Hydraulic Study on the Backwashing of Multi-Media Filter

多介质水过滤器的颗粒通过反冲洗以足够的水量使整个床流化而不相互混合，然后沉淀形成与反冲洗相同的分层顺序的床。对于二元或三元固液流化床，浅水流速必须(1)大于颗粒的最小流化速度，(2)小于颗粒的终端流速，(3)小于较大较重颗粒层堆积密度与较大较轻颗粒层堆积密度相等的流速，(4)小于不同颗粒混合的开始流速。对于极限(1)和(2)，现有公式可用。在本项目中，开发了临界速度的计算方法和方程，以获得满足极限(3)和(4)的晶粒。实验证实了它们的有效性。

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.