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Investigation of design parameters for an air supply device based on wall confluent jets
Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology. Department of Building, Energy and Environmental Engineering, University of Gävle, Sweden.
Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology.
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Numerical predictions of the flow field generated by an air supply device based on wall confluent jets are investigated. The numerical predictions of three turbulence models (RNG 𝑘 − 𝜀, Re 𝑘 − 𝜀, and SST 𝑘 − 𝜔) are compared by velocity and temperature measurements. Ventilation performance in terms of thermal comfort and ventilation efficiency is numerically investigated by systematically varying the design of the air supply (nozzle array configuration, nozzle diameter, number of nozzles, and inlet discharge height). The numerical predictions accomplished by the SST 𝑘 − 𝜔 model provide the best agreement with the experimental results. The numerical predictions for supply devices of varying design configuration show that different device designs provide acceptable thermal environments and efficient heat removal. The nozzle diameter and number of nozzles play important roles in determining the airflow pattern, temperature field, and draught distribution. Increased temperature stratification and less draught distribution are achieved by increasing the nozzle diameter and number of nozzles. The spreading rates of the wall jet along the vertical direction for the cases studied are in close agreement with each other and independent of the studied parameters. The flow behavior is rarely independent of the inlet discharge height and configuration of the nozzle array for the studied range.

Place, publisher, year, edition, pages
2015.
Keyword [en]
Wall confluent jets supply device, Numerical predictions, Parametric studies, Ventilation performance, Ventilation efficiency, Thermal comfort
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:liu:diva-117437OAI: oai:DiVA.org:liu-117437DiVA: diva2:808159
Available from: 2015-04-27 Created: 2015-04-27 Last updated: 2015-04-27Bibliographically approved
In thesis
1. A Ventilation Strategy Based on Confluent Jets: An Experimental and Numerical Study
Open this publication in new window or tab >>A Ventilation Strategy Based on Confluent Jets: An Experimental and Numerical Study
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This study presents air distribution systems that are based on confluent jets; this system can be of interest for the establishment of indoor environments, to fulfill the goals of indoor climate and energy-efficient usage. The main objective of this study is to provide deeper understanding of the flow field development of a supply device that is designed based on wall confluent jets and to investigate the ventilation performance by experimental and numerical methods. In this study, the supply device can be described as an array of round jets on a flat surface attached to a side wall. Multiple round jets that issue from supply device apertures are combined at a certain distance downstream from the device and behave as a united jet or so-called confluent jets. Multiple round jets that are generated from the supply device move downward and are attached to the wall at the primary region, due to the Coanda effect, and then they become wall confluent jets until the floor wall is reached. A wall jet in a secondary region is formed along the floor after the stagnation region.

The characteristics of the flow field and the ventilation performance of conventional wall confluent jets and modified wall confluent jets supply devices are investigated experimentally in an office test room. The study of the modified wall confluent jets is intended to improve the efficiency of the conventional one while maintaining acceptable thermal comfort in an office environment. The results show that the modified wall confluent jets supply device can provide acceptable thermal comfort for the occupant with lower airflow rate compared to the conventional wall confluent jets supply device.

Numerical predictions using three turbulence models (renormalization group (RNG k– ε), realizable (Re k– ε), and shear stress transport (SST k– ω) are evaluated by measurement results. The computational box and nozzle plate models are used to model the inlet boundary conditions of the nozzle device. In the isothermal study, the wall confluent jets in the primary region and the wall jet in the secondary region, when predicted by the three turbulence models, are in good agreement with the measurements. The non-isothermal validation studies show that the SST k– ω model is slightly better at predicting the wall confluent jets than the other two models. The SST k– ω model is used to investigate the effects of the nozzle diameter, number of nozzles, nozzle array configuration, and inlet discharge height on the ventilation performance of the proposed wall confluent jets supply device. The nozzle diameter and number of nozzles play important roles in determining the airflow pattern, temperature field, and draught distribution. Increased temperature stratification and less draught distribution are achieved by increasing the nozzle diameter and number of nozzles. The supply device with smaller nozzle diameters and fewer nozzles yields rather uniform temperature distribution due to the dominant effect of mixing. The flow behavior is nearly independent of the inlet discharge height for the studied range.

The proposed wall confluent jets supply device is compared with a mixing supply device, impinging supply device and displacement supply device. The results show that the proposed wall confluent jets supply device has the combined behavior of both mixing and stratification principles. The proposed wall confluent jets supply device provides better overall ventilation performance than the mixing and displacement supply devices used in this study.

This study covers also another application of confluent jets that is based on impinging technology. The supply device under consideration has an array of round jets on a curve. Multiple jets issue from the supply device aperture, in which the supply device is positioned vertically and the jets are directed against a target wall. The flow behavior and ventilation performance of the impinging confluent jets supply device is studied experimentally in an industrial premise. The results show that the impinging confluent jets supply device maintains acceptable thermal comfort in the occupied zone by creating well-distributed airflow during cold and hot seasons.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 78 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1671
Keyword
Multiple interacting jets, round jets, confluent jets, wall jet, ventilation strategy, air distribution system, air supply device, ventilation performance, thermal comfort, energy-saving potential, measurement, numerical predictions, RANS turbulence models, renormalization group (RNG k– ε), realizable (Re k– ε), and shear stress transport (SST k– ω)
National Category
Mechanical Engineering Energy Engineering
Identifiers
urn:nbn:se:liu:diva-117442 (URN)10.3384/diss-diva-117442 (DOI)978-91-7519-063-1 (print) (ISBN)
Public defence
2015-05-29, ACAS, Hus A, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-04-27 Created: 2015-04-27 Last updated: 2015-05-13Bibliographically approved

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