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International Heat Transfer Conference 15

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Loss Coefficients for Compressible Flows in Conduit Components Under Different Thermal Boundary Conditions

Bastian Schmandt
Institute for Thermo-Fluid Dynamics, Hamburg University of Technology, Hamburg, Germany

Heinz Herwig
Institute of Thermodynamics, Hamburg University of Technology, Hamburg, D-21073, Germany

DOI: 10.1615/IHTC15.tdy.008482
pages 7827-7842


键词 Thermodynamics, Energy Efficiency, Compressible Flow, Micro Scale, Conduit Components

摘要

Losses in flows through conduit components of pipe systems are usually accounted for by head loss coefficients K. For incompressible flows they are often determined based on measurements of total head in different cross sections. If, however, the flow is compressible but still subsonic, the physical interpretation of this method is problematic, since then the difference in total head does neither exactly correspond to dissipation nor to an exergy loss, i.e. the loss of available work. As an alternative, a method is presented, which makes use of the local entropy generation in order to determine the loss of available work instead of the loss of total head induced by a conduit component. Furthermore, a method for a meaningful visualization of the loss distribution within the component and its adjacent flow field is introduced. Based on this visualization the spatial extent of the additional losses due to the component can be quantified leading to a nondimenional length of impact. The procedure is illustrated for the special case of ideal flow through a 90deg bend of square cross section in the laminar flow regime which prevails in mini and micro flow situations. Nondimensional values for the loss coefficient K, now based on entropy generation, are shown for various Mach and Reynolds numbers and for different thermal boundary conditions. They are a constant wall heat flux for heating or cooling, respectively, compared to the case of adiabatic walls.

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