Liquid Reservoir Research Articles

Developing New Natural Surfactant from Date Seeds for Different Field Applications

The increase in using natural surfactants for enhanced oil recovery (EOR) purposes in recent years is mainly attributed to the widespread global awareness of the environmental effects the oil and gas industry causes. In accordance with KSA Vision 2030 and the corresponding global direction, the purpose of this study is to discover a cost effective, readily available, environmentally friendly, and locally sourced surfactant. This surfactant will help reduce the interfacial tension (IFT) between reservoir liquids to enhance the reservoir’s productivity and increase its ultimate recovery. In this study, date seeds have been chosen as the green surfactant source due to the abundance of such seeds. Al-Khalas, which is a well-known palm tree that grows in Qassim, Al-Kharj, and Al-Ahsa provinces in KSA was chosen. Properties such as surface tension (ST), IFT, pH, and density were measured to evaluate the effectiveness of date seeds as a natural surfactant. ST results showed a reduction from 72 mN/m (of distilled water) to 43 mN/m using the new surfactant in formation water at 10 wt% comprising a 40% reduction. Moreover, IFT of the new surfactant with Saudi medium oil (26 API) was 10 mN/m compared to 18 mN/m of a formation water-oil system which represents a 49% reduction in interfacial tension. Overall, the novel surfactant studied in this research shows great promise in being an effective EOR agent in addition to eliminating the negative impacts of regular surfactants on the environment.

Screen-Printable Iontronic Pressure Sensor with Thermal Expansion Microspheres for Pulse Monitoring.

Constructing microstructures to improve the sensitivity of flexible pressure sensors is an effective approach. However, the preparation of microstructures usually involves inverted molds or subtractive manufacturing methods, which are difficult in large-scale (e.g., in screen printing) preparation. To solve this problem, we introduced thermally expandable microspheres for screen printing to fabricate flexible sensors. Thermally expandable microspheres can be constructed into microstructures by simple heating after printing, which simplifies the microstructure fabrication step. In addition, the added microspheres can also be used as ionic liquid reservoir materials to further increase the capacitance change and improve the sensitivity. The prepared sensors exhibited superior performance, including ultrahigh sensitivity (Smax = 49999.5 kPa-1) and wide detection range (0-350 kPa). Even after 30,000 cycles at a high pressure of 300 kPa and a low pressure of 30 kPa, the sensor showed minimal signal degradation, demonstrating long-term cycling stability. In order to verify the practical potential of the sensors, we performed human radial artery beat detection experiments using these sensors. The variations in the intensity of the 3D radial artery pulse wave can be observed very clearly, which is important for human health monitoring. The above demonstrates that our strategy can provide an effective approach for the large-scale preparation of high-performance flexible pressure sensors.

Impact of cryogenic environment on piezoelectric transducers used in SHM applications

A high number of actors of the space industry, including ESA (European Space Agency) and CNES (French national space agency), are engaged in a program aiming at developing future European reusable space launchers. In this context, PYTHEAS Technology has developed an embedded Non-Destructive Testing (eNDT) solution to ensure that strategic structural elements of the launcher are free of damage before a new launch, performing Structural Health Monitoring (SHM). The sensors used for this application are subject to severe temperature variations, including cryogenic temperatures. Cryogenic conditions are present in other fields requiring SHM solutions, such as liquid hydrogen reservoirs, increasing the importance of this study. Results of experimental tests are presented, where piezoelectric transducers are glued with two types of glue on samples of aluminum plates and carbon composite plates. A reference measurement is carried out before plunging the plates in a climatic chamber, down to -196°C. Pulse-echo and admittance measurements are performed during the temperature decrease and after the temperature rise. The admittance measurements show no deterioration of the samples after being immersed in liquid nitrogen: the transducers, wires, glue, and samples themselves have resisted to the temperature cycle. The pulse-echo signals’ time and frequency analysis show a linear attenuation of the signals relative to temperature. A difference in signal intensity and wave behavior has also been observed relative to the sample’s material: composite or aluminum. No difference regarding the type of glue is witnessed. These results pave the way for damage detection in harsh environments, since the system’s performance is maintained through a whole temperature cycle in cryogenic conditions.

Capillarity in Interfacial Liquids and Marbles: Mechanisms, Properties, and Applications.

