The Experts below are selected from a list of 4380 Experts worldwide ranked by ideXlab platform
Jelena Srebric - One of the best experts on this subject based on the ideXlab platform.
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Contaminant Dispersion with personal displacement ventilation part i base case study
Building and Environment, 2009Co-Authors: Xudong Yang, Caiqing Yang, Jelena SrebricAbstract:Abstract Personal displacement ventilation (PDV) is a new ventilation concept that combines the positive features of displacement ventilation with those of task conditioning or personalized ventilation. PDV is expected to create a micro-environment around an occupant to control the environment individually. In this study, a base PDV case with a Contaminant source at different locations was modeled for Contaminant Dispersion in a full-scale chamber. Computational fluid dynamics (CFD) was used to simulate the indoor airflow and pollutant transport, and the simulation results were validated against the experimental data. The Contaminant concentration field for three different Contaminant source locations was analyzed. Based on our results, it seems that this kind of PDV system cannot create the expected “micro-environment” to avoid the disturbance of the outside airflow. Further studies on how to improve the PDV performance are given in the companion paper.
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CFD boundary conditions for Contaminant Dispersion, heat transfer and airflow simulations around human occupants in indoor environments
Building and Environment, 2008Co-Authors: Jelena Srebric, Vladimir Vukovic, Xudong YangAbstract:Abstract Indoor computational fluid dynamics (CFD) simulations can predict Contaminant Dispersion around human occupants and provide valuable information in resolving indoor air quality or homeland security problems. The accuracy of CFD simulations strongly depends on the appropriate setting of boundary conditions and numerical simulation parameters. The present study explores influence of the following three key boundary condition settings on the simulation accuracy: (1) Contaminant source area size, (2) convective/radiative heat fluxes, and (3) shape/size of human simulators. For each of the boundary conditions, numerical simulations were validated with experimental data obtained in two different environmental chambers. In CFD simulations, a small release area of a Contaminant point source causes locally high concentration gradients that require a very fine local grid system. This fine grid system can slow down the simulations substantially. The convergence speed of calculation is greatly increased by the source area enlargement. This method will not influence the simulation accuracy of passive point source within well-predicted airflow field. However, for active point source located within complicated airflow filed, such an enlargement should be carried out cautiously because simulation inaccuracy might be introduced. For setting thermal boundary conditions, convection to radiation heat flux ratio is critical for accurate CFD computations of temperature profiles around human simulators. The recommended convection to radiation ( C : R ) ratio is 30:70 for human simulators. Finally, simplified human simulators can provide accurate temperature profiles within the whole domain of interest. However, velocity and Contaminant concentration simulations require further work in establishing the influence of simplifications on the simulation accuracy in the vicinity of the human simulator.
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removal of Contaminants released from room surfaces by displacement and mixing ventilation modeling and validation
Indoor Air, 2005Co-Authors: Xudong Yang, Jelena SrebricAbstract:UNLABELLED This paper presents the experimental and numerical modeling of Contaminant Dispersion in a full-scale environmental chamber with different room air distribution systems. For the experimental modeling, an area source with uniform emissions of a hypothetical Contaminant (SF6) from the entire floor surface is designed and constructed. Two different types of ventilation are studied: displacement and mixing ventilation. A computer model for predicting the Contaminant Dispersion in indoor spaces was validated with experimental data. The validated model is used to study the effects of airflow and the area-source location on Contaminant Dispersion. Results show that the global airflow pattern has a strong impact on the distribution of the Contaminants. In general, the personal exposure could be estimated by analyzing the relative source positions in the airflow pattern. Accordingly, the location of an exhaust diffuser may not greatly affect the airflow pattern, but can significantly affect the exposure level in the room. PRACTICAL IMPLICATIONS When designing ventilation in addition to bringing fresh air to occupants, it is important to consider the removal of Contaminants released in the off-gassing of building materials. Typical indoor off-gassing examples are emissions of volatile organic compounds from building enclosure surfaces such as flooring and painted walls. In this study, we conducted experimental and numerical modeling of different area sources in a mock-up office setup, with displacement or mixing ventilation. Displacement ventilation was as successful as mixing ventilation in removing the Contaminant source from the floor area. Actually, the most important consideration in the removal of these Contaminants is the relative position of the area source to the main airflow pattern and the occupied zone.
