Effect Of Back Pressure Research Articles

Non-equilibrium condensation flow characteristics of wet steam considering condensation shock effect in the steam turbine

A non-equilibrium condensation flow occurs in steam turbines, accompanied by condensation shock. At present, there are limited studies on the influence of condensation shock on the flow and condensation characteristics of wet steam, and the unsteady influence of condensation shock on the flow field of wet steam always have been ignored. In this paper, the unsteady flow characteristics of condensation were presented by considering the condensation shock effect. First, the condensation flow models and corresponding source terms were programmed and loaded with UDS (user-defined scalar) and UDF (user-defined function), respectively, and the governing equations were discretized using a high-resolution calculation method. The calculated results agreed well with the reported experimental results. Based on the models, the non-equilibrium condensation flow characteristics with inlet and outlet pressures in Laval nozzle considering the condensation shock effect were analyzed. Finally, during the unsteady phase change process, the effects of back pressure and saturation of the inlet on the liquid phase parameters were examined considering the condensation shock effect in the Dykas cascade. The results show that a decrease in the back pressure and an increase in the inlet pressure improve the condensation shock intensity in Laval nozzle. With the increase of condensation shock intensity, the nucleation rate increases. Moreover, in Dykas cascade, with the increase of back pressure from 48.8 kPa to 73.2 kPa, the maximum wetness decreases from 4.8 % to 2.1 %, whereas with the increase of relative saturation from 0.58 to 0.88, the maximum wetness increases from 2.4 % to 3.6 %. The results obtained in this paper are of significance to accurately analyze the actual situation of non-equilibrium condensation flow of wet steam and to develop methods for reducing wet steam loss in turbine stage.

Experimental Investigation on the Backpressure Effect on the Performance of a High Temperature Proton Exchange Membrane Fuel Cell Stack

This study investigated the impact of backpressure of anode and cathode on the performance of a high-temperature proton exchange membrane fuel cell stack consisting of 30 cells, initially operating at a current density of 0.4 A/cm², temperature of 160 ℃, and 0 bar with pure H2. Subsequently, the backpressure on both sides was varied from 0 bar to 1.5 bar, and the changes in stack performance were recorded throughout the testing period. Additionally, the impact of backpressure was also investigated with reformates (H2/CO2/CO/N2 = 69.4%/22.3%/1.40%/6.9%) as anode feed for the stack. The results showed that increase in operating backpressure improves the fuel cell performance. A stack voltage increase of 20 mV per cell and 40 mV per cell were achieved for the pure hydrogen operation and reformate gas operation respectively when increasing backpressure from 0 bar to 0.5 bar. This signifies potential to improve the system’s overall efficiency with only minor penalty in terms of auxiliary power loss to increase the back pressure.

Experimental Investigation on the Backpressure Effect on the Performance of a High Temperature Proton Exchange Membrane Fuel Cell Stack

This study investigated the impact of backpressure of anode and cathode on the performance of a high-temperature proton exchange membrane fuel cell stack consisting of 30 cells, initially operating at a current density of 0.4 A/cm², temperature of 160 ℃, and 0 bar with pure H2. Subsequently, the backpressure on both sides was varied from 0 bar to 1.5 bar, and the changes in stack performance were recorded throughout the testing period. Additionally, the impact of backpressure was also investigated with reformates (H2/CO2/CO/N2 = 69.4%/22.3%/1.40%/6.9%) as anode feed for the stack. The results showed that increase in operating backpressure improves the fuel cell performance. A stack voltage increase of 20 mV per cell and 40 mV per cell were achieved for the pure hydrogen operation and reformate gas operation respectively when increasing backpressure from 0 bar to 0.5 bar. This signifies potential to improve the system’s overall efficiency with only minor penalty in terms of auxiliary power loss to increase the back pressure.

