The Analysis Of Influencing Factors On Medium Temperature Field In Overhead Pipe During Shutdown Process

During the process of shutdown for overhead pipeline，the heat is transported from themedium to the environment. With the drop of the medium temperature in pipe，the wax crystalappears, releasing latent heat. When the tempertature dip under freezing point，crude oilgelatinizes. With the development of shutdown，the thickness of congealable oil，which leadstothe flow area decrease in pipe and the restart pressure increase，even though the restart isfailed and has condensate pipe accidents. Therefore，it has significant theoretical andapplication value to study the transformation law of the medium temperature field in pipe，analysis the influencing factors sensibility and determine solidification interface position.This paper studied on the heat transfer in overhead pipe for shutdown, supplied thephysic model for overhead pipe with hot oil. Taking latent heat of wax crystallization intoaccount, the partitioning method mathematical model was adopted, energy conservationequations were established respectively in solid and liquid phase areas，and used fluentsoftware for simulation. For the temperature drop of oil in pipe center, comparing thesimulation results with existing experimental data, the maximum relativeerror is3.14%,which verified the model and solving method were right. Because of the influence of naturalconvection heat transfer，condensate oil appears firstly in the lower end of the pipeline.Circumferential condensate reservoir thickness was different, liquid oil center located abovethe center of pipeline. This paper simulated medium velocity field in pipe to determine fluidvelocity in pipeline within shutdown different stages, determined the strength of the naturalconvection heat transfer by contrasting velocity variation, and analysis the heat transferprocess of natural convection to the conduction. The influence of factors on temperaturefield in pipe for shutdown was quantitatively analyzed, which included environmental factors(eg.the atmospheric setting vaule, temperature cyclical changes in a day, air speed), pipediameter and insulation conditions, the initial conditions of shutdown(eg.initial temperature ofshutdown, the thikness of wax in pipe), physical property of crude oil(eg.density, heatconductivity coefficient，specific heat capacity，viscosity)，and the sensibilities were analyzed.The results showed that the effect of viscosity can be ignored. The transformation law of themedium temperature field in pipe was analyzed, with the shutdown development, condensateoil reservoir continuously moved inward and the last freezing point position is above thecenter of pipe.