High Pressure Difference Research Articles

Computational multiphase mixture simulations of a two-phase R-744 ejector geometry in transcritical R-744 heat pump applications

Purpose Two-phase R-744 ejectors are critical components enabling energy recovery in R-744 heat pump and refrigeration systems, but despite their simple geometry, the flow physics involve complex multiphase mixing phenomena that need to be well-quantified for component and overall system improvement. This study aims to report on multiphase mixture simulations for a specific two-phase R-744 ejector with supercritical inlet conditions at the motive inlet side. Design/methodology/approach Four different operating conditions, which have motive inlet pressure range of 90.1 bar–101.1 bar, are selected from an existing experimental data set. A two-phase thermodynamic equilibrium (TPTE) model is used, where the fluid properties are described by a thermodynamic look-up table. Findings The results show that the TPTE model overpredicts mass flow rates at the motive inlet, resulting in a relative error ranging from 15.6% to 21.7%. For the mass flow rate at the suction inlet, the relative errors are found less than 1.5% for three cases, while the last case has an error of 12.4%. The maximum deviation of the mass entrainment ratio is found to be 8.0% between the TPTE model and the experimental data. Ejector efficiency ranges from 25.4% to 28.0%. A higher pressure difference between the ejector outlet and the diverging nozzle exit provides greater pressure lift. Research limitations/implications Based on the results, near future efforts will be to optimize estimation errors while enabling more detailed field analysis of pressure, density, temperature and enthalpy in the computational domain. Originality/value The authors have two main original contributions: 1) the presented thermodynamic look-up table is unique and provides unique computation for the real-scale ejector domain. It was created by the authors and has not been applied before as far as we know. 2) To the best of the authors’ knowledge, this study is the first study that applies the STAR-CCM+ multiphase mixture model for R-744 mixture phenomena in heat pumps and refrigeration systems.

Numerical study on the inner spray and combustion of active pre-chamber jet ignition for achieving higher performance of a hybrid engine under ultra-lean conditions

The mechanism of active pre-chamber (APC) inner fuel-air mixing, initial flame kernel formation, and jet flame evolution is still not clear. In this study, different APC inner geometry structures coulped with different mixture status were designed to synthetically analyze the inner gas flow, spray mixing, and hot jet flame evolution. The results showed that the APCs with small cone angles of 45° and 50° could promote the fuel-air mixing and spray atomization in a wider APC top space compared to APCs with large cone angles of 60° and 65°. An appropriate APC cone angle of 55° could reduce rich mixture zone and facilitate rapid flame kernel formation, fast flame propagation, and high jet activity, which was good for igniting the in-cylinder ultra-lean mixture. APCs with real fuel injection showed one heat release rate (HRR) peak, while APCs filled with homogeneous mixture showed the typical two peaks in the HRR profiles, the suitable mixture in APC duct section burned and formed the second HRR peak. The short thick APC induced the rich mixture distributed around the spark plug to form the initial flame kernel and showed a faster concentrated combustion process along with a higher pressure difference between APC and MC.

Effectiveness of Gas Recombination Catalyst Layers in Mitigating H2 Crossover in PEM Water Electrolyzers Operating at High Differential Pressure

Gigawatt-scale deployment of proton exchange membrane water electrolyzers (PEMWE) to produce green hydrogen at $1/kg of H2, the US department of energy’s (DOE) ultimate cost target, requires the use of thinner membranes to reduce ohmic losses at high current densities as well as differential pressure operation to improve the overall system efficiency.1 High differential pressure operation results in significant hydrogen crossover through PEMs leading to safety concerns due to the formation of a flammable gas mixtures at anode (> 4% H2 in O2).2 Therefore, the successful deployment of PEMWEs at scale relies on successful implementation strategies to reduce the hydrogen concentration at anode to enable safe operation at high efficiency. These strategies include incorporating gas recombination catalyst (GRC) in the membrane, PTL or downstream in the anode gas outlet. However, the impact of GRC layers on PEMWE performance and hydrogen crossover rates at high differential pressure is not well understood.In this work, we employ in-operando gas chromatography coupled with thermal conductivity detector along with PEMWEs operating at differential pressures (up to 30 bar) to quantify hydrogen crossover rates through PEM at differential pressure. Using this setup, we evaluate the effectiveness of gas recombination layers incorporated in PEMWE membrane electrode assemblies (MEA) in mitigating the risk of formation of the flammable gas mixture. Further, we will also discuss implications of high differential pressure operation on PEMWE performance, durability, and operational safety.

