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This article discusses a focused study on visualizing the flow patterns in a two-phase pulsating heat pipe (PHP) using Fe 3 O 4 /water as the working fluid at 3 V/V% concentration. The research also aims to meticulously examine phase change phenomena in the heating section, particularly focusing on bubble formation and expansion processes. A high-speed video camera was utilized to capture dynamic insights into the behavior of the Fe 3 O 4 /water mixture. Based on the findings, a straightforward model was developed to explain bubble generation and growth in the mixture, serving as a useful reference for future PHP designs and optimizations. Visual observations also noted the stable nature of the Fe 3 O 4 /water nanofluid over a 4-day period, confirming its consistency throughout the experiments. Moreover, the impact of heat load variation on the evaporator section was assessed using controlled heat inputs ranging from 10 to 80 W. Observations on the arrangement of slugs and plugs at a 50% filling ratio revealed interesting self-adjusting flow patterns in response to increasing heat inputs, providing valuable insights into PHP operational dynamics. Notably, the oscillatory flow behavior of Fe 3 O 4 /water, the chosen working fluid, exhibited greater activity in comparison to water. This distinctive flow behavior contributed to achieving heightened thermal performance efficiency for the Fe 3 O 4 /water system, attributed to its faster attainment of the annular flow condition.

A MCOHP (micro-channel oscillating heat pipe) can provide lightweight and efficient temperature control capabilities for aerospace spacecraft with a high power and small size. The research about the heat flow effects on the thermal performance of MCOHPs is both necessary and essential for aerospace heat dissipation. In this paper, the heat flow effects on the thermal performance of MCOHPs are summarized and studied. The flow thermal performance enhancement changes of MCOHPs are given, which are caused by the heat flow work fluids of nano-fluids, gases, single liquids, mixed liquids, surfactants, and self-humidifying fluids. The use of graphene nano-fluids as the heat flow work medium can reduce the thermal resistance by 83.6%, which can enhance the maximum thermal conductivity by 105%. The influences of gravity and flow characteristics are also discussed. The heat flow pattern changes with the work stage, which affects the flow mode and the heat and mass transfer efficiency of OHP. The effective thermal conductivity varies from 4.8 kW/(m·K) to 70 kW/(m·K) when different gases are selected as the working fluid in OHP. The study of heat flow effects on the thermal performance of MCOHPs is conducive to exploring in-depth aerospace applications.

Due to the widespread application of new technologies such as increased production and injection, the output of many old wells has improved, but this has also led to varying degrees of sand production. Increased sand production has affected oil well production, increased equipment wear, wellbore plugging, and safety risks. To increase the sand particle transport performance within wellbores, indoor experiments have been conducted to study the sand transport characteristics, transformation relationships, and critical flow velocities for fluid carrying sand. The experimental results indicate that sand particle transport within wellbores can be classified into four modes: stationary, rolling, skipping, and suspended. The flow pattern characteristics of the sand particles were further subdivided into eight categories, and the transformation relationships between these flow patterns were established. Experiments on the critical flow velocities for different grain sizes of sand in inclined wellbores have shown that the fluid velocity required for lifting sand particles is greater than that for rolling and sliding. When the wellbore inclination angle is greater than or equal to 70°, the fluid velocity required for lifting sand particles is approximately 1.9 times greater than that for rolling, and the rolling velocity is approximately 1.6 times greater than that for sliding. In vertical wellbores, the critical velocity for the sand particle suspension is approximately 0.81 times the terminal settling velocity of the sand particles in water. This research provides important scientific evidence for improving and optimizing sand removal techniques in oil wells, as well as a systematic approach and experimental foundation for further studies on sand transport in complex wellbores.

Visual and pressurized pipeline systems with single- and multi-undulation layouts were used to study experimentally and analyze theoretically the transient characteristics of water-air two-phase flow during water fillings in undulation pipelines based on the combination action analyses of both the communicating pipe and the gravity of the water-air two-phase flows in the descending pipe. For the single undulation pipeline, the complex two-phase flow-pattern evolutions including full pipe flow and stratified flow for low, medium, high water-filling velocity cases, respectively, lead to a great difference in transient pressure, flow pattern and the water-filling duration. Especially for low and medium water-filling velocity cases, the hydraulic theories related to hydraulic drop and hydraulic jump were employed to investigate the entrapped air pocket evolutions in the descending pipe, and the mechanism of negative pressure at the top of the undulation pipes was analyzed. For the same multi-undulation pipeline, due to the different elevations of the three undulation points along flow direction, namely three different types of pipeline layout, high-medium-low case (high elevation undulation point, medium one, and low one), low-medium-high and high-low-medium ones, their water-filling durations are significantly different, i.e., approximately 80.02 s, 227.34 s and 617.78 s. Meanwhile, there are significant differences in flow patterns in water filling, namely larger entrapped air pockets in three descending pipes for the high-medium-low case, entrapped air pockets in the first two descending pipes and open channel stratified flow in the last one for low-medium-high case, some bubbles in three descending pipes for the high-low-medium case.

