For estimating environmental impact due to releasing CO{sub}2 into the deep ocean by a towed pipe of a moving ship, released liquid CO{sub}2 droplet size and entrainment of seawater behind the pipe are dominating factors for dilution process of injected CO{sub}2. In this study, we conducted experiments to understand (1) liquid CO{sub}2 injection behaviors with hydrate film and (2) highly turbulent flow behind the pipe. The liquid CO{sub}2 injected from a nozzle under deep sea condition were precisely observed in a variety of injection velocity and temperature that considerably affect injection behaviors and thus resultant droplet size. We classified behaviors of liquid CO{sub}2 droplet with hydrate film into three types; (1) formation of single droplet whose surface is perfectly covered with hydrate film before departing from the nozzle, (2) formation of single droplet not perfectly covered with hydrate film and (3) droplet formation from a laminar flow. Furthermore, to examine turbulent mixing and entrainment of flows behind the pipe, an experimental apparatus to realize highly turbulent flow over the critical Reynolds number were constructed, because turbulent flow behind the towed pipe can be over the critical Reynolds number. We confirmed that the turbulent flow observed around the cylinder in our apparatus, in which a circular cylinder of 0.1 (m) in diameter is fixed in the test section, was over the critical Reynolds number and thus typical turbulent behaviors behind the towed pipe could be simulated. Visualization of the flow fields confirmed that flow separation point moves downward on the cylinder.
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