Search

In this paper, a series of monotonic triaxial tests were carried out at a relatively wide range of backpressure conditions (from 100 kPa to 29MPa) to investigate its influence on the shear properties of silt sand. Backpressure effect on the shear strength, excess pore pressure, and volumetric strain behavior were analyzed, and the underlying influencing mechanism was preliminarily discussed. According to test results, the application of higher backpressure conditions on quasi-saturated samples resulted in a significant buildup of negative excess pore water pressure, which led to an increase in shear strength. The trend became less pronounced after the backpressure exceeded 5MPa. Nevertheless, within this range, the shear strength increased by approximately 40 kPa for every 100 kPa increase in backpressure. Furthermore, the consolidated-drained (CD) test results revealed that the value of backpressure (at least within 29MPa) had no detectable influence on the shear properties of saturated samples. It was indirectly proved that the undrained shear strength was influenced by the change of effective stress caused by excess pore water pressure in the shear dilation stage of quasi-saturated samples. The applicability of the effective stress principle to predict soil strength even in ultra-high backpressure conditions was confirmed. [ABSTRACT FROM AUTHOR]

A vast scientific literature has shed light on hydrogen as a promising vector for carbon-free mobility. Within this scope, over the last few decades several efforts were directed towards the characterization of hydrogen spray, given its significant influence on the combustion efficiency. Nevertheless, several aspects underlying the hydrogen spray development are still far from being fully understood. This framework prompted the authors to undertake a robust experimental campaign, performing hydrogen injections over a wide range of injection settings. In this study, the schlieren method was utilized to capture the image of jets performed at injection pressure of 3.6 MPa and exiting an outward-opening injector. Afterwards, the spray images were processed by means of an in-home developed Matlab script. In order to assess the spray characteristics, such as the penetration length, area and volume, the analysis of the results was focused on the combined impact of backpressure, ranging from 0.12 to 1.5 MPa, with current profile determining the pintle dynamic. Besides, a qualitative analysis of the injection setting impact on the shock wave position was carried out. In the light of emerged findings, the research serves as a further baseline for forthcoming research activities dealing with hydrogen spray. • The pintle motion engenders a rarefaction wave, benefiting the hydrogen momentum. • Greater currents, energizing the injector coils, boost the pintle descent, and the jet penetration is faster. • Increasing backpressure and weaker currents curb the spray area and volume developments. • Weaker currents prolong the transient of the shock wave position. • Higher backpressures and lower currents lead the shock wave to arise more closely to the injector. [ABSTRACT FROM AUTHOR]

Purpose: To construct a detailed mechanistic and physiologically based biopharmaceutics model capable of predicting 1) device-formulation-tissue interaction during the injection process and 2) binding, degradation, local distribution, diffusion, and drug absorption, following subcutaneous injection. This paper is part of a series and focusses on the first aspect. Methods: A mathematical model, SubQ-Sim, was developed incorporating the details of the various substructures within the subcutaneous environment together with the calculation of dynamic drug disposition towards the lymph ducts and venous capillaries. Literature was searched to derive key model parameters in healthy and diseased subjects. External factors such as body temperature, exercise, body position, food or stress provide a means to calculate the impact of "life events" on the pharmacokinetics of subcutaneously administered drugs. Results: The model predicts the tissue backpressure time profile during the injection as a function of injection rate, volume injected, solution viscosity, and interstitial fluid viscosity. The shape of the depot and the concentrations of the formulation and proteins in the depot are described. The model enables prediction of formulation backflow following premature needle removal and the resulting formulation losses. Finally, the effect of disease (type 2 diabetes) or the presence of recombinant human hyaluronidase in the formulation on the injection pressure, are explored. Conclusions: This novel model can successfully predict tissue back pressure, depot dimensions, drug and protein concentration and formulation losses due to incorrect injection, which are all important starting conditions for predicting drug absorption from a subcutaneous dose. The next article will describe the absorption model and validation against clinical data. [ABSTRACT FROM AUTHOR]

Overflow accidents are frequent in deepwater managed-pressure drilling, and the monitoring basis and control methods of risks are vague, necessitating the establishment of a suitable risk matrix. Based on the traditional risk matrix analysis method, this paper establishes a overflow-backpressure risk matrix with overflow size and backpressure threshold as judgment criteria, and formulates 11-level backpressure application plans and backpressure application calculation models. The results show that the overflow-backpressure risk matrix with overflow size and backpressure threshold as judgment criteria meets the requirements of deepwater managed-pressure drilling design and can significantly determine the risk level of overflow occurrence. The formulated backpressure application calculation model refines the backpressure control situation of managed-pressure drilling and can apply different backpressure according to different risk levels. After applying risk control measures, the maximum allowable drilling speed and backpressure in different working conditions of the 3950-4130 m wellbore section were designed on-site at well A1, and the risk level was reduced to 0. This overflow-backpressure risk matrix can classify and control the risk of overflow in deepwater managed-pressure drilling. [ABSTRACT FROM AUTHOR]

A significant rise in the adoption of streaming applications has changed the decision-making processes in the last decade. This movement has led to the emergence of several Big Data technologies for in-memory processing, such as the systems Apache Storm, Spark, Heron, Samza, Flink, and others. Spark Streaming, a widespread open-source implementation, processes data-intensive applications that often require large amounts of memory. However, Spark Unified Memory Manager cannot properly manage sudden or intensive data surges and their related in-memory caching needs, resulting in performance and throughput degradation, high latency, a large number of garbage collection operations, out-of-memory issues, and data loss. This work presents a comprehensive performance evaluation of Spark Streaming backpressure to investigate the hypothesis that it could support data-intensive pipelines under specific pressure requirements. The results reveal that backpressure is suitable only for small and medium pipelines for stateless and stateful applications. Furthermore, it points out the Spark Streaming limitations that lead to in-memory-based issues for data-intensive pipelines and stateful applications. In addition, the work indicates potential solutions. [ABSTRACT FROM AUTHOR]

Flow distortions caused by ambient wind can have complex negative effects on the performance of direct air-cooling condensers, which use air as their cooling medium. A control-oriented model of the direct air-cooling condenser model, considering fan volumetric effectiveness and plume recirculation rate, was developed, and its linearization model was derived. The influences of fan volumetric effectiveness and plume recirculation rate on backpressure were analyzed, and the optimal backpressure was calculated. To improve both the transient performance and steady-state energy saving of the condenser, a multi-model-based predictive control strategy was proposed to divisionally adjust the fan array. Four division schemes of the direct air-cooling fan array constituted the local models, and in each division scheme, axial fans were divided into three groups according to the wind direction: windward fans, leeward fans, and other fans. The simulation results showed that the turbine backpressure can be increased by 15 kPa under the influence of plume recirculation and the reduction of the fan volumetric efficiency. The fan division adjustment strategy can achieve satisfactory control performance with switching rules. [ABSTRACT FROM AUTHOR]

