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Damkohler number

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Latest revision as of 13:50, 6 February 2012

The Damkohler number is used in turbulent combustion and corresponds to the ratio of chemical time scale  \tau_c and turbulent time scale  \tau_t . This turbulent scale is usually taken as the integral scale.

Da \equiv \frac{\tau_t}{\tau_c}

Damkohler number measures how important is the interaction between chemistry and turbulence. Most combustion models are placed in the extremes of Damkohler.

If  Da << 1 the turbulence is much faster than the chemistry. This regime is the "well-stirred reactor", where products and reactants are rapidly mixed. The Karlovitz number is linked to the Damkholer number.

The Damkohler number is also defined in a chemical non-equilibrium process at very high velocities of the fluid or vehicles (with reference to fluid). There are two ratios of Damkohler number that can be defined and are as follows:

1. First Damkohler Number or DAM 1

DAM 1 = \frac{t_{res}}{\tau}

Where  t_{res} is the residence time of the flow, where  \frac{L_{ref}}{U_{ref}} where  L_{ref} is the reference length of the vehicle and  U_{ref} is the reference velocity of fluid or vehicle with respect to fluid

2. Second Damkohler Number or DAM 2

DAM 2 = \frac{q_{ne}}{h_o}

Where  q_{ne} is the energy involved in a non-equilibrium process and  h_o is the total enthalpy of the flow

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