Thermal ignition of a heterogeneous system in a stirring semibatch reactor

The thermal ignition of a heterogeneous two-phase system of two immiscible liquids in a stirring semibatch reactor was modeled. The model took into account the dispersion of one phase in the other, the mass transfer of a reagent from the disperse phase into the dispersion medium, and the bimolecular exothermal reaction that occurred in the latter. The kinetic dependences of reagent concentrations, the dynamics of reactor heating, and the critical conditions of thermal ignition were studied. It was found that the initial temperature of the reactor had a considerable effect on its dynamic behavior.     

Steady regimes of exothermic autocatalytic reaction in a continued stirred-tank reactor

A continued stirred-tank reactor with an exothermic autocatalytic reaction running in it is modeled. In contrast to the simple kinetic law formulated in terms of a first-order equation, a variety of possible types of thermal isoclines, including isoles, are found for the autocatalytic process in the dimensionless “degree of conversion-temperature” coordinates. A bifurcation curve separating the domains of existence of one and three steady states is constructed in the Se-Da coordinates.     

Thermal regimes in a primary fluid heated by solar energy in a linear collector

Summary The steady-state heat transfer equation has been solved for the determination of temperature profiles in a diathermic oil flowing through a linear boiler placed on the focal line of cylindrical parabolic solar concentrators. Finite-difference methods have been employed to solve the equation, by assuming Nikuradse velocity profiles and available experimental data to supply boundary conditions and to estimate equation parameters. A set of solutions for several physical and geometrical situations is shown and discussed in order to give useful indications on the design of solar power plant.

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Riassunto Si risolve l'equazione del calore in regime stazionario per la determinazione dei profili di temperatura in un olio diatermico che scorre in una caldaia lineare posta sull'asse focale di un concentratore cilindrico parabolico solare. Per risolvere l'equazione si sono impiegati metodi alle differenze finite, assumendo profili di velocità di Nikuradse e i dati sperimentali disponibili per fornire le condizioni al contorno e per stimare i parametri dell'equazione. Si mostra e si discute una serie di soluzioni per parecchie situazioni fisiche e geometriche, così da fornire utili indicazioni sul progetto di una centrale solare.

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Резюме Решаются уравнения сохранения энергии для определения переходного поведения солнечной силовой установки. Используя типичные параметры установки и имеющиеся экспериментальные данные, указанные уравнения решаются с помощью метода конечных разностей. Рассматриваются различные физические и геометрические конфнгурации. Анализируются полученные результаты и делаются указания, касающиеся проекта солнечной силовой установки.

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To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Possible regimes of molecular excitation in a hypothetical laser-chemical reactor based on an infrared free-electron laser

Different modes of operation of a hypothetical infrared free-electron laser-chemical reactor are discussed. Simple relationships are obtained for estimating the parameters of the reactor and the radiation intensity necessary for the excitation of molecules in each particular case. Zh. Tekh. Fiz. 67, 55–59 (April 1997)     

气液混输管线与立管系统严重段塞流数值研究

针对气液混输管线与立管系统严重段塞流问题, 采用严重段塞流形成条件一致的等效原则, 发展了一种将三维管道系统等效为二维管道系统的计算流体力学(CFD)数值模拟方法. 以文献中某下倾管与立管组合系统为对象, 结合其实验工况, 对严重段塞流气液流动过程进行了数值模拟, 获得了其周期、压力波动幅值及喷发时间等关键参数的变化规律, 数值模拟与文献所述实验结果符合. 在此基础上, 建立了立管入口气液折算速度、立管含气率以及立管出口平均速度的理论模型, 获得了这些关键参数随时间的变化规律, 并给出了确定立管内气液流型变化的理论方法, 理论结果与CFD数值模拟结果一致. 建立的CFD方法大幅缩减了严重段塞流数值模拟所需的时间和资源, 推导的理论模型揭示了严重段塞流特性参数之间的关联, 可以对严重段塞流所引发的危害进行快速评估及预测,具有一定的工程应用价值.     

Thermal regimes of passivative oxide film formation on Al surface: Theoretical and experimental study

We report results of ab initio molecular dynamics simulations of an Al surface exposed to an oxygen atmosphere. The results, supported by experiments performed in this study, demonstrate that the Al surface, by reacting with the oxygen molecules, can be heated above melting temperature and transformed into a liquid. This process is potentially capable of creating an amorphous corrosion scale which might possess an enhanced resistance to deterioration.     

