No abstract

This paper presents a full set of numerical methods for predicting the effective thermal conductivity of natural fibrous materials accurately, which includes a random generation-growth method for generating micro morphology of natural fibrous materials based on existing statistical macroscopic geometrical characteristics and a highly efficient lattice Boltzmann algorithm for solving the energy transport equations through the fibrous material with the multiphase conjugate heat transfer effect considered. Using the present method, the effective thermal conductivity of random fibrous materials is analyzed for different parameters. The simulation results indicate that the fiber orientation angle limit will cause the material effective thermal conductivity to be anisotropic and a smaller orientation angle leads to a stronger anisotropy. The effective thermal conductivity of fibrous material increases with the fiber length and approach a stable value when the fiber tends to be infinite long. The effective thermal conductivity increases with the porosity of material at a super-linear rate and differs for different fiber location distribution functions.

Electroosmotic flow (EOF), a consequence of an imposed electric field onto an electrolyte solution in the tangential direction of a charged surface, has emerged as an important phenomenon in electrokinetic transport at the micro/nanoscale. Because of their ability to efficiently pump liquids in miniaturized systems without incorporating any mechanical parts, electroosmotic methods for fluid pumping have been adopted in versatile applications—from biotechnology to environmental science. To understand the electrokinetic pumping mechanism, it is crucial to identify the role of an ionically polarized layer, the so‐called electrical double layer (EDL), which forms in the vicinity of a charged solid–liquid interface, as well as the characteristic length scale of the conducting media. Therefore, in this tutorial review, we summarize the development of electrical double layer models from a historical point of view to elucidate the interplay and configuration of water molecules and ions in the vicinity of a solid–liquid interface. Moreover, we discuss the physicochemical phenomena owing to the interaction of electrical double layer when the characteristic length of the conducting media is decreased from the microscale to the nanoscale. Finally, we highlight the pioneering studies and the most recent works on electro osmotic flow devoted to both theoretical and experimental aspects.

Spontaneous imbibition of fracturing fluid into shale matrix is one of the primary reasons for the low flowback rate in shale gas wells after the hydraulic fracturing. This leads to concerns of impacts on both environment and shale gas production. A direct pore‐scale simulation is crucial to gain a deep understanding of spontaneous imbibition behavior and its impacts. The porous structures in the shale matrix are characterized by not only a geometrical complexity but also a mixed wettability, which bring great challenges to simulation methods. An improved pseudo‐potential lattice Boltzmann method is proposed to simulate the spontaneous imbibition behavior in a reproduced three‐dimensional porous structure of shale. The results show that the nanoscale hydrophilic pores provide the driving force and a storage place for the residual treatment fluid. The pore size and wettability heterogeneity lead to the nonuniform menisci propagation and fracturing fluid distribution in the model. Specifically, the fracturing fluid imbibed quicker in the larger pores at the early stage and gradually migrated into the smaller pores during the process. With a limited volume of the fracturing fluid, a portion of the larger pores was finally reopened. The analysis of saturation and apparent gas permeability data during the spontaneous imbibition process showed a great recovery of the model permeability along with the reopened pores. These results provide direct evidence of the residual fracturing fluid migration pattern in the shale reservoir and its influence on shale gas production.