Till Örebro universitet

The use of supply jet flows is the most common type of air distribution for general ventilation. Usually the supply flow rate is constant or slowly varying (VAV-systems) to cope with a varying load. A novel air distribution method, with the potential to reduce stagnation and to increase the ventilation efficiency, is to introduce rapid flow variations (pulsations). This paper reports on a fundamental study of this type of air distribution. The purpose of the study was to explore the effect of flow variations on stagnant zones and the levels of the turbulent kinetic energy and the relative turbulence intensity. A small scale room model is used that consists of an enclosure with a ventilation supply at the bottom and an extract at the top of the opposite wall. Water was used as an operating fluid and the model had a design which mainly generated a two-dimensional flow. The size of the model made it possible to investigate the two-dimensional velocity vector field using the Particle Image Velocimetry (PIV) method in regions corresponding to occupied regions. Further post processing was conducted from the resulting vector fields. The comparison between cases of constant inflow and pulsated inflow (flow variations with frequency of 0.5 Hz) was conducted for three domains: two belonging to the far-field occupied zone and one belonging to the near-field, downstream of the supply wall jet.

Soiling of surfaces in historical buildings by deposition of particles is a common problem. Minimizing soiling is an important goal for conservation of structures and objects. The surfaces give rise to an interference with the air motions along the surfaces. Properties of surfaces may therefore influence the particle deposition. It is well known that with increasing roughness of the surfaces the particle deposition rate increases. The properties of surfaces in historical buildings are not well documented.  We have investigated samples of surfaces finished by wood float finish, steel float finish and brushed finish. As a reference we have used an MDF board. The geometrical properties of the surfaces have been documented by using the stripe projection method. The resistance to airflow along the surface and the turbulence generated by the surfaces has been investigated by recording the boundary layer flow over the surfaces in a special flow rig. The work reported is part of a project where the process of soiling is studied both in laboratory and in field studies. The air velocity adjacent to the surfaces will be recorded with both PIV (Particle Image Velocimetry) and hot-wire technique. The temperature gradient close to the walls will be recorded with cold-wire technique.

With the fast-growing use of nanoparticles (NPs) in a wide range of production and manufacturing processes, and great health and environmental risks associated to NPs, it is important to treat the industry-produced NPs in a proper way. Ventilation of industrial workplaces lies within the concept of sustainability challenges for the development of nanoproducts. Due to the decreased grain size of material to nano limits and thus the appearance of either new or changed properties, health risk of workers in such environments is critical concerning the complicated and unknown characteristics of nanoparticles. There is great evidence over the past few years that ultrafine particles and especially NPs in the breathing air are strong toxins. Different mitigation measures for air-borne nanoparticles in industrial workplaces are substitution, engineering controls such as ventilation and provision of personal protective equipment. In this paper selection criteria for ventilation systems and different ventilation methods (hood ventilation and global enclosure/room ventilation systems) as engineering controls of nanoparticles within industrial enclosures will be reviewed. Novel methods for improvement of ventilation efficiency in general and industrial work places with an eye on ventilation of nanoparticles will be presented.