Flow In Small Channels Research Articles

Energy-saving, high-pressure resistant mini valve based on a bistable electromagnetic actuator

As core components of microfluidic and wearable pneumatic electronic systems, mini valves are attracting a growing intellectual interest. However, most existing mini valves exhibit either excessive energy consumption or limited flow rate and holding pressure. To address these issues, this study proposes an energy-saving mini valve with large flow rate and high holding pressure. The implementation of electromagnetic bistable structure allows the valve to remain open or closed without energy consumption. In contrast to the small and intricate flow channels seen in conventional mini valves, the straight-through flow channel design with reduced flow resistance improves its flow rate properties. And the pressure resistance characteristics are enhanced by the use of permanent magnetic attraction for sealing. Furthermore, the valve is driven by a single coil to switch between two steady states, resulting in a more compact structure. We have developed valve prototypes with diameters of 10 mm and 6 mm. Performance evaluation tests have shown that it sustains a holding pressure as high as 100 kPa and a flow rate of 1.5 L/min (@ 3 kPa), while only expending an energy of 0.37 J during switch transitions. Given these attributes, this valve demonstrates significant potential for integration within wearable pneumatic electronic systems.

Advanced ultrasound techniques for studying liquid–liquid dispersions in confined impinging jets

Advanced ultrasound techniques were used to study liquid–liquid dispersed flows formed in impinging jets confined in small channels. Ultrasound speed and attenuation coefficient spectra of the propagated sound waves were used to obtain volume fraction and drop size distributions, respectively. The results were compared against drop size distributions obtained with high-speed imaging. Experiments were conducted in a 2 mm internal diameter tube for both kerosene oil continuous and glycerol/water continuous dispersions. The overall mixture flow rate was set at 60 ml/s, and the dispersed phase fractions were 0.02, 0.05, and 0.10. The measured volume fractions were found to be very close to the input ones, indicating a very small slip between the phases in the dispersed flows. From the ultrasound measurements, the drop size distributions were found to range from 32 to 695 μm under the different conditions used. The drop sizes at the two low input volume fractions were in reasonable agreement with the results from the imaging. Imaging, however, could not be used for the 0.10 input dispersed phase fraction. These results demonstrate the applicability of the ultrasound techniques to measurements in dispersed liquid–liquid flows in small channels.

Dissolution behavior of different lubricating oils in liquid and supercritical CO2

In deep drilling, lubrication and cooling tremendously affect drill life and machining quality. In this work, we investigate on the cryogenic Minimum Quantity Lubrication (cMQL) with oil and liquid or supercritical CO2. In the drilling process, both fluids are conducted through small flow channels inside the drill to the cutting edge. For a stable process, single-phase conditions are required. Systems of five different lubricants with carbon dioxide are investigated at 25 °C, 40 °C and 60 °C. Investigations are made optically in a view cell at pressures between 60 bar and 300 bar and quantitatively between 60 bar and 250 bar using the static-analytical method. For the application, information on the mixing kinetics of the oils and CO2 is further required. To get an insight into the flow behavior under pressure, an optically accessible flow duct is presented that resembles the conditions in the real drilling process.

A New Flow Pattern Identification Method for Gas–Liquid Two-Phase Flow in Small Channel Based on an Improved Optical Flow Algorithm

A New Flow Pattern Identification Method for Gas–Liquid Two-Phase Flow in Small Channel Based on an Improved Optical Flow Algorithm

Influence mechanism and optimization of the plugging capacity of temporary plugging zones with different particle sizes based on pore structure

Reducing the temporary plugging zone permeability is the key to the success of temporary plugging and diverting fracturing. The pore structure of the plugging zone determines the permeability of the temporary plugging zone. This paper introduces a new method based on micro-computed tomography (micro-CT) to quantitatively characterize the pore structure of temporary plugging zones with different particle size. The permeability of temporary plugging zone was measured, and seepage simulation was carried out based on pore network model (PNM). The particle compound method and formula were proposed to reduce the permeability of the temporary plugging zone. Finally, a permeability prediction model of temporary plugging zone based on pore structure was established. The results show that the porosity and tortuosity of the temporary plugging zone are independent of particle size under natural accumulation, and the pore radius decreases with the decrease in particle size. After compaction, the pore structure of the temporary plugging zone changes more obviously with smaller particle size. The seepage simulation shows that the number of flow channels in the temporary plugging zone formed by 2–3 mm particles is only 23.5% of the 0.6–1 mm flow channels. However, several obviously dominant channels are found in the 2–3 mm particles, resulting in a higher permeability. The 0.6–1 mm particles are used to fill the pores formed by 2–3 mm particles so that the dominant channel is divided into several small flow channels to significantly decrease the permeability of the 2–3 mm particles. When 2–3 mm and 0.6–1 mm particles are mixed according to the established particle size recombination formula, the pore radius and permeability of the temporary plugging zone decreased by 42.3% and 53.2% compared with 2–3 mm particles. The permeability prediction model can predict the permeability of temporary plugging zone well, and the average error is 9.145%. The sample preparation methods, pore structure testing and permeability prediction model were established in this work, providing a new method for the selection and design of temporary plugging agents.

