Mesh Sensor Research Articles

Capacitive measuring system for two-phase flow monitoring. Part 2: Simulation-based calibration

Two-phase gas–liquid flows are present in many industrial processes and therefore monitoring of such flow is highly desired for either quality or efficiency assurance. Capacitive probes are widely used for two-phase investigation in experimental facilities and may have the potential for industrial use in the future. In this paper, we apply a simulation-based approach for increasing the accuracy of void fraction measurement of capacitive probes. We also employ the simulation data to find the electric response of a capacitive probe under different flow conditions. Moreover, by means of a horizontal flow test bench, we compare the void fraction measurements of the capacitive probe with the output of a reference wire mesh sensor. Experimental tests for air–water flow were performed. We show that from simple normalization approach (as widely employed) average deviation of measured void fraction values (compared to reference sensor) can be heavily reduced from up to 30% to less than 5% in most cases. The approach presented can be also applied to other types of capacitive probes.

Cyclic operation strategies in inclined and moving packed beds—Potential marine applications for floating systems

The hydrodynamics of a periodically operated packed bed subjected to column oscillations and obliquity was studied. Electrical capacitance tomography (ECT) and capacitance wire mesh sensors were employed to measure the local instantaneous liquid saturation in stationary slanted and moving packed beds, respectively. A swell simulator with six‐degree‐of‐freedom motions was applied to emulate the behavior of floating packed beds. The results revealed that column inclination from the vertical position considerably decayed liquid waves excited by different cyclic operation strategies. However, ON–OFF liquid and gas/liquid alternating cyclic operations showed an attempt to conserve wave identity in the slanted bed and to decrease phase maldistribution resulting from bed inclination. It was also found that symmetric and non‐symmetric split ratios of ON–OFF liquid cyclic mode were able to noticeably decrease fluid maldistribution in the oscillating packed bed. This study opens up possible prospects for process intensification of floating packed bed reactors and contactors. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4157–4172, 2016

Elongated bubble shape in inclined air-water slug flow

The shape of elongated bubbles in upward inclined air-water slug flow was studied experimentally by quantitative measurements of the cross sectional distribution of the phases within the pipe, using a wire mesh sensor. Ensemble-averaged shapes of elongated bubbles were determined for a wide range of gas and liquid flow rates, as well as for different pipe inclination angles. The elongated bubble nose can be characterized by an annular domain where liquid is present above the gas. The effect of gas and liquid flow rates, as well as of the pipe inclination angle on the bubble shape (front and tail) is studied. A simplified theoretical model is proposed to determine the bubble front shape. The model predictions compare favorably with the experimental results.

On packet transmission scheduling for min-max delay and energy consumption in wireless mesh sensor networks

Optimization of channel utilization in wireless networks is typically based on transmission parallelization under signal-to-interference and noise constraint assuming minimum frame-length scheduling. In application scenarios like sensor networks this approach may not be suitable since it does not explicitly consider end-to-end packet delay nor energy consumption. In the paper we propose a mixed-integer programming formulation for scheduling optimization in wireless sensor networks characterized by periodic data gathering where minimization of the maximum packet delay and sensor node energy consumption are the main objectives. The model, which assumes cooperation in packet forwarding and interference cancellation, is compared to traditional single path forwarding.

Study of phase distribution in pipe cyclonic compact separator using wire mesh sensor

Separation of gas–liquid mixture, which is achieved by using either large gravity separators or compact separators is a common and vital operation in the petroleum industry. Where space and cost are key project considerations, gas–liquid compact separators are very attractive because of their versatility and cost effectiveness. Efficient performance of the cyclonic separator depends on smooth and steady swirling flow. Unsteady swirling flow in the separator may be due to capacity constraint, improper design or unforeseen flow instability at the inlet. An understanding of phase distribution in gas discharge section of these separators would help design engineers make a better decision when selecting and sizing inlet nozzle, diameter and length of the separator. In this paper, the structure of phase distribution and liquid holdup in the gas discharge section of the separator was obtained using a 24x24 resolution wire mesh sensor (WMS). The acquired area average liquid holdup and the images were analysed using time series and 2D slice to discriminate between partial separation and critical separation condition.The liquid holdup as a function of separator inlet superficial velocity was quantified.

