Stereoscopic particle image velocimetry study of the single side entrainment behaviour of multiple air jets with different nozzle cross-sections

Abstract

Achieving energy savings in the building sector while maintaining high air quality of indoor environments requires efficient ventilation systems. Active chilled beams (ACBs) are a promising solution for the ventilation in non-residential buildings. Their functionality is often based on the single side entrainment of multiple air jets. In order to enhance this entrainment and thus increase the efficiency of ACBs, this study investigates the specific flow situation of a single side entrainment experimentally. Additionally to the reference circular type, three different cross-sections (elliptic, cross-like, lobed) of an orifice nozzle are investigated with different experimental methods. The unique flow situation in ACBs with multiple interacting jets entraining air from one side is extracted to a test bench. First, the general nozzle efficiency and total entrainment is investigated. Then, the detailed understanding of the entrainment process is achieved with stereoscopic particle image velocimetry (stereo-PIV). The results show that a minimum distance between the jets is necessary for the development of individual flow behaviour affecting the entrainment. For a larger nozzle distance we measured an increased overall entrainment for the non-circular nozzle geometries, with the lobed geometry showing the greatest improvement. The PIV results show how the jets from the different nozzle geometries pass through different stages of entrainment behaviour and profile transformation.