A New Contactless Cross-Correlation Velocity Measurement System for Gas–Liquid Two-Phase Flow

Based on the principle of Contactless Conductivity Detection (CCD), a new contactless cross-correlation velocity measurement system with a three-electrode construction is developed in this work and applied to the contactless velocity measurement of gas–liquid two-phase flow in small channels. To achieve a compact design and to reduce the influence of the slug/bubble deformation and the relative position change on the velocity measurement, an electrode of the upstream sensor is reused as an electrode of the downstream sensor. Meanwhile, a switching unit is introduced to ensure the independence and consistency of the upstream sensor and the downstream sensor. To further improve the synchronization of the upstream sensor and the downstream sensor, fast switching and time compensation are also introduced. Finally, with the obtained upstream and downstream conductance signals, the velocity measurement is achieved by the principle of cross-correlation velocity measurement. To test the measurement performance of the developed system, experiments are carried out on a prototype with a small channel of 2.5 mm. The experimental results show that the compact design (three-electrode construction) is successful, and its measurement performance is satisfactory. The velocity range for the bubble flow is 0.312–0.816 m/s, and the maximum relative error of the flow rate measurement is 4.54%. The velocity range for the slug flow is 0.161 m/s–1.250 m/s, and the maximum relative error of the flow rate measurement is 3.70%.

Response Characteristics of Contactless Impedance Detection (CID) Sensor on Slug Flow in Small Channels: The Investigation on Slug Separation Distance.

In recent years, CID sensors have displayed great development potential in parameter measurement of gas-liquid two-phase flow in small channels. However, the fundamental/mechanism research on the response characteristics of CID sensors is relatively insufficient. This work focuses on the investigation of the influence of separation distance between slugs on the impedance (real part, imaginary part and amplitude) response characteristics of slug flow in small channels. Experiments were carried out with the CID sensors in four small channels with inner pipe diameters of 1.96 mm, 2.48 mm, 3.02 mm and 3.54 mm, respectively. The experimental results show that for a CID sensor, the slug separation distance has significant influence on the impedance response characteristics. There is a critical value of slug separation distance. When the slug separation distance is larger than the critical value, the impedance response characteristics of each slug can be considered independent of each other, i.e., there is no interaction between the slugs. When the slug separation distance is less than the critical value, the impedance response characteristics show obvious interaction between the slugs. It is indicated that the ratios of the critical values to the pipe inner diameters are approximate 100.

Electrical Impedance Characteristics of Slug Flow in Small Channels and its Application to Void fraction Estimation

This work focuses on the electrical impedance characteristics of slug flow in small channels and its potential on the void fraction estimation. Experiments are carried out with a new contactless impedance detection (CID) sensor in four small channels (1.48mm, 2.02mm, 2.54mm and 2.98mm i.d.). The experimental results show that in small channels there exists scale effect. With the increase of the inner diameter, for the relationships between the imaginary/amplitude part and void fraction, there exist monotonic and regular dispersions. The slug velocity is the root of the regular dispersion and has significant influence on the relationship between the imaginary/amplitude part and void fraction. With the investigated impedance characteristics, void fraction estimation models are developed. The void fraction estimation experimental results indicate that using the imaginary part and the amplitude are effective approaches to realize void fraction estimation in small channels and satisfied estimation performance could be expected.