Evaluating the Impact of Cell Assembly and Operating Conditions on the Performance of Anion Exchange Membrane Electrolyzers

The alkaline water electrolyzer (AWE) and proton exchange membrane water electrolyzer (PEMWE) are the two dominant commercial platforms to produce hydrogen through electrolysis. Recent efforts have focused on combining the benefits of the two technologies, leading to the creation of the anion exchange membrane water electrolyzer (AEMWE). AEMWEs operate under high pH conditions, like AWEs, enabling the use of cost-effective materials as cell components and non-noble electrocatalysts. AEMWEs also utilize the same high-performance zero-gap design PEMWEs and also have the ability to operate at high differential pressures. Therefore, AEMWEs offer the opportunity to optimize both cost and performance, out-pacing both incumbent technologies after further development.As the “active” materials in AEMWEs, the anion exchange membranes and ionomers and the catalysts have been widely studied and a number of materials have been proposed and reported on in the literature and throughout the last several ECS meetings. However, such materials are only one piece of the overall puzzle when it comes to the operation of AEMWEs. There are several aspects of cell assembly and operation that go a long way to dictating the performance of an operating cell.Therefore, the overarching goal of this study was to investigate several operational variables for AEMWEs with a known high-quality set of anion-exchange materials, known commercially as Aemion+™ paired with commercially available catalysts – PtNi/C at the cathode and either IrOx or NiFeOx at the anode. For cell assembly, representative variables that were changed were the type of membrane and electrode pre-treatment, gasket thickness, cell torque and membrane thickness. Operationally, temperature, current density and break-in procedure were adjusted. This talk will link each of these variables to the polarization performance and galvanostatic durability

(Invited) Mechanical Properties of Proton Exchange Membranes for Water Electrolysis Applications

Water electrolysers are critical to the advancement of sustainable hydrogen technologies. A key component of proton-exchange membrane water electrolysers (PEMWE) is the ionomer membrane which transports protons and water from the anode to the cathode and physically separates the H₂ and O₂ reaction products. Importantly, the barrier properties of the membrane must be maintained at high differential pressure over the lifetime of the PEMWE. To help predict the mechanical durability and operational safety of the PEMWE, it is important to understand the mechanical properties of the PEM as a function of temperature, differential pressure, and time.The main component of a typical modern PEM is a perfluorosulfonic acid (PFSA) ionomer. PFSAs have a hydrophobic perfluorinated backbone with pendant perfluorinated side chains terminating in sulfonic acid groups. The general chemical structure of PFSAs is understood to result in phase separation into hydrophilic, sulfonate-rich domains that act as transport pathways and hydrophobic, tetrafluoroethylene-rich domains that impart thermomechanical stability. In PEMWE applications, short-side chain PFSAs are a promising alternative to the benchmark Nafion, a long-side chain PFSA. At a given ion-exchange capacity (IEC), the ratio of perfluorinated backbone to sulfonic acid side chain increases as the side chain length decreases. Thus, short-side chain PFSAs may be more thermomechanically stable while maintaining good proton and water transport necessary for PEMWE efficiency.In this work, the mechanical properties of short-side chain PFSAs are investigated as a function of IEC, temperature, differential pressure, and time. Particular focus is given to compressive mechanical measurements to simulate the conditions experienced by the membrane in PEMWE applications. The findings are expected to help inform the design of next-generation membranes for hydrogen technology applications.

Experimental investigation of a transcritical CO2 refrigeration system incorporating rotary gas pressure exchanger and low lift ejectors