Distributed Dynamic Memetic Algorithm Based Coding Aware Routing for Wireless Mesh Sensor Networks

Network coding has been confirmed as a potential technology to improve performance of wireless mesh networks (WMNs); network coding has great advantages for sensor networks like minimization of communication needed to collect sensor data and error recovery. A few network coding aware routings have been proposed. However, these mechanisms detect coding opportunities through local traffic pattern checking, which hardly obtains optimal routes. This paper proposes a Distributed Dynamic Memetic Algorithm Based Coding Aware Routing (DDMCAR) for wireless mesh networks, which employs memetic algorithm to optimize routes and coding opportunities. This paper proposes an improvement over GCAR algorithm by employing memetic algorithm and also meme sharing among nodes to increase the chance of finding optimal solution and continuous monitoring and update of meme fitness to achieve a dynamic tracking of network conditions, and finally using most fit memes for load balancing elevating congestion. Through simulations on randomly generated wireless mesh networks, DDMCAR is to be shown to find optimal routes within a short time and achieve more improvements than GCAR.

UTILIZING ACTIVE RFID ON WIRELESS SENSOR NETWORK PLATFORM FOR PRODUCTION MONITORING

In today’s manufacturing environment, delay in monitoring output performance might cause production mess in the industry. Therefore, an efficient communication and real time feedback to maximize uptime and improve productivity seems vital. Adapting the capabilities of RFID technology and Wireless Mesh Sensor Network (WMSN) through web-based monitoring system might solve this problem. Thus, an embedded system namely ERFIDC was developed as a potential solution in addressing this demand. This paper reports the proposed embedded system architecture and evaluation of its reading range in point-to-point and WMSN setup at the selected production plant.

A dynamic active shield against shield rerouting attack

An active shield is a sensor mesh devised and implemented on top of most secure chips or in a secure embedded system as a good protection for circuits and sensitive data stored in the chips. It is one of the most effective annoyances for microprobing attackers. But, a shield rerouting attack can defeat active shield by disclosing the geometry structure of the shield, and causing a short circuit of the sensor mesh. This paper proposes a dynamic active shield to resist the shield rerouting attack. A dynamic active shield is a sensor mesh which contains some routing nodes and connects metal lines between adjacent nodes. Changing the connection statuses of routing nodes results in different paths of the shield sensor mesh. The dynamic active shield increases the security of circuits and defeats the shield rerouting attack by changing the path of the sensor mesh every few clock cycles, making it more difficult to distinguish the geometry structure of the top layer sensor mesh. At last, we present security and performance analysis of dynamic active shield.

Global and local hydrodynamics of bubble columns – Effect of gas distributor

Global (level swell) and local (WMS – Wire Mesh Sensor) measurements were made on waters of different purities and air, in a cylindrical laboratory bubble column (2m tall, 0.127m dia) using two different gas distributors: a perforated plate (to produce homogeneous flow) and a spider sparger (to produce heterogeneous flow). The level swell method provided the steady space-averaged gas holdup/gas flow rate data. The WMS method provided the actual gas holdups and bubble sizes resolved in time and space at one cross-sectional horizontal plane (1m above distributor), whose integration yields the time-averaged data. The following results were obtained: The global and local data agree relatively well; there are distinct differences between the radial profiles and bubble size distributions between the two main flow regimes; the local information identifies why the predictions of published models, which account for the smaller and larger bubbles in the flow, may not perform well; the modelling approaches based on the hindrance and enhancement concepts prove to be suitable for the flow regime identification and description, including the transition range between the homogeneous and heterogeneous flows; based on the hydrodynamics, the specific interfacial area is obtained, together with the mass transfer coefficient.