Three-dimensional modeling study of all-vanadium redox flow batteries with the serpentine and interdigitated flow fields

• A comprehensive 3-D VRFB model with different flow fields is proposed. • The SFF with smaller channel and rib widths enhances the mass transfer in the carbon paper electrodes. • The performance of the carbon paper-based VRFBs is more sensitive to channel width than rib width. A comprehensive three-dimensional (3-D) model is developed to study the performance of all-vanadium redox flow batteries (VRFBs) with both serpentine flow field (SFF) and interdigitated flow field (IFF) by using 9 cm 2 carbon paper electrodes. Thanks to the induced stronger electrolyte convection in the electrodes, the batteries with SFF have better performance than IFF, though SFF may cause a higher pressure drop, especially at high flow rates. The effect of flow field geometry of SFF on the battery performance is further studied. Decreasing the channel depth of SFF enhances the mass transfer of electrolytes in the electrode, and the battery performance is more sensitive to the change of channel depth at high current densities. In addition, the battery performance declines with the increase of SFF channel width and rib width, and the influence of channel width is more pronounced than that of rib width. Reducing the rib width increases the electrolyte convection in the electrode more evidently for SFF with a wider channel while avoiding an excessive increase in pressure drop. Therefore, in the case of high current density or low electrolyte flow rate, the SFF with small flow channel depth and small rib width is conducive to improving the performance of VRFBs.

Significant Differences in the Value of the Void Fraction in Various Types of Low-Viscosity Two-Phase Flow Patterns in Capillary Tubes with a Particular Slope

A two-phase flow is the simplest form of multi-phase flow. Two-phase flow has basic parameters, including flow behavior, flow pattern, void fraction, pressure gradient, or pressure drop. The development and application of fluid flow in small channels (mini and micro) are in the Micro Electromechanical System (MEMS). In general, the application of two-phase flow can be found in various applications in the industrial world, such as boilers, cores, and steam generators in nuclear reactors, petroleum transportation, electronic cooling, and different other types of chemical reactors. One of the most common challenges is void fractions and flow patterns in horizontal and vertical pipelines. The purpose of this study was to find out the significant difference in the characteristic value of fundamental parameters, primarily void fractions and flow patterns that occur in capillary pipes with a slope of 15o to horizontal. The fraction value and shape of this flow pattern are essential because it determines the pressure drop value, which means determining the level of danger that can occur if the pressure drop value reaches the extreme value. The fluid used a mixture of air-water and glycerin with 0, 10, 20, and 30% concentrations. To determine the void fraction is used digital image processing method with MATLAB R2014a application. A 1200 fps high-speed camera and 640 x 480-pixel resolution are used for video shooting. The experiment was conducted at superficial gas (JG) velocities of 0.025 - 66.3 m/s and superficial fluid velocities (JG) intervals of 0.033 – 4.935 m/s. The experiment results showed a significant difference between the void fraction value for the bubbly flow pattern and the churn flow pattern, which has not been widely discussed in previous studies. The analysis concluded that the higher the velocity of superficial gases, the void fraction value increases. This increase in the void fraction is why there is a significant change in flow patterns from bubble flow patterns to churn. In addition, it was also found that the increased viscosity of the fluid significantly affected changes in flow patterns, incredibly bubbly and plug, but its velocity decreased. It is also the result that the higher homogeneous void fraction (β) value affects the increase in the length of bubbly flow patterns and plugs.

Simulation of cooling plate effect on a battery module with different channel arrangement

Lithium-ion battery pack is widely used in electric vehicles (EVs), for which reasonable heat dissipation measures must be taken to keep battery working in a suitable temperature range. Liquid cooling is popular for its efficient heat dissipation performance. In order to evaluate the effect of layout and channel design of cooling plates on the heat dissipation of a battery module, numerical modeling and analyses were carried out. Two arrangements of the cooling plates with different coolant channels (i.e., single channel, multiple small channels, and S-shaped channel) are discussed. The Z-score method is applied to evaluate the six cooling plate designs with various inlet flow rates. It is found that the design with two cooling plates sandwiching one battery module shows a better cooling performance. In terms of the channel structures, the comprehensive performance of the cooling plates with multiple small flow channels is optimal, when inlet flow rate is between 7.817 × 10−4 kg s−1 ∼ 0.0105 kg s−1 under the New European Driving Cycle (NEDC) condition.

Gas-liquid flow in small channels: Artificial neural network classifiers for flow regime prediction

To design and operate multiphase apparatus with mini- and microchannels, it is important to know how the fluids stream inside. Most literature reports the occurrence of flow regimes in dependence on gas and liquid superficial velocities in flow maps that are valid for fluids with similar properties and channels with similar geometry. Attempts to develop universally applicable flow maps show limitations in the number and variation of considered model parameters or in the number of considered flow regimes. This paper presents artificial neural network classifiers able to predict all relevant flow regimes: (a) Taylor flow, (b) bubbly flow, (c) Taylor-annular flow, (d) churn flow, (e) dispersed flow, (f) annular flow, (g) rivulet flow, and h) parallel flow in dependence on geometric and operational parameters as well as fluid properties with a high precision (R=0.92...0.95 and classification rates were generally above 80%). The classifiers were developed and validated by using more than 13,000 experimental data on gas-liquid flows extracted from 97 flow maps and are based on 7 significant dimensionless groups, namely, ReG, ReL, WeG, WeL,CaL, Θ*, and the channel form factor FC.