The mechanics of capillary force in biological systems have critical roles in the formation of the intra- and inter-cellular structures, which may mediate the organization, morphogenesis, and homeostasis of biomolecular condensates. Current techniques may not allow direct and precise measurements of the capillary forces at the intra- and inter-cellular scales. By preserving liquid droplets at the liquid-liquid interface, we have discovered and studied ideal models, i.e., interfacial liquids and marbles, for understanding general capillary mechanics that existed in liquid-in-liquid systems, e.g., biomolecular condensates. The unexpectedly long coalescence time of the interfacial liquids revealed that the Stokes equation does not hold as the radius of the liquid bridge approaches zero, evidencing the existence of a third inertially limited viscous regime. Moreover, liquid transport from a liquid droplet to a liquid reservoir can be prohibited by coating the droplet surface with hydrophobic or amphiphilic particles, forming interfacial liquid marbles. Unique characteristics, including high stability, transparency, gas permeability, and self-assembly, are observed for the interfacial liquid marbles. Phase transition and separation induced by the formation of nanostructured materials can be directly observed within the interfacial liquid marbles without the need for surfactants and agitation, making them useful tools to research the interfacial mechanics.

Selective and Real‐Time Ion Monitoring with Integrated Floating‐Gate Organic Electrochemical Transistor Sensing Circuits

AbstractIon‐selective transistor‐based sensors play a pivotal role in quantifying ion concentrations in aqueous media. Existing solutions rely on direct coupling between ion‐selective membrane and channel, requiring bulky electrolyte reservoirs or complex technological approaches and material interfaces. This work introduces a transformative paradigm with ion‐selective floating‐gate organic electrochemical transistors (ISFG‐OECTs) and their integration in sensing circuits. ISFG‐OECTs feature spatial separation between ion‐selective gating and ionic‐electronic current modulation. Leveraging volumetric capacitance and solid‐state ionic liquid, efficient ionic coupling with the channel is obtained. These distinctive features make them an ideal solution for streamlined materials integration, eliminating the need for liquid reservoirs. Theoretical foundations and design guidelines for efficient ISFG‐OECT implementation are elucidated. Experimental results demonstrate the effectiveness of ISFG‐OECTs in both transistor‐sensors and current‐driven circuit configurations, revealing highly selective detection of K+ ions with a limit of detection as low as 11 × 10−6 m, even in the presence of interfering Na+ ions at concentrations two orders of magnitude higher. The proposed approach is simple, reliable, and scalable, offering opportunities for a broad range of fields, such as medical diagnostics, precision agriculture, and environmental monitoring.

Versatile Capillary Cells for Handling Concentrated Samples in Analytical Ultracentrifugation.

In concentrated macromolecular dispersions, far-from-ideal intermolecular interactions determine the dispersion behaviors including phase transition, crystallization, and liquid-liquid phase separation. Here, we present a novel versatile capillary-cell design for analytical ultracentrifugation-sedimentation equilibrium (AUC-SE), ideal for studying samples at high concentrations. Current setups for such studies are difficult and unreliable to handle, leading to a low experimental success rate. The design presented here is easy to use, robust, and reusable for samples in both aqueous and organic solvents while requiring no special tools or chemical modification of AUC cells. The key and unique feature is the fabrication of liquid reservoirs directly on the bottom window of AUC cells, which can be easily realized by laser ablation or mechanical drilling. The channel length and optical path length are therefore tunable. The success rate for assembling this new cell is close to 100%. We demonstrate the practicality of this cell by studying: (1) the equation of state and second virial coefficients of concentrated gold nanoparticle dispersions in water and bovine serum albumin (BSA) as well as lysozyme solution in aqueous buffers, (2) the gelation phase transition of DNA and BSA solutions, and (3) liquid-liquid phase separation of concentrated BSA/polyethylene glycol (PEG) droplets.