Modelling and optimization of an existing onshore gas gathering network using PIPESIM

Pakistan has limited natural gas reserves, and most are found onshore. This article reports on the problems of an onshore gas gathering network (GGN) analysed through steady-state simulation modelling using PIPESIM software. The research methodology incorporates a comprehensive steady-state hydraulic analysis considering fluid flowing velocity limitations, liquid holdup and slugging along with other issues faced by gas gathering networks. The steady-state hydraulic analysis has led us to pinpoint specific GGN pipelines facing critically low gas velocities and consequent liquid holdup. Addressing these issues involved application of PIPESIM software for modelling, considering various operating schemes of gas-producing wells and their associated pipelines. To select an optimal operating scheme, the study utilized the Analytic Hierarchy Process (AHP) for operational optimization, to identify the most effective solution for reduced liquid holdup, improving production, and ensuring the safe operation among available alternatives. Findings from our hydraulic analysis highlight the importance of reducing GGN outlet pressure to mitigate challenges associated with liquid holdup which causes slugging and back pressure effect at source leading to low production and poor performance of the GGN. Study of three alternative cases reveals that decreasing outlet pressure lowers the liquid holdup, improve gas flowing velocities, and enhanced overall production. These findings validate our hypothesis that reducing GGN outlet pressure is a viable strategy to lower the liquid holdup in pipelines. This research offers significant value by providing a comprehensive solution to GGN liquid holdup, low flowing velocities, back pressure and low production challenges. The integration of steady-state hydraulic analysis, simulation modelling with PIPESIM, and the application of AHP for optimization contributes novel insights into the optimization of operation of gas gathering networks. Emphasizing the reduction of liquid holdup and enhancing production through outlet pressure adjustments offers a practical framework for optimizing the functionality of gas gathering networks.

Experimental and numerical investigation of the effects of porous bleed systems on a model scramjet inlet under high backpressure conditions

In this study, we conducted experimental and numerical investigations to assess the effects of backpressure and configurations of porous bleeds on a scramjet inlet's performance at Mach 5. Experiments in a high-enthalpy wind tunnel, using a backpressure controller and a porous bleed with 1 mm holes and 10 mm lateral spacing, were paired with Reynolds-averaged Navier-Stokes simulations to explore the mitigation of flow separation and the prevention of inlet unstart under various backpressure conditions. The simulations provided insights into how backpressure levels and porous bleed geometries impact internal flow structures, as well as the critical backpressure ratio at which inlet unstart occurs. Additional simulations varied the bleed system's hole diameter and spacing, identifying configurations that optimize aerodynamic performance by enhancing total pressure recovery and Mach number at the isolator exit, while reducing bleed mass flow rates. The study also quantified the impact of these configurations on engine thrust, determining that certain bleed system designs significantly improve thrust by efficiently suppressing the interaction between the core flow and corner recirculation zones. This study examined the internal three-dimensional flow structure characteristics under high back pressure and provided insights into porous bleed configuration capable of efficiently suppressing inlet unstart.

Variations of the shock and secondary flow structure in a transonic compressor cascade with outlet back pressure

The effects of back pressure on the transonic cascade operating state are crucial and can determine the structure of internal shock waves and secondary flows. In this paper, numerical methods validated by experiments were employed to investigate the evolution mechanisms of the inlet flow field, shock structure, secondary flow structure, and cascade performance under different back pressures. Analysis revealed that transonic cascade exhibited unique incidence characteristics in the inlet flow field under both subsonic and supersonic regimes, although these two regimes involved different physical mechanisms. The results revealed that the operating state of the transonic compressor cascade under the unique incidence condition was influenced by the outlet back pressure, and there existed a critical static pressure ratio. The critical static pressure ratio shifted from 1.61 for two-dimensional flow to 1.37 for three-dimensional (3D) flow at M1 = 1.1, due to the corner separation and the characteristics of 3D shocks. The 3D shock structure exhibited a non-uniform distribution along the spanwise direction due to the influence of back pressure and the separated boundary layer. The vortex structures analysis revealed that the secondary flow structure on the sidewalls of the transonic compressor cascade was primarily dominated by corner vortices, whose formation mechanism was related to the interaction between the shock wave and the sidewall boundary layer. Additionally, this interaction also led to the formation of detached shock and lip shock vortex structures. Finally, loss analysis indicated that the wake region of the transonic cascade primarily includes six types of loss, and the total loss of the cascade decreased with the rise in back pressure.

