Experimental study on the performance of an air-lift pump for artificial upwelling

Abstract

Air-lift pumps for artificial upwelling of ocean water are finding increasing use as marine primary productivity could be enhanced by pumping nutrient-rich deep water to the surface to feed phytoplankton. This paper presents experiments and theoretical analysis to obtain the performance of an air-lift pump for artificial upwelling. Experiments are performed at one submerged depth, with four different air injection nozzle designs and various injected air volume flow rates. A theoretical model is proposed taking into account the flow characteristics of air-lift artificial upwelling. The performance of the model has been confirmed by the experimental findings. The present results show that the pump capacity and efficiency are functions of the geometrical parameters of the upwelling pipe, air volume flow rate, air injection method and vertical distribution of water density. It is found that the upwelling efficiency increases with the increase of the pipe diameter due to the reduction of the frictional loss, the kinetic energy and the power demand of the sea surface rise. Moreover, the air injector design has a considerable effect on the upwelling efficiency. Further work will have to determine the optimal design of the geometrical parameters of the upwelling pipe and the air injection nozzle.