Experimental simulation study on influencing factors of liquid production capacity in heterogeneous water drive reservoirs

Oilfield development involves a complex, dynamic flow process of oil and water, with reservoir characteristics and environmental conditions continually evolving as the field evolves. Particularly when a waterflooding reservoir reaches a stage of ultra-high water cut, prolonged waterflooding intensifies challenges in reservoir development: the exacerbation of reservoir heterogeneity and development behaviors disrupts the initial understanding of the reservoir's liquid production capacity from current development conditions. Thus, it becomes imperative to adjust the productivity prediction methods for oil wells in heterogeneous waterflooding reservoirs. Leveraging the flow simulation of reservoir micro channel networks, and integrating features such as the geometric characteristics of the reservoir percolation field, micro channel characteristics, interlayer differences of mixed layers, degree of plane heterogeneity, production pressure differentials, and fluid properties, a visual sand filling experimental model is established that adheres to specific similarity criteria. Using this sand filling experimental model, we simulate the percolation characteristics of oil–water two-phase flow during the waterflooding process, and uncover the diverse influencing factors and their varying degrees of impact on the oil-phase flow during this waterflooding phase. Qualitative and semi-quantitative percolation simulation experiments are employed to intuitively demonstrate the interlayer interference, degree of plane heterogeneity, and oil–water distribution in heterogeneous reservoirs, which influence the change in oil well productivity during waterflooding. This lays bare the microscopic percolation mechanisms behind the productivity changes in heterogeneous waterflooding reservoirs. The simulation experiment results show that the higher the permeability, the stronger the micro-heterogeneity, and the smaller the overall mobility increase after flooding, the smaller the JLDmax obtained by testing or calculation. At the same permeability, the greater the driving pressure difference, the greater the microscopic sweep coefficient within the pore network, and the greater the mobility increase after flooding, the greater the JLDmax. There is interlayer interference in commingled mining, and the higher the permeability of the high-permeability layer (the greater the interlayer difference), the higher the initial productivity of the commingled well. However, due to the high permeability layer being prone to flooding, resulting in ineffective water circulation, the low-permeability tube is difficult to completely flood, resulting in a small increase in overall mobility, and therefore, JLDmax is small. Water drive preferentially breaks through the high permeability zone on the plane, and the shape of the water drive sweep zone is controlled by the planar permeability gradient, the width of the high permeability zone, and the displacement pressure difference.

Changes in The Electrical Output Power and Efficiency of A Photovoltaic Panel Cooled by A Hybrid Method

During the process of generating electrical energy from photovoltaic panels, high ambient temperatures and radiation tend to cause excessive heating of the photovoltaic panel, resulting in a decrease in its efficiency. In this experimental study, two cooling methods were employed. The first method involved active cooling using water, while the second method combined active cooling with passive cooling using an aluminum heat sink, all while using water as the cooling medium. The experiment involved the analysis of changes in electrical output power and efficiency from three identical 100 W monocrystalline photovoltaic panels, one of which served as the reference. The first panel was considered the reference panel. The second panel featured active cooling, with a liquid reservoir created on its rear surface to be filled with transformer oil. Copper pipes were placed at specific intervals within this liquid reservoir, and the rear surface was covered with a thin flat metal plate. The third panel was prepared for the hybrid method, featuring a liquid reservoir covered with a rectangular finned aluminum heat sink, distinct from the second panel. In both methods, transformer oil was used for electrical insulation and thermal conduction between the panel and the copper pipes at the rear. The copper pipes were connected to an automotive radiator and a pump to form a closed circuit. The water inside the radiator was cooled using a radiator fan and circulated by a pump. In the first method, active cooling was achieved by cooling through the radiator, while in the hybrid method, active cooling through the radiator was combined with passive cooling using the rectangular finned aluminum heat sink. In the experiment setup, temperature and liquid flow were measured using radiation, electrical sensors, and other measuring instruments. The data obtained from the measurements were used to compare the increases in electrical power and efficiency of the panels. The electrical power increase and efficiency were calculated as follows: in the hybrid method, it was found to be 4.7% and 0.84%, respectively, while in the active method, it was 2.94% and 0.52%, respectively. The energy consumed in the study was provided by wind energy

Role of thermodynamic and turbulence processes on the fog life cycle during SOFOG3D experiment