• The effect of "backpressure" on responsive signal control performance in one simple network is studied. • Only a simple network is considered and travellers are supposed to choose their own best routes. • It is shown that on the simple network having backpressure increases equilibrium delays. • It is shown that on the simple network having backpressure reduces network capacity. Many responsive traffic signal control strategies are "pressure-driven". These strategies move green-time from stages with a lower pressure to stages with a higher pressure, at each junction; often aiming to approximately equalise stage pressures at each junction. In some of these pressure-driven strategies each stage pressure at a junction includes a "backpressure" term, which depends on downstream links. Such backpressure terms reduce the pressure on stages and reduce pressure most for those stages leading toward the most highly congested downstream road links. The expectation is that there will then be a reduction in traffic flow exiting the junction toward already highly congested road links, and that this will reduce queue lengths and network delays. This paper shows that this is not always the case by giving two examples where having backpressure within the control policy on a network with two signal controlled junctions (1) increases both equilibrium delays at one of the junctions for certain demands, and (2) never reduces any of the equilibrium delays at either junction. A simple dynamic evolution with a steady reduction in demand is also shown in which two of the considered policies, one with backpressure, give rise to equilibrium delays and queues which tend to infinity, and reveal a gap; in this gap feasible demands have no equilibrium consistent with the two control policies and in a day-to-day dynamical context delays and queues are unbounded. This paper considers only the simple network shown in figure 1 under certain specified conditions. One main avenue for further research might be to consider whether the results shown here also hold in different networks under different conditions. [ABSTRACT FROM AUTHOR]

Hemispherical aluminum alloy parts are extensively used in modern aerospace and other manufacturing fields. However, wrinkling and cracking easily occur due to the large deformation of the parts, which leads to a complicated forming process. This research proposes a viscous backpressure forming method for hemispherical aluminum alloy parts. The forming limit diagram of LF2 sheet is established through the forming limit experiments. By the combination of finite element analysis and experimental verification, the forming process of the parts under different viscous backpressure and loading path conditions as well as the distribution law of stress–strain and wall thickness of the parts, are obtained. By comparing with the forming limit diagrams, technical feasibility of this forming process is discussed. The research results show that qualified parts can be formed using the viscous backpressure forming method under the conditions of viscous backpressure loading throughout the process with the backpressure at or above 12.5 MPa. This provides a reference for the backpressure forming of hemispherical aluminum alloy parts. [ABSTRACT FROM AUTHOR]

In this paper, we propose a data aggregation back pressure routing (DABPR) scheme, which aims to simultaneously aggregate overlapping routes for efficient data transmission and prolong the lifetime of the network. The DABPR routing algorithm is structured into five phases in which event data is sent from the event areas to the sink nodes. These include cluster-head selection, maximization of event detection reliability, data aggregation, scheduling, and route selection with multi attributes decision making metrics phases. The scheme performs data aggregation on redundant data at relay nodes in order to decrease both the size and rate of message exchanges to minimize communication overhead and energy consumption. The proposed scheme is assessed in terms of packet delivery, network lifetime, ratio, energy consumption, and throughput, and compared with two other well-known protocols, namely "information-fusion-based role assignment (InFRA)" and "data routing for in-network aggregation (DRINA)", which intrinsically are cluster and tree-based routing schemes designed to improve data aggregation efficiency by maximizing the overlapping routes. Meticulous analysis of the simulated data showed that DABPR achieved overall superior proficiency and more reliable performance in all the evaluated performance metrics, above the others. The proposed DABPR routing scheme outperformed its counterparts in the average energy consumption metric by 64.78% and 51.41%, packet delivery ratio by 28.76% and 16.89% and network lifetime by 42.72% and 20.76% compared with InFRA and DRINA, respectively. [ABSTRACT FROM AUTHOR]

The power consumption of axial flow fans may account for more than 1% of the rated power output of the power generating unit, so it is of benefit to the energy efficiency of the power generating unit to propose an operation adjustment approach to axial flow fans. On the basis of representative 2 × 600 MW direct dry cooling generating units, a computational model of air‐side flow and heat transfer of an air‐cooled condenser (ACC) combined with exhaust steam condensation is developed, by which the airflow rate, inlet air temperature of ACCs, the power consumption of axial flow fans, turbine backpressure, and net power output of power generating units at various wind speeds and in various wind directions are obtained. The results show that the net power output in the presence of winds always decreases when the rational speeds of the first upwind row axial flow fans increase from the rated speed of 79 rpm by 10% to 86.9 rpm. However, the net power output will increase in various wind directions if the rational speeds of all the fans except the upwind first row fans increase to 86.9 rpm. This can contribute to the optimal operation of the ACC by rotational speed adjustment of axial flow fans. [ABSTRACT FROM AUTHOR]

• A backpressure approach built on macroscopic traffic theory. • A decentralized approach suitable for implementation in large urban networks. • Theoretical proof of network-wide traffic stability properties. • Very low computational costs. • Extensive experiments and comparisons that highlight the superiority of the proposed approach. Decentralized intersection control techniques have received recent attention in the literature as means to overcome scalability issues associated with network-wide intersection control. Chief among these techniques are backpressure (BP) control algorithms, which were originally developed of for large wireless networks. In addition to being light-weight computationally, they come with guarantees of performance at the network level, specifically in terms of network-wide stability. The dynamics in backpressure control are represented using networks of point queues and this also applies to all of the applications to traffic control. As such, BP in traffic fail to capture the spatial distribution of vehicles along the intersection links and, consequently, spill-back dynamics. This paper derives a position weighted backpressure (PWBP) control policy for network traffic applying continuum modeling principles of traffic dynamics and thus capture the spatial distribution of vehicles along network roads and spill-back dynamics. PWBP inherits the computational advantages of traditional BP. To prove stability of PWBP, (i) a Lyapunov functional that captures the spatial distribution of vehicles is developed; (ii) the capacity region of the network is formally defined in the context of macroscopic network traffic; and (iii) it is proved, when exogenous arrival rates are within the capacity region, that PWBP control is network stabilizing. We conduct comparisons against a real-world adaptive control implementation for an isolated intersection. Comparisons are also performed against other BP approaches in addition to optimized fixed timing control at the network level. These experiments demonstrate the superiority of PWBP over the other control policies in terms of capacity region, network-wide delay, congestion propagation speed, recoverability from heavy congestion (outside of the capacity region), and response to incidents. [ABSTRACT FROM AUTHOR]