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effects of source type and location on Contaminant Dispersion in a displacement ventilated room
ASHRAE Transactions. 2005 Winter Meeting. Volume 111 part 1 + CD-ROM., 2005Co-Authors: X D Yang, Jelena SrebricAbstract:The research studies the effects of source type and location on Contaminant Dispersion and exposure in a displacement ventilated room. A full-scale environmental chamber is used to measure the airflow and Contaminant distributions in a mockup office setting. A point source is positioned at four different locations to examine the sensitivity of the Contaminant distribution to source locations. This is followed by the exposure measurements in the same room with an area of Contaminant sources on the floor. Experimental data are used to validate a computational fluid dynamics (CFD) model, and the CFD program is further applied to simulate the Contaminant Dispersion with more area sources.
Xudong Yang - One of the best experts on this subject based on the ideXlab platform.
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Contaminant Dispersion with personal displacement ventilation part i base case study
Building and Environment, 2009Co-Authors: Xudong Yang, Caiqing Yang, Jelena SrebricAbstract:Abstract Personal displacement ventilation (PDV) is a new ventilation concept that combines the positive features of displacement ventilation with those of task conditioning or personalized ventilation. PDV is expected to create a micro-environment around an occupant to control the environment individually. In this study, a base PDV case with a Contaminant source at different locations was modeled for Contaminant Dispersion in a full-scale chamber. Computational fluid dynamics (CFD) was used to simulate the indoor airflow and pollutant transport, and the simulation results were validated against the experimental data. The Contaminant concentration field for three different Contaminant source locations was analyzed. Based on our results, it seems that this kind of PDV system cannot create the expected “micro-environment” to avoid the disturbance of the outside airflow. Further studies on how to improve the PDV performance are given in the companion paper.
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CFD boundary conditions for Contaminant Dispersion, heat transfer and airflow simulations around human occupants in indoor environments
Building and Environment, 2008Co-Authors: Jelena Srebric, Vladimir Vukovic, Xudong YangAbstract:Abstract Indoor computational fluid dynamics (CFD) simulations can predict Contaminant Dispersion around human occupants and provide valuable information in resolving indoor air quality or homeland security problems. The accuracy of CFD simulations strongly depends on the appropriate setting of boundary conditions and numerical simulation parameters. The present study explores influence of the following three key boundary condition settings on the simulation accuracy: (1) Contaminant source area size, (2) convective/radiative heat fluxes, and (3) shape/size of human simulators. For each of the boundary conditions, numerical simulations were validated with experimental data obtained in two different environmental chambers. In CFD simulations, a small release area of a Contaminant point source causes locally high concentration gradients that require a very fine local grid system. This fine grid system can slow down the simulations substantially. The convergence speed of calculation is greatly increased by the source area enlargement. This method will not influence the simulation accuracy of passive point source within well-predicted airflow field. However, for active point source located within complicated airflow filed, such an enlargement should be carried out cautiously because simulation inaccuracy might be introduced. For setting thermal boundary conditions, convection to radiation heat flux ratio is critical for accurate CFD computations of temperature profiles around human simulators. The recommended convection to radiation ( C : R ) ratio is 30:70 for human simulators. Finally, simplified human simulators can provide accurate temperature profiles within the whole domain of interest. However, velocity and Contaminant concentration simulations require further work in establishing the influence of simplifications on the simulation accuracy in the vicinity of the human simulator.
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removal of Contaminants released from room surfaces by displacement and mixing ventilation modeling and validation
Indoor Air, 2005Co-Authors: Xudong Yang, Jelena SrebricAbstract:UNLABELLED This paper presents the experimental and numerical modeling of Contaminant Dispersion in a full-scale environmental chamber with different room air distribution systems. For the experimental modeling, an area source with uniform emissions of a hypothetical Contaminant (SF6) from the entire floor surface is designed and constructed. Two different types of ventilation are studied: displacement and mixing ventilation. A computer model for predicting the Contaminant Dispersion in indoor spaces was validated with experimental data. The validated model is used to study the effects of airflow and the area-source location on Contaminant Dispersion. Results show that the global airflow pattern has a strong impact on the distribution of the Contaminants. In general, the personal exposure could be estimated by analyzing the relative source positions in the airflow pattern. Accordingly, the location of an exhaust diffuser may not greatly affect the airflow pattern, but can significantly affect the exposure level in the room. PRACTICAL IMPLICATIONS When designing ventilation in addition to bringing fresh air to occupants, it is important to consider the removal of Contaminants released in the off-gassing of building materials. Typical indoor off-gassing examples are emissions of volatile organic compounds from building enclosure surfaces such as flooring and painted walls. In this study, we conducted experimental and numerical modeling of different area sources in a mock-up office setup, with displacement or mixing ventilation. Displacement ventilation was as successful as mixing ventilation in removing the Contaminant source from the floor area. Actually, the most important consideration in the removal of these Contaminants is the relative position of the area source to the main airflow pattern and the occupied zone.