Abstract. In this study, we use a synergy of in situ and remote sensing measurements collected during the SOuthwest FOGs 3D experiment for processes study (SOFOG3D) field campaign in autumn and winter 2019–2020 to analyse the thermodynamic and turbulent processes related to fog formation, evolution, and dissipation across southwestern France. Based on a unique measurement dataset (synergy of cloud radar, microwave radiometer, wind lidar, and weather station data) combined with a fog conceptual model, an analysis of the four deepest fog episodes (two radiation fogs and two advection–radiation fogs) is conducted. The results show that radiation and advection–radiation fogs form under deep and thin temperature inversions, respectively. For both fog categories, the transition period from stable to adiabatic fog and the fog adiabatic phase are driven by vertical mixing associated with an increase in turbulence in the fog layer due to mechanical production (turbulence kinetic energy (TKE) up to 0.4 m2 s−2 and vertical velocity variance (σw2) up to 0.04 m2 s−2) generated by increasing wind and wind shear. Our study reveals that fog liquid water path, fog top height, temperature, radar reflectivity profiles, and fog adiabaticity derived from the conceptual model evolve in a consistent manner to clearly characterise this transition. The dissipation time is observed at night for the advection–radiation fog case studies and after sunrise for the radiation fog case studies. Night-time dissipation is driven by horizontal advection generating mechanical turbulence (TKE at least 0.3 m2 s−2 and σw2 larger than 0.04 m2 s−2). Daytime dissipation is linked to the combination of thermal and mechanical turbulence related to solar heating (near-surface sensible heat flux larger than 10 W m−2) and wind shear, respectively. This study demonstrates the added value of monitoring fog liquid water content and depth (combined with wind, turbulence, and temperature profiles) and diagnostics such as fog liquid water reservoir and adiabaticity to better explain the drivers of the fog life cycle.

Experimental investigation of heat transfer characteristics in a miniature flat heat pipe with multi-channels

The heat transfer characteristics of a miniatured flat heat pipe (MFHP) with multi-channels, featuring a port diameter of 1.18 mm, is investigated experimentally. Various operating parameters are considered, including the working fluid volume (Vf = 1.5, 2.5, and 3.5 ml), length of the liquid reservoir (Lres = No reservoir, 5, and 10 mm), orientation such as axial face (αa) or lateral side (αl), inclination angles (α = −15 to 90o), and cooling water flow rates (ṁi = 10, 15, and 20 LPH). Based on the experiments, the optimal values for the working fluid volume, reservoir length, and flow rate are determined as Vf = 2.5 ml, Lres = 5 mm, and ṁi = 20 LPH, respectively. Further analysis reveals that, the heat dissipation rate for the axial face is significantly higher than that of the lateral side, with an average percentage increase of 35.4 %. However, the lateral side outperforms the axial face in terms of stabilizing the evaporator wall temperature, reducing fluctuations by an average of 24.5 %. Moreover, the presence of multi-channels allows the MFHP in axial face orientation to dissipate a maximum heat load of 15 W against gravity at an inclination angle of αa = −15o. Finally, the variations in MFHP operation based on the orientation and its underlying physical mechanisms that contribute to enhancing heat transfer are discussed.

Water cooling structure design and temperature field analysis of permanent magnet synchronous motor for underwater unmanned vehicle

Unmanned underwater vehicles (UUVs) have extremely harsh cooling conditions for permanent magnet synchronous motor (PMSM) due to global sealing and compact space, and an efficient heat dissipation system is essential for the safety and operational reliability of PMSM. Currently, with the introduction of seawater and the addition of heat exchanger, liquid reservoir are typically used for open-circuit heat dissipation, which not only adds weight, but seriously affects the flow characteristics of the UUV. In this paper, a novel dual channel water cooling structure is designed to achieve internal circulating heat dissipation without additional auxiliary devices. The temperature field of the PMSM with different water cooling structures is solved by Computational Fluid Dynamics (CFD) under rated operating conditions. The results show that the cooling efficiency of water cooling structures is more affected by low flow rates, accompanied by increasing the flow rate from 0.5 L/min to 24 L/min, the cooling performance is enhanced, but does not entirely obey a strict linear variation. Furthermore, at a flow rate of 6 L/min, the dual spiral water cooling structure performs the best heat dissipation, the maximum operating temperature of the PMSM is reduced by 51.72 K, the maximum temperature rise suppression rate reaches 53.02 %, and the minimum differential pressure of 10.18 kPa.

Testing and modelling of transient adhesion phenomena in rolling-sliding contacts

Transient adhesion effects in rolling–sliding contacts influence all aspects of train–track interaction. This is of high importance specifically when these effects result in critically low adhesion, which poses a risk to traction and braking of railway vehicles. This study presents a model that can replicate the transient changes of the coefficient of adhesion with tested water and solid particle mix. The experimental data for the model are measured using a commercial ball-on-disc tribometer. The experimental results showed a liquid reservoir in front of the contact area that slowly reduces in size. This observation was used in the modelling approach to divide the calculation into two stages where the reservoir is present and when it disappears. The model was able to reproduce the occurrence of low adhesion region seen in experimental results with different particle concentrations.