This study investigated polycyclic aromatic hydrocarbons (PAHs) and soot formation characteristics in laminar jet flames fuelled by primary reference fuels (PRFs) at elevated pressures. Qualitative PAHs and quantitative soot profiles were acquired by using laser-induced fluorescence and laser-induced incandescence, respectively. The backpressure of flames ranged from 1 bar to 5 bar. Proper flames with the volume fraction of iso-octane in PRFs varying between 0% and 100% and flame equivalent ratio varying between 3.0 and 11.4 were stabilised in a pressurised chamber. The effects of backpressure, equivalent ratio and iso-octane ratio on PAHs and soot formation were evaluated. PAHs and soot formation can be promoted by increasing iso-octane ratio, equivalent ratio and backpressure. The data suggest that PAHs with large molecular size are more sensitive to the increase of backpressure compared with those with small molecular size. Backpressure played a positive role in the growth of PAHs size. The averaged soot volume fraction showed an approximate power-law relation with pressure. The measured averaged soot volume fraction was proportional to pn. Pressure exponent n was 1.34–2.17, 1.41–2.12 and 1.56–2.20 at equivalent ratios of 6.2, 8.5 and 11.4, respectively. [ABSTRACT FROM AUTHOR]

• A theoretical analysis model has been presented to analyze the flow pattern in recess chamber. • With the increase of backpressure, self-pulsation is intensified initially and then suppressed. • Self-pulsation is the strongest when the liquid film angle is around the recess angle. • Backpressure has less effect on the spray angle when the spray transforms to stable behavior. A combined experimental and theoretical investigation is conducted to explore the self-pulsation characteristics generated by a liquid-centered swirl coaxial injector (LCSC) under various chamber backpressures. Filtered water and dried air were employed as simulant mediums. Data were obtained at pressures from 0.1 to 3.01 MPa and the momentum flux ratios from 0.004 to 15.99. The back-lighting photography technique was employed to capture the instantaneous self-pulsated spray and stable spray images with a high speed camera. A new empirical equation was presented to calculate the liquid film thickness at the pressure swirl injector exit without trumpet, and the flow characteristics in the trumpet of the inner injector have been calculated. Based on these researches, a theoretical analysis model has been proposed to analyze the flow pattern by calculating the liquid film angle in recess chamber. With the increase of backpressure, the flow in the LCSC injector changes from the outer mixing flow to the critical mixing flow, and develops into the inner mixing flow ultimately. Meanwhile, self-pulsation is intensified initially and then suppressed, while self-pulsation frequency fluctuates within a certain range. Self-pulsation is the strongest when liquid film angle is around the recess angle. Both variations of backpressure and injection conditions can change the flow pattern in recess chamber of the LCSC injector. When the flow pattern deviates from the critical mixing flow, self-pulsation is suppressed and the spray angle decreases accordingly. Backpressure affects self-pulsation by transforming the flow pattern in recess chamber and then strengthening or weakening the blocking actions of the conical liquid sheet. [ABSTRACT FROM AUTHOR]

The use of charcoal and firewood for cooking is common in Zambia, and its utilization is such that the deforestation rate is high, energy utilization is low, and unfavorable cooking methods lead to high death rates due to indoor air pollution mainly from particulate matter and carbon monoxide. By using an alternative cooking method, such as pellet stoves, it is possible to offer a sustainable solution, provided that sustainable pellet production can be achieved. In this study, 12 different available biomaterials were pelletized in a single pellet unit to investigate their availability as raw materials for pellet production in Zambia. The study showed that sicklebush and pigeon pea generated the same pelleting properties correlated with compression and friction and that both materials showed low moisture uptake. The study also identified two groups of materials that broadened the raw material base and helped to achieve sustainable pellet production. Group 1 consisted of materials with equal pelleting abilities (miombo, peanut shell, pigeon pea, and sicklebush) and Group 2 consisted of materials that showed low impact of varying moisture content (eucalyptus, miombo, peanut shell, pigeon pea, and sicklebush). The hardest pellet was made from Tephrosia, which was followed by Gliricidia. [ABSTRACT FROM AUTHOR]

Internal combustion engines are found to be extensively used in both mobile and stationary applications. The major drawbacks in diesel engines are the release of harmful gases like HC, CO, NOx and PM into atmosphere. There is several pre combustion and post combustion techniques are available to control these emissions effectively. Although CO2 emissions from I.C engines considered as a regulated emission but it is a leading contributor towards Greenhouse gases. In this work a numerical investigation on backpressure was carried out by varying porosity factor of activated carbon. Activated Carbon seems to be viable substance to capture CO2 emission from diesel exhaust. To evaluate the backpressure an analysis was carried out using CFD ANSYS fluent software. In the present investigation an analysis is carried out by placing activated carbon at three different variations. Then the analysis are done by varying three different porosity percentages 30,35 and 45 by placing activated carbon at three different locations. Final study reveals that activated carbon placed at PC35-3 layout shows optimum backpressure and high filtration efficiency while compared with other two layouts. [ABSTRACT FROM AUTHOR]

This research focuses on understanding how the relative pumping orientation and backpressure of a vacuum facility affects the measured performance and plasma plume parameters of a Hall-effect thruster (HET). A HET was operated in two opposite directions: plume ejection towards the vacuum pump and plume ejection away from the pump. The HET plume for each orientation was individually characterized at three vacuum facility operating pressures to study the effect of the facility pumping orientation and backpressure on the measured plume parameters and thruster performance. The ion current density, divergence angle, beam current, and ion energy distribution were measured using a Faraday probe and a retarding potential analyzer (RPA). The variation in the direction of the plume with respect to the pumping orientation leads to a clear difference in the measured performance of the HET when operating at an elevated backpressure. These are the first experiments that take the effect of the pumping orientation of a vacuum facility with respect to the thruster's exhaust direction into consideration. The results here will aid future research in selecting an adequate thruster exhaust direction when performing different Hall thruster ground tests such as plume diagnostics, lifetime tests, and erosion tests. [ABSTRACT FROM AUTHOR]

For the widespread application of thermoelectric generators, it is of vital importance to have convenient simulation tools in order to test the behavioral consequences of a thermoelectric generator in almost real conditions. The simulation by numerical methods of the performance of automotive thermoelectric generators (ATEG) allows for time- and cost-saving assessment of material combinations and variations of crucial design parameters. However, even in the case of promising simulation results, it is complicated to guarantee the ATEG capacity for reducing the vehicle’s fuel consumption. This work presents a method to assess the fuel economy of an ATEG design. The procedure, which takes into account the ATEG power generation, backpressure, weight and the coolant pumping power, reveals that the maximum fuel economy value does not occur with the maximum ATEG power generation point. The method applied to the ATEG presented predicts a maximum fuel economy value of 0.18%. [ABSTRACT FROM AUTHOR]

In this paper, we study the joint routing–scheduling problem in energy harvesting communication networks. Our policies, which are based on stochastic subgradient methods on the dual domain, act as an energy harvesting variant of the stochastic family of backpressure algorithms. Specifically, we propose two policies: first, the stochastic backpressure with energy harvesting, in which a node's routing–scheduling decisions are determined by the difference between the Lagrange multipliers associated to their queue stability constraints and their neighbors’; and second, the stochastic soft backpressure with energy harvesting, an improved algorithm where the routing–scheduling decision is of a probabilistic nature. For both policies, we show that given sustainable data and energy arrival rates, the stability of the data queues over all network nodes is guaranteed. Numerical results corroborate the stability guarantees and illustrate the minimal gap in performance that our policies offer with respect to classical ones that work with an unlimited energy supply. [ABSTRACT FROM AUTHOR]

