Estimation of maximum shell-side vapour velocities through heat exchangers

Shell-side vapour velocities through heat exchangers should be kept low to prevent erosion when moisture or suspended particles present. In this work, simple-to-use equations, which are easier than currently available models and involve a fewer number of fitted parameters, requiring less complicated and shorter computations, are formulated to arrive at an appropriate prediction of maximum shell-side vapour velocities through heat exchangers for wide range of conditions as a function of molecular weight and pressure. The proposed fitted equations accurately estimate the maximum shell-side vapour velocities through heat exchangers for pressures up to 7500 kPa(abs), and molecular weights up to 400. The values calculated here are maximum for reasonable operation. In order to reduce pressure drop, velocities must be well below the maximum values. Estimations are found to be in excellent agreement with the reported data in the literature with average absolute deviation being around 3.9%. The fitted equations developed in this study can be of immense practical value for the engineers and scientists to have a quick check on the maximum shell-side vapour velocities through heat exchangers at wide range of conditions without opting for any experimental measurements. In particular, chemical and process engineers would find the simple equations to be user-friendly with transparent calculations involving no complex expressions.     

PVC-U异型材耐候性评价方法分析

分析了硬质聚氯乙烯(PVCU)异型材耐候性的各种试验评价方法。指出刚果红试验、动态热稳定性试验、烘箱试验、紫外灯照射试验等4种试验方法因破坏因素单一而距异型材的实际老化情况有一定差距;快速紫外线(QUV)老化试验和氙灯老化试验均兼顾了热、紫外线、氧和湿度的环境因素,能较准确地预测异型材的长期耐候性;而暴晒场试验是在完全真实环境下的检测,对异型材的长期耐候性预测结果最为准确。     

煤燃烧中铬与氧的反应机理研究

探索使用了高级量子化学从头计算法来研究来铬与氧的反应机理。分别优化了两个研究反应的反应物，过渡态，中间体和产物的几何构型，并且计算出反应的热效应，熵变，活化能和绝对速率常数，并与文献数据进行了比较，计算结果与文献数据比较吻合，表明量子化学计算是研究铬等痕量元素气相反应机理和计算热力学及动力学参数的一种有效手段。     

A DIFFERENTIAL APPROACH TO HEAT PIPE PRIMING IN MICROGRAVITY

Presented here is a study of the forces governing the liquid and vapor flow, in an external artery heat pipe. A differential analysis was performed on the heat pipe based upon the continuity and momentum equations.

Using these fundamental equations, a computer model was developed, capable of predicting the fluid motion resulting from the surface tension and viscous frictional forces in a microgravity environment. The model used a nested iterative technique to first establish the pressure distribution along the longitudinal axis of the heat pipe for a known displacement. Then the time necessary, for a given fluid to initially assume or return to the configuration required for proper operation was calculated.

In addition to providing an estimate of the required priming time, the model predicted that priming could be prematurely terminated. Comparisons of the predicted priming time and priming limitations were made with the results of an experimental test package flown on the NASA KC-135 Zero-g aircraft. The results of this comparison helped to establish the accuracy of the modeling techniques.     

A DISTRIBUTED PARAMETER APPROACH TO THE DYNAMICS OF ROTARY DRYING PROCESSES

A nonequilibrium distributed parameter model for rotary drying and cooling processes described by a set of partial differitial equations with nonlinear algebraic constraints is developed in this work. These equations arise from the multi-phase heat and mass balances on a typical rotary dryer. A computational algorithm is devekped by employing a polynonial approximation ( orthogonal collocation) with a glotal splinc technique leading to a differential-algebraic equation ( DAE) system. The numerical solution is carried out by using a standard DAE solver.

The two- phase-flow heat transfer coelficient is computed by introducing a correction factor to the commonly accepted correlations. Since interaction between the falling particles are considered in the correction factor,the results are more reliable than those computed by assuming that heat transfer between a single falling particle and the drying air is unaffected by other particles. The heat transfer computations can be further justified via a study on the analogies between heat and mass transfer.

The general model devloped in this work is mathematically more ritorous yet more flexible that the lumped parameter models established by one of the authors (Douglas et al., (1993)). The three major assumptions of an equilibrium operation, perfect mixing and constant drying raic, are removed in the distributed parameter model.

