摘要:

The direct coupling of a thermally stabilized combustor and a steam generator has previously been shown by Strenger and Churchill to result in minimal concentrations of NO and CO and exceptionally high rates of heat transfer relative to conventional processes. Across the flame front, the Reynolds number falls from above to below 2100, leading to decaying turbulence and laminarization in the stream of hot burned gas. In the heat exchanger the cooling increases the Reynolds number and results in a sudden transition back to turbulent flow. The development and transition in the flow as well as the confinement are responsible for the high rates of heat transfer. The k-ϵ model has been adapted successfully to predict this complex behavior by using a controlled perturbation to trigger the transition at the experimentally observed point. The predictions not only agree well with experimental measurements of heat transfer but also provide insight into the fluid-mechanical and thermal behavior.

ISSN:1040-7782    

DOI:10.1080/10407789208944756

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The formulation and numerical investigation of free surface transport within a hollow glass ampule art presented. The glass ampule is treated as a vertical film with a finite pressure difference across the film. A modified form of the marker and cell method within a semi-implicit algorithm is used to deal with the free surface problem, and full consideration of surface tension and viscosity effects is taken into account. It is found that the viscous effects on the free surface pressure conditions can be neglected because of the dominance of the surface tension effects. Furthermore, it is found that the convective terms have less than 1% effect on either the pressure or the velocity fields. The results clearly show the effects of a pressure differential across the glass ampule. The movements of the inner and outer free surfaces and the corresponding pressure distributions at these surfaces are analyzed. An interesting phenomenon corresponding to the reversal of direction of the movement of the free surfaces is shown to be related to a reversal in direction of the pressure differential.

ISSN:1040-7782    

DOI:10.1080/10407789208944757

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper considers the flows induced by symmetrical heating of two vertical parallel surfaces for a Grashof number range of l03-105, a Prandtl number of 0.7, and slot height-to-width ratios of 1.0 and 2.0. A nonorthogonal curvilinear coordinate system in conjunction with an adaptive grid method and second-order accurate discretization schemes were employed in the numerical method. The entire flow field is modeled, including the region beneath the parallel surfaces, the region between the parallel surfaces, the outflow region above, and the downstream wake. The adaptive grid method, based on the concept of equidistribution of a weighting function, clearly shows the evolution of the grid distribution pattern with respect to the change of Grashof number in a way that cannot be prescribed a priori. The resulting improvements of the length scale resolution make the temperature and the velocity fields vary as the Grashof number changes. A converging/diverging convection pattern can be identified within the slot. The effect of aspect ratio on the flow characteristics is also observed, and the slot of unity aspect ratio depicts recirculating eddies for high Grashof numbers.

ISSN:1040-7782    

DOI:10.1080/10407789208944758

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper presents a numerical study of laminar, fully developed mixed convection in vertical eccentric annular duets. The equations governing the velocity and temperature are solved on a body-conforming grid by using a finite-volume technique. The effects of radius ratio, eccentricity, and Rayleigh number on the friction factor and the Nusselt number are discussed. The buoyancy forces significantly increase both friction and heat transfer. The effect of buoyancy is stronger for configuration with larger eccentricities.

ISSN:1040-7782    

DOI:10.1080/10407789208944759

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Axial flow and heat transfer in a horizontal cylindrical annulus can be influenced by eccentricity of the inner cylinder and the presence of buoyancy forces. A numerical study is presented for the combined forced and free convection for the fully developed flow and heat transfer for eccentric annuli of different eccentricities and radius ratios. The flow field is characterized by large cross-stream secondary currents and significant flow distortion. The Nusselt number increases significantly with the Rayleigh number; the corresponding increase in the friction factor is relatively small. The eccentricity introduces additional nonuniformity of the flow and temperature fields.

ISSN:1040-7782    

DOI:10.1080/10407789208944760

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A method is proposed for determining the thermal diffusivity of high-temperature liquid metals by levitating a small sample in microgravity conditions, melting it, and predicting Us response to a laser pulse. The solution is obtained by determining the initial temperature distribution in the thermal penetration depth created by the laser pulses and then solving the two-dimensional conduction equation in spherical coordinates for the cooling history of the droplet. The solution is obtained by assuming a short duration for the experiment. The correct diffusivity is obtained by minimizing the difference between the predicted and the experimentally obtained temperatures. The method is demonstrated for nickel, iron, and copper using analytical data, and is shown to have good accuracy.

ISSN:1040-7782    

DOI:10.1080/10407789208944761

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor