Abstract
Disinfection is a basic and effective microorganism inactivation method and historically contributed a decrease in waterborne diseases. To guarantee the disinfection ability, improving T in CT value is important. Many indexes are used to estimate the hydraulic efficiency, however, these are black-box analysis. Therefore it is need to develope new estimation method. In this study, internal short-circuiting estimation method (ISEM) is developed using CFD and we inquire into the factor which causes increase of $T_{10}/T$ value as LW ratio increases. And the effect of shape on the relation of LW ratio and $T_{10}/T$ is analyzed. As LW ratio increases, internal short-circuiting index (ISI) of influent and effluent zone is rapidly reduced and recirculation and dead zone are reduced in channel zone. Therefore, as the $T_{10}/T$ value converges maximum value, ISI curve is changed from "V" shape to "U" shape and hydraulic efficiency is improved especially in downstream portion of clearwell. The less the shape ratio(width/length of clearwell) is the less the $T_{10}/T$ value is at a same LW ratio because the portion of turning zone increases as shape ration decreases, therefore more boundary separation is generated.
