The principal pressure drop in a subsea riser is generally the gravitational pressure drop component due to liquid holdup. Surfactant is a kind of Chemical compound related to flow improvement. Gas‐liquid two‐phase ...
The principal pressure drop in a subsea riser is generally the gravitational pressure drop component due to liquid holdup. Surfactant is a kind of Chemical compound related to flow improvement. Gas‐liquid two‐phase flow in subsea riser with zero and small liquid flow rates was simulated in two vertical tubes with diameters of 40 mm and 65 mm, respectively. Liquid holdup reduction of subsea riser was investigated with surfactant. The simulation was conducted at low pressure, using air as the gas phase and water as the liquid phase. Pressure drop was measured by using differential pressure transducer and holdup was obtained by trapping the liquid in the pipe section. Different trace amounts of surfactant were used in this vertical two‐phase flow system. The liquid holdups were measured at different surfactant concentrations and different gas‐liquid flow ratios. Liquid holdups with and without surfactant additives are compared and analyzed. How the foamer influences the two‐phase flow pattern was observed and the range of foamer concentration corresponding to the best holdup reduction was obtained.
The morphology of fuel nitrogen in coal and its fate during pyrolysis and the nitrogen species including N2, HCN and NH3 during coal pyrolysis and gasification have been investigated to clarify the evolution mechanism...
The morphology of fuel nitrogen in coal and its fate during pyrolysis and the nitrogen species including N2, HCN and NH3 during coal pyrolysis and gasification have been investigated to clarify the evolution mechanism of fuel nitrogen in heat treatment process. Experimental results show that the morphology of coal nitrogen in the studied Chinese raw coals generally include pyrrolic nitrogen (N‐5), pyridinic nitrogen (N‐6), quaternary nitrogen (N‐Q) and nitrogen‐oxide (N‐X). Generally, nitrogen in char is transformed to volatile and more stable components during pyrolysis. Char‐N is the major source of NOx precursors during temperature programmed pyrolysis in 600–800° C. N‐5 and N‐X in char is converted to HCN first, and HCN is then hydrogenated to NH3. N‐Q in char is the main source of nitrogen gas. The major nitrogenous gas products during rapid coal pyrolysis are N2, HCN and NH3, amongst which N2 is dominant. The yields of N2 and NOx precursors, such as HCN and NH3, increase with increased pyrolysis temperature. The major gaseous nitrogenous products during coal gasification in steam include HCN, NH3 and N2. H2O is the main source of the groups containing hydrogen, which not only participates in the reaction as a gasification agent, but also has catalysis on the reaction.
The moving particle semi-implicit method (MPS) was used to simulate the typical free surface problem, 2D dam break problem, and the effect of initial particle configuration on the simulated results was analyzed. It is...
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The moving particle semi-implicit method (MPS) was used to simulate the typical free surface problem, 2D dam break problem, and the effect of initial particle configuration on the simulated results was analyzed. It is found that the reasonable results can not be achieved for too large or too small particle distance. The comparison of the results by MPS, SPH or VOF with the experimental data shows that the result by MPS is between those by VOF and by SPH. Without the consideration of viscosity, the result by MPS is closer to the experiment than that by VOF. However, the result by MPS with the consideration of viscosity may be similar to that by SPH.
A simple line interface calculation-volume of fluid(SLIC-VOF) interface reconstruction technology was developed on the basis of the triangular unstructured grid. For a cell containing the interface, a straight line se...
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A simple line interface calculation-volume of fluid(SLIC-VOF) interface reconstruction technology was developed on the basis of the triangular unstructured grid. For a cell containing the interface, a straight line segment parallel with one side of the triangle cell was set on the interface according to the volume fractions in the three neighbor cells. The volume flux of the fluid with the assigned phase was determined by the geometry relation between the interface line and the volume flux on each side. Three tests were performed to verify the feasibility of the present unstructured SLIC-VOF interface reconstruction method, including an advection test of a right-angled triangle, the Zalesak slotted disk rotation test, and a single-vortex shearing flow test. The results show that the accuracy of the present method for the unstructured grid with 7600 cells is comparative with that of the conventional SLIC-VOF method for the structured grid with 6400 cells after the interface restoration in the reversed velocity field.
Bubbly mixing layer with polymer additives is investigated by PIV. The void fraction is 0.5%. The comparison between single-phase and bubbly mixing layer shows that the dynamic development of mixing layer is greatly i...
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Bubbly mixing layer with polymer additives is investigated by PIV. The void fraction is 0.5%. The comparison between single-phase and bubbly mixing layer shows that the dynamic development of mixing layer is greatly influenced by the bubble injection. Similar with single phase, the Reynolds stress and vorticity still concentrate in a coniform area of central mixing flow field and the width increases with increasing the Reynolds number. Mean Reynolds stress decreases with bubble injection at high Reynolds numbers and the decreasing of Reynolds stress with polymer additives is much more than that in a pure water case. There is an obvious decreasing to the peak value of vorticity when bubbles are injected into the fluid, and the influence on the viscoelastic fluid is smaller than that on the pure water.
