A system for the phase concentration measurement of biomass/pulverized coal/air threephase flow based on electrostatic sensor and capacitive sensor data fusion in pneumatic conveying fuel system at power stations is d...
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flow and temperature fields during the solidification of hypereutectic and hypoeutectic NH4Cl‐H2O solution in rectangular cavities were measured by a particle image velocimetry(PIV) and a weak perturbation thermocoup...
flow and temperature fields during the solidification of hypereutectic and hypoeutectic NH4Cl‐H2O solution in rectangular cavities were measured by a particle image velocimetry(PIV) and a weak perturbation thermocouple network, respectively. Double‐diffusive convections caused by the coupling effects of temperature and solute gradients were studied by the experiment. During the solidification of hypereutectic solution, the rejected water near the solidification interface will lead to dilute solute layers and double‐diffusive interfaces. As the continued rejection of water, the layer and interface will evolve into instability and a multi‐layer and multi‐interface structure will be formed. To the hypoeutectic solution, the rejection of NH4Cl near the solidification interface will form a dense solute layer. When the thickness of the dense solute layer is large enough, the coupling effects of stabilizing solute gradient and unstable temperature gradient will lead to new solute layers. The solute layers and double‐diffusive interfaces will evolve stably and have no breakup of the double‐diffusive interfaces during the solidification of hypoeutectic solution.
A model coupling two basic models, the model with interface tracking method and two‐fluid model, for simulation of incompressible gas‐liquid two‐phase flow is proposed. A united solution frame shared by the two bas...
A model coupling two basic models, the model with interface tracking method and two‐fluid model, for simulation of incompressible gas‐liquid two‐phase flow is proposed. A united solution frame shared by the two basic models is built. In the shared solution frame, the Navier—Stokes equations of the two basic models can be dealt with in a uniform form. In the proposed model, there are three phases, which are divided not only by physics but also by the length scale of interface, including the liquid phase, the large‐length‐scale‐interface gas phase and the small‐length‐scale‐interface gas phase. The special treatment named by “void fraction redistribution” is adopted for the special grids which contain all three phases. Based on the united solution frame, MCBA—SIMPLE algorithm is used to solve the equations. Two problems are calculated to show that the proposed model has the merits of the two basic models.
The dynamic characteristics of molten droplets and hot particles at the very beginning of their fall into coolant pools are presented. The falling course of a single droplet or a single hot particle was recorded by a ...
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The dynamic characteristics of molten droplets and hot particles at the very beginning of their fall into coolant pools are presented. The falling course of a single droplet or a single hot particle was recorded by a highspeed camera and a curve of velocity vs. time was obtained. Emphasis was placed on the effects of the droplet's size and temperature, the coolant's temperature and properties, and the droplet's physical properties on the moving behavior. The results for the all cases showed that the velocity of a falling droplet/particle decreased rapidly but rebounded shortly, at the beginning of droplet/particle falling in the coolant. Following such a V-shaped evolution in velocity, the droplet/particle slows down gradually to a comparatively steady velocity. An increase in either coolant temperature or droplet temperature results in a larger velocity variation in the 'J-region', but a smaller deceleration when it moves out of the 'J-region'. The elevated volatility of a coolant leads to a steeper deceleration in the 'J-region' and beyond. The bigger size of a particle leads to a greater velocity variation in the 'J-region' and terminal velocity. A high melting point and thermal conductivity as well as lower heat capacity contribute to dramatic variation in the 'J-region' and low terminal velocity.
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.
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