Abstract Interpretation of production logging in oil–water two-phase flow wells is challenging, especially for horizontal wells. The complexity of the distribution of phase and velocity field of multiphase fluid has caused great problems in the measurement of traditional production logging tools, resulting in low interpretation accuracy. To address the challenges, an intelligent production profile interpretation method for oil–water two-phase flow in horizontal wells is proposed. This method uses the multiple array production suite instrument and machine learning algorithm as the core to obtain the production contribution of each layer in the oil well. First, the probability density function method is used to determine the characteristic parameters of capacitance array tool (CAT) data. Then, a support vector machine is used to identify oil–water two-phase flow patterns based on these characteristic parameters. Finally, on the basis of determining the flow pattern, an artificial neural network is used to predict the phase-specific flow rate of oil and water based on the characteristic parameters such as the spinner array tool and CAT. The validity and accuracy of this method are verified by empirical analysis of experimental data. Research shows that the method has good application prospects, and can be adjusted for stable reservoir production and development to provide strong technical support.

The liquid-gas two-phase flow in rock fractures is of great significance for oil and gas field development, groundwater pollution control and underground nuclear waste disposal. In this study, liquid-gas two-phase flow experiments under different liquid and gas flow rates were carried out on a self-developed transparent-plate fracture apparatus with liquid-gas two-phase flow. Typical liquid-gas two-phase flow patterns, i.e., bubble flow, fingering flow and annular flow, were obtained. The relationship between the relative permeability and phase saturation indicates obvious inter-phase interference between the liquid and gas phases. The mesoscopic flow characteristics of bubbles under different flow patterns are obtained. With the change of flow pattern, the phenomena of bubble merging and dispersion occur, resulting in area fluctuation, and the actual flow velocity of the gas phase in the fracture is greater than the “nominal” flow velocity. Based on the generalized Darcy’s Law, a surface tension model for liquid-gas two-phase flow in a smooth parallel-plate fracture was proposed, which can well reflect the effect of surface tension between the liquid and gas and the inter-phase interference. Based on the experimental data, it is verified that the surface tension model has a better description of the relative permeability variation compared with other classical two-phase flow models. Finally, the connection between mesoscopic and macroscopic flow characteristics is analyzed and discussed. Furthermore, surface tension correction factors are proposed to represent the effect of surface tension on the inter-phase interference in the fracture.

As an important component of the deep tunnel drainage system for dealing with urban waterlogging, the rotating stepped dropshaft has been proposed due to its small air entrainment. However, the hydraulic characteristics inside the shaft still need to be fully studied. In this study, the flow patterns, water velocity, and pressure in the rotating stepped dropshaft under different flow rates and geometric parameters were studied using a three-dimensional numerical model. The results show that increasing the central angle of the step and reducing the step height can both reduce the terminal velocity. A theoretical formula for predicting the terminal velocity was established and well validated. The connection between the shaft and the outlet pipe poses a severe threat to the structural safety due to alternating positive and negative pressures. Wall-attached swirling flow generates a circular high-pressure zone at the bottom of the dropshaft and the larger the flow rate, the greater the pressure gradient at the center of the bottom. By using the momentum theorem and considering the impact pressure range of the swirling flow, the shaft bottom pressure can be predicted reasonably well.

A high-speed backlight system was adopted to investigate the evolution process of the inside-out-gas (IOG) effervescent atomizer and subsequent influence on spray morphology. The results show that bubble flow and annular flow are the most obvious flow patterns when the liquid flow rate is 20 g/s. During the transition from bubble to annular flow, slug flow occurred at gas–liquid mass ratio (GLR) of 3.2%. The annular flow was observed when the GLR further increased to 6.4%. In particular, when the mixing chamber is in a large bubble flow, an annular flow can still be formed at the orifice for the small exit diameter. For the annular flow, a relatively stable spray cone angle was observed. On the contrary, the slug flow has a greater oscillation for the spray cone angle. It was found that bubble flow in the orifice has little effect on atomization effect. For the spray cone angle, the oscillation in the slug flow is larger. Furthermore, the effects of GLR and liquid injection pressure drop are carefully considered in the empirical formula fitting compared to the widely used empirical formula. The empirical formula of the discharge coefficient of the effervescent atomizer is fitted, which provides fast data support for engineering applications.

Liquid hydrogen storage and transportation is an effective method for large-scale transportation and utilization of hydrogen energy. Revealing the flow mechanism of cryogenic working fluid is the key to optimize heat exchanger structure and hydrogen liquefaction process (LH2). The methods of cryogenic visualization experiment, theoretical analysis and numerical simulation are conducted to study the falling film flow characteristics with the effect of co-current gas flow in LH2 spiral wound heat exchanger. The results show that the flow rate of mixed refrigerant has a great influence on liquid film spreading process, falling film flow pattern and heat transfer performance. The liquid film of LH2 mixed refrigerant with column flow pattern can not uniformly and completely cover the tube wall surface. As liquid flow rate increases, the falling film flow pattern evolves into sheet-column flow and sheet flow, and liquid film completely covers the surface of tube wall. With the increase of shear effect of gas-phase mixed refrigerant in the same direction, the liquid film gradually becomes unstable, and the flow pattern eventually evolves into a mist flow.