Subsurface structure regulates water storage in the alpine critical zone on the Qinghai-Tibet Plateau

The subsurface critical zone (CZ) structure in alpine regions has a profound influence on water storage that is not well understood due to a lack of available accurate spatiotemporal measurements. This work is to reveal that the organic layer (A), leaching-deposit layer (B), saprolite layer (C) and freeze–thaw processes regulate changes in subsurface liquid water storage (CSWS). We performed in situ field surveys, ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) along an elevation gradient (4221–3205 m) in the Qinghai Lake Basin Critical Zone Observatory (QLBCZO) on the Qinghai-Tibet Plateau. The results showed that the saprolite layer (thickness of 0.84–41.85 m) and the liquid water storage (SWS) increased along the decreasing elevation. The saprolite layer was the main subsurface liquid water storage reservoir, with average value of 595.49 ± 729.87 mm, which occupied 76.10 % of the total water storage of layers A, B and C. The SWS of the saprolite layers increased the most, by 39.41 mm and 45.88 mm in the thawing and nonfreezing periods, respectively, and that of layer B decreased maximally by 52.50 mm in the freezing period. The subsurface layer and elevation had the contribution to SWS at 68.07 % during the nonfreezing period. Comparing other climate and environmental factors, the seasonal frozen thickness (SFT) and precipitation contributed most to CSWS during the thawing and freezing period (27.95 % and 19.87 %), respectively. This study contributes to advancing the mechanistic understanding of the interactions between the subsurface CZ structure and water storage processes and provides high-quality data with which coupled ecohydrological models can be developed.

Model of a post-caldera volcano-hosted and vapor-dominated system through a numerical simulation study of the Bedugul geothermal field, Bali Island, Indonesia

To significantly increase the use of geothermal resources, describing geothermal systems in post-calderas is essential because this type of system is infrequent and has not yet been thoroughly researched. The Bedugul geothermal field (BGF), Bali Island, Indonesia, is a representative system with a complex structure composed of a vapor-dominated zone formed above a deep liquid reservoir. This study examines the BGF system and updates a conceptual model, particularly the fluid flow and heat transfer in the reservoir. A dual-porosity model and TOUGH2 EOS1 equation of state for water and steam module are used to simulate natural state conditions, including calderas with a domain area of 148.8 km2 and a thickness of 3.3 km. The BGF model was calibrated using the available geosciences data, temperature core holes and deep explorations wells and then evaluated statistically. A reliable natural state model with decent accuracy was obtained by optimizing the parameter calibration of the physical and structural properties of the reservoir model; the anisotropic and heterogeneous fracture permeability distribution and specific boundary conditions are crucial to the calculation accuracy. The BGF model reveals hot hydrostatic liquid, vapor-dominated, and transition zones and an overpressured liquid domain that is specific to a vapor-dominated geothermal system overlying a liquid reservoir. Occurrence of counterflow is also a noted feature in the vapor-dominated zone. Because of the high pressure in the steam zone, around 47 bar at a near-saturation temperature of 260 °C, the BGF is characterized as a premature field of a vapor-dominated system.

Detectability of Local Water Reservoirs in Europa's Surface Layer Under Consideration of Coupled Induction

AbstractThe icy moon Europa is a primary target for the study of ocean worlds. Its subsurface ocean is expected to be subject to asymmetries on global scales (tidal deformation) and local scales (chaos regions, fractures). Here, we investigate the possibility to magnetic sound local asymmetries by calculating the induced magnetic fields generated by a radially symmetric ocean and a small, spherical water reservoir between the ocean and Europa's surface. The consideration of two conductive bodies introduces non‐linear magnetic field coupling between them. We construct an analytical model to describe the coupling between two conductive bodies and calculate the induced fields within the parameter space of possible conductivity values and icy crust thicknesses. Given the plasma magnetic field perturbations, we find that a reservoir cannot be detected during a flyby at 25 km altitude using electromagnetic induction. Potential detection of liquid water reservoirs can be achieved by deploying magnetometers on Europa's surface, where one magnetometer is placed directly on the target region of interest and a second one in the nearby vicinity as reference to distinguish from global asymmetries. With this method, the smallest reservoir that can be detected has a radius of 8 km and a conductivity of 30 S/m. Larger reservoirs are resolvable at lower conductivities, with a 20 km reservoir requiring a conductivity of approximately 5 S/m.

