摘要:

A new method has been developed for simulation of heat regenerators in periodic operation. The procedure is based on describing the system by a number of backmixed cells in series, in contrast to the differential equation formulation used in earlier studies. The method is highly efficient computationally and the calculation of thermal efficiency and temperature profiles in the system is reduced to the solution of a simple set of linear algebraic equations. The validity of the method is established by comparing it with other solution procedures. Finally, some illustrative results are presented to show the effect of switching time, normalized variance of the system, and mode of operation.

ISSN:0149-5720    

DOI:10.1080/10407788708913546

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The issues of the large cell Reynolds number and large Damkohler number are examined. Thirteen finite-difference schemes for solving a system of highly nonlinear convection-diffusion-reaction integrodifferential equations are studied. The system models the propagation of a one-dimensional unsteady laminar flame in closed or open combustors. The numerical schemes include an explicit scheme with upwind, central, and hybrid differencing, a predictor-corrector explicit scheme, a sequential implicit scheme, a quasi-linear implicit scheme, a block implicit scheme, the standard Crank-Nicolson implicit scheme, two methods of lines, a projection implicit scheme, an operator-splitting scheme, and the QUICK scheme. The efficiency, accuracy, and stability of these schemes art discussed. In particular, it is shown that the treatment of convection terms and of reaction terms, as well as the flow conditions, has a strong impact on the selection of an optimum numerical technique. Generally, for a large Damkohler number the explicit methods are judged superior to the implicit methods. For a large cell Reynolds number, the QUICK scheme is the most promising.

ISSN:0149-5720    

DOI:10.1080/10407788708913547

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The problem of Marangoni convection in a horizontal fluid layer with internal heat generation is solved using the sequential gradient-restoration algorithm (SGRA) developed for optimal control problems. A general discussion of the method is given. The effects of the temperature-dependent surface tension and viscosity are studied by examining the critical Marangoni numbers and wave numbers. The validity of the method is established by comparison with the work in the literature for the case of a linear temperature profile across the fluid layer.

ISSN:0149-5720    

DOI:10.1080/10407788708913548

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Natural convection in a stratified fluid enclosed within an annulus formed by confocal elliptical cylinders is examined analytically. The flow modeled is two-dimensional, laminar, incompressible, and steady state. Except for the Boussinesq approximations for density, fluid properties are constant. Stratification is modeled by assigning a variable temperature profile to the outer cylinder. The inner cylinder is isothermal. Either thermally stable or thermally unstable stratification is modeled by assigning either positive or negative values of the steepness parameter S. The effects of the varying RaLand e, the eccentricity of the inner cylinder, are also examined. The results are presented in terms of fluid flow patterns, isotherms, and graphs of shear stress and local Nusselt numbers on the plate's surface for various values of the angle of orientation, α,

ISSN:0149-5720    

DOI:10.1080/10407788708913549

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Natural convection from a horizontal cylinder dissipating a uniform heat flux is analyzed by solving the full two-dimensional Navier-Stokes and energy equations. For Pr=- 0.7 flow fields and transport results are determined in the range 10-2≤ Ra* ≤ 107, For Ra* ≤ 0.1 the surface temperature variation becomes less than 5% and the uniform heat flux and isothermal boundary conditions become equivalent. A correlation for the average Nusselt number is suggested. Some experimental data are also reported. The agreement between the computed and measured transport results is found to be very good.

ISSN:0149-5720    

DOI:10.1080/10407788708913550

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A numerical model based on a finite-element method is used to estimate the heat transfer between a solid and a fluid flow through an interface. The interface has a periodic shape, which is commonly the case in many natural phenomena or technical processes. The Navier-Stokes equations were solved with a penalty function formulation and the heat transfer equation with a classical Galerkin one. Results are presented using velocity vector plots, isotherms, and variations of the heat transfer coefficient as a function of Reynolds number and thermal conductivity ratio for a special shape of the interface.

ISSN:0149-5720    

DOI:10.1080/10407788708913551

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A numerical model is described that calculates lateral and downstream mixing of contaminant species in two-dimensional confined flows. It consists of partially parabolized, vertically averaged time-dependent equations of motion, continuity, and concentration of non-conservative species. Pertinent equations are solved using finite differences for both laminar and turbulent flow. Results of calculations using the present model are compared with results of other investigators. The model is used to study species mixing for two different discharge concepts.

ISSN:0149-5720    

DOI:10.1080/10407788708913552

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The problem of heat conduction in composite media is formulated in terms of integral equations by use of the tempered elementary solution of the unsteady diffusion operator. The integral equations are discretized in both time and space. Each homogeneous subre-gion and its surface and interfaces are represented by tetrahedral and triangular finite elements with quadratic variation of geometry and of unknown functions with respect to intrinsic coordinates. The time dependence of the unknown functions is assumed to be linear over each time step. Integration in the time domain is performed analytically, while integration with respect to spatial coordinates is developed by numerical quadrature formulas. As a result, a linear algebraic system of equations for the unknown in the nodal points is obtained. The procedure was checked with a number of test cases. The numerical experiments show that good accuracy may be obtained provided the parameters of the computation, in particular the number of Gaussian quadrature points and the time step for a given nodal mesh, are suitably chosen. Proper choice of these parameters is particularly important when dealing with composite media in which the thermal diffusivtiy varies widely.

ISSN:0149-5720    

DOI:10.1080/10407788708913553

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor