PRESSURE DROP FOR LOW-CONCENTRATION SAND WATER MIXTURES IN A LOW-PRESSURE PIPELINE

摘要

This article discusses the relationship between the pressure drop of sand water mixture and the flow and sediment conditions. The study is based on laboratory experiments that were carried out in a 190 mm pipe with various sand concentration and different flows. Sixteen flows of clear water and 22 sand water mixtures and sand concentrations were tested, respectively, to establish the relationship between pressure drop and flow and sediment conditions. For the pressure drop of clear water, the relationship between the pressure gradient and flow velocity and the relationship between the friction factor and the Reynolds number were obtained, respectively, which can be used to calculate the pressure gradient of clear water. For the pressure drop of sand water mixture, experimental results show that the pressure gradient along the pipe always increases with the increase of flow velocity under different sand concentrations. However, variations of the pressure gradient with different sand concentrations suggest contrary results, i.e., the pressure gradient increases with the increase of sand concentration at low sand concentrations, and it decreases with the increase of sand concentration at somewhat high sand concentration, flowing at the same flow velocity. This article also focuses on the relationship between the friction loss coefficient and flow and sediment conditions, and a comprehensive coefficient is introduced, including sand concentration, the Reynolds number, mass density of the sand, and the median particle size. Study results indicate that the friction loss coefficient decreases with the increase of the comprehensive coefficient, and the relationship between them was obtained, which can be used to calculate the pressure gradient of sand water mixture. The relative pressure gradient data measured in the present study was compared with the calculated results of the Durand equation (1953), which confirmed that the pressure drop for low-concentration mixture couldn't be described by the Durand equation. A new form of calculating the pressure drop of the mixture is developed, which shows that the relative pressure gradient is closely related to the product of the Froude number and the sand concentration, and the relationship between them is a power regression. The comparison of the predicted values of relative pressure gradient by the method developed in this study with the measured values shows that they are generally in good agreement.