RELATIVE VELOCITIES OF LARGE PARTICLES SUSPENDED IN A VERTICAL TURBULENT LIQUID FLOW
垂直湍流液-固流中大颗粒的相对速度

A dimensionless formula for estimating the time-mean velocity differences between fluid and large particles has been given. The Particles are suspended in a homogeneous turbulent liquid flow. and their sizes are larger than the size of the micro-eddy of the turbulent liquid flow.A comparison between the orders of the accelerations of the eddy and the gravity shows that in a flow with considerable high Reynolds number, the dynamic force of eddy is dominant and the influence of the gravity to the motion of the particles can be ignored, on the other hand, in a flow with sufficiently low Reynolds number, the gravity is dominant and the influence of the dynamic force of eddy to the motion of the particles can be ignored. By combining these two situations,it is possible to predict theoretically the general form of the dimensionless relationship between the relative Reynolds number of the large particles and the other four dimensionless numbers.In addition to the dimensional analysis, experimental measurements are provided, the coefficient and the powers of the dimensionless numbers in the formula have been determined and examined by the results of the measurements. The experiments are carried out in a pipe water flow with suspended particles, for different set of the experiments, the densities and sizes of the particles are different. Measurements of two-phase velocities in the pipe center have been made by using two phase velocity separation technique of LDV. It is shown that the relative velocity depends on the relative size of the particle to the liquid flow with a power of 1.25, and strongly depends on the Reynolds number of the fluid flow with a power approaching to 1.5 for rather high fluid flow Reynolds numbers.