摘要:

The Galerkin spectral method with basis Junctions previously introduced by Gelfgat 111 is applied for analysis of oscillatory instability of convective flows in laterally heated rectangular cavities. Convection of water and air in a square cavity, and convection of a tow-Prandtl-number fluid in a square cavity, and a cavity with a ratio length / height of 4 are considered. Patterns of the most unstable perturbations of the stream function and the temperature are presented, and mechanisms of oscillatory instability are discussed. Comparison with other numerical investigations shows that the Galerkin method with divergent-free basis functions, which satisfy all the boundary conditions, needs fewer modes than other methods using discretization of the flow region.

ISSN:1040-7782    

DOI:10.1080/10407789408955970

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Fully developed turbulent flow through simulated rod bundle subchannels formed by a rod-trapezoidal duct was numerically studied. With a simple coordinate system transformation from an orthogonal cylindrical system to a nonorthogonal curvilinear system, the highly irregular flow passage of a rod-trapezoidal duct was converted to that of a regular rectangle. An empirical anisotropic eddy viscosity distribution based on existing experimental data was used in conjunction with the algebraic stress model to address the influence of coherent large-scale cross-gap eddy motion, whose existence in closely spaced rod bundle subchannels has been substantiated by extensive hot-wire measurements. Results of the calculation are compared with experimental data, with emphasis on secondary flow and turbulence kinetic energy. The credibility of this numerical scheme was established through a series of numerical tests on simple geometry flows.

ISSN:1040-7782    

DOI:10.1080/10407789408955971

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A numerical analysis has been made of the conjugate natural convection in a rectangular enclosure filled with a fluid-saturated porous medium and surrounded with four solid walls. The conductance of the walls is assumed to be much greater than that of the cavity filled with a porous medium. The main objective was to investigate the influences of the ratio of thermal conductivity of the wall to that of the fluid-porous matrix composite, the Darcy-modified Rayleigh number, the Prandtl number, and the aspect ratio. The streamlines and isotherms are presented; also, the local and average Nusselt numbers are presented along the interface between walls and cavity. A non-Darcian model was employed and the numerical method was SIMPLE-C. The numerical results indicate that the wall heat conduction effects decrease the heat transfer rate. When the wall heat conduction is considered, the greater the conductance of the solid walls surrounding the cavity, the greater is the rate of heat transfer.

ISSN:1040-7782    

DOI:10.1080/10407789408955972

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:1040-7782    

DOI:10.1080/10407789408955973

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A computer program developed to analyze nucleate boiling over a heated surface is described. The model solves the three-dimensional transient conduction equation within the heater. The conduction solution is coupled with closure relationships to mimic the bubble dynamics and the associated heat transfer coefficients. Sample problems are run using a copper surface subject to partial nucleate boiling in saturated water at atmospheric pressure. The results are shown to be in good qualitative agreement with the pertinent experimental observations.

ISSN:1040-7782    

DOI:10.1080/10407789408955974

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Turbulent flow in axisymmetric enhanced tubes with repeated transverse rectangular disruptions was simulated using the two-layer turbulence model of Chen and Patel 111. The predictions were in good agreement with experimental data for friction factors and both local and average Nusselt numbers. The low-Reynolds-number two-equation model of Lam and Bremhorst 121 was considered, and the predicted results were also compared with local heat transfer measurements. This model overestimated the local Nusselt numbers at some locations by about a factor of 2. Results from the two turbulence models were also compared for a sudden pipe-expansion geometry. The Lam and Bremhorst model yielded acceptable local Nusselt number predictions, while the Chen and Patel model underpredicted the local Nusselt numbers and predicted the location of the heat transfer maximum further upstream.

ISSN:1040-7782    

DOI:10.1080/10407789408955975

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the event of a loss of coolant accident in a pressurized water reactor, swelling of the fuel rod cladding will lead to reduction of the subchannel flow area and worsening of the core heat transfer in the region of the blockage. The four-cusped duct is an ideal geometry for the simulation of such a channel blockage. Understanding the characteristics of flow and heat transfer in the cusped duct is essential for better design of the emergency core cooling system. Thus, in this paper, combined natural and forced convection in a vertical cusped duct has been investigated in the region of both hydrodynamically and thermally fully developed flow. The thermal boundary condition imposed on the cusped duct is the axial uniform heat flux with peripheral uniform temperature. The results indicate that the fluid flow and heal transfer in the comer region of the cusped duct are improved because of the influence of natural convection. As the Rayleigh number increases, the friction factor and Nusselt number increase accordingly. It was also found that the critical Rayleigh number is 1200, at which flow reversal occurs in the buoyancy-assisted flow ( heated upflow). The velocity, temperature, and local Nusselt number distribution are presented for a range of Rayleigh numbers.

ISSN:1040-7782    

DOI:10.1080/10407789408955976

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor