  This paper investigates the self-cleansing performance of an airlift pump
with a u-bend. For this purpose, an experimental test model is used to assess
the effect of air supply on the pump's ability to lift water and remove
particles under different submergence ratios and particle concentrations. In
addition, a simple yet accurate fluid mechanical model is used to rationalize
the experiments with individual particles, and to predict the critical water
velocity required for removal from the pipe bend.
  Our experimental results show that the airlift pump is self-cleansing for
particle concentrations corresponding to as much as 70% of the cross-sectional
area in the u-bend. Furthermore, the self-cleansing ability is relatively
independent of the submergence ratio and almost entirely determined by the
shear stress. However, the submergence ratio strongly affects energy use, and
we find that submergence ratios around 0.75 provide a good compromise between
energy use and particle removal efficiency.
