摘要:

Coupled conduction and natural convection heat transfer has been investigated numerically for protruding heat sources mounted to one vertical wall of a rectangular cavity. The heat sources simulate an array of computer chips mounted on a substrate of finite thermal conductivity. The back of the substrate and the horizontal walls of the cavity are assumed to be adiabatic, while the opposing vertical wall provides an isothermal heal sink. The fluid Prandtl number and the heater/fluid thermal conductivity ratio are fixed at 25 and 2350, respectively, corresponding to a dielectric fluid (FC-77, manufactured by 3M Company) and silicon chips. With increasing modified Rayleigh number (104 < Ra*LZ < 109), the cavity flow approaches boundary layer behavior, and more fluid penetrates the regions between protrusions. The effect of contact resistance between the heater and substrate is shown to be small for Rnth < 10 cm2 °C/W. With decreasing substrate thermal conductivity [1.48 W/ (m K) <. Ks < 148 W/(m K)], fluid circulation decreases and the maximum heater temperatures increase.

ISSN:1040-7782    

DOI:10.1080/10407789608913775

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Numerical calculations were performed for the melting of phase change material in a rectangular cavity to examine the possibility of using the melting process for cooling of a surface heated at a constant rate. Two orientations of the heated surface, i.e., at the bottom and at the side of the cavity, were examined. In addition, the effects of uniform- and discrete-heating conditions on the cooling of the heated surface were studied. Because of strong natural convection, the temperature of the heated surface was kept almost constant for a long period, and the value was smaller for the heated surface located at the bottom of the cavity than at the side. The discrete arrangement of the heated portions strongly affected the cooling of the surface.

ISSN:1040-7782    

DOI:10.1080/10407789608913776

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Mixed convection in fully developed flows of air (Pr = 0.7) inside a channel subjected to oscillatory pressure gradients is studied numerically. The lower wall of the channel is periodically grooved to form square cavities, which are heated uniformly from the bottom. The following three pertinent parameters evolve as a result of the proper nondimensionalization of the governing equations: Re, the oscillatory flow Reynolds number (based on an oscillation velocity scale); Wo, the Womersley number; and Grq, a modified Grashof number. A low-Re range (10 < Re < 100), in which the flow properties are sensitive to small changes in Wo and / or Grq, is of primary interest in the present investigation. When the buoyancy effect is neglected, a circulatory roll cell appears inside the cavity, which remains over almost the entire cycle. However, the formation of such a vortex does not take place with the mixed convection mode; this difference stems from a deeper penetration of the throughflow to the cavity. Heal transfer enhancement at the heat flux surface prompts this structure change in the flow field as a manifestation of the buoyancy effects.

ISSN:1040-7782    

DOI:10.1080/10407789608913777

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

An enthalpy-porosity fixed-grid method has been applied to the melting and solidification of pure metals in a rectangular cavity. Flow structures and isotherms are compared with literature information based on multidomain analysis. During solidification, recirculation cells are observed to vanish with time, whereas the multidomain method predicted their enlargement. The cell near the interface significantly affects the local solidification rate at the cavity top. Results of the present study agree well with the experimental data in the literature. The effect of neglecting the viscous diffusion term for a phase change problem involving low Prandtl number liquid metals is also studied. The maximum value of the stream function is higher by 10% and the melt volume by 5%, in the absence of viscous effects.

ISSN:1040-7782    

DOI:10.1080/10407789608913778

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Numerical studies by the Galerkin finite element method are presented for the suppression of natural convection heat transfer in a horizontal porous annulus heated from the inner surface. Azimuthal partitions are employed to reduce heat transfer, and the effects of the number of partitions and their positions are examined. For a single partition, its position has a negligible effect on heat transfer in the boundary layer regime. An increase in the number of partitions is effective in suppressing natural convection, and it is found that the Nusselt number Is inversely proportional to (N + 1), where N is the number of partitions.

ISSN:1040-7782    

DOI:10.1080/10407789608913779

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Transient natural convection over a sphere has been studied numerically for 101< Gr < 108and Pr = 0,72. Shortly after the sphere temperature is raised, a vortex of small radial extent appears in the wake of the sphere for very high Gr, which grows radially until the plume formed on the top of the sphere is fully developed. The evolving plume has a mushroom-shaped cap for moderate and high Gr, and in agreement with experiment, presents a temperature peak on the cap's base, an off-axial peak in the middle of the cap, and an axial peak near the cap's leading edge. The mechanism driving the onset of significant convection has been clearly delineated, and the relevant critical Rayleigh numbers have been obtained. The temperature gradient at θ = 90°seems to lead the onset of convection.

ISSN:1040-7782    

DOI:10.1080/10407789608913780

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A numerical study of transient natural convection heat transfer from a finned surface has been conducted for thermal storage in an enclosure. The motivation of this work is found in solar thermal storage tanks. The finned heat exchanging surface provides a means to charge and discharge the thermal energy in the tank. The governing time-dependent conservation equations are solved by a finite difference method. Solutions are obtained for 106< Ra < 108, for 0-3 fins, for fins of length L/H = 0.3 and 0.75, and for fins parallel and perpendicular to the gravity vector. Results indicate that the storage process is characterized by three distinct heat transfer regimes and that most of the energy is stored during the last regime, referred to as the decay period. The time-changing Nussett number at the heat exchanging surface is strongly dependent on the Rayleigh number and the number of fins. It is, however, much less sensitive to the size of the fins and their orientation. The storage times are shortened as Ra increases and/or the number of fins and/or their size increases.

ISSN:1040-7782    

DOI:10.1080/10407789608913781

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:1040-7782    

DOI:10.1080/10407789608913774

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor