Linear Irreversible Phenomenological Characteristics Study Of Energy Flow And Exergy Flow In Waxy Crude Oil Pipeline Transportation

A considerable part of Chinese crude oil is waxy crude oil.Its normal temperature fluidity is poor and rheological property is complex,so it needs to be heated.In the process of oil flow forward transportation,the heat is constantly lost in hot oil pipeline.The wax gradually precipitates and deposits in the pipeline which is dissolved in crude oil.The energy consumption is increased.It brings many difficulties to transportation,which influenced the safe and economic operation of pipelines.Therefore,it is an important problem to pertinently reduce the energy consumption of waxy crude oil pipeline transportation.At present,the analysis and evaluation of energy consumption only focuses on the representation of entropy and exergy.The phenomenological relationship based on the interaction between “flow” and “force” in non-equilibrium thermodynamics is neglected.The multi-field coupling action mechanism for energy flow and exergy flow is also neglected.it is necessary to further reveal the multi-field coupling linear irreversible phenomenological characteristics of energy flow and exergy flow.On the basis of nonequilibrium thermodynamics,the general form of the entropy equilibrium equation is obtained from irreversible field equilibrium equations in the paper.For waxy crude oil pipelines,the entropy production which is irreversibility measurement is transformed into a linear form of "force" and "flow".Comprehensively considering the characteristic temperature in the oil transportation process and the liquid-solid two-phase equilibrium foundation,the entropy production rate formula is deduced according to the energy flow coupled equation and calculation method.By establishing the phenomenological relationship of energy flow,an energy flow transfer multi-field coupling analysis model including energy flow density ratio,energy flow transfer coefficient and energy flow resistance coefficient is proposed.Considering the wax precipitation characteristics of waxy crude oil,an exergy transfer multi-field coupling equation for waxy crude oil pipeline transportation is established,which is combined with the derived phenomenological relations of pressure exergy,thermal exergy and diffusion exergy.Then an exergy transfer multi-field coupling analysis model including potential field driving force,exergy flow density,exergy transfer and coupling coefficients and exergy flow field influencing factors is proposed.Taking an actual pipeline as an example,the influence of pipeline parameters which include pipeline outbound pressure,outbound temperature,pipeline flow and insulation layer thickness on above indicators is calculated.It provides a theoretical basis for energy-saving transportation of crude oil pipelines.