Noise-induced collective regimes of complex system in contact with a random reservoir

Based on a system-reservoir model, where the reservoir is driven by an external white Gaussian noise, we study the behavior of system components in Weiss mean-field approach and Gaussian approximation for moments. Crossover from individual to cooperative dynamics of the system components is due to noise. The system displays a transition similar to diversity-induced phase transition. The analytical results are compared with the numerical simulations.     

Investigation of oscillation regimes for a modified Carnot engine: I. Conservative oscillation regimes

The Carnot engine, the model from which the concept of entropy arose, is a parametric generator. A certain modification of the engine has allowed it to be brought into the periodic regime of a stable limit cycle. A formula identical to the expression for the oscillation frequency of a Helmholtz resonator has been derived for the piston oscillation frequency in a quasi-harmonic small-amplitude regime. The shape of the piston oscillations and the form of the phase trajectories are considered in computer simulations for various initial conditions and large amplitudes.     

Thermal fluctuations in a Knudsen flow system

Spatial correlations of thermal fluctuations in a model system are examined. The system is a one-dimensional chain of cells containing a dilute gas and connected by Knudsen apertures. A Monte Carlo simulation is described in which the long range correlations observed agree quantitatively with a general master equation formulation.     

Thermal conduction in a homogeneous two-phase system

Assuming a regular geometry of dispersed phase (λ ₂) an integrated theory for the effective thermal conductivityλ _e of all kind of two-phase materials (including loose materials) is developed. The flux modification is carried out by considering the effective neighbouring interactions in the solution of Poisson’s equation. A comparison of calculatedλ _e values with the reported experimental results over a wide range of two-phase materials shows a good agreement.     

Consecutive reactions in a countercurrent plug-flow reactor. Gas-liquid system

A mathematical model of a bimolecular two-step consecutive exothermic reaction in the liquid phase of a gas-step consecutive exothermic reaction in the liquid phase of a gas-flow reactor is proposed. Spatial profiles of the heatings and relative concentrations of the reactants in both phases for the steady state of the system are presented. The behavior of the reaction intermediate product is examined. The kinetic characteristics of the reaction are demonstrated to substantially influence the behavior of the system in the reactor.     

重力再循环供液制冷系统气液分离器的试验研究

通过计算得出气液分离器有效高度和气液分离器的直径,设计出两种气液分离器,并分别实验对比。实验结果表明,气液分离器的结构形式对重力供液制冷系统的性能影响较小,由于分离器直径减小了25%,分离器内制冷剂存储量大大减少,当液位处于控制液位时,分离器存储量仅为原来的19.1%,而压缩机的吸气压力基本保持不变,排气压力有所降低,并且对系统制冷量及COP影响很小,最大差值在-20℃工况,相差0.043。     

气力提升系统气液两相流数值模拟分析

污水处理、油田采油、液态金属冷却反应堆和磁流体动力转换器等领域采用气力提升系统有其显著优势.由于不同液体介质与气体介质密度对气力提升系统性能影响较大,因此本文基于Fluent仿真软件,采用欧拉模型、k-ω剪切应力输运湍流模型数值模拟了氮气-水、氮气-煤油、氮气-水银及空气-水、氩气-水、氮气-水下气力提升系统内气液两相流动行为,分析了系统稳定时提升立管内气相体积分数、提升液体流量、提升效率、提升管出口处液体径向速度的变化规律.研究结果表明:1)氮气-水、氮气-煤油、氮气-水银系统中,提升管内液体介质密度越大,提升管内气相体积分数越小、提升液体流量越大、提升效率越高;2)空气-水、氩气-水、氮气-水系统中,提升管内气体介质密度越大,提升管内气相体积分数越小、提升液体流量越大、提升效率峰值越小;3)提升管出口处提升液体径向速度随气体充入量的不断增加而整体波动升高,最终管轴中心附近液体速度较大,管壁附近液体速度较小.本文研究成果为污水处理、气举采油、液态重金属冷却核反应堆和磁流体动力转换器等应用领域的气力提升技术的优化提供科学的理论基础.     

Self-organized phenomena of pedestrian counterflow through a wide bottleneck in a channel

The pedestrian counterflow through a bottleneck in a channel shows a variety of flow patterns due to self-organization.In order to reveal the underlying mechanism,a cellular automaton model was proposed by incorporating the floor field and the view field which reflects the global information of the studied area and local interactions with others.The presented model can well reproduce typical collective behaviors,such as lane formation.Numerical simulations were performed in the case of a wide bottleneck and typical flow patterns at different density ranges were identified as rarefied flow,laminar flow,interrupted bidirectional flow,oscillatory flow,intermittent flow,and choked flow.The effects of several parameters,such as the size of view field and the width of opening,on the bottleneck flow are also analyzed in detail.The view field plays a vital role in reproducing self-organized phenomena of pedestrian.Numerical results showed that the presented model can capture key characteristics of bottleneck flows.     

