Study On Fluid-solid Two-phase Flow And Heat Transfer Characteristics In A Coil Wire Inserted Tube

With the development of the technology of heat transfer enhancement in heatexchanger, the composite enhanced heat transfer technology of spiral inserts and fluid-solidtwo-phase realizes two effects including heat transfer enhancement, fouling removal andpreventing, which will have great prospect in engineering application. Based on theory,numerical simulation, experiment and application, the analysis of flowing and heat transferproblems has been done to research the influence of spiral inserts on the liquid-solidtwo-phase flow. Meanwhile the characteristic of fouling removal and preventing has alsobeen analyzed. The main contents are as follows:First of all, based on the brief analysis of trends and status of heat transferenhancement on heat exchanger, the condition of development of heat transfer enhancementon the liquid-solid two-phase flow at home and abroad, numerical simulation and testingmethods are summarized. The application and research status at home and abroad of theDEM-CFD coupling methods on the liquid-solid two-phase flow has been generalized.Further more, the ideas and solutions are put forward in the paper.Secondly, the basic principle of discrete element method has been introduced. Thedynamic model of the collision of particles in the liquid-solid two-phase flow is analyzed,including the selection of particle model, the judgment of particle contact, the analysis ofmodel and the equation of particle motion.Thirdly, the influence of spiral inserts on the liquid-solid two-phase flow is simulatedby Fluent-DEM coupling methods. The law of heat transfer enhancement among blanktubes, tubes with spiral inserts, tubes added solid particles and a combination of both isanalyzed comparatively. Based on the analysis of orthogonal factor, Influence of the outerdiameter of helix, particle concentration on heat transfer and pressure drop in the pipesection has been researched. Based on speed and direction of movement of particles, themovement of solid particles in the fully developed region of fluid, the collision frequency ofparticles-particles, particles-wall and the contact force of particle-wall. The micro influenceof particles on the enhancement of heat transfer is analyzed in this multiple technology ofenhancement of heat transfer.Fourthly, according to the theory of heat transfer and fluid mechanics, designcomposite interpolation spiral liquid and fluid-solid two-phase flow heat transfer experimentscheme. The effect of heat transfer and flow was considered in the model by interaction offluid-solid; the effect of heat transfer in blank tubes, tubes with spiral inserts, tubes addedsolid particles and a combination of both were compared. From the experiment result, heat transfer can be effectively enhanced for coil wire and add particles unified, the walltemperature can be reduced and induction period of fouling can be extended.Comprehensive the numerical simulation and experiment research for coil wireinserted and add particles can be discover that journey of fluid flow was increased, particlescan be more closely to the wall, boundary layer of flow and temperature were disturbanced,the turbulence intensity was increased, at the same time the heat transfer received a shearforce from fluid. These factors comprehensive effect made the Nusselt number of bothunified is the largest compared with smooth tube, coil wire insert and add particles. So theheat transfer technology of both unified has the extensive prospect.