Contact angle hysteresis is a basic phenomenon in many industrial applications, such as material surface engineering and enhanced oil recovery. The mechanism of continuous change of the contact angle during hysteresis is not well understood and described, and it is also important to predict advancing and receding angles by the Young contact angle and surface roughness. In this work, a contact angle hysteresis model is developed based on several metastable contact angle models. The fraction difference between gas and liquid prefilling the solid grooves is assumed to be variable, so is the fraction difference of gas and liquid displaced by the other phase. Besides these two newly introduced variables, the solid area fraction, the ratio of the real surface area to the projected surface area, and the Young contact angle together influence the advancing and receding angles. Energy input or work is the external cause of hysteresis. The new variables are the intrinsic cause of hysteresis, enabling the continuous change of the contact angle and ensuring a minimal surface energy during hysteresis. The advancing and receding angles are explicitly expressed in a function of the factors mentioned above. The results from this model are in good coincidence with experiments from the literature. Through comparison, it is found that the model in this paper can be reduced as the Wenzel model, Cassie−Baxter model, etc., under special conditions.

Mastering the breakthrough process and predicting the breakthrough pressure in partially saturated porous media (PSPM) are crucial for evaluating the sealing ability of reservoir caprock to hydrocarbon, CO 2 , radiation, etc. An accurate model for predicting the breakthrough pressure in PSPM has not been put forward since the characteristic of the breakthrough point in PSPM is still mystified. In this paper, a microvisualization experimental system was set to capture gas−liquid displacement images in partially saturated glass planar pore networks (glass-PPNs) in real time. Breakthrough pressures and capillary pressures were measured by a step-by-step method. The measured capillary pressure curves (CPCs) were consistent with the van Genuchten model. The experimental results manifested that the inflection point of the CPC in PSPM characterizes the breakthrough point. Moreover, the effect of initial wetting phase saturation (IWPS) on breakthrough pressure was analyzed. The breakthrough pressure increases with the increasing IWPS at first. After achieving a specific level, IWPS exerts a weak influence on the breakthrough pressure, which is finally asymptotical to a maximum value. An asymptotic model was proposed to describe the law of breakthrough pressure with IWPS. Compared with the exponential model, the asymptotic model shows to be better consistent with other breakthrough pressure experiment results in partially saturated three-dimensional (3D) cores. Moreover, the theoretical expression of the asymptotic model when IWPS = 1 was derived based on the above inflection point theory and the porous media capillary bundle hypothesis.

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Bolted joints are broadly used in various industrial products. Especially in chemical engineering, the reliability of bolted joints can have a significant influence on the safety of chemical systems. In some fields, such as liquefied natural gas (LNG) industry, equipment usually works in low temperature (−162°C). Different materials with various thermal expansion rates are usually used in bolted joints; Therefore the preload and stress distribution of bolted joints in low temperature can change apparently due to the different axial and radial thermal deformation. If the preload design in normal temperature is inappropriate, the bolted joints may either encounter relaxation or over-tightening in working temperature. In this study, a theoretical analysis is proposed in order to evaluate the appropriate preload selection of bolted joints work in low temperature. FE analysis is made to examine the accuracy of the theoretical formula. The result shows that the error is less than 10% in most cases. The stress distribution on the bolt thread region is studied and the result shows that the maximum tensile stress on the bolt thread region is much higher than in non-thread region. Availability and safety should be both considered in preload selection of bolted joints working in low temperature. Finally the effect of radial thermal deformation difference is discussed when the thermal expansion rate difference is high. The effect of radial thermal deformation difference should not be neglected in some cases.