Evaluating the efficiency of thermo-electric conversion of heat from gas combustion in a small-scale system with counterflow heat exchange

The efficiency of thermoelectric conversion of heat from gas combustion was evaluated in a small-scale system consisting of two channels with opposing gas flows and thermocouples located in the separating wall. Combustion occurred in the chamber fed with fresh mixture heated by combustion products through heat-conducting walls of the channel. In the channel walls, there were thermoelectric converters. It has been shown that in this system, the maximum conversion efficiency of heat from gas combustion may be close to the maximum efficiency of thermoelectric conversion calculated by the maximum acceptable working temperature of the hot side of the converter. This conclusion is valid in the case when the adiabatic combustion temperature of the gas mixture is below the maximum allowable operating temperature of the hot side of the thermoelectric converter. The considered system is promising for the burning of low-calorific gas mixtures and does not require additional energy for cooling the cold side of the thermoelectric converter.     

Stabilized,flat iron flames on a hot counterflow burner

Metal powder combustion has traditionally been studied to mitigate the risk of industrial accidents and to determine the contributions of metals as additives to the performance of energetic materials. Recently, there has been growing interest in exploring the potential of metal powders as recyclable, zero-carbon energy carriers as an alternative to the hydrocarbons known to contribute to climate change. The present work introduces, for the first time, a stabilized flat iron flame. The counterflow burner used in this work is comprised of an inverted ceramic nozzle which sits above, and is aligned axially with, a lower nozzle producing a laminar flow of particles suspended in an oxidizing gas. A stabilized methane flame sits inside the top nozzle and the hot combustion products impinge upon the two-phase flow from the bottom nozzle, creating a stagnation plane. Spherical iron powder, with 90% of the particles less than 2.5 µm in size, is pre-loaded into a piston and dispersed using mixtures of 30% and 40% oxygen balanced in argon. Flame speeds are measured using particle image velocimetry (PIV), while flame temperatures are determined using multicolour pyrometry. It is found that flame speeds range between 30 cm/s and 45 cm/s for both oxidizing mixtures. Despite having fuel loadings below stoichiometric concentrations, the observed particle combustion temperatures are close to the adiabatic flame temperature of the stoichiometric mixture, indicating combustion in the diffusion-controlled regime for these small particles. Finally, the independence of the flame speeds with respect to oxygen concentration suggests flame propagation in the discrete regime.     

Thermal entanglement in a triple quantum dot system

We present studies of thermal entanglement of a three-spin system in triangular symmetry. Spin correlations are described within an effective Heisenberg Hamiltonian, derived from the Hubbard Hamiltonian, with super-exchange couplings modulated by an effective electric field. Additionally a homogenous magnetic field is applied to completely break the degeneracy of the system. We show that entanglement is generated in the subspace of doublet states with different pairwise spin correlations for the ground and excited states. For the doublets with the same spin orientation one can observe nonmonotonic temperature dependence of entanglement due to competition between entanglement encoded in the ground state and the excited state. The mixing of the states with an opposite spin orientation or with quadruplets (unentangled states) always monotonically destroys entanglement. Pairwise entanglement is quantified using concurrence for which analytical formulae are derived in various thermal mixing scenarios. The electric field plays a specific role – it breaks the symmetry of the system and changes spin correlations. Rotating the electric field can create maximally entangled qubit pairs together with a separate spin (monogamy) that survives in a relatively wide temperature range providing robust pairwise entanglement generation at elevated temperatures.     

汽液分离器对两相流引射器制冷系统性能的影响

针对汽液分离效果差的问题,重新设计了应用于两相流引射器制冷系统的汽液分离器,将使用新汽液分离器的两相流引射器制冷系统的性能与原系统进行了比较,分析了汽液分离器对引射器性能及制冷系统性能的影响。实验结果表明:重新设计的汽液分离器分离效果大大改善,对于不同的实验工况条件,采用新设计的汽液分离器的两相流引射制冷系统,主蒸发器制冷量由占总制冷量的21.1%~27.8%,提升到82.2%~87.3%,主蒸发器起到了主要作用;在引射器结构参数相同的条件下,引射器的引射比由0.2~0.46提升到0.56~0.64;采用新设计的汽液分离器系统制冷量和COP均与原系统基本相同。