Natural refrigerants like CO2 are playing a significant role in making refrigeration and heat pump systems climate-friendly by slowly phasing out the high global warming refrigerants like hydrofluorocarbons (HFCs). However, the efficiency of a transcritical CO2 refrigeration system declines significantly when the ambient temperature increases, primarily attributed to the high-pressure lift and the losses incurred during expansion. To remedy this issue, this paper presents a novel rotary gas pressure exchanger (PXG) device, which simultaneously achieves high differential pressure expansion work recovery and the “free compression” of the portion of the flash gas in a compact, rotary machine. For this, a PXG device is designed, fabricated, and tested to achieve free compression of CO2 over the entire differential pressure of approximately 70 bar between a receiver and a gas cooler. This is one of the highest free-pressure lift provided by any device to date in CO2 refrigeration. However, there is a small pressure loss of approximately 1–2 bar in the system due to viscous and inertia losses in the piping and in the PXG itself, which needs to be overcome by an external booster device. Results on a baseline PXG integrated system with two low lift booster compressors are presented, which show up to 60 bar free pressure lift and up to 18.2 % COP improvement provided by PXG. Additionally, key performance characteristics of the PXG, like the expansion work recovery, the mass boost ratio, direct fluid-to-fluid contact, and no pass-through operation are experimentally quantified. This work also presents a novel method to integrate two low lift ejectors with PXG to eliminate the need for separate low lift compressors. The low lift ejectors are designed, fabricated, and tested in-house, followed by their integration with the PXG device. A new type of transcritical CO2 refrigeration system is designed to integrate these low lift ejectors with PXG, and experiments are conducted at various evaporator thermal duties and gas cooler exit temperatures, simulating varying ambient temperature conditions. A novel control system to control the gas cooler pressure to optimal thermodynamic levels using PXG rotational speed is demonstrated experimentally. Further, automated control of high-pressure low lift ejector mass flow using an in-built needle design has been successfully demonstrated to optimise PXG mass boost performance. The LP low lift ejector achieved a successful pressure lift of 3.8 bar, and the HP low lift ejector showed a lift of 5.7 bar on the top of 42 bar free pressure lift provided by PXG for up to 5.8 kg/min mass flow delivered by free PXG compression. The results from this study demonstrate that the PXG device provides a significant energy efficiency improvement to the transcritical CO2 refrigeration system, and the novel low lift ejectors, when integrated with PXG, provide a successful method to maximise PXG’s thermodynamic potential.

Performance assessment of stairwell smoke prevention techniques in a model high-rise building

The complexities of construction and increased fuel loading in high-rise buildings implied engineers to shift towards performance-based design (PBD) instead of prescription design to ensure a higher level of fire safety. Since PBD is an iterative process, so engineering models and tools based on numerical techniques are generally used to evaluate the trial designs. In the present study, various methods of stairwell smoke prevention have been analysed and compared using Fire Dynamics Simulator (FDS) in a model high-rise building. Optimization is done by defining critical values of smoke layer height and maximum pressure differential as 2 m and 55 Pa, respectively. Results demonstrated that natural and cross ventilation in the stairwell are not fully effective for smoke prevention due to the enhanced stack effect observed in them. Further, the pressurization of stairwell at a minimum differential pressure of 25–30 Pa seems to be effective only when all windows in the stairwell are closed. Effectiveness of single and multiple injection pressurization techniques are also assessed. The single injection system fails to maintain the required pressure differential when multiple doors are opened and causes high-pressure differentials at the top stories. Open windows in the stairwell reduce the effectiveness of the pressurization method. Placing an exhaust duct near windows enhances the effectiveness of the PPV method, even at lower capacities of supply vents, and proves effective when stairwell windows are open by creating a higher stack effect in the exhaust duct. The current research involved a comparative analysis of various stairwell smoke prevention methods, as outlined in NFPA 92 and in accordance with the National Building Code of India. The findings may have broader applicability beyond the studied context.

Interfacial exchange of airflow and bacteria-carrying particles induced by door opening and foot traffic in an operating room

Maintaining high air cleanliness in operating rooms (ORs) can reduce surgical site infections (SSIs). However, door openings and foot traffic during surgery may allow the intrusion of contaminated air and increase microbial contamination in ORs. In this study, numerical methods were applied to investigate the dynamic airflow and bacteria-carrying particle (BCP) dispersion during sliding door opening and foot traffic in an OR. The door movement and realistic human walking were modeled by the dynamic mesh technique. The interfacial exchange of airflow and BCPs was evaluated as the medical staff entered and exited the OR under fixed supply air temperatures and various differential pressures, respectively. Results showed that walking across the door interface caused a sharp increase in airflow exchange between the OR and the anteroom (ANT). An average walking speed of 1.2 m/s induced a maximum inflow rate of approximately 1.32 times greater when entering the OR than when leaving the OR. Once the door was open, the temperature difference convection effect was more significant than the pressure difference outflow effect. Differential pressure outflow indirectly affected airflow exchange at the door interface by changing the direction and temperature of airflow in the ANT. Whether entering or leaving the OR, the BCP intrusion ratios were on average 1.5 times higher at high pressure differentials (15 and 20 Pa) than at low pressure differentials (5 Pa and 10 Pa). This study is expected to improve the understanding of the impact of door opening and foot traffic on OR air quality during surgery.