Max-pressure (MP) control is one of the few traffic signal controllers proven to maximize network throughput or maximally stabilize the network. According to the theoretical results published so far, it can stabilize a network if all intersections are equipped with MP control for all stabilizable demands. However, budget constraints may not allow the installation of MP control on all intersections. Previous work did not consider a limited number of MP controlled intersections while proving the stability properties. Therefore, it is not clear whether a network can still be stabilized with a limited deployment of MP control. Using Lyapunov drift techniques this paper proves that even with a limited deployment, MP control can stabilize a network within feasible demand. Then we present an optimization formulation to find the optimal intersections to install MP control given a limited budget. We also present a greedy efficient algorithm to solve that optimization problem and prove that the algorithm solves the problem to optimality. Numerical results from simulations conducted on the downtown Austin network using an in-house custom simulator called AVDTA are then presented. The change in theoretical maximum servable demands for different amounts of deployments obtained from the optimization problem seemed to match with simulation results most of the times. We found that limited deployment of MP control almost always performed better than random deployment of MP control in terms of servable stable demand. Average total queue length and link density were observed to decrease as the number of MP controls increased which indicates better network performance. Average travel times per vehicle also decreased with installations of MP controls which shows how the travelers would benefit from more MP controls. • Proved that MP under limited deployment is stable if average demand is in D μ ∘. • Provided a methodology to find the optimal intersections to install MP controls. • Analyzed practical implications of stability. • Presented advantages over randomly selecting locations to install MP control. • Demonstrated performance gains using limited deployment in simulation. [ABSTRACT FROM AUTHOR]

For a better understanding of the flow instability in TBCC inlet, the unstart/restart characteristics have been investigated. Firstly, the flow field of TBCC inlet at different transition stages are analyzed. As the splitter rotates from upside to downside (transition from low-speed inlet to high-speed inlet) with a fixed backpressure, the shock train moves downstream. The maximum backpressure that the inlet can tolerate also rises. Secondly, according to the unstart boundary (namely maximum backpressure) and restart boundary, it can be found that if the inlet is propelled to transit from started state to unstarted state, inlet restart cannot be achieved along the same control route. Unstart/restart hysteresis loops in each transition phase are discussed according to the simulation results. Besides the hysteresis behavior under backpressure, the same phenomenon is also observed during the inlet transition process. Finally, the distinctiveness of the hysteresis caused by inlet mode transition is also discussed. [ABSTRACT FROM AUTHOR]

The development of novel in-situ diagnostic techniques allows new insight into the internal working of polymer electrolyte fuel cells (PEFCs) so that improved performance can be realised. Electrochemical impedance spectroscopy (EIS) is a widely used characterisation technique that takes advantage of the dynamic relationship between current and voltage to deconvolute critical mechanisms and sources of performance loss occurring with different time constants. Here, we apply electrochemical pressure impedance spectroscopy (EPIS) which examines the transfer function relating reactant gas pressure modulation to the electrical response of the fuel cell. A sinusoidally oscillating perturbation is applied to the cathode backpressure using a loudspeaker arrangement and the resulting voltage perturbation is monitored. It is shown that the technique can be used to separate the explicit effect of water management from reactant starvation when a PEFC is operated under different reactant humidification conditions. [ABSTRACT FROM AUTHOR]

In order to prevent the backward flow of piezoelectric pumps, this paper presents a single-active-chamber piezoelectric membrane pump with multiple passive check valves. Under the condition of a fixed total number of passive check valves, by means of changing the inlet valves and outlet valves' configuration, the pumping characteristics in terms of flow rate and backpressure are experimentally investigated. Like the maximum flow rate and backpressure, the testing results show that the optimal frequencies are significantly affected by changes in the number inlet valves and outlet valves. The variation ratios of the maximum flow rate and the maximum backpressure are up to 66% and less than 20%, respectively. Furthermore, the piezoelectric pump generally demonstrates very similar flow rate and backpressure characteristics when the number of inlet valves in one kind of configuration is the same as that of outlet valves in another configuration. The comparison indicates that the backflow from the pumping chamber to inlet is basically the same as the backflow from the outlet to the pumping chamber. No matter whether the number of inlet valves or the number of outlet valves is increased, the backflow can be effectively reduced. In addition, the backpressure fluctuation can be significantly suppressed with an increase of either inlet valves or outlet valves. It also means that the pump can prevent the backflow more effectively at the cost of power consumption. The pump is very suitable for conditions where more accurate flow rates are needed and wear and fatigue of check valves often occur. [ABSTRACT FROM AUTHOR]

In this paper a novel approach is presented for determination of the main components in MgO-Cr refractory material. With the approach, the intensity conversion of fused sample at different dilution ratios can be obtained by establishing the correlation between elements' intensity and dilution ratio. MgO-Cr refractory material is fused hardly and the dilution ratio requires more than 20 in XRF analysis. Nevertheless, high dilution can reduce the detection sensitivity of low content elements. Using the technology of intensity conversion at different dilution ratio in this paper, a calibration curve was obtained with different dilution ratios. In this method, we obtained a calibration curve successfully and got the satisfactory results for MgO-Cr refractory which was fused well. The new method suggests consistent accuracy and precision with standard method, and it can also simplify the preparation process of samples. The approach shows high sensitivity, good accuracy and precision, meanwhile, it reduces the technical difficulty and labor intensity greatly in analysis method. [ABSTRACT FROM AUTHOR]

Sharp edged injection orifices used in thrust chambers and thermal regulation system of liquid rocket engines have to maintain a steady flow to ensure optimum performance. These orifices are subjected to backpressure and elevated temperature during actual operation. The sharp edged orifices do not always run full due to the orifice geometry and/or flow conditions. In some cases, the flow may change its characteristics from attached to detached flow or vice versa. Length of the orifice in relation to its diameter and the backpressure have been observed to play an important role in the abrupt changes in the flow characteristics. In order to comprehensively characterize this phenomenon and to clearly identify the governing parameters, discharge characteristics were determined experimentally for sharp edged injection orifice of 0.6 and 1.4 mm diameters with length-to-diameter ratios in range between 1.4 and 11.5. Cavitation numbers were varied in the range of 0.06 to 20.9 while Reynolds numbers were varied in the range of 13 000 to 62 500. The backpressure for the injection orifice was varied upto 3.6 MPa. The effect of backpressure, Reynolds number, cavitation number, length-to-diameter ratio, and injection pressure drop-to-backpressure ratio on discharge characteristics was brought out. The experimental investigation gives the detailed flow characteristics of sharp edged orifices in the presence of backpressure. [ABSTRACT FROM AUTHOR]

