CFD Analysis of Pollutant Dispersion in Kitchens
HPAC ENGINEERING MARCH/APRIL 2025
Author:
Kishor Khankari
Abstract:
In this CFD study, a three-dimensional, transient, non-isothermal CFD model was developed to study the transient temperature distribution and the dispersion of NO2 in the kitchen and the adjacent living room. The effectiveness of the kitchen ventilation was evaluated using newly developed metrics of Spread Index and Purge Time.
The study analyzed the conditions with closed windows and doors which is most common during the winter in cold climates. It was found that an exhaust flow rate of 75 cfm is inadequate for effectively removing pollutants from a kitchen space. Increasing the exhaust flow rate was shown to reduce the spread of high-concentration zones of pollutants into adjacent spaces, as indicated by the Spread Index analysis. Additionally, increasing the exhaust flow rate reduces the Purge Time and helps in the effective removal of residual pollutants after cooking when the burner is turned ‘OFF’.
The analyses also suggest that the thermal plume from occupants and the buoyancy of hot gases can help reduce the cumulative NO2 exposure. While occupant NO2 exposure levels remained significantly low during the first few minutes of cooking when the burner is ‘ON’, the exposure level starts increasing during the purge phase when the burner is turned ‘OFF’.
However, an increase in the exhaust flow rate significantly reduces cumulative NO2 exposure levels. It is important to note that for all exhaust flow rates analyzed in the study the cumulative NO2 exposure levels remained significantly below the EPA-acceptable level of 100 ppb-hr for short-term exposure. The analyses also indicate that thermal stratification causes pollutants to accumulate and migrate along the ceiling above the breathing zone of occupants. Furthermore, the thermal plume from an occupant can form a “protective shield” to help reduce pollutant exposure. This study suggests that CFD can be a valuable tool in analyzing these parameters cost-effectively and optimizing the performance of kitchen ventilation systems.
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About the author
Dr. Kishor Khankari
ASHRAE Fellow, ASHRAE Distinguished Lecturer
Dr Kishor Khankari is the founder of AnSight LLC. As a specialist in Computational Fluid Dynamics (CFD), his passion for solving engineering problems and providing sound scientific solutions has led to innovations and optimized designs in the industry.
A noted expert in his field, he has a Ph.D. from the University of Minnesota and has published in several technical journals and trade magazines. As a well sought-after speaker Dr. Khankari makes regular presentations in various technical conferences and professional meetings worldwide.