The simulation results are compared with the operational data from an industrial sugar dryer and predictions from earlier models. The model and algorithm successfully predict the steady state behaviour of rotary dryers and collers. The generalized model can be applied to fertilizer drying processes in which the assumption of constant drying rate is no longer valid and the existing dynamic models are not applicable.     

A DISTRIBUTED PARAMETER APPROACH TO THE DYNAMICS OF ROTARY DRYING PROCESSES

ABSTRACT

A nonequilibrium distributed parameter model for rotary drying and cooling processes described by a set of partial differitial equations with nonlinear algebraic constraints is developed in this work. These equations arise from the multi–phase heat and mass balances on a typical rotary dryer. A computational algorithm is devekped by employing a polynonial approximation ( orthogonal collocation) with a glotal splinc technique leading to a differential–algebraic equation ( DAE) system. The numerical solution is carried out by using a standard DAE solver.

The two– phase–flow heat transfer coelficient is computed by introducing a correction factor to the commonly accepted correlations. Since interaction between the falling particles are considered in the correction factor,the results are more reliable than those computed by assuming that heat transfer between a single falling particle and the drying air is unaffected by other particles. The heat transfer computations can be further justified via a study on the analogies between heat and mass transfer.

The general model devloped in this work is mathematically more ritorous yet more flexible that the lumped parameter models established by one of the authors (Douglas et al., (1993)). The three major assumptions of an equilibrium operation, perfect mixing and constant drying raic, are removed in the distributed parameter model.

The simulation results are compared with the operational data from an industrial sugar dryer and predictions from earlier models. The model and algorithm successfully predict the steady state behaviour of rotary dryers and collers. The generalized model can be applied to fertilizer drying processes in which the assumption of constant drying rate is no longer valid and the existing dynamic models are not applicable.     

CALCULATING PSEUDO-STEADY-STATE HORIZONTAL OIL WELL PRODUCTIVITY IN RECTANGULAR DRAINAGE AREAS USING A SIMPLE METHOD

To determine the economical feasibility of drilling a horizontal well, engineers need reliable methods to estimate its productivity. In this work, a simple-to-use method is developed to rapidly estimate a pseudo-steady-state horizontal well's productivity. Estimations are found to be in excellent agreement with the reliable data in the literature, with average absolute deviation being less than 1%. The tool developed in this study can be of immense practical value for petroleum engineers to make a quick check on a pseudo-steady-state horizontal well's productivity at various conditions without opting for any field trials. The predictive tool is simple and straightforward, and it can be readily implemented in a standard spreadsheet program. The prime application of the method is as a quick-and-easy evaluation tool in conceptual development and scoping studies where horizontal wells are being considered. The method may also serve as a benchmark in numerical reservoir simulation studies.     

SPECTRAL ANALYSIS OF A STATIONARY BIVARIATE POINT PROCESS WITH APPLICATIONS TO NEUROPHYSIOLOGICAL PROBLEMS

Abstract. In this paper we discuss the spectral analysis of a stationary bivariate point process applied to the study of a complex physiological system. An estimate of the cross-spectral density can be obtained by smoothing the modified cross-periodogram statistic. The smoothed estimate is calculated by dividing the whole length of the data into a number of disjoint subrecords. Estimates of the coherence function and the cross-intensity function follow directly from the estimate of the cross-spectral density. It is shown that the asymptotic properties of the estimate of the cross-intensity function can be improved by inserting a convergence factor in it. Examples of the estimates are illustrated by using two data sets from neurophysiological experiments and their importance is emphasized by examining the behaviour of the complex physiological system under study.     

An experimental facility for determination of steady flame spread rate of materials employing the Quasi-stationary flame front technique

An experimental facility based on the Quasi-stationary Flame Front Technique for determination of steady flame spread rate of materials at discrete levels of external radiant heat flux was developed. The method employs an external radiant heat source in front of which an element of a specimen of the material is positioned at a location corresponding to the desired level of external radiant heat flux. A specimen movement assembly, which can be operated manually, was designed for moving the specimen towards the stationary external radiant heat source such that the flame front could be maintained quasi-stationary. The experimental technique employed is simple in operation yet is capable of yielding reliable flame fornt displacement–time data. In the paper the design considerations of the experimental facility, details of its components, calibration and typical experimental results obtained are presented.     

