Hybrid solution for the laminar flow of power-law fluids inside rectangular ducts

 The so-called generalized integral transform technique (GITT) is employed in the hybrid numerical–analytical solution of two-dimensional fully-developed laminar flow of non-Newtonian power-law fluids inside rectangular ducts. The characteristic of the automatic and straightforward global error control procedure inherent to this approach, permits the determination of fully converged benchmark results to assess the performance of purely numerical techniques. Therefore, numerical results for the product Fanning friction factor-generalized Reynolds number are computed for different values of power-law index and aspect ratio, which are compared with previously reported results in the literature, providing critical comparisons among them as well as illustrating the powerfulness of the integral transform approach. The resulting velocity profiles computed by using this methodology are also compared with those calculated by approximated methods for power-law fluids, within the range of governing parameters studied. Received 16 March 2000     

Laminar flow inside hexagonal ducts

Analytical solutions are obtained for fully developed laminar flow inside hexagonal ducts and, as a special case, rhombic ducts, through application of the recently advanced generalized integral transform technique for the solution of diffusion-type problems within irregular domains. First, the formal complete solution of the original problem is obtained, in terms of a denumerable system of coupled ordinary differential equations. Then, an explicit and quite straightforward lowest order solution results from the appropriate simplification of the coupled system. Quantities of particular interest in the field of heat exchanger thermohydraulics are then systematically presented, and utilized to establish the accuracy and suggest application ranges for the approximate solution.Communicated by S. N. Atluri, May 11, 1989     

Decay of laminar flow inside a retarded rotating cylindrical vessel

Summary The effect of finite retardation of a rotating cylindrical vessel on the decay process of viscous fluid flow inside the vessel is considered analytically. Exact solution for instantaneous velocity profiles is presented. An instability layer is defined in accordance with Rayleight's criterion. The thickness of this layer is derived and dependence on retardation is discussed.Nomenclature a cylinder radius - D _inst instability thickness, dimensionless - j _n n-th zero of Bessel functionJ ₁,n=1, 2, ... - r, R dimensional and dimensionless radial co-ordinate - R _inst (1–D _inst) - s complex Laplace variable - t, T dimensional and dimensionless time - t ₀,T ₀ dimensional and dimensionless time constant - U complement velocity=R–V - U ^* auxiliary velocity, see text - V tangential velocity, dimensionless - kinematic viscosity - initial angular speed of cylinder - circulation With 4 Figures     

Finite element analysis of laminar flow in the entrance region of ducts

This paper presents a generally applicable approach to developing laminar flow problems in straight ducts of arbitrary shape. A three-level central alogrithm which does not require iterations is used to march ahead with the solution in the axial direction. The calculation procedure can be implemented by utilizing, with minor modifications, any standard finite element code for linear heat conduction. Several illustrative examples demonstrate accuracy and versatility of the proposed technique.     

Improved resolution three-dimensional integral imaging using optimized irregular lens-array structure

A rigorous approach is proposed to improve the resolution of integral imaging (InI) by finding the appropriate form of irregularity in the arrangement of the InI lenslets. The improvement of the resolution is achieved through redistribution of the sampling points in a uniform manner. The optimization process for finding the optimum pattern of the lens-array irregularity is carried out by minimizing a cost function, whose mathematical closed-form expression is provided. The minimization of the proposed cost function ensures the uniform distribution of sampling points and thus improves the resolution within the desired depth of field (DOF) and field of view (FOV). A set of standard resolution charts is used to demonstrate the improvement of the quality of the three-dimensional (3D) images obtained by using the optimized irregular lens array. It is shown that the overall level of the lateral and depth resolutions is improved at the same time.     

Model for chemical vapor deposition of nanostructured ceramics inside tubes under high temperature laminar flow conditions

This paper describes the mathematical modeling of a CVD process designed to coat the inside of a tube with a ceramic film. The film was analyzed by XPS to reveal layers of nanostructure where SiCO changed to SiOC stoichiometry at sputtering depths of 33 nm. Relevant expressions are either derived from first principles or constructed using commonly measured processing parameters. These equations include parameters, such as the gas residence time and precursor pump rate, which are both useful to the researcher and necessary for a plant operator.     

