Although nano- and micro-scale phenomena for fluid flows are ubiquitous in tight oil reservoirs or in nano- or micro-sized channels, the mechanisms behind them remain unclear. In this study, we consider the wall–liquid interaction to investigate the flow mechanisms behind a compressible liquid flow in nano- or micro-sized circular tubes. We assume that the liquid is attracted by the wall surface primarily by the Lifshitz–van der Waals (LW) force, whereas electrostatic forces are negligible. The long-range LW force is thus introduced into the Navier–Stokes equations. The nonlinear equations of motion are decoupled by using the hydrodynamic vorticity-stream functions, from which an approximate analytical perturbation solution is obtained. The proposed model considers the LW force and liquid compressibility to obtain the velocity and pressure fields, which are consistent with experimentally observed micro-size effects. A smaller tube radius implies smaller dimensionless velocity, and when the tube radius decreases to a certain radius R_m, a fluid no longer flows, where R_m is the lower limit of the movable-fluid radius. The radius R_m is calculated, and the results are consistent with previous experimental results. These results reveal that micro-size effects are caused by liquid compressibility and wall–liquid interactions, such as the LW force, for a liquid flowing in nano- or micro-sized channels or pores. The attractive LW force enhances the flow’s radial resistance, and the liquid compressibility transmits the radial resistance to the streaming direction via volume deformation, thereby decreasing the streaming velocity.

Although microscale phenomena are ubiquitous in fluid flow through nano- or microsized channels and pores, the mechanisms remain unclear. To clarify these mechanisms, we investigate herein Bingham-plastic liquids with electroviscous effects (EVEs) in nano- and microsized circular tubes. The constitutive equation and electroviscous forces are introduced into the governing equations, and approximate analytical solutions are obtained. Velocity reduction results from the combined effects of the Bingham characteristics and EVEs. The Bingham behavior reduces the strength of the EVE electric field, and EVEs increase the width of the flow core. The dimensionless average velocity decreases as the tube radius decreases and goes to zero upon approaching the lower limit of the movable fluid radius (R_m). As the pressure gradient decreases, the average velocity first decreases linearly, then decreases nonlinearly in a concave shape, and finally approaches zero as the pressure reaches the threshold pressure gradient (TPG). The Bingham plastic behavior causes both the R_m and the nonlinear flow with TPG, and R_m is still caused by the van der Waals forces under liquid compressibility more obviously. The EVE parameters only affect the degree of nonlinearity when the liquid exhibits Bingham-plastic behavior. These results are consistent with experimentally observed de-ionized water flowing in microscale silica tubes. We infer that the Newtonian fluid displays the Bingham-plastic behavior in nano- or microsized channels in what we call “microscale effects.” These results elucidate the mechanism that leads to nonlinear or low-speed non-Darcy flow in nano- or microsized channels and pores from the liquid characteristic and liquid-solid interaction.

The uniformity of hot air flow inside the airflow dryer not only affects the moisture distribution at the outlet, but also affects the quality of the product. Based on the guide plate structure of the SH23A airflow tobacco dryer, a gradient curved guide plate dryer is designed, and the flow field distribution of the dryer is numerically investigated under different flow distribution conditions at the hot air inlet and flue gas inlet. The results show that the airflow uniformity is affected by the flow distribution at the inlet of the heated air and the inlet of the cigarette smoke, the structure of the guide plate, etc., the non-uniformity coefficient decreases with the increase of hot air inlet flow rate. The non-uniformity coefficient of tapered arc deflector decreases by 9–12 %.