Amir A Aliabadi - One of the best experts on this subject based on the ideXlab platform.
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are aircraft acceleration induced body forces effective on Contaminant Dispersion in passenger aircraft cabins
Science and Technology for the Built Environment, 2019Co-Authors: Hossam A Elmaghraby, Yi Wai Chiang, Amir A AliabadiAbstract:Numerical simulations for the effect of body forces due to aircraft acceleration on the airflow and Contaminant Dispersion in a model for a passenger aircraft cabin are performed in this study. Sul...
Anne Molcard - One of the best experts on this subject based on the ideXlab platform.
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Impact of wind-driven circulation on Contaminant Dispersion in a semi-enclosed bay
Estuarine Coastal and Shelf Science, 2020Co-Authors: Camille Mazoyer, Heleen Vanneste, Christiane Dufresne, Yann Ourmieres, Marcello G. Magaldi, Anne MolcardAbstract:Abstract Mediterranean semi-enclosed bays are often exposed to high levels of Contaminants originating from anthropogenic activities in the bay. To assess their fate and impact on the environment, it is essential to investigate coastal circulation regimes which may play an important role in the Dispersion of Contaminants across the bay and beyond. In this study, a high resolution coupled hydrodynamic - passive tracer model was combined with ADCP observations, to identify major circulation patterns and associated dissolved Contaminant Dispersion pathways in the contaminated semi-enclosed bay of Toulon (South of France, NW Mediterranean Sea). Two dominant circulation patterns and two derived ones could be identified, driven by winds (Mistral and easterly winds) and offshore water intrusions. Medium to strong Mistral events (> 6 m s−1) with a WNW direction cause a bi-layer pattern with surface waters flowing out of the bay and marine waters entering at depth. Less frequently, west Mistral winds of medium to strong strength (> 6 m s−1) may generate an anticyclonic circulation. During easterly wind conditions (> 6 m s−1), an inward flow can be observed which is sometimes reinforced by offshore water intrusions, probably from the local boundary current, the Northern Current (NC). Furthermore, dissolved Contaminant Dispersion pathways were simulated under typical wind forcing conditions with three point sources of copper (Cu) that were identified based on surface Cu observations. While most of the WNW Mistral wind events transport dissolved copper plumes across and out of the bay, Contaminant Dispersion can remain confined to the bay under certain west mistral conditions. Conversely, during easterly wind events, Contaminants are exiting the bay as a narrow vein along the Saint-Mandrier peninsula, before probably converging on the NC offshore. Accordingly, this study demonstrates the important impact of hydrodynamic-driven processes on the Dispersion of Contaminants within a semi-enclosed bay.
James B. Grotberg - One of the best experts on this subject based on the ideXlab platform.
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Bolus Contaminant Dispersion for oscillatory flow in a curved tube.
Journal of biomechanical engineering, 1996Co-Authors: Yahong Jiang, James B. GrotbergAbstract:The Dispersion of a bolus of soluble Contaminant in a curved tube during volume-cycled oscillatory flows is studied. Assuming a small value of delta (the ratio of tube radius to radius of curvature), the Navier-Stokes equations are solved by using a perturbation method. The convection-diffusion equation is then solved by expanding the local concentration in terms of the cross-sectionally averaged concentration and its axial derivatives. The time-averaged dimensionless effective diffusivity, , is calculated for a range of Womersley number alpha and different values of stroke amplitude A and Schmidt number Sc, where D is the molecular diffusivity of Contaminant. For the parameter values considered, the results show that axial Dispersion in a curved tube is greater than that in a straight tube, and that it has a local maximum near alpha = 5 for given fixed values of Sc = 1, A = 5 and delta = 0.3. Finally, it is demonstrated how the time history of concentration at a fixed axial position can be used to determine the effective diffusivity.
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Bolus Contaminant Dispersion in oscillatory tube flow with conductive walls.
Journal of biomechanical engineering, 1993Co-Authors: Yahong Jiang, James B. GrotbergAbstract:Dispersion of a bolus Contaminant in a straight tube with oscillatory flows and conductive walls is solved by using a derivative-expansion method. Using asymptotic methods when small conductance exists, the axial Dispersion, as measured by the time-averaged effective diffusivity, increases over the insulated case, as long as the dimensionless frequency (Womersley parameter), alpha, is smaller than a critical value. When alpha exceeds this value, axial Dispersion is diminished by wall conductance. The functional dependence of this critical alpha on the system parameters is investigated. We examine the radial wall transport both for total mass and localized flux, which is found to be independent of velocity field, and compute the time-dependent total mass of wall transport and asymptotic Sherwood number for large times as a function of the wall conductance.