Simulation of rate dependent fracture in concrete using an irregular lattice model

An irregular lattice model is used to simulate concrete fracture behavior under dynamic loadings. The numerical approach is based on rigid-body-spring networks, in which a visco-plastic damage model is applied to describe the rate dependency. A direct tensile test is simulated at various strain rates, and the dynamic strength increase is obtained in terms of dynamic increase factor (DIF). The DIFs are compared with a previous experimental and empirical study to calibrate the visco-plastic parameters. Next, a three-point-bending test is conducted numerically under impact and slow loadings, where the mixed-mode fracture is set up with a notch offset from the midspan. The rate-sensitive failure features are shown at the two different loading rates, and the rate effect on the failure mechanism is related with the peak load in the loading history. This study provides qualitative and quantitative understandings of the rate dependent failure behaviors in concrete.     

Effects of wetted wall on laminar natural convection in vertical annular ducts

Abstract

A detailed numerical analysis is performed to investigate the effects of latent heat exchange, in connection with evaporation of the liquid film on the wall, on the natural convection heat transfer in vertical concentric annuli. Major governing parameters identified are Gr_T, Gr_M, Pr, Sc, and N. Results are specifically presented for an air‐water system under various heating conditions to illustrate the latent heat transport during the evaporation process. The effects of the channel length, ratio of radii N and wetted wall temperature on the momentum, heat and mass transfer are examined in detail. Tremendous enhancement in heat transfer due to the exchange of latent heat was clearly demonstrated.     

Numerical analysis of nanofluid flow inside a trapezoidal microchannel using different approaches

In this study, developing laminar forced convection of ${\text{Al}}_2{\text{O}}_3$/water nanofluid flow inside a trapezoidal microchannel has been investigated. The numerical simulation is conducted using two different methods which consider the effect of non-uniform nanoparticle distribution: Buongiorno’s Two-component nonhomogeneous model, and Eulerian-Lagrangian two-phase method. The results are compared to experimental data and also single-phase and dispersion methods. It is shown that the Eulerian-Lagrangian method predicts microchannel Nusselt number more accurately than Buongiorno’s model. Particle distribution is not uniform in the cross section of microchannel, and with increasing Reynolds number this nonuniformity is more. Moreover, the effect of different forces on heat transfer is discussed. It is found that the influence of Saffman’s lift force is negligible while Brownian and thermophoretic forces affect the heat transfer coefficient slightly. Furthermore, it is shown that the use of experimental correlation for nanoparticle Nusselt number makes the numerical results more accurate, so it is important to take into account the scale effects and use the suitable correlations.     

Structure of two-phase piston flow in vertical ducts

A simplified model of the piston flow of a two-phase mixture is analyzed. A comparison of the results of the analysis with experimental data exhibits good agreement between them.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 5, pp. 727–731, November, 1984.     

Comparison of unitary transforms using Franson interferometry

Unknown unitary transforms may be compared to each other in a way which makes it possible to obtain an unambiguous answer, indicating that the transforms are different, already after a single application of each transform. Quantum comparison strategies may be useful for example if we want to test the performance of individual gates in a quantum information or quantum computing network. It is then possible to check for errors by comparing the elements to a master copy of the gate, instead of performing a complete tomography of the gate. In this paper we propose a versatile linear optical implementation based on the Franson interferometer with short and long arms. A click in the wrong output port unambiguously determines that the tested gate is faulty. This set-up can also be used for a variety of other tasks, such as confirming that the two transforms do not commute or do not anticommute.     

层流流量计计算数学模型和标定方法的研究

为解决气体层流流量计在不同性质气体使用和标定中存在的换算问题,以及流量与差压的非线性关系,建立了适用于各种气体的层流流量计流量计算数学模型,提出层流流量计的流量计算不仅与气体的牯度有关,同时与气体的密度有关,引入双流量系数及标定方法.通过试验和比对验证,表明流量计的非线性误差减小,同一台流量计对不同气体有显著的通用性.     

Advances in the acoustics of flow ducts and mufflers

This review paper deals with advances made in the last two decades in the acoustics of flow ducts for heating, ventilation and air-conditioning (hvac) systems and engine mufflers. The context, concepts, methods used and results have been highlighted. Frequency-domain one-dimensional analysis of reflective mufflers has been emphasized because of its basic importance and wide application. Finally, problems needing further research have been identified.     

