Using the principle of dynamic temporal separation to determine the range hood direct capture efficiency

Range hoods are commonly used in residential kitchens to capture pollutants generated during cooking. Direct capture represents the true capture performance of the range hood as a local exhaust device. A better metric for evaluating range hood capture performance is direct capture efficiency (DCE), defined as the ratio of pollutant directly captured by the hood to the total pollutant emission from the source. This paper clarifies the dynamic functioning mechanism of direct capture and reflux capture, analyzes the dynamic characteristics of exhaust concentration, and deduces a simple method for DCE determination based on dynamic temporal separation, where DCE is the ratio of the peak concentration of direct capture (C₁) to the peak concentration of total capture (C₂). Experimental and simulation studies on dynamic exhaust concentration were conducted under different ventilation conditions, and the results were in good agreement. Then, the determination methods of C₁ and C₂, including the experimental methods, were further studied to calculate the DCE. The measured and simulated results for DCE based on dynamic temporal separation showed good consistency, with a deviation of less than 2.0%. Finally, the two spatial separation methods for determining DCE (mass flux ratio and virtual purification) proposed and verified in our previous study showed good agreement with the dynamic temporal separation method based on C₁/C₂ proposed here, with a maximum deviation of 2.0%. The determination method of DCE based on dynamic time separation, particularly the experimental method, is of great significance for evaluating the real capture performance of range hoods.