Theoretical evaluation of dilution processes versus thermal effects induced on the transport of heavy oil

In the present work, the dilution mechanism is investigated as an option to avoid considerable flow reductions in the non-isothermal transport of heavy oils (high-viscous fluids). In this case, we assume that environmental conditions can imply appreciable thermal effects in such flows; thus, to perform an appropriate analysis, the governing equations must be modeled considering the behavior of the dynamic viscosity as a function of the temperature and composition of the fluid. To evaluate the above, the non-isothermal transport of a heavy oil along buried pipelines is analyzed, it represents a good engineering example, given that, millions of crude oil barrels are transported daily using pipeline networks. In these systems, heat transfer processes and the flow hydrodynamics work in a coupled manner due to the thermal dependence of the fluid viscosity; in addition, the present formulation is extended to include the influence of the fluid composition as a part of the study. In summary, the main results in this work allow estimating how the dilution mechanism can mitigate all thermal effects induced by the environment, which are responsible for the changes in the volumetric flow rate when the non-isothermal condition is considered. Moreover, the theoretical formulation reveals that this type of engineering application represents a version of the Graetz–Nusselt problem; where, for values of Gz∕N̄_u≪1, the thermal effects dominate the flow hydrodynamics and the dilution mechanism is inefficient, obtaining a relatively small improvement in the volumetric flow rate. Conversely, for values of Gz∕N̄_u≫1, the dilution mechanism controls the flow hydrodynamics, resulting in an exponential increment in the volumetric flow rate. Clearly, for the case of Gz∕N̄_u∼1, both the dilution mechanism and thermal effects dispute the control of the flow hydrodynamics. Thus, we can infer that by using together an adequate thermal insulation and a good handling of the dilution mechanism, heavy oils can be transported through conventional pipelines even under unfavorable environmental conditions.