International Journal of Ambient Energy, Volume 28, Number 3 July 2007 Push-pull ventilation system: a CFD approach for the performance analysis V. Betta*, F. Cascetta*" and A. Palombo *** Vittorio Betta, DETEC, University of Naples, Federico 11, Piazzale Tecchio 80, 801 25 Naples, Italy. " Furio Cascetta, DIAM, Second University of Naples, Via Roma 29, 81031 Aversa, Italy. *** Adolfo Palombo, DETEC, University of Naples, Federico II, Piazzale Tecchio 80, 80125 Naples, Italy. (To whom all correspondence be addressed) e-mail: palombo@unina.it O Ambient Press Limited 2007 SYNOPSIS In this paper the results of a CFD investigation for a push-pull local ventilation system are presented. The velocity field and the capture efficiency prediction are investigated for different system arrangements. The analysis is carried out for systems respectively with and without fluid- dynamic obstacle in the working plane and for dust pollutants with particle diameters ranging from 1.0 to 100 pm and emission velocities between 1.0 and 7.0 mls. The analysis, carried out using the commercial code FLUENT, shows that the system performances are dependent on operating conditions and are influenced by the presence of the above-mentioned obstacle on the working plane. In the case of working plane emission without obstacle the system capture efficiency is in general very low never exceeding 25%. Higher efficiencies are instead achieved for particle emission from a vessel placed in the system's working plane centre. In this case even unitary peak efficiencies are reached for particular operating conditions. INTRODUCTION In modern industrial processes different chemical compounds and toxic substances are often utilised. Besides the possible health hazards, such pollutants (gases, dusts or vapours) can be dangerous for processing facilities, equipment and products as well [I]. For these reasons, in industrial work spaces, the adoption of suitable ventilation systems is recommended. The best way to safeguard the operators is to adopt a Local Exhaust Ventilation (LEV) system that typically consists of a suction hood [2-41. In this paper the performance of a push-pull LEV system is dealt with. Such a device, in addition to a suction hood, consists of a jet nozzle that pushes the airborne contaminant from the source where it is generated towards the system suction opening (Figure 1). Push-pull systems are typically adopted for surface metal treating in open wide vessels but can be conveniently utilised in other industrial processes too. Some examples are the control of dust in the mining industry [5] and of solder fume in the electrical and electronics industry [6] where the solder pyrolysis products, that contain volatile and particulate compounds, cause sensitisation of the operator's respiratory tract. With push-pull systems the capture efficiency is up to 15 - 20% higher than that of conventional hoods for the same operating conditions. Alternatively, for the same capture efficiency, push-pull systems are 25 - 30% more cost-effective due to lower airflow [7]. The first studies in this field dealt with push- pull system design [8] and the relative developments [9] by experimental approach. More recent analyses investigated the reverse flow problem generated by obstacles between the push