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This paper presents a new two-layer model that can be used to calculate natural, forced, and mixed convection flow in a room

Simulation of mixed convection flow in a room with a two-layer turbulence model.

Indoor air, no. 4 (2000): 306-314

Cited by: 17|Views3
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Abstract

Most indoor airflows are mixed convection. In order to simulate mixed convection accurately and efficiently, this paper uses a two-layer turbulence model. The two-layer model combines a one-equation model for near wall flow together with the standard k-epsilon model for outer-wall flow. The model has been used to predict the mixed convect...More

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Introduction
  • Design of an acceptable indoor environment requires detailed information of indoor air distribution, thermal comfort, indoor air quality, etc.
  • The CFD application to indoor environment design has enjoyed a great success in the past two decades.
  • There are still some uncertainties in the CFD results.
  • This is because most indoor airflows are turbulent.
  • The existing turbulence models are either inaccurate (such as the standard k-e model (Launder and Spalding, 1974)) or inefficient to predict indoor airflow
Highlights
  • Design of an acceptable indoor environment requires detailed information of indoor air distribution, thermal comfort, indoor air quality, etc
  • This paper presents a new two-layer model that can be used to calculate natural, forced, and mixed convection flow in a room
  • A turbulence model should be used in the computational fluid dynamics (CFD) to make the flow solvable with the present computer capacity and speed
  • This paper presents a two-layer turbulence model (Xu, 1998) that performs two tasks: 1) The model can accurately predict indoor airflows under various conditions, i.e., from purely forced to purely natural convection airflows (Xu, 1998)
  • With a two-layer turbulence model recently developed from the data of direct numerical simulation and two-layer models for natural and forced convection, it is possible to accurately predict mixed convection in a room
  • Since displacement ventilation design requires accurate information of airflow, this study used the twolayer model to predict the airflow pattern and distributions of air temperature, air velocity, air velocity distributions, and contaminant concentration simulated by a tracer gas in a room with displacement ventilation
Results
  • In the region close to the floor, some discrepancies occur but the largest difference between the calculated temperatures and measured ones is less than 1æC, about 4% of the measured temperature, which can be considered as a good agreement.
Conclusion
  • This paper briefly reviews the effort to predict mixed convection with computational fluid dynamics.
  • Since displacement ventilation design requires accurate information of airflow, this study used the twolayer model to predict the airflow pattern and distributions of air temperature, air velocity, air velocity distributions, and contaminant concentration simulated by a tracer gas in a room with displacement ventilation.
  • Designing such ventilation system often requires accurate information of airflow.
  • It is more difficult to predict the turbulence and contaminant concentration
Summary
  • Introduction:

    Design of an acceptable indoor environment requires detailed information of indoor air distribution, thermal comfort, indoor air quality, etc.
  • The CFD application to indoor environment design has enjoyed a great success in the past two decades.
  • There are still some uncertainties in the CFD results.
  • This is because most indoor airflows are turbulent.
  • The existing turbulence models are either inaccurate (such as the standard k-e model (Launder and Spalding, 1974)) or inefficient to predict indoor airflow
  • Results:

    In the region close to the floor, some discrepancies occur but the largest difference between the calculated temperatures and measured ones is less than 1æC, about 4% of the measured temperature, which can be considered as a good agreement.
  • Conclusion:

    This paper briefly reviews the effort to predict mixed convection with computational fluid dynamics.
  • Since displacement ventilation design requires accurate information of airflow, this study used the twolayer model to predict the airflow pattern and distributions of air temperature, air velocity, air velocity distributions, and contaminant concentration simulated by a tracer gas in a room with displacement ventilation.
  • Designing such ventilation system often requires accurate information of airflow.
  • It is more difficult to predict the turbulence and contaminant concentration
Tables
  • Table1: Boundary conditions and computation details
Download tables as Excel
Funding
  • This study is supported by the National Science Foundations through grant CMS-9623864
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