A finite volume solver for Casson fluid flow based on SIMPLE algorithm of Newtonian fluid on unstructured collocated grid is developed to simulate haemodynamics in complex vessel. The discretization of convective flux...
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A finite volume solver for Casson fluid flow based on SIMPLE algorithm of Newtonian fluid on unstructured collocated grid is developed to simulate haemodynamics in complex vessel. The discretization of convective flux and source term are similar with Newtonian fluid. For the discretization of diffusion flux, viscosity will take the value calculated from the flow field of previous iteration so as to avoid the complexity caused by the complicated viscosity expression as a function of shear rate. Then the discretization of momentum equation is similar with that of Newtonian fluid with variable viscosity and SIMPLE algorithm can be used to resolve the pressure-velocity coupling. With this algorithm, blood flows in a T-typed bifurcation are simulated. The simulation results of Casson fluid are more consistent with experimental data than that of Newtonian fluid, which indicates that using Casson model to simulate non-Newtonian characteristics of blood flow is successful and necessary.
This paper considers an epidemic model of a vector-borne disease which has the vectormediated transmission only. The incidence term is of the bilinear mass-action form. It is shown that the global dynamics is complete...
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This paper considers an epidemic model of a vector-borne disease which has the vectormediated transmission only. The incidence term is of the bilinear mass-action form. It is shown that the global dynamics is completely determined by the basic reproduction number Ro. If Ro ≤ 1. the diseasefree equilibrium is globally stable and the disease dies out. If Ro 〉 1. a unique endemic equilibrium is globally stable in the interior of the feasible region and the disease persists at the endemic equilibrium. Numerical simulations are presented to illustrate the results.
Turbulent mixing layer flow was simulated by the discrete vortex method, and viscosity was modeled by the random walk method and the solid wall was represented by the vortex sheet in the simulation. The predictions of...
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Turbulent mixing layer flow was simulated by the discrete vortex method, and viscosity was modeled by the random walk method and the solid wall was represented by the vortex sheet in the simulation. The predictions of the profiles of mean velocity and turbulent flow parameters agree well with experimental data. The results show that the peak value of Reynolds shear stress increases but the fluctuations of the peak value occur because of vortex-pairing, and vorticity peak value increases in the downstream direction. Then the effect of Reynolds number on the distribution of the turbulent flow parameters at the same velocity ratio was explored. It seems that the peak values of Reynolds shear stress under different Reynolds numbers will increase at the similar slope in the downstream direction. The average vorticity peak value will decrease in the downstream direction, and the decrease rate will increase with Reynolds number. In addition, the vorticity peak value in each section will increase nearly linearly with Reynolds number.
The dimension of erythrocyte is close to capillary diameter and in microcirculation blood should be treated as a two-phase flow system, i.e., erythrocytes suspended in plasma. The rheological property of erythrocytes ...
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The dimension of erythrocyte is close to capillary diameter and in microcirculation blood should be treated as a two-phase flow system, i.e., erythrocytes suspended in plasma. The rheological property of erythrocytes will significantly influence the hemodynamics. In our experiment, the motion and deformation of erythrocytes in a microfluidic chip with rectangular cross-section microchannel was captured by optical microscope and high speed CCD camera. The aggregation, deformation and common movement forms of erythrocytes were observed under different viscosity, hematocrit and velocity. It was found that erythrocytes behaved a regular biconcave disc shape at low velocity and low-to-medium viscosity, and always rolled and rotated themselves in their movement. At high velocity and medium viscosity, RBCs elongated obviously along the flow direction and presented a flat oval shape together with a tank-treading motion (TTM).
multiphase {1. induced CO2 corrosion has resulted in serious losses in oil and gas production. In this paper, gas‐liquid two‐phase vertical upward slug {1. has been analyzed from aspects containing {1. structure,...
multiphase {1. induced CO2 corrosion has resulted in serious losses in oil and gas production. In this paper, gas‐liquid two‐phase vertical upward slug {1. has been analyzed from aspects containing {1. structure, hydrodynamic characteristics, mass transfer characteristics and their effects on pipe wall and corrosion product film, and it is found that slug {1. has a distinct effect on transports of corroding species to and of corrosion products from the wall, momentum interchange between fluid and wall and the formation and damage of corrosion product film. In addition, the transports of corrosive species and corrosion product are also an important step in CO2 corrosion process. It is assumed that the slug {1. induced CO2 corrosion of pipeline is dependent on the non‐linear coupling of the characteristics including the shear stress, the normal stress, the mass transfer coefficient, and the electrochemical reaction.
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