What are Dufour and Soret effects?

The mass flux created by a temperature gradient is known as thermal-diffusion (Soret) effect. The energy flux caused by concentration differences is known as diffusion-thermo (Dufour) effect.

What is the purpose of a natural convection?

Natural convection is a type of flow, of motion of a liquid such as water or a gas such as air, in which the fluid motion is not generated by any external source (like a pump, fan, suction device, etc.)

What is Dufour number?

[¦dü·fȯr ‚nəm·bər] (thermodynamics) A dimensionless number used in studying thermodiffusion, equal to the increase in enthalpy of a unit mass during isothermal mass transfer divided by the enthalpy of a unit mass of mixture.

What is the most important parameter in natural convection?

Natural Convection from Finned Surfaces One of most crucial parameters in designing heat sinks is the fin spacing, S. Closely packed fins will have greater surface area for heat transfer, but a smaller heat transfer coefficient (due to extra resistance of additional fins).

What is the greatest disadvantage of natural convection?

What is the greatest disadvantage of natural convection? Advantage of natural convection is, it doesn’t require any additional cost for heat transfer. While it’s disadvantage is, it is ineffective in static systems for heat transfer.

What is Thermophoresis parameter?

Thermophoresis is a force generated by the temperature gradient between the hot gas and the cold wall effecting the particulate movement towards the cold wall.

What is the significance of Lewis number?

The Lewis number (Le) is a dimensionless number defined as the ratio of thermal diffusivity to mass diffusivity. It is used to characterize fluid flows where there is simultaneous heat and mass transfer.

What is the difference between forced convection and natural convection?

In natural convection, any fluid motion is caused by natural means such as the buoyancy effect, i.e. the rise of warmer fluid and fall the cooler fluid. Whereas in forced convection, the fluid is forced to flow over a surface or in a tube by external means such as a pump or fan.

What is the law of natural convection?

The heat transfer rate in natural convection is expressed by. Newton’s law of cooling as: Q’conv = h A (Ts ‐ T∞) Fig. 3: Velocity and temperature profile for natural convection flow over a hot vertical. plate.

What is called Brownian movement?

Brownian motion, also called Brownian movement, any of various physical phenomena in which some quantity is constantly undergoing small, random fluctuations. It was named for the Scottish botanist Robert Brown, the first to study such fluctuations (1827).

What is Soret coefficient?

The Soret coefficient is defined as ratio S T = D T/D, which determines the magnitude of thermodiffusion in the steady state.

How are the effects of Soret and Dufour validated?

The analytical solution is validated numerically by using a finite difference method. The combined effects of the Soret and Dufour parameters, the thermal Rayleigh number, the buoyancy ratio, and the Darcy number on the flow intensity and heat and mass transfer are illustrated graphically, and some particular behaviors observed are discussed.

How does the rise of Soret and Dufour affect entropy?

Among others, he showed that the rise of Soret and Dufour parameters enhances the entropy generations due to heat transfer and fluid friction. The present study is devoted to analytical and numerical investigation of Soret and Dufour effects within a horizontal Brinkman layer with a stress-free upper boundary.

How are temperature and concentration gradients related to convection?

Convection in which the buoyancy forces are due to both temperature and chemical concentration gradients is referred to as thermosolutal or double-diffusive convection. The fluid flow behavior driven by temperature and concentration gradients has attracted the interest of researchers worldwide through the decades [ 2 ].