The operating range and wave speed performance of a Rotating Detonation Combustor (RDC) is characterized for hydrogen-air mixtures for three fuel injection schemes and two air injection schemes. The fuel injection scheme is altered by changing the total number of injection orifices and the individual orifice area, while maintaining the same fuel mass flux across the three schemes. The operability, performance and combustion-induced pressure rise due to the addition of a back-pressurizing convergent nozzle is also characterized. While the operating range is largely unaffected by changes in the length-to-diameter ratio of the fuel injector orifices, higher length-to-diameter ratios correspond to a lower number of transitional RDC operation where there is a sudden abatement of the continuously propagating detonation wave, once established inside the combustor. Increased air injection area diminishes the operability, while producing high stochasticity in the performance of the RDC. The length-to-diameter ratio of the fuel orifices has a significant impact on the number of detonation waves that can exist in the chamber. For the highest length-to-diameter ratio of the fuel orifices, and at the highest air flow rates, the RDC supports multiple detonation waves inside the chamber. Without the convergent nozzle attachment, 80% of Chapman–Jouguet (C–J) detonation speed is achieved for all three fuel injection schemes. C–J detonation wave speed is achieved in the annulus when the RDC is back-pressurized using the nozzle. The ratio of reactant fill-height to the detonation cell-width tapers at the lean and rich operating conditions, while peaking at an equivalence ratio of around 1.2. The detonation-induced static pressure rise produced in the RDC is found to be dependent on the air flow rate and the equivalence ratio of the reactants. [ABSTRACT FROM AUTHOR]

Switched queueing networks model wireless networks, input-queued switches, and numerous other networked communications systems. We consider an ( $$\alpha ,g$$ )-switch policy; these policies provide a generalization of the MaxWeight policies of Tassiulas and Ephremides (IEEE Trans Autom Control 37(12):4936-1948, ) and the weighted $$\alpha $$ -fair with allocations of Mo and Walrand (IEEE/ACM Trans Netw 8(5):556-567, ) which are typically applied to Bandwidth Sharing Networks (Massoulié and Roberts in IEEE/ACM Trans Netw 10(3):320-328, ). For single-hop switch networks, we prove the maximum stability property for this class of randomized policies. Thus these policies have the same first-order behavior as the MaxWeight policies. However, for multihop networks some of these generalized polices address a number of critical weakness of the MaxWeight/BackPressure policies. For multihop networks with fixed routing, we consider a policy called the Proportional Scheduler (or (1, log)-policy). In this setting, the BackPressure policy is maximum stable, but must maintain a queue at each node for every route destination, which typically grows rapidly with a network's size. However, the Proportional Scheduler only needs to maintain a queue for each outgoing link, which is typically bounded in number. As is common with Internet routing, by maintaining per-link queueing, each node only needs to know the next hop for each packet and not its entire route. Further, in contrast to BackPressure, the Proportional Scheduler does not compare downstream queue lengths to determine weights; only local link information is required. This leads to greater potential for decomposed implementations of the policy. Through a reduction argument and an entropy argument, we demonstrate that, while maintaining substantially less queueing overhead, the Proportional Scheduler achieves maximum throughput stability. [ABSTRACT FROM AUTHOR]

We propose in this paper a decentralized traffic signal control policy for urban road networks. Our policy is an adaptation of a so-called BackPressure scheme which has been widely recognized in data network as an optimal throughput control policy. We have formally proved that our proposed BackPressure scheme, with fixed cycle time and cyclic phases, stabilizes the network for any feasible traffic demands. Simulation has been conducted to compare our BackPressure policy against other existing distributed control policies in various traffic and network scenarios. Numerical results suggest that the proposed policy can surpass other policies both in terms of network throughput and congestion. [ABSTRACT FROM AUTHOR]

The performance characteristics of proton exchange membrane fuel cells (PEMFCs) can be affected by a degradation of the membrane-electrode-assembly (MEA). In this paper, the performance degradation of MEA in a single cell PEMFC was examined at 80 °C and a backpressure of 10 psi after 100 h of operational time using open circuit voltage (OCV) conditions. A control experiment was conducted by testing the MEA at ambient temperature without backpressure. Both electrochemical impedance spectroscopy (EIS) and an OCV analysis showed that both the conductivity and the performance of the cell operating at 80 °C were less than the control values after 100 h of operation. In contrast, an application of 10 psi of backpressure improved the cell conductivity and can maintain OCV in compare with ambient and 80 °C conditions. Characterizations of the pre- and post-operation of the MEA (cathode, anode and membrane) by scanning electron microscope-energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD) showed that the MEA performance degradation at 80 °C after 100 h resulted mainly from carbon corrosion combined with Pt agglomeration and dissolution, producing a PtS compound with reduced activity at both the cathode and the anode and also drying and cracking of the membrane. [ABSTRACT FROM AUTHOR]

Backpressure has been extensively applied in experimental tests to improve the water saturation of samples, and its effect on the strength of saturated soils has been traditionally regarded as trivial in Soil Mechanics. However, a non-negligible influence of backpressure on the macro mechanical properties of methane-hydrate-bearing-sediments (MHBS) has been surprisingly observed in several recent experiments reported in the literature. This paper aims to shed light on this phenomenon. A theoretical analysis on the microscopic interaction between soil grains and inter-particle methane hydrate (MH) was carried out to highlight how backpressure affects the mechanical properties of the inter-particle MH which in turn affect the macroscopic mechanical behavior of MHBS. The influence of backpressure is accounted for in a new bond contact model implemented into the Distinct Element Method (DEM). Then, a series of DEM biaxial compression tests were run to investigate the link between mechanical properties of MHBS and backpressure. The DEM numerical results show that shear strength, small strain stiffness and shear dilation of MHBS increase with the level of backpressure. As the critical state is approached, the influence of backpressure ceases. Moreover, the elastic modulus and cohesion of MHBS increase linearly while the internal friction angle decreases at a decreasing rate as the backpressure increases. Simple analytical relationships were achieved so that the effect of backpressure on the mechanical properties of MHBS can be accounted in the design of laboratory tests to characterize the mechanical behavior of MHBS. [ABSTRACT FROM AUTHOR]

