ABSTRACT
This chapter discusses the laminar flows in channels and tubes. Laminar flow is the predominant regime in the vast majority of miniature and microsystems. The chapter examines the classical closed-form solutions to the laminar flow field or empirical correlations. The velocity profile in the hydrodynamic entrance region of a flow passage varies along the axial direction. Pressure variation in the axial direction is thus caused by frictional loss as well as the change in fluid momentum flux. The mass flux of the transferred species needs to be small because a high mass flux would disturb and consequently affect the hydrodynamic and mass transfer boundary layers. In fact, close to the inlet, where the boundary layer thickness is much smaller than the characteristic dimension of the duct cross-section, the boundary layer is essentially the same as the boundary layer on a flat plate. The growth of the boundary layer represents the spreading of the effect of fluid viscosity across the channel.
