviscoplastic standard modeling, including a number of material parameters as strain hardening, strain rate sensitivity, and thermal softening. The effect of each material parameter on the shear band spacing is determined by using a power law constitutive relation. The Johnson-Cook and power law models are used to illustrate the influence of the constitutive relation on the results for the adiabatic shear band spacing by studying the response of HY-100 steel. We have compared our results with available experimental results in the literature over a very wide range of strain rates (103-105 s-1). In this study, we show that the variation in the Taylor-Quinney parameter β(γ) as a function of shear strain is an important parameter that plays a significant role in the calculation of the shear band spacing. [ABSTRACT FROM AUTHOR]

This work extends the results of a recently developed theory of a rather complete thermodynamic formalism for discrete-state, continuous-time Markov processes with and without detailed balance. We investigate whether and in what way the thermodynamic structure is invariant in a multiscale stochastic system, that is, whether the relations between thermodynamic functions of state and process variables remain unchanged when the system is viewed at different time scales and resolutions. Our results show that the dynamics on a fast time scale contribute an entropic term to the internal energy function us(x) for the slow dynamics. Based on the conditional free energy us(x), we can then treat the slow dynamics as if the fast dynamics is nonexistent. Furthermore, we show that the free energy, which characterizes the spontaneous organization in a system without detailed balance, is invariant with or without the fast dynamics: The fast dynamics is assumed to reach stationarity instantaneously on the slow time scale; it has no effect on the system's free energy. The same cannot be said for the entropy and the internal energy, both of which contain the same contribution from the fast dynamics. We also investigate the consequences of time-scale separation in connection to the concepts of quasi-stationarity and steady adiabaticity introduced in the phenomenological steady-state thermodynamics. [ABSTRACT FROM AUTHOR]

The spin transfer torque is essential for electrical magnetization switching. When a magnetic domain wall is driven by an electric current through an adiabatic spin torque, the theory predicts a threshold current even for a perfect wire without any extrinsic pinning. The experimental confirmation of this 'intrinsic pinning', however, has long been missing. Here, we give evidence that this intrinsic pinning determines the threshold, and thus that the adiabatic spin torque dominates the domain wall motion in a perpendicularly magnetized Co/Ni nanowire. The intrinsic nature manifests itself both in the field-independent threshold current and in the presence of its minimum on tuning the wire width. The demonstrated domain wall motion purely due to the adiabatic spin torque will serve to achieve robust operation and low energy consumption in spintronic devices. [ABSTRACT FROM AUTHOR]

Abstract: This work presents an experimental investigation to study the characteristics of combustion using a premixed methane–air mixture within a non-homogeneous porous inert medium (PIM) under high pressure and temperature. In order to obtain a stable flame under these operating conditions within PIM, a novel flame stabilization technique in porous inert media (PIM) combustion under high pressure and temperature has been developed and evaluated. The proposed technique avoids the draw backs of the hitherto developed techniques by properly matching the flow and flame speeds and, consequently, ensuring a stable combustion, for a wide range of operating pressure and temperature. The success of this technique permits the extension of PIM combustion to new applications such as gas turbines. The validity of this new technique has been assessed experimentally in detail by analyzing combustion inside a prototype burner. The effects of various operating conditions, such as initial preheating temperature and elevated pressure, have been examined for an output power range between 5 and 40kW. The experiments covered a broad spectrum of operating conditions ranging from a mixture inlet temperature of 20°C and pressure ratio of 1 up to a temperature of 400°C and a pressure ratio of 9. Evaluation of the results revealed excellent flame stability with respect to both flashback and blow-out limits throughout all the operating conditions studied, including relative air ratios far beyond the normal lean limit. While the blow-out stability showed no significant dependence on pressure, it was strongly determined by the preheating mixture inlet temperature. A remarkable broadening of the stability range from 0.6 to 1.0 on preheating to 400°C was observed. This reveals the potential of pre-heat temperature to improve the dynamic modularity of the burner. [ABSTRACT FROM AUTHOR]

