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A modified tracer-gas decay model for ventilation rate measurements in long and narrow spaces

Ventilation is essential to the health and comfort of occupants in enclosed spaces. However, it is difficult to accurately measure the ventilation rates in large, long, and narrow spaces such as aircraft cabins and train compartments. This study has proposed a modified tracer-gas-concentration decay method that combines the multi-zone technique with the genetic algorithm to determine ventilation rate in such spaces. To validate the proposed method, the investigation utilized both the modified decay method and the traditional decay method to numerically measure the ventilation rate in an MD-82 aircraft cabin by computational fluid dynamics technique. The results showed that the modified tracer-gas-concentration decay method can significantly improve the accuracy and reliability of the ventilation rate measurements in such a large, long, and narrow space. The modified tracer-gas-concentration decay method was also used to experimentally measure the ventilation rate in an actual MD-82 aircraft cabin. Although no exact ventilation rate could be measured, but compared with the traditional tracer-gas-concentration decay method, the ventilation rate determined by the modified method was much closer to that obtained by the constant tracer-gas-concentration method, which is considered to be the most accurate measurement.