The present technologies in internal combustion engines for transportation purposes clearly demonstrate the room for improvement still achievable. In a recent past, harmful emission reduction was the main goal: wonderful technologies were developed which strongly reoriented the interest and the use of such engines. Actually, CO 2 is the most important driver: it calls for fuel consumption reduction (energy saving) and energy recovery from that usually wasted. Considering that about one third of the fuel energy is in the flue gases, the possibility to recover this energy and re-use it for engine and vehicle needs is one of the smartest ways to participate to reduce fuel consumption and, therefore, CO 2 emissions. In particular, Organic Rankine Cycle (ORC)-based power units fed by the exhaust gases are promising and technologically ready, but they have a significant impact on the exhaust line and engine behavior. A trade-off between energy recovered in mechanical form and energy lost due to the engine back pressure, vehicle weight increase, discharge energy at the condenser, and the management of the strong off-design operating conditions is a key point which could definitively open the way to this technology or limit it to particular applications. The paper discusses the effects of the pressure losses produced by an ORC-based power unit mounted on the exhaust line of a turbocharged IVECO F1C engine, operated on a test bench. The interactions produced on the turbocharged engine have been experimentally investigated: the presence of an Inlet Guide Vane (IGV) system to manage the turbocharger makes the effect of the back pressure not straightforward to be predicted. The IGV opening and closure degree, in fact, can compensate the effect of the back pressure which intrinsically tends to increase specific fuel consumption. A wide experimental testing of the turbocharging group in order to understand its reaction and the net effect in terms of engine specific fuel consumption is presented. Finally, once the engine performances were verified, the contribution due to the heat recovery inside the ORC-based power unit fed by the exhaust gases in terms of mechanical power was evaluated and experimentally verified in some points, considering the strong off design conditions produced by the engine operating point variations. In fact, exhaust gas flow rate and temperature variations lead the evaporator, even though properly designed, to severe off-design conditions which modify the inlet working fluid conditions till to make the mechanical recovery impossible. Under the hypothesis that the engine propels a light duty vehicle, the effect of the extra weight is discussed re-evaluating the propulsion power increase in terms of fuel consumption. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) sheet was sandwiched between the cathodic GDBL and a bipolar plate of polymer electrolyte membrane fuel cells (PEMFCs). The CNT sheets were synthesized through the direct spinning method and investigated their morphological characteristics. The electrochemical performances of MEA with CNT interlayer were measured via polarizations, iR-free, and electrochemical impedance spectra (EIS) compared to the conventional MEA under elevating backpressure. The performance of the MEA with CNT interlayer at 1.0 bar g was enhanced by 91.8% (364 mW cm−2 at 0.7 V), which was higher than the peak power density improvement of 13.0% (850 mW cm−2 at 0.48 V). We also identified that corresponding ohmic and charge-transfer resistances were reduced. Especially, the ohmic resistance was decreased by up to 42.2% with increasing operating pressure compared to the conventional MEA due to better hydration and interfacial contact. Notwithstanding that the performance was ameliorated with increased pressure, we found that the mass transport loss tends to become more sensitive at the high current density region, and thus optimum operating conditions were proposed. We concluded that the CNT sheet as a functional interlayer would be advantageous in improving the performance of commercialized PEMFCs. [Display omitted] • CNT sheet was sandwiched between cathodic GDBL and bipolar plate in PEMFCs. • CNT sheets were synthesized through the direct spinning method. • Power density at typical operating voltage enhanced 91.8% (364 mW cm−2 at 0.7 V). • Ohmic resistance was reduced by up to 42.2% with increasing operating pressure. [ABSTRACT FROM AUTHOR]

The results from simulation of equal-channel angular extrusion of sintered porous blanks with use of different deformation patterns are presented. It is shown that the maximum equidensity and the minimum volume of the poorly compacted area are observed in the pattern with a movable bottom plate of the die horizontal channel and with backpressure on the sample portion being extruded. This deformation pattern is also determined by the maximum values of deformation force. [ABSTRACT FROM AUTHOR]

In this study we investigate the influence of various magnitudes of backpressure (0 to 200 MPa) during large scale (cross-section 50×50 mm2) equal-channel angular pressing (ECAP). We focus on the homogeneity of the induced strain and, within this context, on the homogeneity of the resulting mechanical properties after one pass of ECAP at room temperature. We find that large scale ECAP without the application of a backpressure clearly leads to heterogeneous shear strains, causing heterogeneous mechanical properties. A pronounced maximum of hardness next to a local minimum at the billet's bottom occurs; in the absence of backpressure during processing, its expansion covers almost one half of the cross-section. The application of a backpressure close to the material's proof stress after processing (in this case 200 MPa) results in an excellent homogeneity with a negligible local heterogeneity at the bottom of the billet. [ABSTRACT FROM AUTHOR]

Although research in finding optimal muffler shapes for low-frequencies noise using reactive mufflers has already been addressed, research into shape optimization of hybrid mufflers that reduce broadband noise within a constrained pressure-drop backpressure is lacking. Therefore, the shape optimization of four kinds of hybrid mufflers using simulated annealing (SA) in conjunction with the generalized decoupling technique and plane wave theory are presented. Here, a numerical case in eliminating nitrogen venting noise is introduced. The reliability of the SA optimization is also verified using the optimization of muffler A for a pure tone. Moreover, the accuracy of the mathematical models is acceptable with minor deviations between the theoretical and experimental data. Results reveal that the higher backpressure limit will result in a higher acoustical performance. Consequently, the acoustical performance for a hybrid muffler equipped with multiple reactive chambers and one dissipative chamber is superior to that of reactive mufflers. [ABSTRACT FROM AUTHOR]

The cross-layer utility maximization problem, which is subject to stability constraints for a multicommodity wireless network where all links share the same number of orthogonal channels, is considered in this paper. We assume a time-slotted network, where the channel gains randomly change from one slot to another. The optimal cross-layer network control policy can be decomposed into the folloing three subproblems: 1) flow control; 2) next-hop routing and in -node scheduling; and 3) power and rate control, which is also known as resource allocation (RA). These subproblems span the layers from the physical layer to the transport layer. In every time slot, a network controller decides the amount of each commodity data admitted to the network layer, schedules different commodities over the network's links, and controls the power and rate allocated to every link in every channel. To fully exploit the available multichannel diversity, we consider the general case, where multiple links can be activated in the same channel during the same time slot, and the interference is controlled solely through power and rate control. Unfortunately, the RA subproblem is not yet amendable to a convex formulation, and in fact, it is NP-hard. The main contribution of this paper is to develop efficient RA algorithms for multicommodity multichannel wireless networks by applying complementary geometric programming and homotopy methods to analyze the quantitative impact of gains that can be achieved at the network layer in terms of end-to-end rates and network congestion by incorporating different RA algorithms. Although the global optimality of the solution cannot be guaranteed, the numerical results show that the proposed algorithms perform close to the (exponentially complex) optimal solution methods. Moreover, they efficiently exploit the available multichannel diversity, which provides significant gains at the network layer in terms of end-to-end rates and network congestion. In addition, the assessment of the improvement in performance due to the use of multiuser detectors at the receivers is provided. [ABSTRACT FROM PUBLISHER]

Abstract: This paper presents a design guideline for a piezoelectric actuated check valve diaphragm micropump for microfluidic applications. Diaphragm average displacement was adopted in analyzing a piezoelectrically actuated diaphragm. For the first time, the relationship between the stroke volume and backpressure of a check valve diaphragm micropump were simulated with a Finite Element Analysis (FEA) tool. The simulated results reasonably agreed to the experimental results of the micropump. [Copyright &y& Elsevier]

