Thermal impact induced by the environment in the transport of heavy oils in offshore insulated pipelines: Evaluation of heat transfer

In this work, the non-isothermal transport of heavy oils in offshore insulated pipelines is theoretically analyzed. Here, because heavy oils show poor thermostability in terms of the dynamic viscosity, the evaluation of the two physical phenomena involved in the mentioned process (flow hydrodynamics and heat transfer) must be carried out in a coupled manner. In addition, if the performance of this type of transport system is considered, and a novel numerical approach is employed, the present mathematical formulation allows defining the relationship between flow assurance and the thermal impact induced by certain environmental conditions. The above is the main contribution of this work, which is achieved by obtaining the results considering an eigenvalue condition, and making the numerical scheme a useful tool to determine an adequate thermal shielding. First, the heat transfer in the transport system is estimated for given thermal–hydrodynamic conditions, and then, the numerical algorithm corrects the thermal shielding (insulation thickness) in such a way that the flow rate is preserved. In summary, the main results indicate that, when a section of the pipeline has a deficient thermal shielding, the flow hydrodynamics receives a considerable thermal impact, causing a significant reduction in the flow rate. Instead, when the thermal shielding is improved, the flow rate increases as the heat flux that is emitted by the pipeline to the environment is confined. Unfortunately, introducing a strong thermal shielding along the entire length of the pipeline implies an excessive use of thermal insulation (cost–benefit); therefore, rational and adequate use of thermal insulation barriers is the most appropriate condition. Such a conclusion is demonstrated by comparing the two study cases using the same amount of thermal insulation (value of the Graetz–Nusselt relationship); here, the flow rate increases more than double for the case as the thermal shielding is numerically corrected, in comparison to the case when the thermal insulation thickness is constant.