Loss coefficients for compressible flows in conduit components under different thermal boundary conditions

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 gas 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.

Subjects

Thermodynamics

Energy Efficiency

Compressible Flow

Micro Scale

Conduit Components

DDC Class

530: Physik

600: Technik

620: Ingenieurwissenschaften

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Loss coefficients for compressible flows in conduit components under different thermal boundary conditions