In this review we describe theoretical and Experimental investigations
of general slip phenomena in context with the flow of the quantum liq
uids He-3, He-4 and their mixtures at low temperatures. The phenomenon
of slip is related to a boundary effect. It occurs when sufficiently
dilute gases flow along the wall of an experimental cell. A fluid is s
aid to exhibit slip when the fluid velocity at the wall is not equal t
o the wall's velocity. Such a situation occurs whenever the wall refle
cts the fluid particles in a specular-like manner, and/or if the fluid
is describable in terms of a dilute ordinary gas (classical fluid) or
a dilute gas of thermal excitations (quantum fluid). The slip effect
in quantum fluids is discussed theoretically on the basis of generaliz
ed Landau-Boltzmann transport equations and generalized to apply to a
regime of ballistic motion of the quasiparticles in the fluid. The cen
tral result is that the transport coefficient of bulk shear viscosity,
which typically enters in the Poiseuille flow resistance and the tran
sverse acoustic impendance, has to be replaced by geometry dependent e
ffective viscosity, which depends on the details of the interaction of
the fluid particles with the cell walls. The theoretical results are
compared with various experimental data obtained in different geometri
es and for both Bose and Fermi quantum fluids. Good agreement between
experiment and theory is found particularly in the case of pure normal
and superfluid He-3, with discrepancies probably arising because of d
eficiencies in characterization of the experimental surfaces.