APEX Group is proud to congratulate Bastiaan Bijvoet for his successful graduation at the Technical University of Delft. Bastiaan has written his master thesis in the R&D department of Apex Group. The results of his thesis will be presented at the 13th International Symposium on Particle Image Velocimetry taking place in Munich, Germany from July 22-24, 2019. The title of the presentation is “Investigation of a large angle diffuser in the bistable steady stall regime via 3D3C mean vector field statistics”. Large angle diffusers are an integral part of a heat exchanger system. The design of the diffuser has a major influence on the performance of the heat exchanger system. If you are interested to learn more, please visit Bastiaans presentation in Munich or get in contact with us via info@apexgroup.eu.

In heavy duty industry, such as the petro-chemical industry, often the efficiency of fired heaters is increased with air-preheaters. On their cold side, the flow is driven with forced draft centrifugal fans. Due to space limitations the transition from the outlet of the fan (small cross section) to the inlet of the air preheater (large cross section) needs to be overcome in a small distance. Naturally there is the requirement for a low total pressure drop, and additionally a large degree of uniformity at the diffuser outlet, i.e. the air preheater inlet. This paper aims to extend the knowledge on flows in large angle diffusers. These are often the most unstable component in fluid mechanical systems, as their performance, expressed in terms of pressure recovery and flow distribution, can vary a lot. Some 60 years ago, Kline and Fox (1958) were the first to come up with a predictive tool for diffuser performance. Their study considers a uniform velocity distribution at the inlet of the diffuser. This is not the case in industrial applications as the velocity field emerging from centrifugal fans is non-uniform, and can have secondary flow structures such as swirl. Another discrepancy between literature and industry, is the resistance just downstream of the diffuser, in the form of the air preheater. The poor performance itself of fan-diffuser systems, and the discrepancies with literature have led to this research. A windtunnel was built with a diffuser shaped measurement section. Laser optical measurements were performed to characterize the flow, also pressure measurements were performed. With knowledge of the flow, in terms of velocity and pressure, it was possible to judge the performance of the system. The measurements have the goal of extending the knowledge on diffuser flow itself, and to define the boundary conditions for subsequent CFD analyses.