The soret effect is where small light molecules and large heavy molecules separate under a temperatue gradient. Usually this effect is important where more than one chemical species is present under a very large temperature gradient such as CVD problems and chemical reactors. This effect is found when solving the species mass fraction equations.

The Dufour effect describes the energy (heat) flux created when a chemical system is under a concentration gradient. This could also be important in CVD problems. This effect is found in the energy equation.

The soret coefficient is the ratio of the thermal diffusion coefficient divided by the ordinary diffusion coefficient.

Dear Zeng

Dufour Effect : Concentration gradients produce a heat flux. Soret Effect : Reverse of Dufour effect

It is known that both Soret & Dufour effects are negligible, for most applications.

Sincerely, Jinwook

Soret effect- This is a mass flux due to a temperature gradient and appears in the species continuity equation when you have a multicomponent mixture where each species has its own diffusional velocity.

Dufor Effect-This is enthalpy flux due to a concentration gradient and appears in the energy equation for a multicomponent mixture.These effects depend on thermal diffusion which is generally very small but can be sometimes significant when the participating species are of widely differing molecular weights

Venkat

Can you help me to understand: (1) Soret effect (2) Soret diffusion coefficent (3) Dufour effect

Thanks in advance.

[eslamian]

In isothermal mixtures of two or more species (gases, liquids and even
solids), mass diffusion occurs if the species are initially distributed
unevenly, i.e., when a concentration gradient exists. A temperature
gradient can also work as a driving force for mass diffusion, in a
phenomenon which is called thermodiffusion, thermal diffusion, or in

liquid mixtures Soret (Ludwig-Soret) effect.


Free open access paper on Soret effect

http://www.thermalfluidscentral.org/...hp?a=206&g=242

[michujo]

Hi, as far as I know, Soret effect is not negligible when you compute the transport of light species (typically H radical in combustion applications).
Cheers.

[eslamian]

Whenever there is a temperature gradient in the mixture, Soret effect is present. The higher the temperature gradient, the larger the Soret effect. Pressure diffusion is usually negligible but not the Soret effect.

[mohsenclick]

Originally Posted by Chuck Leakeas
;8860

The soret effect is where small light molecules and large heavy molecules separate under a temperatue gradient. Usually this effect is important where more than one chemical species is present under a very large temperature gradient such as CVD problems and chemical reactors. This effect is found when solving the species mass fraction equations.

The Dufour effect describes the energy (heat) flux created when a chemical system is under a concentration gradient. This could also be important in CVD problems. This effect is found in the energy equation.

The soret coefficient is the ratio of the thermal diffusion coefficient divided by the ordinary diffusion coefficient.

I am confused.....on one side when we have temperature gradient the different species seperate to omit this gradient so temperature gradient decreases but the concentration gradient created as a result....so now due to dufour effect this concentration gradient should create heat flux that will lead to temperature gradient again....and now it is again soret effect turn and this cycle continues.....so when these two effects reach to a balance......?????????????????????????

[mohsenclick]

Originally Posted by eslamian

Whenever there is a temperature gradient in the mixture, Soret effect is present. The higher the temperature gradient, the larger the Soret effect. Pressure diffusion is usually negligible but not the Soret effect.

I am confused.....on one side when we have temperature gradient the different species seperate to omit this gradient so temperature gradient decreases but the concentration gradient created as a result....so now due to dufour effect this concentration gradient should create heat flux that will lead to temperature gradient again....and now it is again soret effect turn and this cycle continues.....so when these two effects reach to a balance......?????????????????????????

[Arberta]

Hey, in the case of forced convection can we study the effect of Soret and Dufour ???
If the answer is yes, it makes a notable difference when we neglect these parameters ?
Thanks in advance