Hybrid evolutionary approaches to maximum lifetime routing and energy efficiency in sensor mesh networks

Mesh network topologies are becoming increasingly popular in battery-powered wireless sensor networks, primarily because of the extension of network range. However, multihop mesh networks suffer from higher energy costs, and the routing strategy employed directly affects the lifetime of nodes with limited energy resources. Hence when planning routes there are trade-offs to be considered between individual and system-wide battery lifetimes. We present a multiobjective routing optimisation approach using hybrid evolutionary algorithms to approximate the optimal trade-off between the minimum lifetime and the average lifetime of nodes in the network. In order to accomplish this combinatorial optimisation rapidly, our approach prunes the search space using k-shortest path pruning and a graph reduction method that finds candidate routes promoting long minimum lifetimes. When arbitrarily many routes from a node to the base station are permitted, optimal routes may be found as the solution to a well-known linear program. We present an evolutionary algorithm that finds good routes when each node is allowed only a small number of paths to the base station. On a real network deployed in the Victoria & Albert Museum, London, these solutions, using only three paths per node, are able to achieve minimum lifetimes of over 99% of the optimum linear program solution's time to first sensor battery failure.

Assessment of a hybrid CFD model for simulation of complex vertical upward gas–liquid churn flow

Gas–liquid multiphase flow can be observed within different industrial processes, and Computational Fluid Dynamics (CFD) can be utilized as a tool for scrutiny of this kind of flows. Although the CFD simulations of multiphase are computationally-demanding, they can deliver a great deal of information. But, the larger point is whether the available CFD multiphase flow models are able to deliver a realistic solution for a complex flow pattern like churn flow? And if yes, to what extent are the results accurate?To shed light on these issues, the Eulerian–Eulerian MultiFluid VOF model offered by ANSYS FLUENT 15 (2015. 15.0 User's Guide, ANSYS Inc.) was used to simulate high flow rate air–water multiphase flow in a 76.2mm-diameter pipe upstream of an elbow in the vertical-horizontal configuration. In the simulations, superficial gas velocity ranged from 10.3m/s to 33.9m/s, and two superficial liquid velocities of 0.3, and 0.79m/s were employed.From the CFD simulations, data such as phase distributions, mean void fractions, and average void fraction time series were extracted. They were then compared to experimental Wire Mesh Sensor (WMS) data formerly obtained. Interestingly, evaluation of the model revealed that it was successful in terms of capturing different liquid structures present within the flow and delivering void fraction data which were in agreement with those of experiments.

Structures in gas–liquid churn flow in a large diameter vertical pipe

Gas–Liquid two phase co-current flow in a vertical riser with an internal diameter of 127 mm was investigated in the churn flow pattern. This paper presents detailed experimental data obtained using a Wire Mesh Sensor. It shows that the most obvious features of the flow are huge waves travelling on the liquid film. Wisps, large tendrils of liquid and the product of incomplete atomisation, which had previously detected in smaller diameter pipes, have also been found in the larger diameter pipe employed here. The output of the Wire Mesh Sensor has been used to determine the overall void fraction. When examined within a drift flux framework, it shows a distribution coefficient of ∼1, in contrast to data for lower gas flow rates. Film thickness time series extracted from the Wire Mesh Sensor output have been examined and the trends of mean film thickness, that of the base film and the wave peaks are presented and discussed. The occurrence of wisps and their frequencies have been quantified.

Graphene meshes decorated with palladium nanoparticles for hydrogen detection

We fabricated flexible and transparent hydrogen gas sensors based on a palladium-decorated graphene mesh. Electron microscopy analysis confirmed that ~2–3 nm diameter Pd nanoparticles were uniformly dispersed on the graphene mesh surfaces. The sensors were highly transparent with an average optical transmission of >90% to visible light and they exhibited good electrical stability with a resistance change of 1.5% under a tensile strain of 1.1% in a cyclic bending-unbending test. Compared with graphene-based sensors, the graphene mesh sensors exhibited a faster response to hydrogen gas with sensitivity as high as ~5% at a low concentration of 10 ppm H2/air, even at room temperature. The enhanced H2 detection characteristic of the graphene mesh sensors is attributed to the existence of edges.

