jet

An air curtain generated by a jet is used to enhance an exhaust hood’s capture ability in many research studies on local ventilation systems. This paper focuses on experimental methods to investigate the flow characteristics formed by an exhaust hood associated with a jet. The basic flow characteristics of this kind of exhaust hood are obtained by smoke visualization as a jet forms an air curtain, and the flow field is a combination of three parts: the jet flow region, the exhaust flow region and the vortex flow region.

When designing the outlets for the ventilation or hot-air heating of particular spaces, we meet usually the problems to specify a form and reach of the air jet and a distribution of velocities and temperatures in the space followed. In practice the calculations of nonisothermal air jets are made using a number of calculation relations to be found e.g. in lit. (1) and other. But when applying the analogical relations derived by different authors we can find out considerable differences in results.

This paper presents results belonging to a larger investigation on low velocity indoor air jets. The experiment is undertaken in a climate room where an isothermal air jet is issued from the centre of one lateral wall. Measurements are performed with a single fiber film probe, and with Particle Streak Velocimetry system. With Particle, Streak Velocimetry has been developed a three dimensional analysis of the instantaneous velocity field. With the use of fiber filmprobe, the fluid-dynamics of the jet flow is explored in terms of mean longitudinal velocity, and relative turbulence intensity.

A problem in a livestock building ventilated in the system with wall inlet at two sides is wind effects to the indoor air flow patterns. The in-proper inlet jet penetration profiles may cause draught at occupied zone and unnecessary stress of animals. The wind effects on such a system can be reduced by applying windbreak to the inlets from design point of view. However, a remain issue is if the effect could be reduced by regulating inlet opening and how to perform the control operation.