Exhaust Hoods

Overview

Engineering reference data for Exhaust Hoods in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Variables

Symbol	Description	Unit
$x$	Input value	—
$y$	Output value	—
$k$	Conversion factor	—

Design Guidelines for Exhaust Hood Efficiency

For optimal performance, adhere to these spatial and operational constraints:

• Hood Height (y): Should not exceed 1.20 m (4 ft) above the source.
• Hood Position (x): The horizontal distance from the hood edge to the source should be at least 1/3 of the height (y).
• Capture Velocity (v₁): Must be at least 0.15–0.20 m/s (30–40 ft/min) to effectively capture contaminants.

Note: Applications involving hazardous or polluting substances require specialized solutions. Always verify compliance with local regulations during the design phase.

Hood Modifications for Improved Efficiency

Modifying the hood geometry can significantly enhance capture efficiency and reduce the required air volume flow.

Hood with Internal Plate

Adding an internal baffle plate within the hood can reduce the required air volume by approximately 20% compared to a standard open hood, improving airflow distribution and capture effectiveness.

Hood with Side Walls

Incorporating side walls around the hood creates a semi-enclosed capture zone. This further reduces the air volume needed and improves the capture of fumes and contaminants, especially from processes with strong cross-drafts.

References

• Original Source