Heat transfer enhancement in natural convective channel flows by vortex streets

  • Erhöhung der Wärmeabgabe in vertikalen Kanalströmungen mit natürlicher Konvektion durch Wirbelstraßen

Mathis, Paul; Müller, Dirk (Thesis advisor); Schmidt, Michael (Thesis advisor)

1. Auflage. - Aachen : E.ON Energy Research Center, RWTH Aachen University (2022)
Book, Dissertation / PhD Thesis

In: E.ON Energy Research Center ; EBC, Energy efficient buildings and indoor climate 100
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

Heat transfer in vertical heated channels is a common means to operate thermodynamic devices like panel radiators for room heating. Reducing the required material amount or increasing the performance leads to positive effects in terms of economical and ecological aspects. Thus, the principle of convective mixing through vortex streets in vertical heated channel flows is investigated both numerically and experimentally in this thesis. Cylinders of different blockage ratios are placed at different positions in the purely natural convection flow, triggering vortex streets in the downstream region. Through the vortices, cooler fluid from the central part of the channel is brought to the vicinity of the heated walls, decreasing the thermal boundary layer and by that increasing heat transfer. The problem is studied generally for two-dimensional channels heated from two sides as well as for three-dimensional channels heated from four sides. A considerable potential of heat transfer enhancement is found, depending on geometrical parameters like blockage ratio, channel position and distance of multiple cylinders. Then, the principle is applied to various regions of panel radiators, leading to heat transfer enhancement and thus increasing the overall specific performance. The heat transfer enhancement is achieved without any additional energy costs, as the flow is driven by natural convection only. The additional pressure losses of the cylinders are compensated by the convective mixing alone.

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