Numerical simulation study of natural gas hydrate extraction by depressurization combined with CO2 replacement

Utilizing depressurization combined with CO2 replacement for extracting natural gas hydrates (NGHs) is vital for sustainable energy and carbon sequestration. In this study, a NGH reservoir numerical model was developed to investigate the impacts of depressurization combined with CO2 replacement on hydrate extraction at a field scale. Findings reveal an increase in methane production with reduced bottom hole pressure. When the bottom hole pressure is 3.5 MPa, the methane production reaches its maximum at 1.71 × 106 m3. Methane hydrates near production and injection wells decompose first, with deeper hydrates decomposing more easily. Higher differential pressures between injection and production enhance methane extraction and CO2 hydrate formation. However, excessive pressure differential (1.5 MPa) can lead to CO2 breakthrough across reservoir barriers, adversely affecting the purity of methane. At 1800 d, the methane purity is only 36.2 %. Optimal methane extraction and CO2 sequestration occur at higher injection temperatures (9 °C) below the CO2 hydrate phase equilibrium temperature. Temperatures above this equilibrium adversely affect both processes. The study validates the feasibility of depressurization with CO2 replacement for extracting hydrates in the Shenhu area, offering theoretical guidance for synergistic offshore methane extraction and CO2 sequestration techniques.

Curvature-mediated rapid extravasation and penetration of nanoparticles against interstitial fluid pressure for improved drug delivery

Elevated interstitial fluid pressure (IFP) within pathological tissues (e.g., tumors, obstructed kidneys, and cirrhotic livers) creates a significant hindrance to the transport of nanomedicine, ultimately impairing the therapeutic efficiency. Among these tissues, solid tumors present the most challenging scenario. While several strategies through reducing tumor IFP have been devised to enhance nanoparticle delivery, few approaches focus on modulating the intrinsic properties of nanoparticles to effectively counteract IFP during extravasation and penetration, which are precisely the stages obstructed by elevated IFP. Herein, we propose an innovative solution by engineering nanoparticles with a fusiform shape of high curvature, enabling efficient surmounting of IFP barriers during extravasation and penetration within tumor tissues. Through experimental and theoretical analyses, we demonstrate that the elongated nanoparticles with the highest mean curvature outperform spherical and rod-shaped counterparts against elevated IFP, leading to superior intratumoral accumulation and antitumor efficacy. Super-resolution microscopy and molecular dynamics simulations uncover the underlying mechanisms in which the high curvature contributes to diminished drag force in surmounting high-pressure differentials during extravasation. Simultaneously, the facilitated rotational movement augments the hopping frequency during penetration. This study effectively addresses the limitations posed by high-pressure impediments, uncovers the mutual interactions between the physical properties of NPs and their environment, and presents a promising avenue for advancing cancer treatment through nanomedicine.

DEVELOPMENT OF DOWNHOLE PUMP VALVE ASSEMBLY

The purpose of the work is modernization of the valve, in order to increase reliability, wear resistance, increase the pump flow and reduce the load on the rod string, as well as improve durability. The sucker rod pump is one of the most popular and extensively utilized artificial lift systems. It is a frequently chosen option for lifting oil because of its fundamental simplicity, low operating costs, and adaptability in power supply. In the long run of oil production history, sucker-rod pumping was the first option—and frequently the only option—when artificial lift was required. For this reason, the oldest and most popular method of producing oil wells worldwide is sucker-rod pumping. Since the steel used to make rods has limited strength, sucker-rod pumping is typically thought of as a way to raise moderate to low liquid production rates from shallow to medium well depths due to depth restrictions. Since the correct working of the standing and traveling valves is largely responsible for an efficient pumping operation, valves are regarded as the heart of the sucker-rod pump. The extremely high differential pressures across the valve during pumping necessitate a highly dependable sealing action between the ball and the seat. Small initial flaws in the sealing surfaces or subsequent corrosion- or abrasion-related problems result in greater liquid slipping and a quick decline in valve function because of fluid cutting. Subsurface pumps using traditional ball-and-seat valves suffer a number of basic operational issues: • Because of the greatly high number of pumping cycles per day, the sealing surfaces may sustain significant damage from the frequent collision of the two parts against one another. • In deviated wells, valve wear is uneven and can cause premature failure. • Typical cage constructions, meant to limit impact damage, typically restrict the flow area available through the valve and can be the source of pumping inefficiencies due to low fillage of the pump barrel. Keywords: sucker rod pumps, downhole pump, traveling valve, standing valve, valve assembly.