Surfactant technology for improved hydrocarbon recovery in unconventional liquid reservoirs: a systematic literature review

An unconventional liquid reservoir (ULR) is a type of underground geological deposit containing liquid hydrocarbons, such as crude oil, natural gas liquids, or condensate, not found in traditional oil and gas reservoirs. These formations have distinct properties that make oil and gas production more difficult than in typical reservoirs. Surfactants can be added to the fracking fluid to aid in the release of hydrocarbons. By reducing the amount of water and chemicals used in the process, surfactants can assist to reduce some of the negative environmental implications associated with fracking. In the current study, a systematic literature review was used to analyze and identify existing literature on surfactant technology in unconventional liquid reservoirs from the previous five years. 12 papers out of the 500 papers collected showed that studies had been performed and proved that surfactants can potentially increase the recovery of unconventional liquid reservoirs. The mechanism behind the positive outcome was concluded to be the alteration of wettability of reservoir rock and interfacial tension. Based on the conducted review, evaluation of the environmental impact from the use of surfactant and assessment of economic feasibility of surfactant technology in ULR could be the future research topics.

Temperature-Dependent Gassing Analysis By on-Line Electrochemical Mass Spectrometry of Lithium-Ion Battery Cells with Commercial Electrolytes

Li-ion batteries (LiBs) are known to evolve gases during their first few formation cycles due to the formation of a solid electrolyte interphase (SEI) at the anode active material particle surface. Simultaneously, the electrolyte can react by other mechanisms leading to the formation of volatile species. 1,2 At a high state-of-charge, the cathode can also release reactive oxygen which causes the formation of CO and CO2 from the oxidative decomposition of the electrolyte.3,4 Consequently, by the analysis of evolved gas species one can study the effect of electrolyte additives, reveal substantial degradation processes within LiBs, and rationalize optimized formation strategies.4–6 The evolution of gaseous species is typically quantified in-situ by monitoring the cell pressure (e.g., via the so-called Archimedes principle) or by online mass spectrometry.5,7 Concerning the latter, an on-line electrochemical mass spectrometer (OEMS) was developed for the application in LiB research and proved to be particularly powerful, since it allows a quantitative analysis and the identification of the evolved and consumed gas during the operation of a battery.4,7 The quantification of OEMS data, however, is challenging when the vapor pressure of the electrolyte is high, which, e.g., is the case for linear carbonates, particularly at elevated temperatures. Mixtures of linear and cyclic carbonates are widely used in LiB applications due to their low viscosity, high salt solubility, and high conductivity. In contrast to the cyclic ethylene carbonate (EC) with a vapor pressure of 0.25 mbar, the vapor pressure for the typically used linear carbonates dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) can vary from 23 to 80 mbar at room temperature.8 Their vapor pressure further increases by a factor of ~3 when increasing the temperature from room temperature to 45 °C.9 Thus, a significant share of the gas in the head-space of the OEMS cell consists of electrolyte vapor. As they undergo fragmentation in the mass spectrometer, a background signal is superimposed on the relevant mass traces related to hydrogen, ethylene, carbon monoxide, oxygen, and carbon dioxide.1 Furthermore, the cell pressure inherently decreases due to the continuous leak through the capillary (with a leak rate of ~1 µL/min) that connects the OEMS cell (~10 mL volume) with the mass spectrometer. Because of the liquid reservoir of electrolyte in the OEMS cell and its constant vapor pressure, this results in an enrichment of the gas phase with electrolyte vapor. Analyzing the pressure-dependent flow of gaseous species into the mass spectrometer allowed us to introduce corrections for signal normalization, electrolyte background change, and signal quantification.In the present study, we applied these corrections in the investigation of the influence of LP57 (1 M LiPF6 in EC:EMC 3:7wt/wt) and LP47 (1 M LiPF6 in EC:DEC 3:7wt/wt) electrolyte on the gassing characteristics during the formation of full-cells with a graphite anode and a Ni-rich cathode from low (10 °C) to high (45 °C) temperatures. From that, we were able to conclude how the formation temperature influences the gas evolution related to SEI formation as well as the trans-esterification of the electrolyte and the lattice oxygen reactivity towards different electrolytes. A comparison to a model electrolyte (1.5 M LiPF6 in EC) with a low vapor pressure (< 0.25 mbar) allowed us to assess the detection limits of all the signals depending on the electrolyte’s vapor pressure and to evaluate the validity of our proposed signal corrections. Acknowledgment: The authors thank BMW AG for their financial support.

