摘要:

This investigation concerns the nonlinear dynamics of heat transfer from a surface using an upstream eddy promoter, A numerical model is developed for the coupled fluid flow and heat transfer process based on a modified MacCormack scheme. Numerical simulations are carried out to determine the response and heat transfer enhancement due to the promoter. The average heal transfer from a cavity floor is seen to be increased by a factor of approximately five over the “unpromoted” flow. Another interesting feature of the study is the nonlinear viscous flow dynamics from the cylinder-wall interaction which differ significantly from the familiar cylinder-free stream patterns.

ISSN:1040-7782    

DOI:10.1080/10407789408955940

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A three-phase Stefan-like problem is formulated to solve simultaneous melting and evaporation of spherical metal particles placed in a uniform external alternating magnetic field. A front-fixing transformation and Galerkin finite element method are used in the solution to this problem of two moving boundaries. Numerical simulations show that for lower values of the initial particle radius R0and the amplitude of the external magnetic field B0, the melting and evaporation processes can be separated without any significant loss of precision. For higher R0, B0the solid-liquid and liquid-vapor interface velocities are of the same order of magnitude during most of the process, and a simultaneous solution is necessary. Comparison of results obtained by equilibrium and nonequitibrium evaporation models shows that in shorter time periods, up to 1 s, the equilibrium models with properly chosen vaporization temperatures can effectively simulate the behavior of nonequilibrium models.

ISSN:1040-7782    

DOI:10.1080/10407789408955941

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The present work examines the finite difference discretization effects on the predictions of an existing multidimensional fluid dynamical numerical model, which provides detailed information on liquid droplet evaporation in a high-temperature convective environment. It is found that under practically realistic conditions the convection of energy in the droplet interior dominates diffusional transport at the computational cell level. This condition raises questions related to the reliability of the model predictions based on central-difference discretization of the convective terms of the liquid-phase energy transport equation. A hybrid discretization scheme is selected to improve representation of the physical liquid-phase energy transport processes. The hybrid scheme is shown to provide more accurate predictions when a droplet energy balance is used as the criterion of scheme performance. The implications to the overall droplet vaporization behavior are also discussed.

ISSN:1040-7782    

DOI:10.1080/10407789408955942

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Mixed convection in a horizontal semicircular duct is studied numerical. An axially nonuniform temperature distribution is prescribed on the flat wall, with the midsection at a higher temperature than the end sections. The full three-dimensional Navier-Stokes equations coupled with the energy equation are solved using a control-volume method. Results are presented for two values of the Grashof number (Gr = 5 × 103and 5 × 104) and three values of the Reynolds number (Re = 10, 20, 50), for a gas with Prandtl number of 0.7. For flow conditions characterized by a large value of the parameter Gr / Re2, the buoyancy forces give rise to both longitudinal and transverse rolls in the duct, which cause nonuniformities in the heat flux distribution. The secondary flow pattern and the heat flux distribution on the heated section of the flat wall are strongly dependent on the thermal boundary condition on the curved wall of the duct.

ISSN:1040-7782    

DOI:10.1080/10407789408955943

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An enthalpy method is employed to solve transport processes associated with melting of an unfixed rectangular phase change material (PCM) in a low-gravitational environment. This method permits the phase-change problems to be solved within fixed numerical grids, hence eliminating the need for coordinate transformation. The PCM, initially at its melting temperature, is placed inside a rectangular enclosure. The lower surface of the container is then exposed to a uniform temperature higher than the PCM melting temperature. The difference in densities of solid and liquid causes a force imbalance on the solid in the gravitational and low-gravity environments. In the case where the density of the solid phase exceeds that of the liquid, the solid continually moves downward as melting progresses and hence generates a flow field within the liquid. The problem is formulated as a one-domain problem with the possibility of melting from all the PCM surfaces, and no approximation is mode about the liquid film thickness under the melt. The governing equations are discretized by using a control-volume-based finite difference scheme with a new iterative method to correct for the downward solid-phase velocity. This will also speed up the convergence of the numerical procedure. The results are presented in the form of a parametric study of the effects of Archimedes number, Stefan number, Prandtl number, and the geometric parameters on the melt thickness, the downward solid velocity, the elevation of the top surface, and the volume of the solid PCM. They show that in a low-gravitational environment, the melting rate is very slow.

ISSN:1040-7782    

DOI:10.1080/10407789408955944

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Heat transfer analysis has been done for the movement of the solidification front in the presence of cylindrical reinforcements, including graphite, alumina, iron, and copper in an aluminum-silicon alloy base and lead-base composites. The study showed that for reinforcements with lover thermal conductivity than the melt, the rate of movement of the interface was different at different locations of reinforcement. The rate of movement of the interface is strongly dependent on the thermal conductivity ratio of reinforcement to melt. The analysis indicated that the reinforcements of lower thermal conductivity remain at higher temperature than the surrounding melt during solidification, whereas the reinforcements of high thermal conductivity remain at a lower temperature.

ISSN:1040-7782    

DOI:10.1080/10407789408955945

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The present study investigates the transient temperature behavior of a direct transfer type, single-pass, crossflow heat exchanger with neither gas mixed, accounting for the two-dimensional longitudinal conduction effect on the separator sheet. Numerical results show the variation of the mean exit temperatures of hot and cold gases. The approaching time to steady state is also presented to describe the influence of longitudinal conduction and number of transfer units. Finally, comparisons among step, ramp, and exponential responses are demonstrated to display thermal performance deterioration due to the wall conduction effect.

ISSN:1040-7782    

DOI:10.1080/10407789408955946

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor