key term - Diffusion-viscous flow coupling

Definition

Diffusion-viscous flow coupling refers to the interdependence between the diffusion of particles or molecules in a medium and the viscous flow of that medium. This phenomenon is crucial in non-equilibrium thermodynamics, as it highlights how the movement of particles under a concentration gradient is influenced by the viscosity of the fluid, leading to effects such as drag and shear forces that can modify diffusion rates.

5 Must Know Facts For Your Next Test

1. Diffusion-viscous flow coupling is particularly significant in biological systems, where the movement of nutrients and waste products is affected by both diffusion and fluid flow.
2. In systems with high viscosity, diffusion rates are often reduced due to increased resistance against particle movement.
3. The coupling can lead to complex behaviors such as non-linear diffusion when external forces or gradients are applied.
4. Understanding this coupling is essential for applications in materials science, chemical engineering, and biological transport processes.
5. Mathematically, diffusion-viscous flow coupling can be described using equations that incorporate both Fick's laws of diffusion and the Navier-Stokes equations for fluid motion.

Review Questions

• How does viscosity affect the rate of diffusion in a given system?
  • Viscosity directly influences the rate at which particles can diffuse through a medium. In fluids with higher viscosity, there is greater resistance to flow, leading to slower diffusion rates. This means that when a concentration gradient is present, particles will take longer to spread out compared to a less viscous fluid where they can move more freely. The interplay between diffusion and viscous forces is essential for understanding transport processes in various systems.
• Discuss the significance of Onsager Reciprocal Relations in relation to diffusion-viscous flow coupling.
  • Onsager Reciprocal Relations provide insight into how different fluxes in a system respond to various driving forces. In the context of diffusion-viscous flow coupling, these relations show that the flux of particles due to diffusion is related to the viscous flow of the medium. For example, if a concentration gradient induces particle movement, this can also create shear stress within the fluid that alters its viscosity, demonstrating a reciprocal relationship between these processes. This understanding is key in predicting system behavior under non-equilibrium conditions.
• Evaluate the implications of diffusion-viscous flow coupling for biological transport mechanisms in organisms.
  • The implications of diffusion-viscous flow coupling for biological transport mechanisms are profound. For instance, in blood circulation, nutrient and oxygen delivery relies on both diffusion through capillary walls and the viscous nature of blood flow. Changes in viscosity, such as those caused by varying hematocrit levels or pathological conditions like dehydration, can alter how efficiently substances diffuse into tissues. Understanding this coupling allows scientists and medical professionals to develop better treatment strategies and improve drug delivery systems by optimizing conditions for effective transport within biological systems.

Related terms

Non-equilibrium Thermodynamics: A branch of thermodynamics that studies systems that are not in thermodynamic equilibrium, focusing on processes like diffusion, heat transfer, and chemical reactions.

Onsager Reciprocal Relations:

A set of relations in thermodynamics that link different fluxes and forces in a system, indicating that the response of a system to one type of gradient is related to its response to another.

Viscosity: A measure of a fluid's resistance to flow, which plays a critical role in determining how easily particles diffuse through the fluid.