Effective diffusion of impurity in laminar flow of liquid

The effective diffusion of an impurity in a flow of non-Newtonian liquid is investigated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 2, pp. 342–345, February, 1977.     

烟用层流流量传感器测量准确性研究

为探究烟用层流流量传感器测量准确性的影响因素,介绍烟用层流流量传感器的基本结构,分析烟用层流流量传感器的入口效应,采用Fluent软件进行数值仿真。结果表明:烟用层流流量传感器仿真曲线与实验曲线基本吻合;小流量时仿真值与理论值较为接近,大流量时仿真值与理论值相对误差超过1%;环境因素对烟用层流流量传感器测量准确性的影响,温度最为显著,大气压仅在大流量时有一定影响,湿度基本无影响。通过研究环境因素对烟用层流流量传感器测量准确性的影响,对提高实验室与车间卷烟通风率测量一致性具有指导意义。     

Film flow of magnetic liquid in the laminar regime

The hydrodynamics of the film flow of a magnetic liquid over reflux surfaces in static magnetic fields is studied.Notation g gravitational field - density of liquid - dynamic viscosity - M magnetization of liquid - B magnetic induction - magnetic permeability of liquid - ₀ permeability of free space - a constant film thickness - r radial coordinate of the cylindrical coordinate system - steady-state variable thickness of film - h unsteady variable thickness of film - Q volume flow rate of liquid (per unit time) - I current - b constant gradient of magnetic field in quadrupole lens Translated from Inzhenerno-Fizieheskii Zhurnal, Vol. 31, No. 5, pp. 847–849, November, 1976.     

A numerical study of the similarity of fully developed laminar flows in orthogonally rotating rectangular ducts and stationary curved rectangular ducts of arbitrary aspect ratio

 The present study showed that a quantitative analogy of fully developed laminar flow in orthogonally rotating rectangular ducts and stationary curved rectangular ducts of arbitrary aspect ratio could be established. In order to clarify the similarity of the two flows, the dimensionless parameters K _LR=Re/(Ro)^1/2 and the Rossby number, Ro=w _m /Ωd _h , in a rotating straight duct were used as a set corresponding to the Dean number, K _LC=Re/λ^1/2, and curvature ratio, λ=R/d _h , in a stationary curved duct. Under the condition that the value of the Rossby number and the curvature ratio was large enough, the flow field satisfied the `asymptotic invariance property'; there were strong quantitative similarities between the two flows such as in the friction factors, flow patterns, and maximum axial velocity magnitudes for the same values of K _LR and K _LC. Based on these similarities, it is possible to predict the flow characteristics in rotating ducts by considering the flow in stationary curved ducts, and vice versa. Received: 10 September 2001 / Accepted: 13 May 2002     

Influence of developing flow on the heat transfer in laminar oscillating pipe flow

A theoretical analysis was performed to evaluate the influence of developing flow on the heat transfer associated with laminar oscillating pipe flow. Simplified analytical approaches are briefly discussed before an investigation based on the numerical solution of the conservation equations for mass, momentum and energy is presented, assuming constant wall temperature and an incompressible viscous fluid. Focusing on operating conditions as found in heat exchangers of regenerative thermal machines, like Stirling engines or Vuilleumier heat pumps, numerous calculations of the flow field and the heat transfer have been executed covering wide ranges of the characteristic dimensionless groups. The results are presented in tems of correlations of the mean Nusselt number averaged on the pipe length and a distribution function describing the local heat transfer. Furthermore, it is shown that the derived correlations are also applicable to compressible fluid flow, provided that the relative pressure amplitude is within the limits typical of regenerative thermal machines.     

Image magnification using families of fast orthogonal transforms

We outline a method if image magnification based on parametric families of fast orthogonal transforms which arise from the multiresolution/wavelet paradigm of Mallat and Meyer. The essential idea is to consider the original image as a low-frequency component of a family of potential enlargements, all of which are computable in real time. We sketch the underlying theory and pertinent algorithms. Several specific examples are detailed. © 1996 John Wiley & Sons, Inc.