Cross-sectional phase distribution measurement of slug flow in small channels

Cross-sectional phase distribution measurement of slug flow in small channels

A method for void fraction measurement of bubble/slug flow in small channels based on contactless impedance detection.

The flow parameter measurement of the gas-liquid two-phase flow in small channels is very crucial and challenging in both academia and industry. Conventional techniques based on radiations, optics, acoustics, or electrics most lose their superiorities in the scenario with small channels due to the spatial limitation and the online and contactless measurement requirements. In addition, the conductive characteristic of the two-phase flow is equivalent to an impedance rather than a resistance due to the existence of multi-phases. The equivalent impedance information of the two-phase flow, especially the imaginary part, is promising to provide more flowing details but has seldom been detected or analyzed. In this paper, a method for the void fraction measurement of bubble/slug flow in small channels is proposed. The method implements void fraction measurement in a contactless way, based on the acquisition of the total impedance information of the gas-liquid two-phase flow. First, a new contactless impedance detection sensor is designed, based on the simulated inductor technique and the analogphase sensitive demodulation technique, to obtain the complete equivalent impedance information of the two-phase fluid. Then, based on the flow pattern identification result, the void fraction measurement model is developed, which is a fusion of the relationships between the void fraction and the real part/the imaginary part of the equivalent impedance information, respectively. Experimental results on prototypes with different inner diameters (2.48, 3.64, and 4.52mm, respectively) validate the effectiveness of the proposed void fraction method. The maximum void fraction measurement biases are within 5.0%.

A Review on the Hydrodynamics of the Liquid–Liquid Two-Phase Flow in the Microchannels

The ability of small and microchannels to enhance mass transfer, reduce diffusional limitations, and create a safer process has made them the best choice for process intensification. This study provides a review of the available experimental and computational literature on the hydrodynamics of liquid–liquid two-phase flow in microscale, namely, flow regimes, pressure drop, and flow structure. When two immiscible liquids flow in small channels, various flow patterns can be observed, with the development of those patterns being influenced by several parameters, such as the geometry of the mixing junction and channel, the channel material, the fluids properties, and the orientation of the flow. As part of the flow patterns observations and measurement, the velocity fields and internal circulation reported in the literature were reviewed in the context of the microparticle velocimetry (μPIV) implementation. Also, relevant to our study is the literature outlining, pressure drop, and the available models that have been used to predict it. These models are discussed in detail with special reference to flow patterns and fluids viscosities. Moreover, the numerical studies results using computational fluid dynamics (CFD) have also been reviewed and discussed, in terms of the validity of the simulation and the different parameters affecting slug formation and flow patterns. Each section of the discussion also points out the gaps in the research and proposes future work that could further develop the technology under a review of liquid–liquid two-phase flow in microchannels.

Geomorphology of the Sulden River basin (Italian Alps) with a focus on sediment connectivity

ABSTRACT An area-wide digital geomorphological map consisting of 12,180 non-overlapping polygons was created for the Sulden river basin (South Tyrol, Italian Alps) with the purpose to carry out a GIS-based sediment connectivity analysis. Thirty-one landform types were defined with respect to their role within sediment cascades. As such, the classification and the related symbology partly differ from a traditional geomorphological map where several areal objects are frequently represented by scaled and rotated point symbols. The catchment (∼130 km²), exhibits a high geomorphological variability as well as relatively large glacierized areas. We used the geomorphological map for a first qualitative estimate of the main differences between the two major sub-basins concerning the components of the sediment cascades: while the Trafoi sub-catchment exhibits a high number of small landslides and debris flow channels (i.e. source and transport landforms), the Sulden sub-catchment is rather characterized by large proglacial and talus landforms (i.e. temporary storage landforms).

New method for bubble/slug velocity measurement in small channels.

