Impacts of horizontal length in an induction-type MP recovery device on capture performance

Most marine microplastics (MPs) are released from rivers and are broken down in the ocean. They are attracting attention worldwide due to their adverse effects on the growth of marine organisms and their increasing abundance every year. Besides, once MPs are released into the ocean, it is thought that it’s impossible to recover. The authors have proposed an induction-type MP recovery device which consists of flat plates, is inexpensive to manufacture, does not require the electric power, and can be introduced in large quantities into the ocean. This device operates in natural water currents such as rivers, tidal and ocean currents, and collects MPs using vortex flows that form inside. In this study, the authors investigated the impacts of the horizontal length on capture performance by means of experiments and CFD incorporating a discrete phase model. In the experiments, we have prepared the models in which the length of horizontal part of the standard device was doubled and tripled, and the recovery efficiency was measured for two surrounding flow velocity, 0.6 and 0.3 m/s. The inlet flow velocity was also measured for each case. As the results, it is clarified that the longer horizontal part causes the lower inlet velocity. It is also found that the recovery efficiency considered external flow for 0.3 m/s was high under standard length condition, the recovery efficiency for 0.6 m/s was high when the length of horizontal part was twice and three times longer. More specifically, the maximum value of that efficiency for 0.3 m/s of surrounding flow velocity was 81% given at the length ratio 1.5, and the 1 for velocity 0.6 m/s was 52% given at both cases the length ratios 3.0 and 4.5.