Study of pressure difference influence on air flow, heat recovery efficiency and acoustic performance of a local decentralized ventilation device

In the context of energy-efficient and sustainable building practices, decentralized ventilation units have become increasingly popular. These units offer fresh air supply while recovering heat from exhaust air, enhancing thermal comfort and reducing energy consumption. However, they are subjected to changing affecting forces caused by the pressure difference and wind. This influence is not deeply studied in existing research. This study focuses on pressure differences' influence on airflow, heat recovery efficiency, and acoustic performance of a decentralized ventilation device. Understanding this correlation is vital for occupant comfort and environmental sustainability. The research was conducted in a controlled climatic chamber, replicating external conditions. The main objectives included airflow, heat recovery efficiency, and acoustic performance. Findings showed airflow significantly affected by pressure differences, with extract cycle reductions up to 20 m³/h at Δ30 Pa. Supply cycle airflow moderately increased with pressure differences, maintaining balanced volumes. Heat recovery correlated directly with pressure difference, reaching approximately 96% efficiency at 0 Pa, which is similar to the one stated by the manufacturer, but declining to 76% at Δ30 Pa. The results show that such a ventilation system will serve mostly as an air supply at higher pressure differences and during wintertime in colder climates can lead to cold draught and complaints from users even leading to shutting off the devices This research contributes to improving ventilation device design for more effective and sustainable building practices.

Application of separate layer water injection in high differential pressure wells

With the development of a heavy fine-RRB-layering system and dynamic adjustment, the number of large differential pressure wells increases gradually. The effect of high-pressure difference wells on water injection development is that it is difficult to separate water injection allocation, low pass rate of layers and short effective period of separate sealing, which affects the development effect of water flooding. For this reason, the research on stratified water injection technology with large pressure differences is carried out using step-by-step throttling. The throttling pressure difference borne by the water nozzle is reduced. The large throttling pressure difference produced by the water nozzle is realized. The qualified rate of the layer section is increased to improve the anti-creep performance of the expansion Packer and the sealing effect of large pressure difference injection wells and to extend the service life of the Packer. The field application results of 216 wells in the Shengli Oil Field show that the technique can effectively improve the pass rate of the layers and the sealing effect of the layers and prolong the life of the string.

Leakage performance of hybrid brush seals under high differential pressure conditions

A three-dimensional axial fluid-porous medium-flow field model was designed for the sealing properties of the hybrid brush seal (HBS) seal structure under complex operating conditions. Using a computational fluid dynamics model in view of non-Darcy porous media, the pressure and velocity distributions of the sealing medium in the flow path were simulated, and the flow characteristics of the hybrid brush seal were analysed to obtain the leakage of the hybrid seal structure. The results show the implication of pressure ratio (Rp) on the labyrinth brush seal leakage rate and pressure distribution. Compared with typical brush seal test results, as the inlet and outlet pressure ratio (Rp) increases, the more obvious the hybrid brush seal sealing effect is, when the pressure ratio is 3 bar, the spillage of the hybrid brush seal is reduced by about 39%.

Development of a new MEMS resonant differential pressure sensor with high accuracy and high stability

This paper presents the design method and manufacture of a new resonant differential pressure sensor where the sensitive element is assembled with packaging components through an embedded boss type stress isolation structure. The responses of differential pressure, temperature and static pressure are theoretically modeled, which provide guidance on sensor design. And a method based on finite-element is used to conduct dimensional optimization of sensitive elements and embedded boss type stress isolation structures based on device sensitivities and isolation effect. Fabrication based on bulk micromachining and packaging based on Au-Au bonding and Au/Sn welding are employed to manufacture the sensor. Experimental results indicate that the fabricated sensor yields a high differential pressure sensitivity of − 87.06 Hz/kPa, a low temperature sensitivity of 5.24 Hz/°C and a low static pressure sensitivity of − 0.48 Hz/kPa. Additionally, a high accuracy of 0.05 %FS is reported under full scale. Furthermore, the sensor demonstrates an excellent long-term stability with no decrease on accuracy within a 15-day experiment.

