Zefeng Jing

Detailed Structural and Mechanical Response of Wet Foam to the Settling Particle

Liquid foam, as a complex fluid, provides an observable prototype for studying a discrete fluid system. In this work, a numerical study on the settling behavior of a round particle in wet polydisperse foam has been conducted on the bubble scale. The local and nonuniform distribution of bubble pressure, as well as the localized plastic events, is presented. It shows a foam region of higher pressure in front of the settling particle due to the extrusion deformation of the bubbles applied by the particle. Additionally, the forces exerted on the particle by the disordered wet foam are measured during the sedimentation. It exhibits in particular a power-law dependence of the drag force caused by the bubble as a function of the foam quality. Moreover, sedimentation experiments are demonstrated to verify this power-law relation. The evolution of the components of drag force is demonstrated when a plastic event occurs in front of the settling particle. The result shows that both the contributions of the pulling force of foam films and the bubble pressure to the drag force decrease in that case. Likewise, the variation of both these contributions to the drag force is illustrated as well when a bubble in the wake detaches from the particle. These results assist in understanding the mesoscopic response of wet foam to a settling particle.

Flow Behavior of Two-Dimensional Wet Foam: Effect of Foam Quality

The flow behaviors of two-dimensional (2D) wet monodisperse and polydisperse foams are investigated by the quasi-static simulation. We set the same inlet velocity on the cross section of the foam channel and then focus on the elastic–plastic deformation of the 2D wet foam according to the strain caused by the foam flow. The gas fraction in foam is referred to as foam quality and the effects of foam quality on the shear modulus, bubble dynamics, and stress–strain properties are obtained by the simulation. In the elastic domain, the shear modulus of monodisperse foam decreases exponentially with foam quality, but for the polydisperse foam, the shear modulus tends to increase. The shear banding of the polydisperse foam appears in the low strain and disappears gradually as the strain and foam quality increase. We adopt shear rate to represent the change rate of average bubbles displacements versus y-coordinates and find that the distribution of shear rate in the y-direction changes with iteration. Additionally, energy of the foam is stored and dissipated with the elastic–plastic deformation of the foam. The average shear stress generated by the foam structure and the initial increment of normal stress difference caused by the elastic deformation increase with the increase of foam quality.

Viscoelastic Drag of Particles Settling in Wormlike Micellar Solutions of Varying Surfactant Concentration

Wormlike micellar octadecyl trimethyl ammonium chloride (OTAC) solution is a self-assembled fracturing fluid used to carry proppants into fractures in oil recovery. Slow settling velocity of proppant is desirably resulted from the viscoelastic drag with low viscosity of fracturing fluids for fracturing work. Steel spheres, as a substitute for proppants, fall into three semi-dilute OTAC solutions. The steady rheology demonstrates that OTAC solutions are divided into shear-thickening and shear-thinning regimes by the critical shear rate. The applied steel spheres always lie in the shear-thickening regime of the 2.8 wt% OTAC solution with aggregated micelles as their characteristic shear rates are less than the critical shear rate of the solution. Strong shear-thickening viscous drag results in lower settling velocity of steel spheres. Most of the applied steel spheres, on the other hand, lie in the shear-thinning regime of the 4 wt% OTAC solution with orientated micelles. Although the latter solution has small dissipation coefficient, high Weissenberg number, and consequently high elastic effect, the shear-thinning viscosity results in higher settling velocity of steel spheres. GRAPHICAL ABSTRACT

Corrosion Properties and Mechanisms of Austenitic Stainless Steels and Ni-Base Alloys in Supercritical Water Containing Phosphate, Sulfate, Chloride and Oxygen

The corrosion behaviors of 316 stainless steel (SS), 316L SS, Inconel 625, Incoloy 825 and Hastelloy C276 were studied in supercritical water (SCW) containing phosphate, sulfate, chloride and/or oxygen. The results show that the alloy corrosion rate in SCW containing oxygen and phosphate was increased by adding sulfate and/or chloride. A two-layer structure of oxide film on 316 SS consisted of an inner layer with Cr-rich oxides (i.e., Cr2O3) and an outer layer rich in phosphates (e.g., FePO4 and Ni3(PO4)2). A three-layer oxide film formed on Incoloy 825 including corrosion products Fe2O3, NiO, FePO4, Ni3(PO4)2 and NiCr2O4, with phosphates in each layer. A two-layer oxide film on Hastelloy C276 was composed of metal oxides in the inner layer and metal oxides as well as phosphates in the outer layer, including Fe2O3, Cr2O3, NiO, MoO2, FePO4, CrPO4, Ni3(PO4)2 and NiCr2O4. The existence of sulfate, chloride, and especially both of them destroyed the formation of water-insoluble phosphates on the oxide film of tested alloy in SCW containing oxygen and phosphate.Graphical Abstract

