Hydraulic Study on the Backwashing of Multi-Media Filter

多媒体滤水器的颗粒通过反冲洗来净化，反冲洗的水速足以使整个床层流态化，而不会彼此混合，然后沉淀形成与反冲洗保持相同分层顺序的床层。将反冲洗视为二元或三元固液流态化，表观水速必须(1)大于颗粒的最小流态化速度，(2)小于颗粒的最终速度，(3)小于较重和较小颗粒层的堆积密度等于较轻和较大颗粒层的体积密度的速度，(4)小于不同种类颗粒开始混合的速度。对于限制(1)和(2)，现有的公式是可行的。在本项目中，为了得到满足极限条件(3)和(4)的颗粒，建立了临界速度的计算方法和方程。它们的有效性通过实验得到了证实。

The grains of multi-media water filters are cleansed by backwashing at a water rate sufficient to fluidize the entire bed without mixing one another, and thereafter settle to constitute the bed with keeping the same order of stratification as in backwashing. Regarding backwashing as a binary or ternary solid liquid fluidized bed, the superficial water velocity must be (1)greater than the minimum fluidizing velocity of grain,(2)less than the terminal velocity of grain,(3)less than the velocity at which bulk density of the heavier and smaller grain's layer is equal to that of the lighter and larger grain's layer and (4)less than the velocity at which mixing of different kinds of grains begins.For the limits (1) and (2), the existing formulae are available.In this project,calculation methods and equations for the critical velocities were developed to obtain grains satisfying the limits (3) and (4). Their validity was comfirmed experimentally.