A 2-D MICROSCOPIC SIMULATION OF HEAT AND MASS TRANSPORT IN DRY SNOW

The problem of acid deposition and its effects on the environment is receiving increasing attention in North America and Europe. The interaction between

seasonal snowcovers and deposited pollutants is of particular importance because a snowpack accumulates and stores pollutants which can ultimately be released in a rapid pulse with the first melt water in the springtime. As a direct result of an impurity pulse, water quality degrades with deleterious effects on the local environment and aquatic biological species. The timing and severity of an inpurity pulse is dependent upon the redistribution of pollutants in a snowpack which is attributed to a process known as temperature gradient metamorphism.

This work investigates the influence of geometry, density and temperature on the coupled heat and mass transport in idealized, two dimensional ice lattice cells. Mass flux, concentration and temperature distributions, as well as effective diffusion coefficients and thermal conductivities are presented as functions of temperature, geometry, and density. A finite element model of the coupled, heat and mass transport is used to analyze the problem on a microscopic scale in two dimensions. Deforming meshes are used to simulate the growth/decay process which occurs over time in an ice lattice pore.     

A HYBRID CFD COMPARTMENTALIZATION MODELING FRAMEWORK FOR THE SCALEUP OF BATCH COOLING CRYSTALLIZATION PROCESSES

Crystallizer design is often hindered by the lack of scaleup rules, hydrodynamic information, and predictive crystallization modeling tools. A hybrid CFD compartmentalization batch cooling crystallizer model is proposed to take into account localized mixing, heat transfer, and fluid hydrodynamics, combined with key process engineering information obtained on a laboratory scale. The compartments were identified using CFD simulations based on the crystallizer geometry and operating conditions. The population, mass, concentration, and energy balance of each compartment is modeled separately as a well-mixed MSMPR unit with input and output streams. The software gPROMS (Process Systems Enterprise Limited) is a process-modeling tool that can facilitate compartmental modeling and will be used for the prediction of the crystallization behavior upon scaleup.     

A HYBRID CFD COMPARTMENTALIZATION MODELING FRAMEWORK FOR THE SCALEUP OF BATCH COOLING CRYSTALLIZATION PROCESSES

Crystallizer design is often hindered by the lack of scaleup rules, hydrodynamic information, and predictive crystallization modeling tools. A hybrid CFD compartmentalization batch cooling crystallizer model is proposed to take into account localized mixing, heat transfer, and fluid hydrodynamics, combined with key process engineering information obtained on a laboratory scale. The compartments were identified using CFD simulations based on the crystallizer geometry and operating conditions. The population, mass, concentration, and energy balance of each compartment is modeled separately as a well-mixed MSMPR unit with input and output streams. The software gPROMS (Process Systems Enterprise Limited) is a process-modeling tool that can facilitate compartmental modeling and will be used for the prediction of the crystallization behavior upon scaleup.     

THREE-DIMENSIONAL CALCULATIONS OF EXPLOSION CONTAINMENT IN FAST REACTORS

The application of a general three-dimensional finite-difference solution technique for two-phase flows to calculations of explosion containment in a model geometry representative of a typical fast-breeder reactor is described. The solution method employs phase-conservation equations to determine the locations of gas/liquid interfaces, and a two-velocity-set procedure which allows tangential slip at the interfaces. Results are presented for an idealised axisymmetric geometry and for a case representative of the three-dimensionality occurring in a reactor design, where the sodium pool contains pumps and heat exchangers. These highlight the differences in the flow and forces acting on the containment structure associated with the three-dimensional geometry. It is concluded that three-dimensional containment calculations can be performed reasonably economically, and they are necessary to predict all aspects of practical reactor geometries.     

管式炉传热数学模型

本文研究了管式炉辐射传热,提出了焰墙黑度ε_gω新概念,从而导出了新的传热数学模型 q=4.96ε_0 F_c/(F_c)〔（T_g/100）~4-（T_c/100）~4〕+a_k（T_g-T_c）上述模型可以计算近代生产乙烯裂解管式炉。对于箱式加热管式炉和圆筒加热管式炉的传热计算,也提出了相应的数学模型。 用本文提出的方法和另外两种通用的方法进行了6种裂解管式炉的计算。计算结果表明,此法计算简单,计算值与实际值符合得很好。     

THREE-DIMENSIONAL CALCULATIONS OF EXPLOSION CONTAINMENT IN FAST REACTORS

The application of a general three-dimensional finite-difference solution technique for two-phase flows to calculations of explosion containment in a model geometry representative of a typical fast-breeder reactor is described. The solution method employs phase-conservation equations to determine the locations of gas/liquid interfaces, and a two-velocity-set procedure which allows tangential slip at the interfaces. Results are presented for an idealised axisymmetric geometry and for a case representative of the three-dimensionality occurring in a reactor design, where the sodium pool contains pumps and heat exchangers. These highlight the differences in the flow and forces acting on the containment structure associated with the three-dimensional geometry. It is concluded that three-dimensional containment calculations can be performed reasonably economically, and they are necessary to predict all aspects of practical reactor geometries.     

