Available online 8 February 2013 Publication year: 2013 Source:Building and Environment
This paper analyses the dispersion of the exhaled contaminants by humans in indoor environments, with special attention to the exhalation jet and its interaction with the indoor airflow pattern in both mixing and displacement ventilation conditions.The way in which three different numerical boundary conditions for the exhalation flow (one time-dependent and two steady conditions) predict that contaminant dispersion is also analysed. The first boundary condition is a time-dependent sinusoidal function, which is the most realistic condition (Test a), and it is used to validate the numerical model with experimental data obtained from a previous study. The second one (Test b) maintains the momentum of the exhalation flow and the third (Test c) uses the maximum exhalation velocity.The objectives of this study are to increase knowledge regarding the exhaled contaminant distribution under different environmental conditions and to validate whether a steady boundary condition of the exhalation flow may simulate human breathing in an effective and accurate way. The results show a very good agreement of the numerical results obtained for Test a and the experimental data. This fact confirms the use of numerical simulation as a powerful tool to predict the contaminant distribution exhaled by a human. The numerical tests with steady boundary conditions for the exhalation flow require a transitory resolution procedure and the predictions provided by these models display some discrepancies with respect to Test a. These differences are evaluated by comparing the penetration length and vertical ascendance values for the different tests.
Graphical abstract
Highlights
► We examined the dispersion of exhaled contaminants generated by human breathing. ► The solution may be time-dependent even with steady boundary conditions. ► A zone of elevated contaminant concentration is formed in the upper face area. ► Any constant exhalation will be incapable of predicting the previous highlight. ► We do not recommend substituting sinusoidal exhalation for another stationary one.
