Study on the Diffusion of Water-Soluble Liquid Cargoes in the Sea Water

The amount of transportation of water-soluble toxic chemicals by ships is very large. It is concerned that an outflow accident of such chemicals might cause the undesirable influence on the ocean environment before the dilution process with sea water will make them harmless.The diffusion process beneath the sea surface of water-soluble chemicals spilt from ships at a collision or stranding is similar to that of hot drain from land based power plants. In case of hot drain, a lot of research have been done and its diffusion process, Which is usually treated as the gravitational plume considring the density difference between hot drain and surrounding sea water, has almost been elucidated.In case of watrer-soluble chemicals, however, the density difference distributes widely depending on the substances and usually differs from that of hot drain. Moreover some chemicals release reaction heats when it defuses in sea water. It has not been confirmed yet that the evaluatoin method based on dimensionless numbers and the empirical correlations proposed in the past reports can be applied to such chemicals.Then to make this problem clear, some experiments using a small-scale tank were conducted. As experimental solutes, three kind of typical chemicals with different properties were selected. Experimental parameters were the outflow rate and the relative velocity between the spilling source and surrounding water. The diffusion characteristics such as the direction and width of the plume were observed and compared with the empirical correlations published so far.As a result, it was found that the diffusion characteristics except one chemical can well be estimated by the method applied to the gravitational plume of hot drain if Froude number is chosen as the controlling dimensionless number, although a different result was anticipated because the transport properties and density of chemicals used in the experiment are very different from those of hot drain.