| With the rapid development of science and technology, long-distance pipeline low boiling fluid transport theory and technology development present new research directions. In this paper, the main topic for the long-distance pipeline low boiling fluid transport technology research, including:(1) Research on hydraulic characteristics of the flow field of dynamic slide valve internal;(2)The low-boiling fluid in a pipe elbow computational domain viscous vaporization caused doped flow mixed with air problem. Study the internal flow field characteristics of dynamic slide valve is mainly to the slide valve opening and closing process of the internal flow field of hydraulic characteristics for continuous monitoring, to get the change rule of slide valve internal flow field in transient pressure and flow rate variation when the slide valve opening degree in different conditions. Elbow viscous gasification problems mainly to explore the phenomenon of viscous vaporization generated by low boiling fluid flows through the elbow, analysis of the formation mechanism of the phenomenon of viscous gasification; along with changes in the radius of curvature of the elbow, the vaporization degree of its and its downstream region.This paper, a low boiling point, high viscous nitrogen tetroxide fluid as a research object, using FLUENT software for the internal flow field characteristics of the dynamic slide valve and the viscous gasification problems of the elbow computation domain to numerical simulation research and analysis. First, a mathematical model of the dynamic slide valve and different radius of curvature of the elbow is built, combination of partial differential equations and fluid boundary conditions respectively for the Fluent software secondary development, write a UDF program moving mesh model and the quality of the transmission model, provides a theoretical basis for the further research of the internal flow field of dynamic slide valve and the viscous vaporization problems in different radius of curvature of the elbow.The study of hydraulic characteristics of the flow field of dynamic slide valve internal introduced VOF two-phase model and the dynamic mesh model, to capture the transient change position and rule of the free surface during the slide valve opening and closing process, its contents include the problems of pressure characteristics, flow structure and two-phase flow distribution characteristics of the internal flow field of slide valve in the same inlet pipe inlet flow conditions and the same slide valve opening condition. The research of elbow viscous gasification problems introduced mass transfer model and turbulence model realized the elbow area of fluid collision friction, the formation of gas-liquid two phases into each other. The study includes the rule of elbow pressure distribution, velocity distribution, two-phase distribution and to determine the optimal radius of curvature of the elbow and so on. Through the above numerical simulation analysis for hydraulics problems obtained hydraulic characteristics of dynamic slide valve internal and distribution rule of elbow viscous two-phase flow gasification. Specific research results are as follows:(1) The same inlet velocity working conditions, with the increasing of the slide valve opening degree, the liquid phase flow in the liquid pipe inside increased gradually, the flow field water lines improved gradually, gradually increasing the volume fraction of the liquid phase, the gas phase volume fraction decreases; the internal flow field in the return pipe on the contrary, the gas phase volume fraction increases, the volume fraction of the liquid phase decreases; the slide valve opening degree to fully state, the red liquid phase inside in the liquid pipe will substantially fill the pipe, the return pipe inside water line will fall to the bottom boundary where the pipe.(2) In the working conditions of the same slide valve opening degree, with the increasing of inlet pipe inlet velocity, the gas phase area of the computational domain in the liquid and return pipe were gradually reduced and the length of the gas phase computational domain become shorten, the calculation of the liquid phase fluid domain area increased gradually. Slide valve position fluid in turbulence, local doped flow mixed with air phenomenon in the liquid phase area, the two-phase water lines change are larger; The internal water lines in the return pipe are smooth; it does not exist obvious volatility phenomenon, in the slide valve position yong high water lines is at the obvious.(3) The same inlet velocity working conditions, in the mixed fluid, the liquid phase flow field pressure is significantly higher than the pressure of the gas phase flow field. With the increasing of the slide valve opening degree, the liquid phase flow field pressure in the liquid pipe inside increased gradually, the gas phase flow field in the return pipe inside reduced gradually, the gas phase flow field pressure in the liquid pipe inside increased gradually; the gas phase pressure in the return pipe inside reduced gradually.(4) In the both sides of the slide valve’s level pipe appears different degrees of low pressure flow field area. In the location of the slide valve half opening degree, the slide valve on both sides of the pipe internal flow field in the area of low pressure are basic equal, moving boundary slide valve near wall region appeared high pressure area. In the conditions of the same slide valve opening degree, with the increasing of inlet pipe inlet velocity, the pressure of the gas phase flow field increased gradually, the pressure of the liquid phase flow field has increased at the same time. This law is applicable to the internal flow field calculation domain in the liquid and return pipe.(5) The same inlet velocity working conditions, with the increasing of the slide valve opening degree, the horizontal velocity distribution in the flow field of a straight pipe showing symmetrical features. When moving boundary slide valve opening degree is 50%, the liquid pipe flow and return pipe flow is basic equal. With the increasing of the slide valve opening degree, the average flow velocity of the gas phase flow field in a horizontal pipe increases, the average flow velocity of the liquid phase flow field in the liquid pipe inside increased gradually, the average flow velocity of the liquid phase flow field in the return pipe inside decreased gradually.(6) In the working conditions of the same slide valve opening degree, with the increasing of inlet pipe inlet velocity, the average flow velocity of the liquid phase flow field in a horizontal pipe increased gradually and the average flow velocity of the gas phase flow field in a horizontal pipe increases too, moving boundary slide valve near wall region the lower part of the straight pipe appeared a range of low velocity region. In the inlet pipe internal, the cross section flow field velocity distribution presents parabolic features.