Guangyu Cao

Experimental Investigation and Modeling of the Attached Plane Jet Velocity Development Characteristics in the Transition Process in a Room

Attached plane jets are widely used in room-air distribution solutions. The turbulent attached plane jet behavior in the transition process that determines the jet behavior in the fully developed region is not completely understood, especially at relative low Reynolds numbers (<6000). This study focuses on obtaining the detailed jet mean flowfield velocity data and jet growing characteristics in the transition region. A virtual origin model was set up to predict the maximum jet velocity decay, and the experiment was carried out to validate the model. In this experiment, three Reynolds numbers—1000, 2000, and 4000—were tested at different distances from 2 to 30 slot heights downstream of the jet slot. The results are significantly different from the known theory for the third and fourth jet zones definition. The experimental data show that after six slot heights downstream distance, most of the data start to fit closely the fully developed turbulent jet velocity profiles and present self-preserving characteristics earlier than in previous studies. The maximum velocity calculated by the models showed good agreement compared with the measured data at distances of 10 to 30 slot heights.

Active chilled beam wall jet prediction by the free convection model

Abstract In this study, the measured and predicted air distribution of an active chilled beam in a typical office room is described. A free convection model was applied for the vertical downward air jet along the wall by superposing a free convection velocity and an isothermal jet velocity. The velocity and temperature of the wall jet were measured at six different heights and six distances from the wall in the near wall zone and in the wall-floor corner zone. The experiment implemented two airflow rates of 20 and 28 L/s with three cooling loads of 0, 40 and 100 W/m2. The results of the measurements show that the maximum velocities were close to the wall surface, between 0.025 to 0.05 m from the wall. Below the height of 1.7 m, air velocities decreased quasi-linearly when approaching the floor level. The calculated non-isothermal wall jet velocities superposed with the free convection velocity show that the introduced model can be used for the prediction of the maximum velocity of the wall jet. The model is free of a problem of the conventional non-isothermal jet equation, which predicts velocities slightly increasing downwards, while the measured ones significantly decreased along the wall.

Plane-Air-Jet Corner Zone Modelling in a Room Ventilated by an Active Chilled Beam

Abstract Recent studies have demonstrated the influence that air jets in rooms ventilated by chilled beams have on draught-related thermal sensation. The most critical zone in which people often suffer draught sensation is located near a wall and close to the floor. To avoid the draught sensation, the critical velocities of the returning air jet should be specified and determined before the jet enters the occupied zone. In this study, the velocity of the attached plane jet was modelled and measured at six heights and at eight different distances from the wall. Results showed that the returning corner airflow reattaches to the floor surface with entrained ambient air after separation from the wall. The maximum returning air velocity was found to be close to the floor surface. Air in the rest of the room air was shown to move, rather than remain still. Moreover, the moving room air does enforce free shear at the free boundary of the attached jet. This new model could be applied to estimate the possibility of draught risk and to predict the returning airflow velocity within the occupied zone at the most critical corner region.

Experimental Studies on Air Distribution Using Ceiling Slot Diffusers in a Room

Abstract Nowadays, the ceiling slot diffuser is very popular in offices. However one of the problems, for the producer and designer of linear diffusers, is to determine and specify correctly the throw–length data, in order to achieve optimal air movement in the occupied zone. Here, experimental studies were conducted to identify the variation characteristics in jet behaviour for ceiling slot diffusers. Nine cases, covering different aspect ratios, were measured under isothermal conditions in two test rooms using traversing measurement systems. The results show that the critical aspect ratio for 2D and 3D jet flow is in the range of 30 to 59. The results also confirmed that the coefficient of jet maximum velocity decay depends on the details of the diffuser and thus should be identified for different products. The selection of the jet model should be determined by the aspect ratio of the jet slot to predict the maximum velocity decay.