Modelling the Attached Plane Jet in a Room

OF DOCTORAL DISSERTATION HELSINKI UNIVERSITY OF TECHNOLOGY P.O. BOX 1000, FI-02015 TKK http://www.tkk.fi Author Guangyu Cao Name of the dissertation Modelling the attached plane jet in a room Manuscript submitted 25.02.2009 Manuscript revised 31.08.2009 Date of the defence 13.11.2009 Monograph Article dissertation (summary + original articles) Faculty Faculty of Engineering and Architecture Department Department of Energy Technology Field of research HVAC-technology Reviewers Associate Professor Arsen K. Melikov, Technical University of Denmark, Denmark D.Sc.(Tech.) Kim Hagström, Halton Oy, Finland Opponent(s) Professor Hazim B. Awbi, University of Reading, UK D.Sc.(Tech.) Kim Hagström, Halton Oy, Finland Supervisor Professor Olli Seppänen (2006–2008), Helsinki University of Technology, Finland Professor Kai Sirén (2008–2009), Helsinki University of Technology, Finland Instructor Docent D.Sc.(Tech.) Jarek Kurnitski, Helsinki University of Technology, Finland Abstract The application of the attached plane jet has proved to be an effective way to resolve the draught problem and to create a comfortable indoor environment. The objective of this thesis is to give a basis for improving the existing modelling and calculation method applied to predict the jet velocity in both ventilated and air-conditioned rooms using attached plane jet diffusers to avoid the draught problem. A special consideration is to set up models that could be used to predict the jet velocity along the surface more easily, more accurately and more efficiently than the existing methods under attachment and separation conditions.The application of the attached plane jet has proved to be an effective way to resolve the draught problem and to create a comfortable indoor environment. The objective of this thesis is to give a basis for improving the existing modelling and calculation method applied to predict the jet velocity in both ventilated and air-conditioned rooms using attached plane jet diffusers to avoid the draught problem. A special consideration is to set up models that could be used to predict the jet velocity along the surface more easily, more accurately and more efficiently than the existing methods under attachment and separation conditions. Jet velocity modelling and full-scale experimental measurement have been done to complete the above objectives. Through two measurement phases the whole flow field of the attached plane jet has been investigated experimentally in two fullscale test chambers. A large amount of data on jet velocity, temperature and turbulence intensity has been obtained; beyond that the visualization results are complementary to the understanding of turbulent buoyant jet characteristics. The results showed that: the superimposing model and the free convection velocity are capable of predicting the maximum air jet velocities along the wall under the conditions of the straight downward jet flow and the corner effect jet flow, respectively; the calculated corner-jet velocity profiles by the corner model obtained a good agreement with the measured results; the maximum velocity calculated by the model for the transition zone can be used to predict the maximum velocity decay. This work reveals that the turbulent attached plane jet behaves in a different way compared with the high Reynolds number turbulent jet in a ventilated and air-conditioned room. From the modelling viewpoint, the jet velocity models constructed here can be used to predict the maximum jet velocity decay and velocity profiles from the corner effect region in the indoor airflow studies. The detailed jet information obtained can contribute to the corresponding CFD simulation for further linear slot diffuser development.