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CFD modelling of an industrial air diffuser: predicting velocity and temperature in the near zone
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
Halton OY.
Halton OY.
Finnish Inst. of Occupational Health.
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2005 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 40, no 5, 601-615 p.Article in journal (Refereed) Published
Abstract [en]

This article describes experimental and modelling results from CFD simulation of an air diffuser for industrial spaces. The main objective of this paper is to validate a manufacturer model of the diffuser. In the air diffuser, the low velocity part is placed on top of a multi-cone diffuser in order to increase airflow rates and maximize the cooling capacity of a single diffuser unit. This kind of configuration should ensure appropriate performance of industrial air diffusers, which is discussed briefly at the end of the article. The paper illustrates the importance of a simulation model jointly with the manufacturer's product model and the grid layout near the ventilation device to achieve accurate results. Parameters for diffuser modelling were adapted from literature and manufacturer's product data. Correct specification of diffuser geometry and numerical boundary conditions for CFD simulations are critical for prediction. The standard k-epsilon model was chosen to model turbulence because it represents the best-known model utilized and validated for air diffuser performance. CFD simulations were compared systematically with data from laboratory measurements; air velocity was measured by ultrasonic sensors. Results show that CFD simulation with a standard k-epsilon model accurately predicts non-isothermal airflow around the diffuser. Additionally, smoke tests revealed that the flow around the diffuser is not completely symmetrical as predicted by CFD. The cause of the observed asymmetry was not identified. This was the main reason why some simulation results deviate from the measured values.

Place, publisher, year, edition, pages
2005. Vol. 40, no 5, 601-615 p.
Keyword [en]
industrial air diffuser, CFD, boundary conditions, velocity distribution, temperature distribution, room, validation
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-14557DOI: 10.1016/j.buildenv.2004.08.020ISI: 000227250900002Scopus ID: 2-s2.0-13444306430OAI: oai:DiVA.org:kth-14557DiVA: diva2:332598
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Air diffusion and solid contaminant behaviour in room ventilation: a CFD based integrated approach
Open this publication in new window or tab >>Air diffusion and solid contaminant behaviour in room ventilation: a CFD based integrated approach
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

One of the most fundamental human needs is fresh air. It has been estimated that people spend comparatively much time in indoor premises. That creates an elevated need for high-quality ventilation systems in buildings. The ventilation airflow rate is recognised as the main parameter for measuring the indoor air quality. It has been shown that the ventilation airflow rates have effects on respiratory diseases, on “sick building syndrome” symptoms, on productivity and perceived air quality. Ventilation is necessary to remove indoor-generated pollutants by diluting these to an acceptable level. The choice of ventilation airflow rate is often based on norms or standards in which the airflow rate is determined based on epidemiological research and field or laboratory measurements. However, the determination of ventilation flow rate is far more complex. Indoor air quality in the occupied zone can be dependent of many factors such as outdoor air quality, airflow rate, indoor generation of pollutants, moisture content, thermal environment and how the air is supplied into the human occupied zone. One needs to acknowledge the importance of air distribution which clearly affects the comfort of occupants. To design a ventilation system which considers all aspects of room ventilation can only be achieved by computer modelling. The objective of this thesis is to investigate air diffusion, indoor air quality and comfort issues by CFD (computational fluid dynamics) modelling. The crucial part of the CFD modelling is to adopt BCs (boundary conditions) for a successful and accurate modelling procedure. Assessing the CFD simulations by validated BCs enabled constructing the ventilation system virtually and various system layouts were tested to meet given design criteria. In parallel, full-scale measurements were conducted to validate the diffuser models and the implemented simplified particle-settling model. Both the simulations and the measurements reveal the full complexity of air diffusion coupled with solid contaminants. The air supply method is an important factor for distribution of heat, air velocity and solid contaminants. The influence of air supply diffuser location, contaminant source location and air supply method was tested both numerically and by measurements to investigate the influence of different parameters on the efficiency of room ventilation. As example of this, the well-known displacement ventilation is not fully able to evacuate large 10 μm airborne particles from a room. Ventilation should control the conditions in the human breathing zone and therefore the ventilation efficiency is an important parameter. A properly designed ventilation system could use less fresh air to maintain an acceptable level of contaminant concentration in the human breathing zone. That is why complete mixing of air is not recommended as the ventilation efficiency is low and the necessary airflow rate is relatively high compared to other ventilation strategies. Especially buoyancy-driven airflows from heat sources are an important part of ventilation and should not be hampered by supply airflow from the diffusers. All the results revealed that CFD presently is the only reliable method for optimising a ventilation system considering the air diffusion and contaminant level in all locations of any kind of room. The last part of the thesis addresses the possibility to integrate the CFD modelling into a building design process where architectural space geometry, thermal simulations and diffuser BCs could be embedded into a normal building design project.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 95 p.
Series
Trita-KRV, ISSN 1100-7990 ; 2005:03
Keyword
Technology, CFD modelling, airflow rate, ventilation efficiency, diffusers, solid contaminants, IAQ, TEKNIKVETENSKAP
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-270 (URN)91-7178-037-8 (ISBN)
Public defence
2005-06-16, sal 2105, KTH Syd, Campus Haninge, Haninge, 14:00
Opponent
Supervisors
Note
QC 20101007Available from: 2005-06-07 Created: 2005-06-07 Last updated: 2010-10-07Bibliographically approved

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