A methodology to quantify the uncertainty in liquid holdup measurements with wire mesh sensor

The uncertainty in the holdup measurements of a capacitance based WMS with 32×32 wires has been experimentally evaluated, and a methodology for its quantification is proposed for horizontal flow. Investigation is performed in laboratory and in-situ experiments under stagnant conditions with an emphasis on the effect of the mesh grid orientation on the measurements. Also, potential impact of misalignment in the pipe inclination is explored by slightly inclining the pipe for both tests. Finally, dynamic flow conditions are tested in a high pressure (1.37MPa) facility with horizontal stratified-wavy oil/air two-phase flow for gas and liquid superficial velocity ranges of 2.8m/s≤νSg≤6.9m/s and 0.01m/s≤vSL≤0.05m/s, respectively.The angle between the phase interface and the sensor wires is ineffective while the misalignment in the pipe inclination plays a major role in the deviations of the holdup measurements. Using the proposed methodology, the measurement uncertainty from laboratory tests is shown to follow a logarithmic increase as a function of the measured holdup for smaller holdup values (HL≤15%) and to be lower than 1.5% for HL>15%. This behavior is intrinsic to WMS and a representative of the measurement uncertainty in the actual flow loop installation.Under actual flow conditions, the holdup measurements of the trapped liquid by WMS show an offset compared to the measurements via flow imaging which can be corrected by using the uncertainty quantified in the laboratory tests. However, the dynamic measurements with WMS show a good agreement with the holdup of the trapped liquid volume within the quantified uncertainty bounds.

Dual-modality wire-mesh sensor for the visualization of three-phase flows

Three-phase gas–liquid–liquid flows are very common in petroleum extraction, production, and transport. In this work a dual-modality measuring technique is introduced which may be well applied for three-phase flow visualization. The measuring principle is based on simultaneous excitation with two distinct frequencies to interrogate each crossing point of a mesh sensor, which in turn are linked to conductive and capacitive parts of fluid impedance. The developed system can operate eight transmitter and eight receiver electrodes at a frame repetition frequency up to 781 Hz. The system has been evaluated by measuring reference components. The overall measurement uncertainty was 8.4%, which considering the fast repetition frequency of measurements is suitable for flow investigation. Furthermore, a model-based method to fuse the data from the dual-modality wire-mesh sensor and to obtain individual phase fraction of gas–oil–water flow is introduced. Here a parametrized model is fitted to the measured conductivity and permittivity distributions enabling one to obtain phase fraction from measured data. The method has been applied and tested to the acquired data from a mesh sensor in static and dynamic three-phase mixtures of gas, oil, and water. Fused images and quantitative values show good agreement with reference values. The newly developed dual-modality wire-mesh sensor has the potential to investigate three-phase flows to a good degree of detail, being a valuable tool to investigate such flows.

Application of the MiniPanda test case ‘erosion of a stratified layer by a vertical jet’ for CFD validation

In order to allow development and validation of CFD models for hydrogen mixing and transport in the containment, a comprehensive experimental test campaign was performed at the small scale MiniPanda facility at ETH Zurich. The considered test series aimed at studying the turbulent erosion of a stratified light gas by means of a vertical air jet with different momenta. Due to its new and innovative measurements, e.g., with temperature wire mesh sensors, the global mixing and the local interaction of jet and stratification are characterized in a high resolution in space and time. Both are essential for a detailed model assessment, to identify possible error sources and rate their effect on the global scenario evolution. Consequently, the tests are well suited for CFD model development and validation and complement the data basis gained before, e.g., in the frame of the joint OECD/NEA-SETH-2 Project (2007–2010) (OECD/NEA, 2012).Based on a description of the MiniPanda facility and the ‘layer erosion’ test series, the application of a U-RANS CFD approach, capable to be applied also for large scale application, is discussed. Numerical model uncertainties are minimized according to the best practice guidelines before a systematic comparison against the experimental data is performed and the capability of the model to predict the turbulent mixing at the interface and the inter-compartment mass transfer is successfully validated.