Abstract: Anaerobic treatment of low strength, high flow wastewaters can only be effective if the technology employed can meet key hydrodynamic requirements: maximising the contact surface area and contact period between the influent substrate and the biomass solids, minimising solid washout from the reactor and minimising the backpressure across the system. Backpressure or head loss is an important hydrodynamic property of gravity-flow packed bed reactors, where the flow is the resultant of frictional forces between the incoming fluid and the solid packing material through which the wastewater percolates. Excessive backpressure caused by high influent flow-rates can reduce the contact surface area and increase the influent head on the upstream side of the biomass bed leading to overflow spills, unstable performance and process failure. This study investigates the factors affecting backpressure across a Granular bed baffled reactor (GRABBR) with variable baffle positions. Experimental results were used to develop a mathematical model to quantify backpressure based on physical characteristics of the seed biomass, fluid-flow conditions and reactor geometry. Results have shown that for a constant flow rate the anaerobic baffled reactor exhibits the least backpressure characteristics when both the upflow and downflow areas are roughly 50% of the total compartmental width. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, hydrogen crossover was measured in an environment of high-temperature proton exchange membrane (PEM) fuel cells using a steady-state electrochemical method at various temperatures (T) (80–120°C), backpressures (P) (1.0–3.0atm), and relative humidities (RH) (25–100%). An H2 crossover model based on an MEA consisting of five layers – anode gas diffusion layer, anode catalyst layer, proton exchange membrane (Nafion 112 or Nafion 117), cathode catalyst layer, and cathode gas diffusion layer – was constructed to obtain an expression for H2 permeability coefficients as a function of measured H2 crossover rates and controlled H2 partial pressures. The model analysis suggests that the dominant factor in the overall H2 crossover is the step of H2 diffusing through the PEM. The H2 permeability coefficients as a function of T, P, and RH obtained in this study show that the increases in both T and P could increase the H2 permeability coefficient at any given RH. However, the effect of RH on the permeability coefficient seems to be more complicated. The T effect is much larger than that of P and RH. Through experimental data simulation an equation was obtained to describe the T dependencies of the H2 permeability coefficient, based on which other parameters such as maximum permeability coefficients and activation energies for H2 crossover through both Nafion 112 and 117 membranes were also evaluated. Both Nafion 112 and Nafion 117 showed similar values of such parameters, suggesting that membrane thickness does not play a significant role in the H2 crossover mechanism. [Copyright &y& Elsevier]

Abstract: We developed a novel flow control system for a nanofluidic chemical process. Generally, flow control in nanochannels is difficult because of its high-pressure loss with very small volume flow rate. In our flow control method, liquid pressure in a microchannel connected to the nanochannels is regulated by utilizing a backpressure regulator. The flow control method was verified by using simple structured microchip, which included parallel nanochannels. We found that the observed flow rate was three times lower than the value expected from Hagen–Poiseuille''s equation. That implied a size-dependent viscosity change in the nanochannels. Then, we demonstrated mixing of two different fluorescent solutions in a Y-shaped nanochannel and also a proton exchange reaction in the Y-shaped nanochannel. The flow control method will contribute to further integration of nanochemical systems. [Copyright &y& Elsevier]

Abstract: FEM analysis was used to study the interactions between die friction, backpressure and strain rate sensitivity during equal channel angular pressing. One of the key findings is that strain rate sensitivity causes strain redistribution, resulting in higher equivalent strains and a substantial component of compression in the workpiece. This compression gives rise to effects such as lift-off of the leading end of the workpiece from the die bottom and improved die fill. Friction has different effects at room and elevated temperatures. While a moderate amount is beneficial at room temperature, friction has a detrimental interaction with strain rate sensitivity at high temperature. Backpressure, though largely beneficial, is shown to have negative effects when combined with friction and a high strain rate sensitivity. [Copyright &y& Elsevier]

The mould filling of the aluminium casting alloy AC4C was directly observed by X-ray radiography in order to evaluate the accuracy of simulated results for the mould filling behaviour of a vacuum suction casting process. A numerical method has been applied to simulate mould filling behaviour, in which evacuation of gas through the suction vent is taken into account and the backpressure of gas is coupled with the pressure field of the melt. Backpressure of gas in the empty mould cavity was also measured using a semiconductor pressure sensor. Experiments have been carried out at two different suction pressures (10 and 20 kPa) and three different decompression rates (1·2, 4·2 and 80 kPa s-1), controlled by the aperture of the valve between the gas pipe of the vacuum suction system. Experimental results showed that the effects of suction pressure and decompression rate on the mould filling behaviour were significant. The higher the suction pressure and decompression rate, the more turbulent the free surface of molten metal, resulting in earlier occurrence of gas entrapment, larger volumes of entrapped gas and higher risk of misrun. By comparing simulated results with experimental ones, it was found that good agreement could be obtained in terms of mould filling patterns, positions of gas entrapments and mould filling time. It was also found that results simulated by the conventional method, in which gas evacuation and the effects of backpressure on mould filling are not taken into account, showed poor agreement with experimental values. [ABSTRACT FROM AUTHOR]

A process for increasing both strength and ductility in a brittle Al–5 wt.% Fe alloy by Equal Channel Angular Pressing (ECAP) was investigated. The increase in solid solubility of iron in the Al matrix produced by intense deformation under ECAP permitted age hardening in this alloy although it is not hardenable by conventional processing. An ultrafine-grained microstructure of 325–450 nm was obtained in a brittle, cast Al–5 wt.% Fe alloy by ECAP with various numbers of passes and backpressure levels from 40 to 275 MPa. A supersaturated solid solution with a maximum solubility of 0.6 wt.% of iron in an aluminium matrix was obtained during ECAP, which allowed ageing of the conventionally non-hardenable alloy. Strength, ductility and microhardness of the cast alloy processed by the ECAP technique were significantly enhanced (e.g. strength and ductility from 102 MPa and 3.4% to 261 MPa and 5.8%, respectively). The subsequent artificial ageing resulted in a further increase in strength to 272 MPa. It was shown by scanning electron microscopy (SEM) that the type of fracture of tensile specimens taken from material subjected to ECAP was predominantly ductile. An increase in backpressure retards cracking of intermetallic particles and enhances the workability and ductility of such alloys processed by ECAP. [Copyright &y& Elsevier]

We answer the question on how much memory a packet switch/router needs; more specifically, we propose a systematic method that is simple, rigorous and general for determining the absolute lower bound of packet buffering required by practical switching systems. Accordingly, we introduce a deterministic traffic scenario that stresses the global stability property of finite output queues and demonstrate its usefulness by dimensioning the internal buffer capacity of two popular CIOQ switches. [Copyright &y& Elsevier]