Device‐Scale Nanochannel Evaporator for High Heat Flux Dissipation

AbstractHigh heat flux values in thin film evaporation experiments are typically attained based on short wicking distance, ranging from tens to hundreds of micrometers between the meniscus and the liquid reservoir, thus making such devices vulnerable to quick drying out while also limiting their real‐world applicability. Here, the performance of a nanochannel (122 nm depth and 10 µm width) based evaporator with FC72 is demonstrated as working fluid. FC72 is an ideal fluid for electronics cooling as it is nonpolar and dielectric with a low boiling point. The 1 mm thick evaporator consists of more than 1000 nanochannels connecting two micro‐reservoirs 4.8 cm apart. Thin film evaporation experiments are conducted for four different power inputs, and the steady‐state wicking distance varied from 21 to 8 mm depending on the evaporator's working temperature. Direct weight measurement of evaporated FC72 is used to estimate the interfacial evaporative heat flux. Such a technique mitigates the need for contact angle measurement in micro/nano confined space, a methodology commonly used in literature studies that is prone to error and uncertainties. The maximum evaporative heat flux is 0.93 kW cm−2 at ≈65 °C hot spot temperature. Interestingly, the product of wicking distance and evaporative heat flux remain constant for all power inputs. Numerical simulations are performed to quantify heat loss and effectiveness of the evaporator.

A mass rate-of-rise model for additively manufactured wick structures

The hydraulic performance of heat pipes is typically characterized by the ratio of the wick's permeability to effective pore radius, K/reff. To experimentally quantify these values, mass rate-of-rise (mROR) testing is performed by dipping the tip of the wick into a liquid reservoir to track liquid uptake; the experimental data is then fitted to an ROR model. For conventional wicks, the gravity-based m-t model is free of user decisions and the most reliable. However, here we show that this model poorly fits ROR data for additively manufactured (AM) wicks, resulting in underprediction of K/reff. Experimental tests were conducted using 2 AM wicks—grooved and simple cubic—fabricated by laser powder bed fusion. Visual observations revealed that AM wicks exhibited a superposition of two wicking behaviors: a primary flow and microgroove/corner flow. The primary flow quickly fills the innermost area of the wicking structure. In contrast, the secondary flow gradually creeps up the 3D-printed strut surface through the printed fine scale features. A third term was introduced to improve the data fitting, based on previous research on capillary rise in corners. The revised model measured the AM grooved and simple cubic wicks' K/reff values as 1.23 μm and 1.02 μm, respectively.

An open microfluidic design for contact angle measurement

Spontaneous capillary flow in open microchannels is a phenomenon driven by surface energies. The contact angle that the liquid forms with the channel's substrate material and the cross-section of the microchannel decide whether liquid from a connected reservoir will automatically fill the channel or not. In this work we show how this behavior can be used to design a passive contact angle measurement device (CAMD) based on parabolic open microgrooves. To that end, we present a theory of open capillary flow in such microgrooves and compare the results to minimal energy surface simulations. Additionally, we discuss that the condition for capillary flow of curved microchannels is essentially equal to the condition for their straight counterparts having the same cross-section. Lastly, we present two demonstrators of our CAMD made out of micromilled poly(methyl methacrylate). The devices consist of five open microchannels with different cross-sections which are connected to a common liquid reservoir. We show how the behavior of a liquid placed into that reservoir can be used to evaluate the contact angle between the liquid and the substrate material. A comparison to conventional contact angle goniometry shows that our approach is able to successfully estimate contact angles with an accuracy of 10° by design which can be improved by employing a greater number of microchannels. Since our devices were automatically designed and can be tuned to specific applications, this provides an easy approach to include contact angle measurement into existing lab-on-a-chip devices.