Origin of accelerated and hindered sedimentation of two particles in wet foam

Abstract.To explore the origin of interactional settling behaviors of multi-particles in wet foam, the sedimentation of two particles placed one above the other as well as placed side by side is studied. According to the average settling velocity in experiment and the average settling drag force of the two particles in numerical simulation, we show that the particles display accelerated sedimentation as placed one above the other while they display hindered sedimentation in the case of the ones positioned side by side. Furthermore, the evolution of structure and force parameters of the bubbles, such as T1 topological events, displacement vector and principal stress fields, shows that the reciprocal action between the foam and the settling particles placed side by side is more significant. The different levels of interplay for these two settling cases also give rise to the diverse changes of bubble pressure response. The bubble pressure component of the average drag force is higher for the particles placed side by side. Especially, for the first time, it reveals that these interactional sedimentation behaviors in the foam are mainly attributed to the changed pressure of bubbles caused by these settling particles at the mesoscopic level. The present results may suggest potential explanations to the cause of the complex accelerated or hindered sedimentation of more particles in wet foam.Graphical abstract

Effects of slip and rheological parameters on the flow and heat transfer of a Herschel-Bulkley fluid

Purpose The purpose of this paper is to investigate the combined effects of slip and rheological parameters on the flow and heat transfer of the Herschel-Bulkley fluid. Design/methodology/approach The combinative dimensionless parameter method is introduced into the equations of the slip flow and heat transfer to make the discussion more comprehensive. More specifically, the slip and rheological parameters are transformed into the dimensionless slip number as well as Herschel-Bulkley number. We solve the dimensionless equations and then focus on the effects of these parameters on the slip flow and heat transfer. Findings The results show that, for a given value of Herschel-Bulkley number, there is a finite critical value of slip number at which the pressure gradient reaches the lowest value and both the dimensionless yield radius and slip velocity become 1. Meanwhile, the Nusselt number tends to be infinite at this critical value of slip number. For the case of slip, the Nusselt number also approaches infinity at a finite critical value of Herschel-Bulkley number. Furthermore, the dimensionless velocity as well as temperature of the yield pseudoplastic fluid with higher slip number is lower within a small radius but becomes higher near the wall. Meanwhile, from the velocity and temperature profiles, the effect of Herschel-Bulkley number on these two parameters of the Bingham fluid at the smaller radius is opposite. Originality/value These associated expressions can be generalized to the flow and heat transfer of a Herschel-Bulkley fluid under slip boundary condition. It can provide a reference for the engineering application relating to the heat transfer and flow of a Herschel-Bulkley fluid. Meanwhile, it also suggests some revelations for dealing with this similar problem.

Study on Filtration and Damage Characteristics of Modified Dry CO2 Fracturing Fluid in Shale Gas Reservoir

The filtration and damage characteristics of modified dry CO2 fracturing fluid in the shale is studied in this paper. The results show that the modified dry CO2 fracturing fluid has good leak-off characteristics. Compared with liquid CO2, supercritical CO2 has a better permeation and diffusion capacity in the porous medium. The damage rate of the modified dry CO2 fracturing fluid to shale core is only between 0.63%~3.84% with obvious little damage. Under liquid conditions, the increase of temperature makes the fracturing fluid more harmful to shale formation.

Dry Volume Fracturing Simulation of Shale Gas Reservoir

Application of CO2 dry fracturing technology to shale gas reservoir development in China has advantages of no water consumption, little reservoir damage and promoting CH4 desorption. This paper uses Meyer simulation to study complex fracture network extension and the distribution characteristics of shale gas reservoirs in the CO2 dry volume fracturing process. The simulation results prove the validity of the modified CO2 dry fracturing fluid used in shale volume fracturing and provides a theoretical basis for the following study on interval optimization of the shale reservoir dry volume fracturing.