Based on the C4D technique and cross correlation velocity measurement technique, a new method for bubble/slug velocity measurement of the gas-liquid two-phase flow in small channels is proposed. A new C4D sensor, which is suitable for the parameter measurement of the gas-liquid two-phase flow in small channels, is developed by introducing the principle of capacitive reactance elimination. With two new C4D sensors, a bubble/slug velocity measurement system is developed, and the bubble/slug velocity is determined by the cross correlation velocity measurement technique. To verify the effectiveness of the proposed bubble/slug velocity measurement method, three prototypes of bubble/slug velocity measurement systems with different diameters (1.82 mm, 2.65 mm, and 2.96 mm, respectively) were established, and the bubble/slug measurement experiments were carried out. The research results show that the capacitive reactance elimination is an effective way to overcome the unfavorable influence of the coupled capacitances on measurement results. The experimental results indicate that the proposed method can successfully realize the bubble/slug velocity measurement in small channels, and the velocity measurement accuracy is satisfactory. For the three prototypes of the bubble/slug velocity measurement system, the maximum relative errors of the bubble/slug velocity measurement are all less than 5%.

Optimized Condition for Pairing of Different Friction Factor and Viscosity Equations for the Frictional Pressure Drop of R22 and R290

Accurate prediction of the friction factor and consequently the pressure drop of two-phase flow in small channels is still an issue. Many correlations exist for the determination of the viscosity and the friction factor that appear in the frictional pressure drop and their combination often determined the degree of disagreements between the experimental data and predicted outcomes. Demands for environmentally friendly refrigerants have further posed a challenge to find compatible alternatives with as good a performance as the current coolants. Despite the many available correlations developed to date, many more are studied in effort to reduce the discrepancies. This paper presents the outcomes of a study comparing the optimized conditions when three different viscosity equations are paired with eight different friction factor correlations to minimize the frictional pressure drop. The approach used multi-objective genetic algorithm (MOGA) to assist in selecting the best pairing. Comparison is then completed with available experimental data. The study showed that the Blasius friction factor paired with the Dukler viscosity produced the least percentage difference for R22, while when paired with the McAdams viscosity produced a lower difference for R290, an environmentally friendly refrigerant being considered to replace R22.

An experimental method to visualize shear-induced channelization of fluid flow in a rough-walled fracture

This study proposes an experimental method to visualize the channelization of fluid flow through a rough-walled fracture during the shear-flow process using a visualization technique. Transparent fracture samples that have the same surface morphology as natural fractures are prepared for testing. The coupled shear-flow test is carried out and the tracer distributions at different shear displacements and times are captured. The results show that as the shear displacement increases, the number of contacts reduces significantly due to the shear-induced dilation, yet the area of each contact increases. The tortuosity coefficient, defined as the tortuous length of the representative flow path to the straight length between the inlet and outlet boundaries, exhibits a decreasing trend with the increment of shear displacement. This indicates that the expanded aperture induced by dilation gives rise to a less tortuous streamline and weakens the effect of surface roughness on the permeability. In the initial stage of shear, the fluid flow bypasses the contacts, forming a large number of small flow channels. At the residual stage of shear, the fluid flow is concentrated in two or three major channels that have relatively large permeability. The proposed experimental method provides a platform that has a promising potential to intuitively investigate the complex rock–fluid interactions within fractures.

A New Contactless Bubble/Slug Velocity Measurement Method of Gas–Liquid Two-Phase Flow in Small Channels

A new contactless bubble/slug velocity measurement method of the gas–liquid two-phase flow in small channels is proposed by extending the contactless conductivity detection technique to the contactless impedance detection (CID) technique. Two kinds of CID sensors with different constructions (tubular construction and radial construction) are developed to obtain the total impedance information (the real part, the imaginary part, and the amplitude) of the gas–liquid two-phase flow. Two bubble/slug velocity measurement systems with different constructions, the tubular three-electrode velocity measurement system and the radial four-electrode velocity measurement system, are developed. With the obtained total impedance information, three initial estimation values of the bubble/slug velocity are determined by the principle of the cross correlation velocity measurement. Then, with the real-time flow pattern identification result implemented by the fuzzy C-means, a corresponding velocity measurement model [which is the linear combination of the three initial estimation values of the bubble/slug velocity and is developed by the penalty function method and the Davidon–Fletcher–Powell algorithm] is applied to obtain the final bubble/slug velocity. Two groups of the bubble/slug velocity measurement system prototypes with three different inner diameters are developed. The bubble/slug velocity measurement experiments are carried out. The experimental results show that the proposed method is effective. For the two bubble/slug velocity measurement systems with different constructions, the maximum relative errors of the bubble/slug velocity measurement are all less than 4.5%. The research results also indicate that making full use of the total impedance information is an effective approach to improve the accuracy of the velocity measurement.