ISSN Online: 2377-424X
ISBN Print: 978-1-56700-421-2
International Heat Transfer Conference 15
Loss Coefficients for Compressible Flows in Conduit Components Under Different Thermal Boundary Conditions
Abstract
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.