Gas Air Systems

Overview

Engineering reference data for Gas Air Systems in combustion engineering.

Key Formulas

Heat Release

$Q = \dot{m} \cdot HV$

Fuel energy release rate.

Air-Fuel Ratio

$AF = \frac{m_{air}}{m_{fuel}}$

Mass of air per mass of fuel.

Excess Air

$EA = \frac{O_2}{21 - O_2} \times 100\%$

From flue gas oxygen measurement.

Variables

Definitions

Prandtl Number (Pr): A dimensionless number approximating the ratio of momentum diffusivity to thermal diffusivity. For air, it is often used in heat transfer calculations.

Specific Heat Ratio (γ): The ratio of the specific heat at constant pressure (Cp) to the specific heat at constant volume (Cv). For air, this ratio is approximately 1.4 at standard conditions.

SCFM (Standard Cubic Feet per Minute): The volumetric flow rate of a gas measured at standard conditions (typically 68°F, 14.696 psi).

ACFM (Actual Cubic Feet per Minute): The volumetric flow rate of a gas at actual operating conditions of temperature and pressure.

ICFM (Inlet Cubic Feet per Minute): The volumetric flow rate of a gas at the inlet conditions of a compressor.

Additional Key Formulas

Boyle's Law (Mariotte's Law): $P_1V_1 = P_2V_2$ Relates pressure and volume of a gas at constant temperature.

Charles' Law: $\frac{V_1}{T_1} = \frac{V_2}{T_2}$ Relates volume and absolute temperature of a gas at constant pressure.

Prandtl Number for Air: $Pr = \frac{\nu}{\alpha} = \frac{\mu C_p}{k}$ Where $\nu$ is kinematic viscosity, $\alpha$ is thermal diffusivity, $\mu$ is dynamic viscosity, $C_p$ is specific heat, and $k$ is thermal conductivity.

Specific Heat Ratio: $\gamma = \frac{C_p}{C_v}$ For dry air near standard conditions, $\gamma \approx 1.4$.

Conversion between SCFM and ACFM: $ACFM = SCFM \times \frac{P_{std}}{P_{act}} \times \frac{T_{act}}{T_{std}}$ Where P and T are absolute pressure and temperature.

References

• Original Source