分离式热管蒸发段工质流动不稳定性的试验研究

在试验台架上进行了可视化试验和模型试验,对分离式热管蒸发段工质流动的规律和工质流动的不稳定性进行了试验研究.可视化试验结果表明,对于小倾角布置的蒸发段,随着热流密度的增加,流型依次是泡状流、弹状流、波动泡沫状流;分离式热管蒸发段工质流动出现了流型转化型和密度波型两种不稳定性流动.通过模型试验确定了压力、质量流速、入口过冷度、热流密度、出口节流阻力等因素对不稳定性的影响,得出了流型转化型和密度波型不稳定性的界限.利用一维均相模型给出了计算不稳定性起始条件的无因次方程.     

THE SYNTHESIS OF A REACTIVE PYRIDINE INTERMEDIATE FOR FUEL INSTABILITY STUDIES

Pyridine compounds have been found in significant concentration in middle distillate fuels. These compounds have been implicated in fuel instability reactions and could also be involved in color body formation. Few pyridine compounds are commercially available and those that are available are relatively simple in structure. We report the synthesis of a reactive pyridine intermediate, l-carbethoxy-2-cyano-1,2-dihydropyridine, that could be used for a wide range of further pyridine compound synthesis including pyridines, and many other alkyl derivatives. This particular compound has been reported, but in very low yield. This reported improved synthetic procedure give yields in excess of 90%.     

An Artificial Neural Network (ANN) Model for Predicting Instability Regimes in Copper-Aluminum Alloys

Materials workability is one of the important aspects for any process design to achieve quality products. Identifying optimum process parameters like temperature, strain rate, and strain are normally done by trial and error. In recent years, processing maps are used in choosing these parameters for hot working of materials. Identification of these parameters requires certain high-level expertise as well as detailed microstructural evidences. In this study, using the available copper-aluminum alloy data, an Artificial Neural Network (ANN) model has been developed to classify the hot-working process parameters, like temperature, strain rate, flow stress for instability regime, directly from the corrected flow stress data without applying the Dynamic Materials Model (DMM). This model uses four compositions of Cu-Al system, ranging from 0.5% to 6% Aluminum. Details about the ANN architecture, and the training and testing of these models are explained. The results obtained using the ANN model are compared and validated with those obtained from the processing maps using DMM. It is further shown that even with smaller data set the development of an ANN model is possible as long as the data has some pattern in it.     

Evaluation of some self-sustained capillary effects taking place in slag at the interface during desulphurization process

In the paper are presented and analyzed some specific problems of instability and of Marangoni convection in desulphurizing slags at 1873.15 K, due to the presence of sulphur, during liquid steel treatments. Starting from the quantity sulphide capacity, a limit of sulphur solubility in a homogeneous liquid slag is established. The thermodynamic effect of sulphur in the slag is evaluated using an enthalpy of interaction of sulphur containing the balance of the partial molar enthalpy of mixing for CaS and CaO. The sulphur effect in slag, on the enhancement of the mass transfer coefficient through the interface is evaluated based on the expression of the concentration coefficient of the surface tension related to the mole fraction, the solutal Marangoni number and of the sulphur mass transfer enhancement parameters. It is concluded that during desulphurization, self-sustained capillary effects are present in slags.     

Systematic study of the Grüneisen ratio near quantum critical points

At any pressure-sensitive quantum critical point (QCP), the volume thermal expansion coefficient is more singular than the specific heat. Consequently, the resulting critical Grüneisen ratio Γ^cr∼β_cr/C_cr, where β_cr and C_cr denote the thermal expansion and specific heat after subtraction of non-critical background contributions, diverges. The related critical exponent ε in Γ^cr∼T^−ε can be used to characterize the nature of the underlying quantum critical fluctuations. We have performed a comparative study on various heavy fermion (HF) systems close to antiferromagnetic QCPs. In particular, we have studied (i) CeIn_3−xSn_x, (ii) CeNi₂Ge₂, (iii) YbRh₂(Si_0.95Ge_0.05)₂, as well as (iv) CeCu_5.8Ag_0.2, all of which show a divergent Grüneisen ratio. For the two former systems the critical exponent ε=1 is compatible with the predictions of the well-established Hertz-Millis-Moriya theory for three-dimensional extended quantum critical fluctuations. By contrast, for the two latter systems ε<1 is found to be incompatible with “conventional” quantum criticality. Our results thus suggest the existence of at least two different classes of QCPs in HF systems.     

蒸发液体射流表面三维不稳定色散方程的建立

讨论了蒸发黏性液体射流的不稳定性问题。假设环境介质的运动为势流运动,基态射流为流速恒定的平行流。对液体射流表面扰动采用简正模态分析法,并以贝塞尔函数的形式表达气相和液相控制方程的解,在射流边界上考虑液体蒸发速率对不稳定性的影响,建立了基于时间模式的射流三维不稳定扰动的色散方程,并对色散方程进行了无量纲化处理,论述了该色散方程对以往所建色散方程的兼容性,以此推进液体射流雾化机理的研究。     

Effects of controller and cubic temperature profile on onset of Bénard–Marangoni convection in ferrofluid

This study investigated the instability of Bénard–Marangoni convection in a horizontal layer of ferrofluid under the influence of a linear feedback control and cubic temperature profile. A linear stability analysis was performed. A single-term Galerkin technique was used to obtain the critical Marangoni number and critical Rayleigh number. The possibility of delaying the onset of convection by the application of linear feedback control is demonstrated.     

射流参数对加热条件下液膜射流破碎不稳定性的影响(2)--射流参数对液膜对称模式破碎的影响

利用对具有温度梯度的粘性液膜射流模型进行的不稳定性计算结果，研究了实际射流参数（射流速度）气体密度，液体粘性，液膜厚度，温度梯度，液体种类等）对对称模式扰动作用下液膜射流大，小尺度破碎模式破碎特征的影响规律，并探讨了决定液膜射流破碎尺度的实际因素。     

气体旋转运动对环膜液体射流不稳定性影响的研究

环膜液体射流的破碎机理研究对于GDI汽油机的雾化过程具有重要的意义。利用线性不稳定性理论研究了旋转气体运动对低阶和高阶模式黏性环膜液体射流破碎的影响。对于色散方程的数值计算结果表明,无论是对称模式还是非对称模式,低阶模式的扰动增长率通常较之高阶模式要大得多,但较之低阶模式扰动,高阶模式对气体旋转运动更为敏感。研究结果同时表明,对于非对称模式,无论是低阶模式还是高阶模式的扰动,气体旋转运动都是液体破碎的失稳因素;对于对称模式,气体旋转运动是低阶模式扰动的促稳因素,然而却是高阶模式扰动的强烈的失稳因素。     

An experimental study of flow boiling instability in a single microchannel

A simultaneous visualization and measurement study has been carried out to investigate stable and unstable flow boiling phenomena of deionized water in a single microchannel having a hydraulic diameter of 155 µm with a bottom Pyrex glass wall. Fifteen platinum serpentine microheaters, bonded on the Pyrex glass wall, were used to measure local instantaneous wall temperatures. At low mass flux, a syringe pump was used to drive the subcooled water passing through the microchannel. Stable and unstable flow boiling modes in the single microchannel are identified, and flow pattern maps in terms of heat flux and mass flux as well as in term of exit vapor quality are presented respectively. It was found that unstable flow boiling occurred in the single microchannel if the exit vapor quality x_e > 0.013.