Natural gas hydrate shell model in gas-slurry pipeline flow

A hydrate shell model coupled with one-dimensional two-fluid pipe flow model was established to study the flow characteristics of gas-hydrate slurry flow system.The hydrate shell model was developed with kinetic limitations and mass transfer limitations,and it was solved by Euler method.The analysis of influence factors was performed.It was found that the diffusion coefficient was a key parameter in hydrate forming process.Considering the hydrate kinetics model and the contacting area between gas and water,the hydrate shell model was more close to its practical situations.

THEORETICAL ANALYSIS ON HYDRAULIC TRANSIENT RESULTED BY SUDDEN INCREASE OF INLET PRESSURE FOR LAMINAR PIPELINE FLOW

Hydraulic transient, which is resulted from sudden increase of inlet pressure for laminar pipeline flow, is studied. The partial differential equation, initial and boundary conditions for transient pressure were constructed, and the theoretical solution was obtained by variable-separation method. The partial differential equation, initial and boundary conditions for flow rate were obtained in accordance with the constraint correlation between flow rate and pressure while the transient flow rate distribution was also solved by variable-separation method. The theoretical solution conforms to numerical solution obtained by method of characteristics (MOC) very well.

DOUBLE METHOD OF CHARACTERISTICS TO ANALYZE HYDRAULIC-THERMAL TRANSIENTS OF PIPELINE FLOW

The hydraulic and thermal transients in pipeline flow were studied. The method of characteristics for hydraulic transient analysis of batch transport of pipeline flow had been improved. The thermal transient equation, in which the term with v 3 was involved, had been inferred, while the corresponding method of characteristics was constructed. The double method of characteristics, which can be used to study the coherent hydraulic-thermal transients of batch transport of pipeline flow, was developed.

An experimental study of drag reduction by nanofluids in slug two-phase flow of air and water through horizontal pipes

This study investigates the effect of injecting nanofluids containing nano-SiO_2 as drag reducing agents(DRA) at different concentrations on the pressure drop of air-water flow through horizontal pipe.The test fluid used in this study was air-water with nano-SiO_2 particles at 0.1%-1%mass concentration.The test sections of the experimental set-up were five pipes of the same length of 9 m with ID from 0.0127m-0.03175m(0.5 to 1.25 in).Airwater flow was run in slug flow regime under different volumetric flow rates.The results of drag reduction(η%)indicated that the addition of DRA could be efficient up to some dosage.Drag reduction performed much better for smaller pipe diameters than it did for larger ones.For various nanosilica concentrations,the maximum drag reduction was about 66.8%for 0.75%mass concentration of nanosilica.

Transient Flow in Rapidly Filling Air-Entrapped Pipelines with Moving Boundaries

A mathematical model is presented for transient flow in a rapidly filling pipeline with an entrapped air pocket. The influence of transient shear stress between the pipe wall and the flowing fluid is taken into account. A coordinate transformation technique is employed to generate adaptive moving meshes for the multiphase flow system as images of the time-independent computational meshes in auxiliary domains. The method of characteristics is used to reduce the coupled nonlinear hyperbolic partial differential equations governing the motion of the filling fluid, entrapped air, and blocking fluid to ordinary differential equations. Numerical solution of resulting equations shows that the transient shear stresses have only a small damping effect on the pressure fluctuations. The peak pressure in the entrapped air pocket decreases significantly with increasing initial entrapped air volume, but decreases slightly with increasing initial entrapped air pressure.

Numerical study on critical flow velocity of ice slurry in the pipe of ice source heat pump system

The traditional evaporator of water source heat pump system is easy to freeze when the water source temperature is too low in winter.A novel ice source heat pump system is proposed,which can use low temperature surface water to supply heat to buildings.One of the key problems for safe transportation is velocity range of ice slurry in ice outlet pipeline.In order to study the critical flow velocity of ice slurry in the pipe,an Euler model of horizontal straight pipe and 90°elbow pipe were established by Fluent software.The influence of five factors on the critical flow velocity of two kinds of pipes,including initial ice packing fraction,ice particle size,pipe diameter,length of straight pipe and radius curvature of elbow was studied.It found that the initial ice content should be controlled from 10%to 15%.The inlet flow rate was 20%higher than the critical flow rate under the most unfavorable condition.Ice particle size was less than 0.2 mm.The total length of ice discharge pipeline was less than 50 m.Curvature radius of the bend should be met the minimum requirements of the specification of the pipe used.

AN ALTERNATE METHOD TO PREVENT SAND ABRASIVE EROSION IN PIPELINES FOR TRANSPORTING HIGH-SPEED NATURAL GAS

This paper presents an alternate method to remove the sand carried by natural gas in the upstream pipelines therefore preventing sand abrasive erosion in pipelines used in transporting high speed natural gas. Conventionally, most experts pay much attention to improving the anti erosion characteristics of the pipeline materials to solve the problem of serious abrasive erosion, but without significant success. Based on the theory of multiphase flow and analysis of the characteristics of sandy jets, a new equipment named 'Sand Catcher' is introduced in this article. Experimental results show that the Sand Catcher effectively removes most of the sand in the natural gas and significantly reduces the abrasive erosion of the pipelines. The Sand Catcher can be widely applied in practice in the near future.