| Most of the crude oil produced by China is featured by its high viscosity,high wax content and high condensation point. The transportation of crude oil cann't be achieved by the means of isothermal transportation. The most common way is to transport crude oil with it exposed to heat.The ceaseing will inevitably appear during the operation of hot oil pipeline, due to natural disasters, the power failure of oil land and oilstolen, and so on. In recent years,the the problems about oil production reduction and pipelines Aging in the east of China were becoming More and more serious , the number of shutdown increased Obviously ,which Seriously affected the safe operation of pipeline . Condensate tube was likely to happen if it was left untreated or mismanaged, The temperature drop and parameter variation are needed in order to assure the pipeline runs economically and safely. And they also guide the determination of safe ceaseing time, the proposal of restart program and the maintenance plan.The numerical solving to the unsteady state of heat transfer after hot oil pipeline's ceaseing is developed, and the program for solving differential equations is coded, and the work of the following aspects are mainly developed in this paper.(1)The physical model of crude oil temperature drop after ceaseing is established, the influence of axial temperature drop is neglected, and the factors such as wax precipitation of crude oil and physical property changing with temperature drop are considered in this paper.Based on the research of predecessors, the governing equation of coupling flowing in pipeline, which is unstable and physical property variable, is deduced,meanwhile, the mathematic model of heat and flowing where air, pipeline and crude oil are coupling, is derived, via Law of conservation of mass, law of conservation of momentum and law of conservation of energy.(2)Contrlo volume method was adopted in the calculation, the calculation programme was derived based on two-dimensional staggered mesh, SIMPLE algorithm was used to couple pressure and velocity,and TDMA was adopted to solve the algebraic equations group at last.(3)The computing result was compared with the measured value,we can know that: the average absolute error about simulation results and experimental measurements was less than 0.6℃, It is also showed by the results that the mathematical model of analog computation and its outcomes can well reflect the engineering practice .The conclusion about numerical simulation can be summaried as follows:(1)In the temperature drop process, the rate of temperature drop both tube wall or tube core was fastest when oil temperature was higher than wax precipitation temperature; it was slowest when oil temperature was lower than wax precipitation temperature;it became rise when oil lost mobility.(2)The center of Temperature field rose because of Natural convection, The highest temperature was not at the center of a circle, but on the upper side of it. With the temperature drop, natural convection in a pipe gradually weakened , The center of Temperature field moved toward the center of a circle .(3)The temperature field and velocity field is symmetrical on the vertical direction, but not on the horizontal direction, which is caused by natural convection. When the pipe radiuses are equal at the same time,the value of temperature and velocity is the biggest at the angle of 90 degrees, and it is less at the angle of 0 degrees,and it is the least the angle of -90 degrees.The physical model and mathematical model established in this paper ,as well as the numerical solving method used here, all provide reference to further study of heat transfer mechanism of hot oil pipeline after ceaseing. the solution provides technical support for the pipeline's safe,economical and steady operation. |
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