  Directional and self-propelled flow in open channels has a variety of
applications, including microfluidic and medical devices, industrial filtration
processes, fog-harvesting and condensing apparatuses. Here, we present
versatile three-dimensional (3D)-printed liquid diodes that enable spontaneous
unidirectional flow over long distances for a wide range of liquid contact
angles. Typically, we can achieve average flow velocities of several
millimeters per second over a distance of tens to hundreds of millimeters. The
diodes have two key design principles. First, a sudden widening in the
channels' width, in combination with a small bump, the pitch, ensure pinning of
the liquid in the backward direction. Second, an adjustable reservoir, the
bulga, is introduced to manipulate the liquid velocity with differing expansion
angles. Using a combination of experiments and lattice Boltzmann simulations,
we provide a comprehensive analysis of the flow behavior and speed within the
channels with varying contact angles (CA), pitch heights and bulga angles. This
provides guidelines for the fabrication of bespoke liquid diodes with optimal
design for their potential applications. As a feasibility investigation, we
test our design for condensation of water from fog and subsequent transport
uphill.