Fundamentals of Gas Permeation in PEM Water Electrolyzers Operated at High Pressures

The high cost of clean hydrogen (H2) remains a major hurdle to drive large scale adoption and achieve zero emission goals. For large scale deployment using low cost renewable electricity, polymer electrolyte membrane water electrolyzers (PEMWEs) show high potential based on their high faradaic efficiency and high operating current density. Operation of PEMWEs at high differential pressures can significantly reduce the per kilogram price of H2 and increase the overall energy efficiency while also eliminating the necessity to compress H2 during storage and transportation.1 Thinner membranes reduce the voltage losses from ohmic resistance and achieve high faradaic efficiencies. However, a higher crossover of hydrogen from the cathode through the membrane to the anode is observed for thinner membranes at high cathode operating pressures. As Ir/IrO2 (anode catalyst) is inefficient in oxidizing H2 1, this increased crossover of H2 not only reduces the PEMWE efficiency but also results in formation of an explosive gas mixture. Some initial studies also suggest critical effect of crossover H2 on durability of the anode catalyst. Addition of a gas recombination catalyst (GRC) in the membrane is a highly useful strategy to oxidize permeating H2 and prevent the formation of such explosive gas mixtures. Despite the importance, fundamentals of gas recombination reaction mechanism along with the effects of GRC and its properties on it is not well established.In this study, effect of the GRC and its properties (loading, particle size, distribution, and location) on H2 permeation will be elucidated using a high pressure (up to 30 bar) electrolyzer setup coupled with online gas chromatography (Figure 1). The role of H2 and O2 partial pressures and operating current densities (simulated by varying the flow rates) will also be closely examined. Effects caused by the addition of anode and cathode catalyst layers on H2 permeation will also be presented in addition to long-term membrane durability results.Figure 1. Decreased H2 permeation rate observed with GRC (Membrane A) at different cathode (H2) operating pressures at 80 °C using ex-situ electrolyzer setup. Deactivation of the GRC reaction is observed when switching the anode gas from O2 to N2. Figure 1

Sulfate reduction behavior in response to landfill dynamic pressure changes

During the long-term stabilization process of landfills, the pressure field undergoes constant changes. This study constructed dynamic pressure changes scenarios of high-pressure differentials (0.6 MPa) and low-pressure differentials (0.2 MPa) in the landfill pressure field at 25 °C and 50 °C, and investigated the sulfate reduction behavior in response to landfill dynamic pressure changes. The results showed that the pressurization or depressurization of high-pressure differentials caused more significant differences in sulfate reduction behavior than that of low-pressure differentials. The lowest hydrogen sulfide (H2S) release peak concentration under pressurization was only 29.67% of that under initial pressure condition; under depressurization, the highest peak concentration of H2S was up to 21,828 mg m−3, posing a serious risk of H2S pollution. Microbial community and correlation analysis showed that pressure had a negative impact on the sulfate-reducing bacteria (SRB) community, and the SRB community adjusted its structure to adapt to pressure changes. Specific SRBs were further enriched with pressure changes. Differential H2S release behavior under pressure changes in the 25 °C pressure environments were mediated by Desulfofarcimen (ASV343) and Desulfosporosinus (ASV1336), while Candidatus Desulforudis (ASV24) and Desulfohalotomaculum (ASV94) played a key role at 50 °C. This study is helpful in the formulation of control strategies for the source of odor pollution in landfills.