steady state numerical study of combined laminar mixed convection and conduction heat transfer in a ventilated square cavity is presented. The air inlet gap is located at the bottom of a vertical glazing wall and air exits the cavity via a gap located at the top surface. Three locations for the opening at the top surface: left (case a), center (case b) and right side (case c) are considered. All the remaining surfaces are considered adiabatic. The mass, momentum and energy conservation equations were solved using the finite volume method for different Rayleigh numbers in the interval of 10 < Ra < 10 and Reynolds number in the interval of 100 < Re < 700. Temperature, flow field, and heat transfer rates are analyzed. The effect of the interaction between ambient conditions outside the glazing and the air inlet gap at the bottom for different air outlet gap positions at the top surface modifies the flow structure and temperature distribution of the air inside the cavity. The Nusselt number as a function of the Reynolds number was determined for the three cases. It was found that configuration for case (a) removes a higher amount of heat entering the cavity compared to cases (b) and (c). This is due to the short distance between the main stream and the glass wall surface. Thus, the forced airflow entering the cavity is assisted by the buoyancy forces, and most of the cavity remains at the inlet flow temperature, which should be appropriate for warm climates. These results may provide useful information about the heat transfer and fluid flow for future studies. [ABSTRACT FROM AUTHOR]

The article focuses on the macrokinetic analysis of heat recovery from the internal combustion process of adiabatic reactors to increase productivity. It says that the thermodynamic restriction of temperature near the adiabatic combustion temperature determines and limits the maximum productivity of the reactors. Furthermore, reactor productivity increase can be reached without additional energy consumption through hot reaction products which leave the reactor to heat initial reactants.

The effects of pressure drops on the performance characteristics of the air standard Otto cycle are reported. The pressure drops are assumed as constant values independent of the engine size. It has been shown that the pressure drops to about 60% of the maximum pressure in the ideal cycle (Curto-Risso et al., 2008). Three different models are studied: constant pressure model, reversible adiabatic expansion model and polytropic expansionmodel. The findings of this study show that, at this level of pressure drop, the maximum efficiency of the Otto cycle is reduced by 15% approximately based on the constant pressure model. The combined effect of pressure drop with other modes of irreversibility, for example, internal irreversibility and heat leaks, could reduce the maximum efficiency into very low values (approximately 30%). The reversible adiabatic model predicts reduction of 13% in efficiency at 40% pressure drop levels but at the price of zero power production. On the other hand, the polytropic expansion model predicts 40% reduction in efficiency for the same level of pressure drop (40%). All three models show that the power output is very sensitive to pressure drop. [ABSTRACT FROM AUTHOR]

An idealized reversible Otto cycle working with a single quantum mechanical particle contained in a potential well is investigated based on the Schrödinger equation in this paper. The model of a reversible quantum Otto cycle, which consists of two reversible adiabatic and two constant-well widen branches, is established. As an example, we calculate a particularly simple case in which only two of the eigenstates of the potential well contribute to the wave-function in the well. The relationship between the optimal dimensionless work out put W* vs. the efficiency η for the two-eigenstate system is derived. The efficiency of this quantum cycle is shown to equal that of a classical reversible Otto cycle because quantum dynamics is reversible. [ABSTRACT FROM AUTHOR]

We study the effects of optical nonlinearity in asymmetric adiabatic three-waveguide directional couplers, that consist of both linear and nonlinear waveguides. We consider several combinations of linear and nonlinear waveguides and show that the different combinations have different switching characteristics. We also find that in the structure where the central waveguide is nonlinear and the two outer waveguides are linear the nonlinearity does not play a role. [ABSTRACT FROM AUTHOR]

