Heat flux during boiling of superfluid helium inside a porous body based on a two-fluid model

The calculation of the recovery heat flux density is considered for superfluid helium boiling on the cylindrical heater inside porous structure. System of equations is based on the methods of continuum mechanics and molecular kinetic theory. The new type of boundary condition on the vapor-liquid interface based on the two-fluid model is formulated. Heat transfer in a free liquid is described by the Gorter-Mellink semi-empirical theory. Inside the porous structure the processes is discussed by the two-fluid model and filtration equation. Experimental data on the boiling of superfluid helium inside the porous structure are interpreted based on the formulated mathematical model. The qualitative and in some cases quantitative agreement between the calculated and experimental values of the recovery heat flux were obtained in the considered range of parameters

Inertial Effect on Spontaneous Oil-Water Imbibition by Molecular Kinetic Theory

Imbibition is one of the most common physical phenomena in nature, and it plays an important role in enhanced oil recovery, hydrology, and environmental engineering. For the tight reservoirs, the imbibition method has an obvious advantage in fracturing, shut-in, and huff-puff development. Although the current imbibition studies focus on oil recovery, and the inertial effect in imbibition is neglected and its mechanism is also unclear. In this paper, the inertial effect on spontaneous oil-water imbibition at micron-scale is studied by molecular kinetic theory (MKT). The frictional coefficient in the model is a fitted parameter to match the experimental data during the total imbibition process. Then, the simulation of the initial imbibition stage is conducted and the inertial effect on imbibition is identified by the difference between the model considering the inertial effect (CI) and the model neglecting the inertial effect (NI), or by the proportion of inertial force to the total resistance. Results show that (i) with an increase in the water phase viscosity, the inertial effect time shortens, maximum imbibition height and rate decrease, and thus the inertial effect on imbibition weakens; (ii) with an increase in the oil phase viscosity, the inertial effect time changes little, the maximum imbibition height and rate decrease slightly, namely, the inertial effect depends slightly on the oil phase. (iii) with an increase in the capillary wettability (hydrophilicity), the inertial effect time shortens, the maximum imbibition rate first increases and then decreases, and the inertial effect on imbibition weakens. This work sheds light on the inertial effect on oil-water imbibition by MKT, considering the effects of dynamic contact angle, water phase viscosity, oil phase viscosity, and wettabilities, which is helpful to understand the role of inertia in the oil-water or oil-fracturing fluid imbibition process.

Physics: a workshop in Excel

In the workshop, the program codes of user-defined VBA Excel functions are presented; it is shown how these functions are used to solve typical problems of elementary physics on a computer. The textbook includes problems in kinematics, dynamics, statics, molecular kinetic theory, thermal phenomena and electrodynamics. Each chapter includes: brief information on physics; code for one or more user functions and their description; step-by-step solutions to typical problems using user functions, illustrated with drawings of dialog boxes, fragments of worksheets, etc., made using screenshots. Meets the requirements of the federal state educational standards of secondary vocational education of the latest generation. It is intended for students of secondary vocational education institutions studying physics, but it will be useful for anyone who wants to learn how to solve problems in elementary physics at a modern level — on a computer using Excel.

Effect of Dynamic Contact Angle on Spontaneous Capillary-Liquid-Liquid Imbibition by Molecular Kinetic Theory

Summary Imbibition is one of the most common physical phenomena in nature, and it plays an important role in enhanced oil recovery, hydrology, and environmental engineering. The imbibition in a capillary is one of the fluid transports in porous media, and the effect of a dynamic contact angle that changes with the imbibition rate on liquid-liquid imbibition is not clear. In this paper, the molecular kinetic theory (MKT) is used to study the effect of a dynamic contact angle on spontaneous capillary-liquid-liquid imbibition at a micrometer scale. The results show that: Using a scaling time, the effects of various forces in different imbibition systems can be compared, the influence of a dynamic contact angle on imbibition can be characterized by a frictional effect of the three-phase contact line, and the proposed model considering the effect of a dynamic contact angle is better than the model neglecting the effect of a dynamic contact angle. As the displacing phase viscosity increases, the influence of a dynamic contact angle on imbibition strengthens, which is attributed to a decrease in the viscous effect and an increase in the frictional effect during the imbibition process; as the displaced phase viscosity increases, the influence of a dynamic contact angle on imbibition weakens, which is attributed to an increase in the viscous effect and a decrease in the frictional effect during the imbibition process. As the interfacial tension increases, the frictional effect increases, with the result that the effect of a dynamic contact angle on imbibition increases. As the capillary becomes more hydrophilic, the effect of a dynamic contact angle on imbibition becomes stronger because of a decreasing viscous effect and an increasing frictional effect. As the capillary length increases, the viscous effect increases, whereas the frictional effect decreases, leading to a decrease in the dynamic contact angle effect. As the capillary radius increases, the frictional force decreases, whereas its proportion in total resistance or the frictional effect increases, resulting in an increase in the effect of a dynamic contact angle. This work sheds light on the effect of a dynamic contact angle on capillary-liquid-liquid imbibition, including displacing phase viscosity, displaced phase viscosity, interfacial tension, capillary wettability, length, and radius. It will provide new insights into manipulating a capillary imbibition process and provide a fundamental theory for enhanced oil recovery by imbibition in conventional or unconventional reservoirs. Supplementary materials are available in support of this paper and have been published online under Supplementary Data at https://doi.org/10.2118/205490-PA. SPE is not responsible for the content or functionality of supplementary materials supplied by the authors.

The Historical Background: Molecular Theory as of 1900

The task of this chapter is to explain the sense in which molecular theory—both molecular-kinetic theory and chemical-molecular theory—were still viewed as hypotheses as of 1900 and why the evidence bearing on them during the second half of the nineteenth century was insufficient for them to have achieved standing beyond this. The chapter reviews the strengths and limitations of the evidence in question, taking advantage of two widely read textbooks in physical chemistry published in the 1890s by Wilhelm Ostwald and Walther Nernst and a uniquely comprehensive review of the evidence pertaining to the kinetic theory of gases, by O. E. Meyer, published in 1899. This background defines the historical context within physics and chemistry for the developments covered in the remainder of the monograph.

Implications for Molecular-Kinetic Theory

The question in this chapter is what evidential bearing Perrin’s extraordinary findings on Brownian motion have on molecular-kinetic theory without having to assume that his measured kinetic energies match those of molecules in the surrounding liquid. Three possibilities are assessed: (1) they provide a successful test of the claim that Brownian motion is caused by molecular motion; (2) they “ground” molecular-kinetic theory by establishing values for its fundamental parameters; and (3) they add legitimacy to certain hypothetical molecular phenomena through establishing that Brownian motion exhibits counterparts to them. The conclusion in each case is that Perrin’s results provide some evidence, but of less moment than has generally been claimed. The chapter concludes that his results nevertheless do provide conclusive evidence not that molecules exist, but that sustained, highly localized random fluctuations are occurring in the liquid, fluctuations that are incompatible with its acting as a continuum.