THEORY OF LOW MACH NUMBER COMPRESSIBLE FLOW IN A CHANNEL

The properties of a relatively uncommon regime of fluid dynamics, low Mach number compressible flow are investigated. This regime, which is characterized by an exceptionally large channel aspect ratio L/d simil ar to 10(6) leads to highly subsonic flows in which friction dominates inertia. Even so, because of the large aspect ratio, finite pressure, temperature, and density gradients are required, implying that compre ssibility effects are also important. Analytical results are presented which show, somewhat unexpectedly, that for forced channel flow, stea dy-state solutions exist only below a critical value of heat input. Ab ove this value the flow reverses against the direction of the applied pressure gradient causing fluid to leave both the inlet and outlet imp lying that the related concepts of a steady-state friction factor and heat transfer coefficient have no validity.