双螺杆转速差决定的螺杆间隙之探讨

根据相对运动原理计算了同向旋转双螺杆因螺杆转速差决定的两螺杆之间的径向和轴向间隙,可为工程上设计这些间隙时提供参考。     

散射介质中辐射全交换面积的求解方法

在辐射交换面积叠加方法基础上,从辐射传热机理出发,定义了散射热流密度并给出矩阵表达式,用于分析介质的散射特性,推导出各向同性散射介质参与条件下辐射全交换面积各分量矩阵以及总矩阵的合成,所得结果与Noble方法完全一致。并模拟研究了介质的散射对辐射热交换的影响。该方法物理意义明确,推导过程简便,便于理解与分析,有利于准确求解各向同性散射介质参与的辐射换热问题。     

An exercise in obtaining flame radiation fraction from the cone calorimeter

The radiant fraction of the heat of combustion emitted by flames of burning fuels is an important quantity needed to predict the thermal radiation from pool fires to remote targets and as a local flame parameter in CFD models. Although there are data for radiant fraction of gas flames, there are little data for this parameter for burning solid materials. The sole source of these data is Archie Tewarson, who used the FMGlobal Fire Propagation Apparatus to compute the radiant fraction of the heat of combustion from energy losses associated with enthalpy flow and duct heat losses. This paper describes a similar approach to obtain the radiant fraction of the heat from flames of burning solids using the cone calorimeter. In the present work, the cone calorimeter is calibrated using a Meeker burner with a premixed methane/air flame that is small and blue and has minimum flame radiation. A heat loss correction factor due to thermal conductance from the duct to the ambient air is determined from the calibration by measuring the temperature of the combustion stream in the duct at the gas sampling location. That factor was found to be 13 ± 2 W/K by calibration compared with a theoretical estimate of 9.3 W/K. The effect of the heat capacity of the duct walls is accounted for by de‐convoluting the duct temperature history. The necessary measurements to compute the radiant fraction then become the heat release rate by oxygen consumption, the mass flow rate in the duct, and the gas temperature in the duct at the sampling location. Results were obtained for 15 polymers, eight of which could be compared with data for nominally similar materials obtained by Tewarson. In addition, results are found to be in good agreement with a correlation by Tewarson in terms of combustion efficiency. Copyright © 2016 John Wiley & Sons, Ltd.     

换热网络的同步综合设计

提出了换热网络的一种新的转运模型,以并串模式和非等温混合过程描述换热网络的热力学和经济性的总要求,不使用挟点分离、最小单元数等启发式规则,并允许交叉换热和不同物流间的膜传热系数与温差合理匹配.这一模型与优化模型相结合,自动产生换热网络,确定相应的最优公用工程费用、换热面积、换热器台数与冷热流间的匹配,其可行域由一集线性约束确定,鲁棒性很好,易于求解.该方法克服了换热网络的各种分步骤综合方法的缺陷(包括挟点技术、双温差法及相关数学规划方法).与文献上其它同步优化方法比较,具有模型简单、规模小、可算性强、初始化简易、计算结果可靠的优点.通过对文献中广泛使用的例题的检验,结果优于现有的其它方法.     

ON THE PREDICTION OF HEATS OF VAPORIZATION OF PURE COMPOUNDS

An expression to predict the values of the latent heat of vaporization of pure compounds at their normal boiling point has been developed. A knowledge of the critical temperature, critical pressure, normal boiling point and acentric factor of the compound coupled with the use of generalized correlations for second virial coefficient and liquid molar volume allows to obtain good estimates, particularly for alcohols and ketones. Results for 71 various substances are compared with experimental values and with the results of eight other equations available in the literature. The possibility of using the calculated heats of vaporization at the normal boiling point to estimate values at other temperatures is discussed.