Study on Flow Characteristics of Multisized Sand Slurry in Straight Pipe and Bends

Abstract

The hydraulic slurry transportation system is mainly used in the industry, to transport the solid material in the form of slurry through a pipeline. The hydraulic transportation pumps are used to transport the slurry in the pipelines. The slurry transportation system is widely accepted as it reduces the environmental pollution, ecological disturbance and saves energy consumption. River water from upstream of reservoir is usually collected and conveyed through penstocks to turbine for hydroelectric power generation. Sediments are usually presents in river water and the flow dynamics of sediment laden water is different from flow characteristics of only water. The solid materials present in slurry make the transportation inefficient because of large pressure drop, settlement of solids, erosion of pipe surface, increased power consumption, granular pressure, choking, blockage, etc. The efficient movement of required quantity of water through a pipeline having various transitions requires proper designing of slurry transportation system. The amount of erosion of the pipeline surface mainly depends upon flow velocity, solid concentration, particle size, operational time, angle of attack, surface roughness, surface hardness, etc. For an effective transportation system, the study of the impacts of these parameters on the flow of slurry and pipeline is very important. The present study is focused to determine the influence of the flow parameters upon the solid particle erosion and pressure drop of the pipeline. Particle size distribution (PSD), slurry settling characteristics, pH, Scanning Electron Microscopy, specific gravity, energy-dispersive ray spectroscopy, and X-ray diffraction were carried out for collected sand sample. It is observed that, around 34% of the sand samples are finer than 106 μm, 2% are finer than 53 μm and 32% of sand samples are lying between 106 and 53 μm. Around 68% of the particles are observed to be coarser than 150 μm and 34% of which are within a spectrum of 106-150 μm. The current study investigated the rheological properties of sand water slurry of various particle sizes (<53, 53-106, and 106-150 μm) and the solid concentration ranged from 10 to 40% by mass. The dilatant behavior is observed at higher concentration of sand water slurry. The rheological experiments were also performed using sodium triphosphate additive and the results were compared with the results obtained without addition of additives. It is observed that the apparent viscosity of the slurry is minimum at 0.4% addition of sodium triphosphate and is the optimum dose of the additives. The present study also used the pilot plant test loop to investigate flow dynamics of sand water slurry having different particle sizes and solid concentrations during the flow through a horizontal pipeline and 90o pipe bend. The experiments were performed with different particle sizes (<53, 53-106, and 106-150 μm), for solid concentration ranging from 10 to 40% by mass and influx velocity ranging from 1-4 m/s. The pressure loss during the flow is observed to be a function of slurry concentration, particle size present in slurry and influx velocity. It is also observed that the pressure loss per meter during the flow through a horizontal pipe is more in comparison to pressure loss during the flow through a 90o pipe bend. The percentage change in pressure loss observed to be lying in a range of 1-36% by varying the slurry concentration and for a constant velocity whereas it is lying in a range of 261-1679% for varying the velocity and for a constant slurry concentration during the flow through a 90o pipe bend. The pressure drop during the flow of sand water slurry in a horizontal pipe flow was also calculated through Wasp model and it is observed that the trend obtained for both the methods are similar, but the pressure drop obtained through Wasp model is over predicting in comparison to pressure drop obtained through experimentally for all conditions.

The flow of sand water slurry having different particle sizes and solid concentrations is also investigated numerically using CFD tool and the results obtained through numerical simulation was validated with experimental results. It is seen that SST k-omega turbulence model is an efficient model and this turbulence model results agrees with experimental results. The skin friction coefficient in horizontal pipeline and 90o pipe bend for different sized particle of sand water slurry is observed to be increased with the increase in influx velocity and solid concentration. The present study also investigated the solid particle erosion of slurry pipeline during the flow of sand water slurry and experiments were conducted using erosion pot tester. The amount of erosion is observed for both coated and uncoated specimen. The present study used the six combinations of four coating powders, and they are aluminum oxide, titanium oxide, Nickel, and chromium oxide. It is observed that the coating combination 80Ni+15Cr2O3+5TiO2 has large erosion resistance and the solid particle erosion is reduced in a range of 56-66 % in comparison to uncoated specimen during the rotational movement of sand water slurry having the solid concentration in the range of 10-40% rotated in 1500 rpm for 120 min.