Claudine Beghein

Optimization of a Lobed Perforated Panel Diffuser - A Numerical Study of Orifice Arrangement

Abstract Heating Ventilating and Air Conditioning (HVAC) systems are primarily designed for ensuring good indoor air quality and thermal comfort. However, building energy requirements tend to put demand on reducing air change rates. Passive control of jet flows in order to enhance mixing and entrainment may be a solution to this problem. Our purpose is to develop new air diffusers, in order to ameliorate the users’ thermal comfort and air quality. When the diffuser is a lobed perforated panel (Meslem et al, 2010), the optimization of jet entrainment consists of optimizing the spacing between neighboring orifices and their relative arrangement on the panel. The objective is to conceive a perforated panel diffuser with high entrainment and high perforation rate. In a recent study (Meslem et al, 2011) the flow field of a turbulent twin cross-shaped jet was investigated experimentally and numerically using different turbulence models. In comparison to Particle Image Velocimetry (PIV) measurements, it was shown that among the investigated turbulence models, the SST k-ω model is capable of reproducing reasonably well jet interaction, global expansion and ambient air entrainment when the flow is numerically resolved through the lobed diffuser. Based on the previous experimental validation of the SST k-ω turbulence model, in this work, numerical simulations of parallel cross-shaped jets in different flow configurations are analysed using this model. This study deals with the effect of orifice arrangement and spacing on jet entrainment. The parametric study put into evidence an optimal configuration which will be transferred to the scale of a real air diffuser.

Analysis of Contaminant Removal Efficiency Assessment in a Ventilated Room

Abstract This paper reports a critical analysis of the assessment of contaminant removal efficiency. Measurements have been carried out in a ventilated room equipped with a pine wood floor, which emits Volatile Organic Compounds (VOCs), considered as air pollutants in this paper. Thereafter, Computational Fluid Dynamics (CFD) simulations are performed. CFD results are compared to measurements to check their accuracy. Moreover, air quality within the ventilated room is numerically analysed via indices. From this, it is shown that the currently used contaminant removal efficiency index, εc, can especially reveal the characteristics of contaminant distribution. Unfortunately, εc is not suitable for assessing the contaminant removal efficiency of ventilation scenarios with different air flow rates. Indeed, its definition does not take into account absolute contaminant concentration levels. Furthermore, since the VOC concentrations found in this study were very low compared to the Lowest Concentration of Interest, no health risks could occur, and so, it was inappropriate to use the Indoor Air Quality index IIAQ. Therefore, a new formulation of εc is proposed. Its values are analysed taking into account the conformity degree of the ventilation rate with the nominal air flow rate of the ventilation systems handled. This gives a good tool to compare the contaminant removal efficiency whatever the ventilation rate.

Lois de decroissance d'un jet turbulent tridimensionnel vertical de paroi impactant a forces de poussee defavorables

Abstract This paper presents an experimental investigation of the mean axial velocity and temperature excess of three-dimensional vertical and then horizontal wall jet, with opposite buoyancy forces. The initial Archimed number is used to establish an empirical model to estimate the maximum quantities of the jet, with reference to the inlet conditions. These measurements also enabled us to deduce the penetration law of the vertical jet and the separation distance law of the horizontal flow according to the inlet conditions.