What does Damkoehler number indicate?

What does Damköhler number indicate?

Damkohler number, Da—the dimensionless ratio of a characteristic liquid residence time to the reaction time. High values of the Da number indicate that the forward reaction is fast and low values indicate that the reaction is kinetically controlled.

How is Damköhler number calculated?

The classic definition is to divide the turbulent kinetic energy (k) by the turbulent dissipation (epsilon). You can also estimate it by dividing the integral length scale by the velocity fluctuations (the velocity fluctuations are by definition the Turbulent Intensity multiplied by the Mean Velocity).

What is Damköhler number and explain its significance in reactor design?

Péclet number (Pe) relates the global movement rate of the fluid to the diffusive mass transport rate. P e and D a describe reactors where the diffusion, global movement, and reaction rate of the species take place simultaneously [12].

When Damköhler number is greater than1?

Leckner et al. (2011) recommend that for vertical combustor operation, the Damköhler number should be greater than 1, which means that the transport time of the solids should be greater than the reaction time.

What is the importance of damkohler number?

A word about Damkohler numbers. A Damköhler number (Da) is a useful ratio for determining whether diffusion rates or reaction rates are more ‘important’ for defining a steady-state chemical distribution over the length and time scales of interest.

What is dispersion number?

The dispersion number represents the overall extent of axial dispersion in the system under consideration and is the reciprocal of the Peclet number (Pe = unL/Da). In the dispersion number expression, Da is the axial dispersion coefficient, un is the mean velocity and L is the length between the two measurement points.

What is the unit of dispersion coefficient?

The units of the material dispersion coefficient are usually ps/nm · km. For silica fiber, the term d2n/dλ2 crosses zero near λ ≈ 1.3 μm. This is the zero material dispersion wavelength and is one of the reasons that 1.3-μm light is used in fiber optic systems.

How is dispersion number calculated?

Standard deviation (SD) is the most commonly used measure of dispersion. It is a measure of spread of data about the mean. SD is the square root of sum of squared deviation from the mean divided by the number of observations. This formula is a definitional one and for calculations, an easier formula is used.

What do you need to know about Damkohler numbers?

A word about Damköhler numbers A Damköhler number (Da) is a useful ratio for determining whether diffusion rates or reaction rates are more ‘important’ for defining a steady-state chemical distribution over the length and time scalesof interest. Hence the definition:

How is the Damkohler number related to the Karlovitz number?

The Damköhler numbers ( Da) are dimensionless numbers used in chemical engineering to relate the chemical reaction timescale ( reaction rate) to the transport phenomena rate occurring in a system. It is named after German chemist Gerhard Damköhler. The Karlovitz number ( Ka) is related to the Damköhler number by Da = 1/Ka.

How is the Damkohler number used in turbulent combustion?

The Damkohler number is used in turbulent combustion and corresponds to the ratio of chemical time scale and turbulent time scale . This turbulent scale is usually taken as the integral scale. Damkohler number measures how important is the interaction between chemistry and turbulence.

What is the Damkohler number in fluidized bed technology?

Damköhler number represents ratio of laminar flame speed square to thermal diffusivity and critical velocity gradient in Eq. (53). T.M. Knowlton, in Fluidized Bed Technologies for Near-Zero Emission Combustion and Gasification, 2013