(7) The vertical velocity variation relatively obvious areas in the horizontal pipe internal is slide valve near wall flow field area, the rest of the flow field location of the vertical velocity to near zero. The water lines fall lead to appear a range of reverse and vertical velocity area in straight pipe on both sides, In the conditions of the same inlet velocity, with the increasing of the slide valve opening degree, the direction of vertical velocity of the gas phase flow field in the outflow pipe inside is upward; the direction of vertical velocity of the gas phase flow field in the return pipe inside is downward, and the average velocity of the two pipe are gradually increasing; the vertical velocity of the liquid phase flow field in the outflow pipe inside decreased gradually, the vertical velocity of the liquid phase flow field in the return pipe inside increased gradually.(8) In the working conditions of the same slide valve opening degree, with the increasing of inlet pipe inlet velocity, the average velocity of the gas phase flow field in the liquid pipe inside increases, and its direction is upright, the average velocity of the vertical gas phase flow field in the return pipe inside gradually reduced and its direction is downward. The vertical average velocity of the liquid phase flow field in the liquid and return pipe inside are decreased, the vertical average velocity of the flow field of the slide valve near wall on both sides of a larger change in the calculation area gradually reduced.(9) The same inlet velocity working conditions, the maximum vertical velocity values in the slide valve near wall on both flow field sides substantially equal, indicating that the change of slide valve opening degree does not occurs velocity mutation phenomenon, with the increasing of the slide valve opening degree, the flow field on both sides of the slide valve showed obvious symmetrical features. With the gradual increasing of the slide valve opening degree, the average velocity of the flow field in the liquid pipe inside increased gradually, the average velocity of the flow field in the return pipe inside decreases, the velocity distribution of "fully open" or "fully close" two kinds of moving boundary condition is almost the same logarithmic distribution law, moving boundary slide valve near wall region appeared turbulent conditions.(10) The same upstream pipe inlet velocity conditions, the upstream straight pipe does not occurs viscous vaporization generally, but the downstream straight pipe and ends of elbow viscous vaporization are obvious. With the increasing of the radius of curvature of the elbow, the area of the gas phase flow field in the downstream straight pipe inside presents the variation of decreased at first and then increased, the extent of doped flow mixed with air in the area presents after decreases and then increases. Same the radius of curvature of the elbow conditions, with the increasing of upstream pipe inlet velocity, the extent of doped flow mixed with air in the downstream pipe gradually strengthened, the gas phase volume increase, the liquid phase volume decrease.(11) The same upstream pipe inlet velocity conditions, with 90-degree the radius of curvature of the elbow increasing, the rate of temperature rise in the whole pipe flow field inside presents the variation of decreased at first and then improved, the temperature variations in the entire pipe inside from pipe inlet to the outlet pipe gradually increased, the upstream straight pipe temperature rise gradient is small, the temperature rise gradient of downstream straight pipe is greater, 90-degree elbow internal flow field distribution is more uniform, there was no apparent high-speed flow field area, the average velocity in the gas phase and the liquid phase flow field areas are basically the same.(12) The same radius of curvature of the elbow conditions, with the increasing of upstream pipe inlet velocity, the temperature change gradient in the downstream straight pipe and ends of elbow presents the variation of decreased at first and then improved, the pressure drop area of elbow region is also increased at first and then decreased, so that overall vaporization degree in the elbow downstream apparent presents after decreases and then increases. Due to viscous gasification phenomenon generated by fluid in elbow, resulting in cross-section flow field of upstream straight pipe exhibits parabolic distribution, but the flow field in the downstream straight pipe and elbow area basically exhibits logarithmic distribution.(13) The same upstream pipe inlet velocity conditions, with the increasing of the radius of curvature of the elbow, the velocity in the elbow region increased gradually. The pipe internal pressure distribution from upstream to downstream presents the variation of decreased at first and then increased, and the elbow region pressure inside the pipe is minimum. At the same time, with the increasing of the radius of curvature of the elbow, the low pressure area in the elbow region increased at first and then decreased. Gas phase volume generated by viscous vaporization along the downstream flow field also decreased at first and then increased, and along the downstream straight pipe the extent of vaporization decreased gradually.(14) The flow field inside the pipe, the upstream straight pipe does not occurs viscous vaporization generally, the radius of curvature of the elbow largely affected the extent of vaporization. With 90-degree the radius of curvature of the elbow increasing, the trends of vaporization volume distribution curve variation in the elbow downstream pipe basically the same, a linear relationship between the degree of vaporization gradually increased, the same 90-degree radius of curvature of the elbow conditions, as the upstream pipe inlet velocity increase the vaporization of pipe downstream fluid showing decreasing trends. By studying numerical simulation analysis of the elbow viscous gasification problems, we can gain the viscous vaporization degree of elbow decreased at first and then increased with the decreasing of the radius of curvature of the elbow, therefore, the optimal radius of curvature of the elbow is 0.55 m, and its viscous vaporization degree is lowest.In this paper, the researches will provide the theoretical basis for the low boiling fluid long distance transmission in the field of engineering, and it have high academic significance and engineering application value. |
PDF Full Text Request