Search

• The interphase forces between the fluid and particles were studied. • The particle lifting mechanisms of the HE-ULAR was revealed. • The optimal operation condition of the HE-ULAR was detected. • A series of formulas for the fluidized coal mining parameters were established. Hydraulic ejectors with ultra-large area ratios (HE-ULAR) have potential applications as particle lifting equipment in fluidized coal mining. This study analyzed the effects of area and pressure ratios on the coarse particle lifting performance of HE-ULAR. The cavitation, valid, and failure zones for coarse particle lifting were mapped out. The results show that the pressure gradient force acting on each particle is approximately 2.02–3.70 times greater than the drag force, indicating that the pressure gradient force is the more significant interaction force for particle migration under the influence of HE-ULAR compared to the drag force. Additionally, insufficient energy transfer between the energetic fluid and particles in the valid zone of HE-ULAR reduces the fluid energy density and particle lifting concentration at low pressure ratio conditions. The HE-ULAR exhibits optimal particle performance at the operating conditions with an area ratio of 12.51 and a pressure ratio of 0.0735. Finally, a series of prediction formulas for fluidized coal mining parameters were established based on the optimal operating condition of the HE-ULAR. These results will guide the application of the HE-ULAR in a fluidized mining system. [ABSTRACT FROM AUTHOR]

The passage of a dust devil vortex goes along with a pressure reduction above ground. This leads to a sub-soil overpressure. It has been suggested that this enhances the lift on particles and facilitates dust entrainment by dust devils. We quantify the necessary pressure difference to lift fine sand from sand beds with thickness of 50, 150, and 250 mm in laboratory experiments with basalt samples consisting of 63–125 μ m grains. The absolute pressure was varied between 1,300 and 3,600 Pa. In general, a pressure differences of about 30 Pa per mm depth is needed to lift sand grains. With slight systematic variations this is in agreement to simply accounting for the weight of a lifted particle layer. On Mars observed absolute pressure difference are several Pa. This limits particle lift to a layer smaller than 100 μ m . However, it clearly allows Δp lifting if the top layer has a decreased permeability. This might be the case for dust layers sitting on top of a coarse grained sand bed. These measurements support the idea of enhanced dust entrainment due to the Δp -effect in Martian dust devils under certain conditions. [ABSTRACT FROM AUTHOR]

Particle lifting in dust devils on both Earth and Mars has been studied from many different perspectives, including how dust devils could influence the dust cycles of both planets. Here we review our current understanding of particle entrainment by dust devils by examining results from field observations on Earth and Mars, laboratory experiments (at terrestrial ambient and Mars-analog conditions), and analytical modeling. By combining insights obtained from these three methodologies, we provide a detailed overview on interactions between particle lifting processes due to mechanical, thermal, electrodynamical and pressure effects, and how these processes apply to dust devils on Earth and Mars. Experiments and observations have shown dust devils to be effective lifters of dust given the proper conditions on Earth and Mars. However, dust devil studies have yet to determine the individual roles of each of the component processes acting at any given time in dust devils. [ABSTRACT FROM AUTHOR]

• Demonstrated capability of three-phase foam flow in dewatering unconventional wells. • Examined flow regimes of foam flows in vertical tubing and annulus. • Examined the effect of pressure on dynamic and static foam flow characteristics. • Tested the effect of salt and particles on foam stability. This paper aims to investigate and demonstrate, for the first time, the feasibility of using an artificial lift system, referred to as foam assisted gas lift (FAGL) for dewatering unconventional gas wells to depressurise coal and allow gas to be produced. More specifically, this paper investigates the capability of a three-phase foam flow to lift gas, liquid and solid particulates to the surface to optimise gas production by minimising the flowing bottom-hole pressure (FBHP) and minimising downtime, operational costs and production losses caused by downhole pump failures. A laboratory set-up of a 9 m vertical tubing with 80 mm (3.1 in) ID and a 7 m annulus with a casing inner diameter of 170 mm (6.69 in) and tubing outer diameter of 70 mm (2.76 in) are used to investigate the foam flow behaviour in both geometries for a wide range of gas and water flowrates, 40–6500 L/min and 10–80 L/min, respectively. The 80 mm tubing is pressurised up to 6 bar, allowing examining the foam flow characteristics and foam stability at different depths of a gas well, by changing the operating pressure. Foam flow regimes in the tubing and the annulus, which are key in determining the FBHP are characterised by analysing differential pressure signals, collected at 100 Hz frequency. The addition of foamer (sodium dodecylbenzene sulfonate) significantly advanced the transition from churn to the annular flow regime, resulting in a lower required gas flow rate to obtain the least attainable FBHP. A model is developed to evaluate the FBHP of the FAGL, compared against the measured FBHP in 36 gas wells in Australia, equipped with down-hole pumps for dewatering. Our results indicate that FAGL is capable of maintaining a low FBHP for a wide range of gas and water flow rates. The effective particle lifting capacity of foam flow is also demonstrated. Further, the positive impact of water salinity (0.1 M NaCl) in the presence of particles (15–25 g/l) on foam integrity is presented. [ABSTRACT FROM AUTHOR]

The dynamics of particles of the disperse phase in a turbulent gas flow in planar shock waves sliding along a solid surface with a trapezoid cavity is examined numerically. Lifting of particles from the cavity walls is calculated in the approximation of a rarefied gas suspension. It is shown that the intensity of the transient shock wave and the initial positions of particles have a significant effect on the particle-lifting properties. The height of particle lifting is found to nonmonotonically depend on the initial streamwise coordinate and shock-wave Mach number. It is shown that zones of aggregation and subtraction of particles may be formed at the cavity bottom. [ABSTRACT FROM AUTHOR]