Hydrate Formation from Joule Thomson Expansion Using a Single Pass Flowloop

Hydrate risk management is critically important for an energy industry that continues to see increasing demand. Hydrate formation in production lines is a potential threat under low temperature and high-pressure conditions where water and light gas molecules are present. Here, we introduce a 1-inch OD single-pass flow loop and demonstrate the Joule-Thomson (JT) expansion of a methane-ethane mixture. Initially, dry gas flowed through the apparatus at a variable pressure-differential. Larger pressure differentials resulted in more cooling, as predicted by standard thermodynamic models. A systematic deviation noted at higher pressure differentials was partially rectified through corrections incorporating heat transfer, thermal mass and kinetic energy effects. A wet gas system was then investigated with varying degrees of water injection. At the lowest rate, hydrate plugging occurred close to the expansion point and faster than for higher injection rates. This immediate and severe hydrate plugging has important implications for the design of safety relief systems in particular. Furthermore, this rate of plugging could not be predicted by existing software tools, suggesting that the atomization of liquids over an expansion valve is a critical missing component that must be incorporated for accurate predictions of hydrate plug formation severity.

Tailoring the Mass Transport to Achieve High-Performing Unitized Regenerative Fuel Cells Considering Practical Operating Conditions

Unitized regenerative fuel cells (URFCs) convert electrical energy to chemical bonds in hydrogen during charge and convert chemical energy to output electricity during discharge, offering a promising solution to long-term energy storage. Recent studies indicate that the round-trip-voltaic efficiency (RTE) and longevity of URFCs are limited by complex mass transport during charging and discharging. Here, we first investigate how different porous transport layer (PTL) structures can impact URFC performance. The preferred PTL has a low tortuosity and high porosity, leading to a high RTE above 50% at 1 A cm−2 using Nafion 212. Moreover, thicker membranes, such as Solvay 90, are required to ensure mechanical stability and minimize H2 crossover when operating under high differential pressure. Although this assembly inevitably leads to a higher ohmic loss, the RTE can be improved by further tailoring the electrode structures to facilitate mass transport by using supported catalyst, which still achieves over 50% RTEs at 1 A cm−2. Optimization of porous structure to mitigate mass transport resistance with appropriate materials down selection considering practical application requirements can be a key design principle for achieving high-performing URFCs.

Lithology and Lithofacies Characteristics of Deeply Buried Clastic Reservoirs in Alternating Wet-arid Climate and its Hydrocarbon Significance

There have been series of HPHT (high temperature and high pressure) reservoirs with good quality and high productivity discovered in the Triassic Skagerrak Formation in the Central Graben of the UK North Sea. The bottlenecks for further E&P activity are the complicated depositional facies and high reservoir heterogeneity. The main reservoir space is a mixed porosity network composed of primary pores, micro-pores, secondary pores, secondary micro-pores and micro-fractures. Reservoirs of the Skagerrak Formation have greatly varied lateral connectivity as well as poor vertical connectivity. In the case of sufficiently high pressure differentials, hydrocarbon can be fed from high-potential area to low-potential area. There is no simple linear relationship between depth and reservoir quality. The primary depositional texture (grain size/sorting/clay content, etc.) linked to facies has a fundamental control on reservoir quality. Clean and well sorted cross laminated sandstone has the best reservoir quality, while the reservoir quality of planar laminated sandstone decreased due to increased degree of compaction caused by mica drapes. The reservoir quality of the fine-grained ripple cross laminated sandstone is even poorer than that of the planar laminated sandstone, due to abundant mica and clay drapes. Mottled bioturbated sandstone is fine grained with high clay content, which is more muddy because of containing burrows and insect larva. Pedoturbated sandstone has the poorest reservoir quality due to severe dolomite cementation. The dominant detrital material of the Skagerrak Formation is feldspar that provides abundant secondary porosity by alteration and dissolution. Chlorite coats are commonly developed and stained with residual oil or bitumen, which clearly inhibits quartz cementation and feldspar overgrowth. The presence of these clay coats contributes to the preservation of anomalously high porosity at depth in the cleaner and coarser grained fluvial channel facies. The Skagerrak formation facies is a dryland fluvial-lacustrine depositional system which is controlled by fluctuations of depositional base level due to salt mobilisation. The Skagerrak formation consists of several cycles that are vertically separated by lacustrine mudstone. The reservoir permeability system is composed of active fluvial channel sandstones, terminal splay sandstones, abandoned fluvial channel sandstones, minor channel sandstones connecting fluvial channel and terminal splay, as well as low-permeability faults, while the active fluvial channel sandstone is the “sweet spot”. The analysis of controls on deeply buried reservoir quality is significant to precisely predict “sweet spot” in the Skagerrak Formation.