Capacitance wire mesh imaging of bubbly flows for offshore treatment applications

The impact of ship motion on bubbly flow was emulated using a swell simulator to expose flow structure changes emerging in bubble columns relevant to offshore floating applications. Roll, roll+pitch, yaw, heave and sway were implemented at various frequencies and changes in bubbly flow resulting from the imposed motions were monitored for the first time by means of a dual capacitance wire mesh sensor to measure local gas holdup and velocity. Visualizations of the two-phase flow revealed that roll, roll+pitch, and high-frequency sway were the most impactful in terms of bubble zigzag and swirl, and bubble-clustering and segregation due to vessel dynamic inclinations. As a consequence of these motions, lateral migration of bubbles and their clustering enhanced liquid recirculation and local streamwise gas velocity. Compared to static vertical bubble column, bubbly flow pattern was barely altered by yaw and low-frequency sway except the heave displacements which tended to slowdown the bubble rise.

Hydrodynamics of gas–liquid cocurrent downflow in floating packed beds

An innovative experimental setup combining a robot with six-degree-of-freedom motions (translational: surge, sway, heave, and rotational: roll, pitch, yaw) and an embarked column instrumented with a capacitance wire mesh sensor was built to investigate experimentally the two-phase flow hydrodynamics in porous media within inclined stationary and oscillating packed beds under gas–liquid cocurrent descending flows. The hydrodynamic deviations with respect to the stationary straight column were thoroughly analyzed in terms of bed pressure drop, liquid saturation, regime changeover, and pulse flow properties. Non-tilting oscillations had marginal effects on the packed bed hydrodynamics which remained practically similar to the one prevailing in stationary vertical trickle beds. Conversely, tilting oscillations profoundly influenced the flow regime inside the packed bed as a result of the time-dependent nature of the gravitational and inertial (acceleration/deceleration) forces brought about by the hexapod rotational oscillations which caused important secondary transverse displacements of the fluids in the bed. Using moment analysis of the probability density functions of the registered liquid saturation time series, it was found that due to the periodic gravity-driven stratification, the transition to pulse flow shifted towards higher fluid velocities as the oscillation periods of roll or roll+pitch motions were increased.

Study on void fraction distribution of plunging jet experiment with wire mesh sensor

The plunging jet is a phenomenon of two phase gas-liquid flow, which could be an effective method to sufficiently mix boric acid with de-ionized water, and is suitable for studying the Pressurized Thermal Shock (PTS) accident scenario of Pressurized Water Reactors(PWR). The air is entrained when the liquid jet hits the water surface, which generates bubbles during the air entrainment. This bubble entrainment has a crucial influence on the mixing process. The distribution of void fraction was studied in dependence of the jet length and flow rate. A movable three-layer Wire Mesh Sensor (WMS) is designed to measure sequences of instantaneous two-dimensional gas fractions with a high-resolution in space and time, which, from the data, derives the void fraction distributions. Comparisons of average void fraction are carried out with different jet lengths and flow rates.

Comparison of experimental and Computational Fluid Dynamics (CFD) studies of slug flow in a vertical riser

This paper presents a comparison of the results obtained from experiments and CFD studies of slug flow in a vertical riser. A series of two experimental investigations were carried out on a 6m vertical pipe with a 0.067m internal diameter charged with an air–silicone oil mixture. For the first set of experiments, the riser was initially full of air, and then liquid and gas flows set to liquid and gas superficial velocities=0.05 and 0.344m/s, respectively, electrical capacitance tomography (ECT) and wire mesh sensor (WMS) transducers were employed. In the second one, the riser was initially full of (static) liquid, and then liquid and gas flows set to liquid and gas superficial velocities=0.05 and 0.344m/s, respectively, only ECT was used. A characterisation of the observed slug flow regimes was carried out. This includes the evaluation of the instantaneous distribution of the phases over the pipe cross-section, the Probability Density Function (PDF) of void fraction, time series of cross-sectional void fraction, Power Spectral Density (PSD), structure velocity of the Taylor bubble, lengths of the liquid slug and Taylor bubble and void fractions in the liquid slug and Taylor bubble. The simulation results were validated both qualitatively and quantitatively against experimental data. A reasonably good agreement was observed between the results of the experiment and CFD.