Characterization of mixing dynamics of the transcritical bi-swirl jets

Investigation of the transcritical coaxial swirl injectors, considering their geometrical features along with the thermodynamics nonidealities, is of central importance in science and technology. Toward this aim, the mixing dynamics of transcritical bi-swirling jets has been investigated numerically. The scale-adaptive simulation method which allows formation of a turbulent spectrum is employed to close the governing equations. The Soave-Redlich-Kwong equation-of-state along with a required portion of standard database of the national institute of standards and technology are applied to the numerical framework to estimate the real-gas thermodynamic and transport properties, respectively. Results reveal that the present numerical framework accommodating a rather low-cost turbulence approach is capable of predicting the main characteristics of transcritical coaxial injectors, including central vortex core, central recirculation zone, Kelvin-Helmholtz instabilities, and vortex interaction. Analyzing oscillatory flowfield dynamics via the power-spectral-density and proper-orthogonal-decomposition techniques highlights the prominent influences of shedding, pairing, and merging of the vortices as well as the hydrodynamic Kelvin-Helmholtz instabilities on nearfield mixing dynamics. Effects of transcritical injector back-pressure on the characteristics flow features have been studied for the first time within a wide pressure range. Numerical simulations indicate that mixing quality, in terms of characteristics time- and length-scales, increases with the ambient pressure.

Effects of baffle position in serpentine flow channel on the performance of proton exchange membrane fuel cells

This study used a three-dimensional numerical model of a proton exchange membrane fuel cell with five types of channels: a smooth channel (Case 1); eight rectangular baffles were arranged in the upstream (Case 2), midstream (Case 3), downstream (Case 4), and entire cathode flow channel (Case 5) to study the effects of baffle position on mass transport, power density, net power, etc. Moreover, the effects of back pressure and humidity on the voltage were investigated. Results showed that compared to smooth channels, the oxygen and water transport facilitation at the GDL-Channel interface were added 11.53%−20.60% and 7.81%−9.80% at 1.68 A·cm−2 by adding baffles. The closer the baffles were to upstream, the higher the total oxygen flux, but the lower the flux uniformity and the worse the water removal. The oxygen flux of upstream baffles was 8.14% higher than that of downstream baffles, but oxygen flux uniformity decreased by 18.96% at 1.68 A·cm−2. The order of water removal and voltage improvement was Case 4 > Case 5 > Case 3 > Case 2 > Case 1. Net power of Case 4 was 9.87% higher than smooth channel. To the Case 4, when the cell worked under low back pressure or high humidity, the voltage increments were higher. The potential increment for the backpressure of 0 atm was 0.9% higher than that of 2 atm. The potential increment for the humidity of 100% was 7.89% higher than that of 50%.

Design and performance analysis of hydrogen-fueled micro combustion chamber with focus on back pressure minimization

The combustion chamber is a crucial component in power generation within a micro gas turbine. This paper prioritizes practical over theoretical considerations in designing an efficient, small-scale combustion chamber for micro gas turbine applications. The investigation covers the temperature profile within the combustion chamber, employing 19 reversible reactions and considering 9 different chemical species in reactive flow calculations. Preliminary experiments demonstrate hydrogen as a feasible fuel in a micro combustion chamber, generating approximately 1 kW of thermal power. Turbulence physics are assessed using the accurate k-Ɛ model. Findings indicate a reactant inlet temperature of 300 K and a primary zone temperature of 1750 K. This research suggests that minimizing the back pressure effect in a steady-state micro combustion chamber can improve turbine performance.

Effect of Operating Conditions on Voltage Transient Response of High‐Temperature Proton Exchange Membrane Fuel Cell Under Load Changing

The transient response of a high‐temperature proton exchange membrane fuel cell (HT‐PEMFC) is critical for control and optimization. The objective of this study is to investigate the effects of operating conditions and control parameters on the transient response of the HT‐PEMFC during load variations to optimize the operating conditions. The main causes of the voltage undershoot are investigated experimentally, and the effects of air stoichiometry, air humidity, operating temperature, and backpressure on the transient response of the HT‐PEMFC are evaluated in terms of internal resistance and voltage response. The results show that during load changes, the local gas starvation of the cell and the change in the hydration state of membrane‐electrode‐assembly may be the main cause of the voltage undershoot. The voltage drop is affected by the combination of ohmic resistance, charge transfer resistance, and mass transfer resistance. In addition, operating temperature and air stoichiometry can affect voltage drop and voltage undershoot during load changes. Proper humidification of the air can alleviate voltage undershoot problems. Increasing the backpressure can improve the transient performance of the cell, but does not alleviate the voltage undershoot problem. The study can provide guidelines for the design and control of HT‐PEMFC operating conditions.

