ABSTRACT:

The issues of sediment siltation in vertical pipes for hydraulic lifting are frequently encountered in vertical pipes. Most of the proposed formulas had no physical meaning due to lack of comprehensive analysis of impact factors. Based on the experiments on single particle settling velocity in the static fluid, floating velocity for a single particle and critical velocity in a vertical hydraulic lifting system, a formula was developed for calculation of critical velocity in a vertical hydraulic lifting system. The formula accounts for main factors such as particle size and concentration. The formula was validated by compared with other experimental results. It would be useful for design and operation of vertical hydraulic lifting system.

INTRODUCTION

The issues of sediment siltation in vertical pipes for hydraulic lifting are frequently encountered in processes of deep-sea mining, hydraulic coal-mining, and river sludge removing. Most of the previous studies on solid-liquid two-phase flow for pipeline transportation were concentrated on hydraulic parameters of hypothetical-homogenous flow in a horizontal pipeline. Lifting velocity is the primary issue that should be determined firstly for the design of a vertical hydraulic lifting system. In a horizontal pipeline, transportation velocity should be larger than the critical velocity Ucr to prevent the pipeline from sediment aggradations. Generally speaking, transportation velocity is chosen to be 1.1 to 1.2 times of critical velocity; i.e., U=1.1∼1.2Ucr. In a vertical hydraulic lifting pipeline, if transportation velocity is too small, the pipe will be seriously plugged up; whereas, if it is too large, energy loss and pipeline abrasion will be significantly enhanced since lifting force is in proportion to the square of fluid velocity and pipe abrasion is in proportion to the cube of fluid velocity, respectively. Therefore, it is desired to determine a critical velocity for a vertical hydraulic lifting system.

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