• Self-pulsation characteristics of LCSC injectors under various conditions are studied numerically • Holding MFR constant, backpressure suppresses the oscillation of the spray • As backpressure increases, radial distribution of liquid mass flow rate varies to single-peak • Self-pulsation is closely related to the dominant surface wave and K–H instability This study investigated the effects of backpressure and operating conditions on the self-pulsation characteristics of a liquid-centred swirl coaxial (LCSC) injector. To this end, a three-dimensional numerical simulation via octree adaptive mesh refinement as well as coupled level-set and volume of fluid method were employed. Self-pulsation is suppressed by backpressure for a constant gas–liquid momentum flux ratio (MFR). When backpressure is constant, the strength of self-pulsation varies with the mass flow rate of the gas (m ˙ g), which is constant with experimental data due to the variation in the flow patterns in the recess chambers. The self-pulsation frequency increases with backpressure and m ˙ g. The trends of the spray angle and intensity of self-pulsation are consistent. As backpressure increases, the radial distribution of the mass flow rate of the liquid changes from a double- to single-peak. The central mass flow rate increases with backpressure and m ˙ g , which also affect the pressure oscillations inside and outside the liquid film in the injector. We proposed a self-pulsation mechanism, in which self-pulsation is closely related to the dominant surface wave and Kelvin–Helmholtz (K–H) instability. Self-pulsation under the critical mixing flow pattern is stronger than that under inner or outer mixing flow patterns. Under the critical mixing flow pattern, the K–H vortex is relatively strong, and the spray oscillation is not restricted by the wall of the recess chamber. [ABSTRACT FROM AUTHOR]

In ATM networks, preventive control is widely recognized as a way to avoid congestion efficiently. It is implemented by a conjunction of call admission control (CAC) and usage parameter control (UPC). However, since congestion may still happen because of unpredictable statistical fluctuation of traffic injected into networks, it would be effective to relieve congestion using reactive control together with a preventive measure. In this paper, the performance of backpressure control, which is a reactive approach with an analytical approach, is investigated. Moreover, backpressure control with cell pushout scheme is proposed as a way to overcome some backpressure control weaknesses. It is generally pointed out that if congestion perseveres, congestion can prevail over a wide range of network. This is because the backpressure affects even the traffic that does not go through congested nodes. By applying a cell pushout scheme to the buffer of the nodes where traffic stopped, the performance of backpressure control will be improved. Numerical results show that the control with pushout scheme improves cell loss performance without little increase in delay. © 1997 Scripta Technica. Inc. Electron Comm Jpn Pt 1, 80 (2):24–34, 1997 [ABSTRACT FROM AUTHOR]

A wide scientific literature has proved that engine efficiency is adversely affected by the orifice-to-orifice variability in jet velocities. This results in non-uniform spray exiting from the injector holes, leading to deviations from the expected Air/Fuel ratios within the cylinder. Despite several studies dealing with hole-to-hole variability in jet velocities, the reasons behind this phenomenon are still far from being fully understood. The present study identifies needle wobbles as the possible factor responsible for orifice-to-orifice variability in jet velocities, which underlies the spray non-uniformity. A comprehensive experimental campaign has been carried out employing Diesel fuel at various injection scenarios. Orifice-to-orifice variability in jet velocities has been assessed via a high-speed imaging technique. From the experimental investigation, it emerged that increase in backpressure, along with greater injection pressure, minimizes the spray non-uniformity. This may be attributed to the boosting action exerted by cylinder backpressure on the needle, which experiences a greater acceleration, thus reducing the amplitude of needle wobbles and duration as well. Conversely, reduction both in injection pressure and in backpressure prolong the duration and amplitude of needle oscillations, worsening the spray development uniformity. The paper describes the experimental activity and emphasizes the key-role of backpressure in spray development uniformity. [ABSTRACT FROM AUTHOR]

Inspired by the Industry 4.0 trend towards greater user-friendliness and self-optimization of machines, we present a novel approach to reducing backpressure in foam injection molding. Our method builds on the compressibility of polymer-gas mixtures to detect undissolved gas phases during processing at insufficient backpressures. Identification of a characteristic behavior of the bulk modulus upon transition from homogeneous to heterogeneous polymer-gas mixtures facilitated the determination of the minimum pressure required during production to be determined, as verified by ultrasound measurements. Optimization of the pressure conditions inside the barrel by means of our approach saves resources, making the process more sustainable. Our method yielded a 45% increase in plasticizing capacity, reduced the torque needed by 24%, and required 46% less plasticizing work and lower pressures in the gas supply chain. The components produced exhibited both improved mechanical bending properties and lower densities. From an economic point of view, the main advantages of optimized backpressures are reduced wear and lower energy consumption. The methodology presented in this study has considerable potential in terms of sustainable production and offers the prospect of fully autonomous process optimization. [ABSTRACT FROM AUTHOR]

Shock tunnel tests and CFD simulations are conducted to study effects of vortex generators (VGs) on unsteady unstarted flows of an axisymmetric hypersonic inlet with nose blunt radii of 0.8 mm and 3.2 mm. The inlet exit is throttled with a preseted block to generate unstarted flows at a freestream Mach number of 5.9. Unstarted flows of no VGs, 0.5 mm and 1 mm-thick VGs are recorded through schlieren imaging and pressure measurements. Experimental results show that the unstarted flows are characterized with prominent shock oscillations and pressure fluctuations. VGs reduce scales of the external separations, enlarge angles of the separated shock waves, and increase time-averaged magnitudes of surface pressures. The oscillatory period can be shortened from 4 ms to 3.13 ms by 1 mm-thick VGs for the R 0.8 mm configuration. The maximum increment of the time-averaged pressure magnitudes can reach 16.2 times the freestream static pressure (p ∞) for the R 0.8 mm configuration with 1 mm-thick VGs. In addition, VGs generally increase pressure standard deviations of the measuring points upstream of the throat section within 4.0 p ∞ and decrease those of the downstream measuring points up to 8.6 p ∞ , despite the 0.5 mm-thick VGs condition of the R 3.2 mm configuration. Flow mechanisms dominating the effects of VGs on the unsteady unstarted flows are analyzed with the aid of the CFD simulations. Feasibility of VGs on unstarted flow control is also evaluated. [ABSTRACT FROM AUTHOR]

• Vapor-feed DIFC enabling the direct energy generation out of LOHC-bound hydrogen. • Record-high power densities of a direct isopropanol fuel cell with 254 mW/cm2 at 0.55 V. • High temperature lead to enhanced reaction kinetics and fast desorption of acetone. Liquid Organic Hydrogen Carrier (LOHC) systems offer a very interesting option for hydrogen storage in the existing infrastructure for common fuels. Technically most attractive is the direct use of LOHC-bound hydrogen in a low-temperature PEM fuel cell. Here, the isopropanol/acetone LOHC system is suggested to produce electricity from a condensable liquid without CO 2 emissions. A high-performance direct isopropanol fuel cell using a vaporizer and a commercial fuel cell test system is demonstrated. For the first time backpressure is used to enhance the performance. The self-fabricated GDEs combined with a Nafion composite membrane achieved a power density of 203 mW cm−2 for Isopropanol/Air operation at 300 kPa absolute and 85 °C. By increasing the operation temperature to 100 °C a peak power density of 254 mW cm−2 is achieved, exceeding the highest reported values for isopropanol fuel cells operated with air by over 80%. The observed increase in performance can be attributed to the higher reaction rate of the electrooxidation of isopropanol at the anode side during pressurized conditions and to the reduced acetone-poisoning of the Pt-Ru catalyst at elevated temperatures. [ABSTRACT FROM AUTHOR]