Abstract
For new submarine hot oil pipelines, accurate simulation of preheating is difficult owing to complex transient flow and coupled heat transfer happening. Using quasi-steady equations to simulate preheating is inadequate as the hydraulic transient phenomenon is neglected. Considering this fact, this paper constructs an unsteady flow and heat transfer coupled mathematical model for the preheating process. By combining the double method of characteristics (DMOC) and finite element method (FEM), a numerical methodology is proposed, namely, DMOC-FEM. Its accuracy is validated by field data collected from the Bohai sea, China, showing the mean absolute percentage error (MAPE) of 4.27%. Simulation results demonstrate that the preheating medium mainly warms submarine pipe walls rather than the surrounding subsea mud. Furthermore, during the preheating process, the equivalent overall heat transfer coefficients deduced performs more applicably than the inverse-calculation method in presenting the unsteady propagation of fluid temperature with time and distance. Finally, according to the comparison results of 11 preheating plans, subject to a rated heat power and maximum flow, the preheating parameter at a lower fluid temperature combined with a higher flow rate will produce a better preheating effect.
Highlights
Driven by the progressive exploration of offshore oil fields, the construction speed and total mileage of submarine crude oil pipelines have been dramatically accelerated per year [1,2]
With the employment of annular thermal influence regions, Xing [7] established a coupled heat transfer model for crude oil pipeline commissioning and proposed an finite difference method (FDM) and finite volume method (FVM) combined methodology to solve the temperature of fluid, pipe walls, and soil
The modeled new submarine hot oil pipeline is buried in the Bohai sea, China
Summary
Driven by the progressive exploration of offshore oil fields, the construction speed and total mileage of submarine crude oil pipelines have been dramatically accelerated per year [1,2]. With the employment of annular thermal influence regions, Xing [7] established a coupled heat transfer model for crude oil pipeline commissioning and proposed an FDM and FVM combined methodology to solve the temperature of fluid, pipe walls, and soil. By combining the fluid temperature model with differential equations of unsteady heat conduction, the studies mentioned have established the basic resolving thoughts for preheating submarine hot oil pipelines. It is necessary to establish a computing expression of the overall heat transfer coefficient for submarine hot oil pipelines based on an unsteady-state model. In this way, the operational status of subsea pipelines and transient thermal propagation can be described. Based on the designed scenario, an optimization of preheating parameters is performed at the end of this paper
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