【摘要】 本文通过实验,研究了细颗粒(≤0.01mm)含量对粗颗粒两相高含沙水流流动特性的影响。对于纯粹由细颗粒组成的伪一相悬浮液来说,其流速分布具有典型的宾汉体流速分布的特点,存在明显的流核。管路固体输送中习惯采用的压差-流速关系,可以通过阻力系数-雷诺数关系加以理论上的阐明。对于粗颗粒两相高含沙水流来说,细颗粒的存在,大幅度降低了粗颗粒的沉速,使一部分推移质转化为悬移质,从而改变了水流的流动特性。具体表现为流速及含沙量分布趋于均匀化,阻力损失减小,但当细颗粒含量超过某一临界值以后,继续增大细颗粒含量将会使阻力损失回增,根据流动的宾汉体中粗颗粒泥沙的沉积随流速的变化,可以得出水流的紊动将会影响悬浮液的宾汉结构的推论。更多还原

【Abstract】 The effect of fine particles(≤0.01mm) on the two-phase flow with hy-perconcentration of coarse grains is studied in detail through a series of experiments. A pseudo-one-phase flow will be formed if the flow contains fine grains only. In this case plug flow becomes apparent as long as the Reynolds number of the flow is smaller than 105. The physical background of the pressure drop-average velocity curve commonly used in the practice of solid transport in pipes can be understood much better if such a diagram is employed in coordination with a plot between the coefficient of frictional resistance and the Reynolds number of the flow. At low velocities and high concentrations the pressure drop-mean velocity curve approaches a horizontal line as its limit. The addition of fine sediment to the two-phase flow of coarse grains greatly increases the viscosity of the flow, thereby reducing the settling velocity of the coarse particles to a great extent. Both the velocity and concentration distributions become more uniform in consequence. If part of the coarse grains in the two-phase flow move as bed load or are in a transition state between the suspension and bed load motion, an increase in the content of clay will convert this part of the load into suspension. The energy expenditure of the flow required to support the bed load motion will thus be reduced. On the other hand, if all the sand particles in the two-phase flow move originally as suspended load, then the addition of fine grains will only result in an increase in the viscous drag force.更多还原