Abstract: This numerical study examines the combustion characteristics of premixed ammonia–air mixtures, with equivalence ratios around unity, at elevated pressure and temperature conditions which are encountered in SI engine operations. The laminar burning velocity, final flame temperature and species concentrations were determined using Konnov’s mechanism . A flat, freely propagating flame was considered. Both equivalence and compression ratios have an important impact on both the laminar burning velocity and the adiabatic flame temperature. Furthermore, only the variation of the equivalence ratio has a major impact on the formation of nitrogen monoxide. It was found that the compression ratio and the final temperature do not have a significant impact on NO yields for equivalence ratios above unity. [ABSTRACT FROM AUTHOR]

This paper presents both experimental and modeling investigations of a catalytic wall fuel processor consisting of coupled methane reforming and methane combustion sections. The reacting systems are both catalytic and the latter generates the heat required for the occurrence of the former. The catalytic wall reactor was examined for light-off behavior and for steady-state product distribution. On one hand, the analysis of the reaction products distribution after catalyst ignition indicated that in both combustion and reforming sections catalysts undergo to a relatively long transient (about 40 min) before reaching steady state conditions. On the other hand, a much longer reactor thermal transient was observed and the two transient behaviors appear independent of each other. Analysis of the reactor operating under real conditions (nonadiabatic) showed that a 3D model is needed to accurately predict the reactor performance because a 2D model, although much more convenient, cannot allow for the whole heat loss thereby yielding unreliable results. [ABSTRACT FROM AUTHOR]

n embedded-atom potential for rubidium has been calculated with the parameters chosen with the use of the results of the static tests at a temperature of 300 K and pressures up to 45 GPa, as well as the results of the shock tests at pressures up to 39 GPa. The molecular-dynamics simulation has been performed for temperatures of 300-10 000 K and pressures up to ∼94 GPa. The potential determined from the shock-test data does not provide complete agreement with the static data for 300 K. The pressure, energy, and specific heats C and C have been calculated for the compression up to 20% of the normal pressure and for temperatures up to 10 000 K. The derivative (∂ p/∂ T) is positive for all of the molar-volume and temperature values except for a compression ratio of 30%. Compression up to a factor of 2.5 or more is accompanied by the partial amorphization of the models, which is enhanced with heating. The calculations of the temperature along the Hugoniot curve under the assumption that the Grüneisen parameter and adiabatic compression modulus are independent of the temperature provide an incorrect molar-volume dependence of the pressure at 0 K. [ABSTRACT FROM AUTHOR]

Using a Sagdeev pseudopotential formalism where nonlinear structures are stationary in a comoving frame, large ion-acoustic solitary waves and double layers have been studied in plasmas with positive ions and nonthermal electrons. The velocity range of positive, compressive solitary waves is limited by the ion density reaching infinite compression, whereas negative, rarefactive solitary waves and double layers can exist when the electron nonthermality exceeds a certain minimum. There are even regions of coexistence, the limits of which can be elucidated by considering the properties of the special Sagdeev pseudopotential at the acoustic speed. In particular, when the compositional parameters and Mach numbers admit only compressive or rarefactive solitary structures, these have to be superacoustic, their amplitude vanishing at the acoustic speed. When both compressive and rarefactive modes can occur, one of them is Korteweg-de Vries (KdV)-like, the other having a non-KdV character, with a finite amplitude at the acoustic speed. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the combustion characteristics of low calorific gas in silicon carbide (SiC) foam. The temperature distribution, reaction zone, maximum temperature, and combustion wave propagation velocity were analysed at different inlet velocities, equivalence ratios of premixed gases, and pore densities. The temperature distribution near the reaction zone was determined by a time-based method. Super-adiabatic combustion was obtained in porous media under different conditions. The experimental results showed that higher temperatures were obtained in SiC foams of 30 pores per inch (PPI) than those measured for foam of 20 PPI. Increased equivalence ratio of premixed gases and pore density led to a thicker reaction zone and a higher preheating efficiency in the preheating zone. The combustion wave propagation velocity, which was less than 2mm/s under these experimental conditions, was increased with increased inlet velocity and decreased equivalence ratio of premixed gases. The combustion wave propagation in foams of 20 PPI had the lowest velocity because of the good match of convection and radiation. [Copyright &y& Elsevier]