Questions

What is meant by Knudsen diffusion?

What is meant by Knudsen diffusion?

In physics, Knudsen diffusion, named after Martin Knudsen, is a means of diffusion that occurs when the scale length of a system is comparable to or smaller than the mean free path of the particles involved. This process is known as Knudsen flow or Knudsen diffusion.

What is the main assumption of the Knudsen diffusion?

The solution-diffusion model assumes that the pressure within a membrane is uniform and the chemical gradient across the membrane is expressed only as a concentration gradient.

What is continuum and free molecular flow explain its significance?

Continuum flow is that flow that approaches zero Knudsen number. It can be achieved when the mean free path of a fluid molecule is tiny, or the section is enormous. Free molecular flow is a type of flow in which the mean free path of the gas molecule is larger than the chamber.

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How do I find my Knudsen number?

Hint: Knudsen number is given by Kn=λ/Dh, and the mean free path λ is given by λ = ( μ π / ρ 2 R T ) , where μ is the fluid viscosity, ρ is the fluid density, T is the absolute temperature, and R is the gas constant.

What is continuum flow?

What is Continuum and Fluid Mechanics? A continuum is an area that can keep being divided and divided infinitely; no individual particles. It is a simplification that makes it possible to investigate the movement of matter on scales larger than the distances between particles.

How is Knudsen diffusivity calculated?

Calculation of the Knudsen diffusion coefficients

  1. 1 / D’*A = (α − 1)XA / τmDAB + 1 / τmDAB + 1 / τpDA (22)
  2. 1 / D’*B = (1/α − 1)XB / τmDAB + 1 / τmDAB + 1 / τpDB (23)
  3. mA = (α − 1) /τm DAB (24a)
  4. mB = (1 − α) /α τm DAB. (24b)
  5. α mB = − (α − 1) / τm DAB. (25)
  6. mA +α mB = 0. (26)
  7. α = − mA / mB.
  8. τm DAB = − (mA + mB) / (mAmB).
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What is surface migration?

Surface diffusion is a general process involving the motion of adatoms, molecules, and atomic clusters (adparticles) at solid material surfaces. The process can generally be thought of in terms of particles jumping between adjacent adsorption sites on a surface, as in figure 1.

What are the applications of Knudsen number?

One of the most widely used applications for the Knudsen number is in microfluidics and MEMS device design. Movements of fluids in situations with a high Knudsen number are said to exhibit Knudsen flow .

What is Knudsen diffusion?

Consider the diffusion of gas molecules through very small capillary pores. If the pore diameter is smaller than the mean free path of the diffusing gas molecules and the density of the gas is low, the gas molecules collide with the pore walls more frequently than with each other. This process is known as Knudsen flow or Knudsen diffusion.

What is Knudsen flow in gas chromatography?

If the pore diameter is smaller than the mean free path of the diffusing gas molecules and the density of the gas is low, the gas molecules collide with the pore walls more frequently than with each other. This process is known as Knudsen flow or Knudsen diffusion.

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What is the Knudsen number in fluid mechanics?

If the length scale of the fluidic system is in the same range as the mean free path, i.e., Kn = 1, the fluid cannot be treated as a continuum. The Knudsen number is of particular interest when assessing the boundary of fluid flows.