摘要:

Unidirectional solidification of an aqueous NH4Cl solution has been simulated using a fully three-dimensional model for the strongly coupled transport of momentum, energy, and species in the mushy and melt regions of the solution. The predictions reveal the nucleation and development of pencil-like vertical channels in the mushy region and the complex, three-dimensional flow and thermosolutal conditions associated with channel formation. The number of channels is at a maximum shortly after nucleation and thereafter decreases with increasing time, as solidification progresses. Favorable agreement is obtained between three- and two-dimensional predictions of global parameters such as heat rate and mass fraction of solid formation.

ISSN:1040-7782    

DOI:10.1080/10407789308913659

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A numerical study is reported of melting of a pure metal inside a vertical rectangular enclosure with both natural convection in the liquid and conduction in the solid. A streamfunction/vorticity/temperature formulation is employed in conjunction with boundary-fitted coordinates for mapping the irregular shape of the moving solid-liquid interface. Twenty numerical experiments are conducted for Rayleigh numbers ranging from 8.99 ×: 104to 1.44 × 106and subcooling parameters ranging from 0.5 to 4.0. The results show that the combined effects of natural convection in the melt and subcooling of the solid considerably affect the melting of a pure metal. Subcooling significantly reduces the melting rate and leads to a steady state for which the position and the shape of the solid-liquid interface are dictated by the subcooling parameter and the Rayleigh number. A correlation is proposed for the heated-wall Nusselt number at steady state as a function of the Rayleigh number and the subcooling parameter.

ISSN:1040-7782    

DOI:10.1080/10407789308913660

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The present work consists of comparative evaluation of the finite-element and finite-difference methods for the solution of complex fluid flow and heat transfer problems. The test case considered here is the problem of natural convection in an annular cavity. Both closed and open ended cases are considered. It was found that the finite-difference analysis succeeds in capturing minute details of the solution at high Rayleigh number flows and the finite-element method fails to do so. However, the finite-element method enjoys the advantage of providing sufficiently accurate results even with coarse meshes. This results in significant savings in computational costs without any sacrifice in the accuracy of the solution. Hence, the finite-element method can serve as an optimum tool for most problems of practical interest.

ISSN:1040-7782    

DOI:10.1080/10407789308913661

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

When a solution having a linear concentration gradient along the gravitational direction is heated from a vertical wall and cooled from an opposing vertical wall, multilayered roll cells separated by near-horiwntal sharp interfaces are observed. This paper presents a finite-element computational scheme to simulate this phenomenon. Computations were carried out for Pr = 6, Le = 100, A = 8, N = 2 or S, and Ra = I04or 105. In the numerical simulation, two roll cells appeared, one just below the top free surface and one just above the bottom plane. Subsequently, one or several roll cells appeared between them, and finally they converged to a single roll cell.

ISSN:1040-7782    

DOI:10.1080/10407789308913662

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Computation of recirculating turbulent flow in complex geometries is important in engineering but fundamentally difficult. A procedure using a full multigrid and full approximation storage is developed in conjunction with a pressure-based algorithm using curvilinear coordinates and the k-e two-equation turbulence model. This method is applied to several flow problems with different geometries, grid sizes, and convection schemes. Although the multigrid procedure does not yield a convergence rate independent of these factors. Us performance is noticeably less affected than that of the single-grid method. Degradation of the boundary representation during grid restriction is one effect on the multigrid performance. Some features regarding the treatment of the turbulence quantities that help the performance of the multigrid method are identified. A special grid restriction procedure is also introduced, which accommodates the velocity characteristics in the wall region and kelps improve the convergence rate.

ISSN:1040-7782    

DOI:10.1080/10407789308913663

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An operator-splitting method for solving convective heat and mass transfer equations is described. The method is shown to be equally accurate at low and high Pfélet numbers. At high Pfélet numbers the frontlike solutions are seen to be resolved without excessive damping or oscillations. This method has been tested against analytical solutions of model one-dimensional transient problems and a steady two-dimensional problem to investigate grid orientation effects.

ISSN:1040-7782    

DOI:10.1080/10407789308913664

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A method is presented for estimating the performance of a counter/low cooling tower packed with a regular fill. The model utilized takes into account initial nonuniformity of irrigation and the redistribution of water flow during interaction with the structured fill, In this analysis a local, cellular model for the heat and mass transfer has been formulated, and a compulation scheme has been developed. Solutions for the nonuniform model have been compared to established models that employ the assumption of uniform flow across the plan area of the lower. Results show that regions of nonuniform flow persist for some depth into the flow and that performance of the tower can be degraded.

ISSN:1040-7782    

DOI:10.1080/10407789308913665

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor