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Schlieren Flow Visualization

Schlieren flow visualization is a non-intrusive approach to effluent flow observation. This technique is crucial to understanding the flow of heat and effluents generated by commercial cooking equipment. The videos below demonstrate the Schlieren flow visualization technique applied to commercial kitchen ventilation.


Schlieren technology utilizes a light source, an imaging lens and an image plane to capture "bent" light paths due to light refraction. Light refraction is due to a change in the refractive index of air at different temperatures. The result is a well defined image illustrating air at different temperatures.

In the case of kitchen ventilation, hot air is of interest. The Schlieren flow visualization technique is used to determine whether or not the heat, generated by the cooking equipment, is being captured by the kitchen exhaust hood. From this, a value for exhaust flow rate of the hood can be determined to fully capture the heat generated by the cooking equipment.

Videos and Test Parameters

The product being displayed below is a wall canopy hood with various flows and configurations of make-up air. The videos in the left column demonstrate the heat produced from two gas charbroilers. The videos in the right column are illustrations of heat generated from two electric griddles.

The hood utilized in these videos is 8' in length, 24" tall and 54" wide. The left and right overhang of the hood is 6" and the front overhang is 24".

All make-up air temperatures are 85°F. All tests were conducted to ASTM-1704 and below are the videos and the results of the tests:

Exhaust Only with No Make-Up Air Full Capture and Containment

Gas CharBroiler (700°F)

  • Exhaust rate = 2100 CFM (263 CFM/lnft)
  • Supply rate = 0 CFM (0 CFM/lnft)

Electric Griddle (400°F)

  • Exhaust rate = 1350 CFM (169 CFM/lnft)
  • Supply rate = 0 CFM (0 CFM/lnft)

Gas CharBroiler with End Panels (700°F)

  • Exhaust rate = 1950 CFM (244 CFM/lnft)
  • Supply rate = 0 CFM (0 CFM/lnft)

Closing Comments

We hope this information facilitates the use of this new product into your submittals and application engineering.

We are aware that flow rates determined by the Schlieren flow visualization technique are laboratory produced values and are not suitable for every application. This information is presented to be used as a tool in the design and understanding commercial kitchen ventilation systems.