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Double-Diffusive Convection
Published in Wen-Jei Yang, Handbook of Flow Visualization, 2018
As mentioned earlier, density differences are the basic cause of double-diffusive convection. For this reason flow visualization of these phenomena utilized, in many circumstances, optical methods that are capable of detecting variations in the refractive index, due to local density gradients existing in the fluid. Of these methods the most widely used is the shadowgraph technique, mainly because of its relative simplicity. The interferometry and schlieren methods were rarely used due to the complexity involved in their operation. The “color polarigraph,” a simple and very efficient optical technique suggested by Ruddick [9], is also described.
Chapter 1: Physical Processes
Published in Gunnar Kullenberg, Pollutant Transfer and Transport in the Sea, 1982
Gunnar Kullenberg, Gunnar Kullenberg
It can be concluded that both intrusion, or interleafing, and internal waves can generate fine structure, and that the type of mechanism dominating depends on the area and conditions. In connection with interleafing there is also a relatively large activity in the microstructure range,95,98 which suggests a coupling. The microstructure is considered to be generated mainly by local processes.122 Several mechanisms have been proposed which may be responsible for microstructure formation, and consequently also may be important for mixing in the sea. First, double diffusive convection can occur as a result of the different molecular diffusivities of salt and heat in areas of opposing salinity and temperature gradients. The large difference between the molecular coefficients gives rise to convective modes of motion transporting heat and salt although the density stratification is stable.127,128 Double diffusion is a low Reynolds number process. In the case of a stable temperature and unstable salinity distribution, i.e., both properties decreasing with increasing depth, thin convection cells (salt fingers) occur in which descending elements loose their heat horizontally by diffusion more rapidly than their salt. Thereby they become heavier than their surroundings and continue to descend. The fingers can develop also in conditions of horizontal motion with vertical shear. Turner129 has shown that the fingers occur in thin sheets separated by thicker layers which are kept homogeneous by vigorous convection driven by the salt transported through the fingers. Salt fingers have been observed in the ocean, on scales less than one meter, by means of an optical method130 and by Magnell31 using a towed instrument in the Mediterranean outflow.
Free Convection
Published in Basil N. Antar, Vappu S. Nuotio-Antar, Fundamentals of Low Gravity Fluid Dynamics and Heat Transfer, 2019
Basil N. Antar, Vappu S. Nuotio-Antar
Fluid convection due to both mass and temperature gradients is normally called double diffusive convection, since there are two diffusion mechanisms operating to cause convection: one due to thermal gradients, the other to solute gradients. This type of convection is also known in the literature as thermoso-lutal, or thermohaline, convection. In this section we will analyze a simple but typical configuration in which the double diffusive convection mechanism can be established.
In-situ characterization of double-diffusive convection during unidirectional solidification of a binary solution
Published in Experimental Heat Transfer, 2023
Ila Thakur, Shyamprasad Karagadde, Atul Srivastava
The double-diffusive convection associated with solidification in multi-component systems plays an important role in many natural processes and engineering applications. Crystal growth, alloy solidification, freezing in oceans, magma stratification, thermal energy storage system, etc., are some of the examples of such systems. The process of solidification leads to changes in temperature and composition, which create thermally and solutally induced density gradients taking the form of double-diffusive convection. The double-diffusive convection occurs basically due to the disparity between molecular diffusivities of temperature and composition. It is a well-known fact that the flow behavior of fluid during the solidification process plays a significant role in the phase change process in multi-component systems. The convective flow patterns induced during solidification influence the interface morphology and solidified structure [1]. Hence, it is important to characterize the flow pattern associated with solidification to understand the physics of phase transition.
Double diffusive convection and Hall effect in creeping flow of viscous nanofluid through a convergent microchannel: a biotechnological applications
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Hu Ge-JiLe, Khurram Javid, Sami Ullah Khan, Mohsin Raza, M. Ijaz Khan, Sumaira Qayyum
The double-diffusive convection is another important phenomenon in the fluid mechanics, concerned with a form of convection process determined by two dissimilar density gradients, which have diverse diffusion rate. According to the literature survey, it can be seen that none of the analysis has deliberated the double diffusion convection under creeping phenomena and low Reynolds number assumption. The double diffusion convection and peristaltic pumping have diverse applications in the inherent mechanism, chemical engineering, and industrial domains. Because of these applications, some researchers have performed dynamic research in this domain using different fluid models. Few of them are cited in the following refs (Akram et al. 2018; Prakash et al. 2020; Shivappa Kotnurkar and Giddaiah 2020). The peristaltic flow of nanofluid under an inclined magnetic field is studied by Akram et al. (2018). They have also discussed the physical influence of double diffusion convection on the flow features. Their whole analysis was based on creeping phenomena and low Reynolds number assumption. Shivappa Kotnurkar and Giddaiah (2020) have argued over the role of double diffusion on the peristaltic motion of nanofluid. Furthermore, they discussed the physical influences of magnetic, porous medium, and thermal radiation parameters on the flow characteristics. Prakash et al. (2020) have discussed the influence of double diffusion convection in biomimetic propulsion of ionic nanofluids by an asymmetric microchannel. Additionally, they also highlighted the combined impacts of electric and magnetic fields on the rheological features under creeping phenomenon.
Effects of electro-osmotic and double diffusion on nano-blood flow through stenosis and aneurysm of the subclavian artery: numerical simulation
Published in Waves in Random and Complex Media, 2022
A. M. A. Moawad, A. M. Abdel-Wahab, Kh. S. Mekheimer, Khalid K. Ali, N. S. Sweed
Double-diffusive convection is a fluid dynamics phenomena explains convection which powered by two separate density gradients with differing diffusion rates (temperature and concentration). Thermal diffusion creates a concentration gradient when the temperature differential is kept constant. The concept of double diffusion is crucial for comprehending the development of complex systems with several causes for variations of density. It also contributes significantly for nutrient upwelling.In [29–33], there is some remarkable double diffusion that is pertinent to research.