On the interactions of the induced flow field of heat exchangers with axial fans

Abstract

In a large number of applications, heat exchanger modules consist of a combination of a heat exchanger and a turbomachinery. An axial fan is often used as the turbomachine in these scenarios. These modules are part of the daily life of people and are located in the direct vicinity of them. The interaction of the flow field with the heat exchanger generates disturbed inflow conditions upstream of the axial fan, which are characterized by increased turbulence properties. These disturbed inflow conditions often lead to increased sound radiation from the fan. In this study, the flow field of eight different heat exchangers was characterized and the effects on the sound emissions of the axial fan were analyzed. The main focus was on the geometry of the heat exchanger. By means of smoke visualization, the formation of significant turbulence points in the flow field of heat exchangers could be demonstrated. The spots with increased turbulence intensities are induced by the geometry transition from rectangular to round between the heat exchanger and the duct of the axial fan. It was found that a round geometry of the heat exchanger leads to a more homogeneous flow field and thereby reduces the sound emissions of the axial fan. Also a increase of the flow through area of the heat exchanger brings benefits for the acoustics of the axial fan. Especially the tonal components of the blade passing frequency of the fan were strongly dependent on the chosen heat exchanger. The tonal components could be reduced if the homogeneity of the flow field was increased by a round heat exchanger geometry.