Mixed Double-Diffusive Convection in Gas-Loaded Heat Pipes

1990 ◽  
Vol 112 (1) ◽  
pp. 78-83 ◽  
Author(s):  
P. F. Peterson ◽  
C. L. Tien
Keyword(s):  
Natural Convection ◽  
Heat Pipes ◽  
Double Diffusive Convection ◽  
Concentration Gradients ◽  
Two Phase ◽  
Noncondensable Gas ◽  
Diffusive Convection ◽  
Effects Of Temperature ◽  
Variable Conductance Heat Pipes ◽  
Double Diffusive

This study examines mixed double-diffusive convection in gas-loaded heat pipes and two-phase thermosyphons. The numerical simulation and experiments show that steady, laminar natural convection due to the combined effects of temperature and concentration gradients can greatly redistribute the noncondensable gas within the condenser. This change of the gas distribution, however, does not significantly alter the overall condensation heat transfer. This interesting result implies that even with natural convection present, much simpler integral models can still be applied with confidence for the design of variable-conductance heat pipes and thermosyphons.

Lattice BGK Simulation of Hydromagnetic Double-Diffusive Convection in a Rectangular Enclosure with Linearly Variable Temperature and Concentration Gradients

2010 ◽  
Vol 44-47 ◽  
pp. 2414-2427
Author(s):  
Xue Mei Liu ◽  
Han Jun Lu ◽  
Mei Ying Ye ◽  
You Sheng Xu
Keyword(s):  
Hartmann Number ◽  
Variable Temperature ◽  
Double Diffusive Convection ◽  
Concentration Gradients ◽  
Rectangular Enclosure ◽  
Diffusive Convection ◽  
Binary Gas Mixture ◽  
Left And Right ◽  
Dimensionless Heat ◽  
Double Diffusive

Hydromagnetic double-diffusive convection of a binary gas mixture is simulated by a temperature-concentration latitce Bhatnagar-Gross-Krook (TCLBGK) model in a rectangular enclosure with the top and bottom walls being insulated, while linearly variable temperature or concentration gradient or both are imposed along the left and right walls from the bottom to the top and a uniform magnetic field is applied in x-direction. we take the Prandtl number =1, the Lewis =2, the thermal Raleigh number =105, the Hartmann number =0, 25, 50, the dimensionless heat generation or absorption =0, the aspect ration =2 for the enclosure and the ratio of buoyancy forces =0.8, 1.3. Numerical results are discussed in detail. It is founded that linearly variable temperature and concentration gradients have significant influence on the stratification and direction of streamlines and convection.

Two-dimensional effects in double-diffusive convection

1974 ◽  
Vol 63 (3) ◽  
pp. 577-592 ◽  
Author(s):  
J. S. Turner ◽  
C. F. Chen
Keyword(s):  
Two Dimensional ◽  
Double Diffusive Convection ◽  
Mechanism Of Formation ◽  
Concentration Gradients ◽  
One Dimensional ◽  
Horizontal Gradients ◽  
Diffusive Convection ◽  
Similar Density ◽  
Double Diffusive ◽  
Vertical Gradients

The limitations of existing one-dimensional experiments on double-diffusive convection are discussed, and a variety of new two-dimensional phenomena are described. We have used the sugar-salt system and shadowgraph photography to make exploratory studies of motions which can arise in a fluid with two smooth, opposing, vertical concentration gradients, with and without horizontal gradients. Many different effects have been observed, the most important of which are the following, (a) In the ‘finger’ case, local disturbances can propagate rapidly as wave motions, which cause a simultaneous breakdown to convection over large horizontal distances. (b) Layers formed in the’ diffusive’ sense overturn locally to produce fingers, but propagate more slowly, as convective rather than wave motions, (c) A series of layers, separated by diffusive interfaces, can become unstable, in the sense that successive layers merge in time as their densities become equal, (d) The presence of horizontally separated sources of water of similar density but differentT,Scharacteristics can lead to the development of strong vertical gradients and extensive quasi-horizontal layering.Most of our results are qualitative, but it is hoped that they will stimulate further quantitive work on each of the new processes described. It is already clear that much more needs to be done before the mechanism of formation of layers observed in the ocean can be regarded as properly understood.

Flow and Morphological Conditions Associated With Unidirectional Solidification of Aqueous Ammonium Chloride

1993 ◽  
Vol 115 (4) ◽  
pp. 1036-1043 ◽  
Author(s):  
C. S. Magirl ◽  
F. P. Incropera
Keyword(s):  
Ammonium Chloride ◽  
Unidirectional Solidification ◽  
Mushy Region ◽  
Bottom Surface ◽  
Double Diffusive Convection ◽  
Two Phase ◽  
Cold Surface ◽  
Diffusive Convection ◽  
Injection Techniques ◽  
Double Diffusive

Using a 27 percent aqueous ammonium chloride solution as a transparent analog, shadowgraph and dye injection techniques have been employed to observe flow and morphological conditions associated with unidirectional solidification (UDS) from below. Dendritic crystals, which initially form at the cold surface, reject lighter, solute deficient fluid, and the attendant instability is manifested by finger-type double-diffusive convection phenomena. As a two-phase (solid/liquid), or mushy, region grows from the bottom surface, vertical channels develop in the mushy region, and solutal plumes that emanate from the channels are characterized primarily by an ascending, oscillatory motion and secondarily by wisps of fluid, which detach and descend from bends in the plumes. In time, double-diffusive convection layers also form in the melt. From a numerical simulation of the process, it is concluded that the channels originate from perturbations at the liquid interface, which cause localized remelting and create conditions conducive to development of the channels.

Marangoni Convection With a Deformable Surface

1994 ◽  
Vol 61 (3) ◽  
pp. 681-688
Author(s):  
F. McCaughan ◽  
H. Bedir
Keyword(s):  
Free Surface ◽  
Marangoni Convection ◽  
Interface Temperature ◽  
Double Diffusive Convection ◽  
Governing Equations ◽  
Infinite Domain ◽  
Concentration Gradients ◽  
Diffusive Convection ◽  
Bounded Below ◽  
Double Diffusive

Double diffusive convection is considered in a semi-infinite domain, bounded below by a solid surface and above by a gas interface. Temperature and concentration gradients are imposed normal to the free surface and the linear stability of the fluid is examined. Traditional analyses are extended to include the effects of a deformable free surface. The governing equations are nondimensionalized and the parameter groupings are identified. We particularly focus on the effects of the capillary number, the Nusselt number and the Marangoni temperature and concentration numbers.

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