Feasibility of macroscopic parameters for NS to DSMC solver switching in micronozzle simulations

Enhancing the design and performance of micronozzles could lead to novel applications and advancements in propulsion systems, making the exploration of micronozzles crucial for the future. This paper critically examines the feasibility of utilizing macroscopic property-based Kn as indicator for defining the breakdown region during the transition from the NS solver to the DSMC solver in micronozzle simulations. The aim is to specify a parameter that can be calculated from both NS and DSMC simulations, making it suitable for implementation in hybrid simulations that dynamically switch between the two solvers. The results show that the density-based Kn accurately represents the continuum breakdown, and it exhibits an earlier breakdown compared to pressure and temperature-based Kn values. The study also analyzes the rarefaction effects and introduces the rarefaction parameter (RP), quantifying the increase in Kn for a unit change in the non-dimensionalized distance. The findings demonstrate that at very low exit pressures, the rarefaction effects increase rapidly as the flow moves towards the nozzle exit, leading to a transition from the continuum to the rarefied regime. The hybrid NS-DSMC simulations show good agreement with experimental data, validating the proposed approach. Additionally, the research examines the effect of back pressure on the RP and identifies the transition regime based on the slope of the RP curve. Therefore, the manuscript provides detailed insights into novel elements, such as the quantification of rarefaction within the nozzle using the RP, the classification of the nozzle into different regimes (continuum, slip, and transition), the definition of an easily obtainable parameter for switching between NS and DSMC methods, and an examination of the contributions of the shear stress term and heat addition term to non-equilibrium conditions.

Turbocompound energy recovery option on a turbocharged diesel engine

The transportation sector is living a transition era in which hybrid and electrified vehicles are replacing conventional vehicles, based on internal combustion engines. This is pushed by the recognized need for reducing fuel consumption and tailpipe emissions, considering primary pollutants and carbon dioxide as a greenhouse gas. In the transition path, hybridization and partial electrification of the powertrain play a crucial role. In this regard, the need for on-board electrical energy storage and utilization is increasing significantly and the possibility to recover wasted energy and convert it into electrical form is mandatory. This is especially true for commercial and heavy-duty vehicles, where full electrification is more difficult to be implemented. Waste Heat Recovery (WHR) has therefore become so important for vehicles, not only to directly reduce fuel consumption and related emissions but also to improve the feasibility of a generation of vehicles with a higher degree of hybridization that considers, for example, the electrification of auxiliaries following the so-called auxiliaries-on-demand management. Wasted heat refers mainly to exhaust heat from gases, where about one third of the fuel energy is disposed of. Among the various systems for WHR, engine turbo-compounding is approaching a mature technology. This technological option makes use of an additional turbine on the exhaust line of the engine, downstream of the turbocharging one, which converts the residual gas enthalpy into mechanical form. In this paper, the F1C Iveco 3.0 L turbocharged diesel engine is considered for verifying the performances of a turbo-compounding system. The engine was mounted on a dynamic engine test bench. In particular, the interactions with the original engine produced on the exhaust line were studied. Backpressure effects on the engine introduced by turbo-compounding were evaluated reversed in terms of extra fuel consumption. Moreover, the new equilibrium of the turbocharger was assessed and the related modifications to the engine were measured considering that the turbocharger has a control strategy based on the so-called Variable Geometry Turbine (VGT), via the modification of the Inlet Guide Vanes (IGV). The presence of a secondary turbine for WHR opens to a wider possibility of actuating the IGV and, so, the possibility to optimize the recovery considering the integrated system and all its degrees of freedom.

Моделювання процесів виготовлення тонкостінних втулок з поруватих заготовок з використанням прямого видавлювання та радіального ущільнення

The deformation process of powder materials thin-walled bushings manufacture was investigated by computer modeling. Two shape formation bushings schemeswere considered (direct extrusion and radial compaction).A continuum approach was used to create a modeling method. The method is based on rheological models of porous body plastic deformation and the finite element method. The accepted material rheological model allows describing the deformation of both powder and porous blanks. It takes into account the different resistance of these materials in tension and compression. Modeling of the deformation process was carried out in stages, using the method of successive loads. The elastic stresses were determined, the plastic potential was calculated and, if it was necessary, the stresses and material parameters of the model were corrected at each load step. The porosity value is reach maximum in blank and area, that is free from the loads, and the accumulated deformation is reachminimum in direct extrusion. The effect of back pressure leads to a more uniform distribution of these parameters, a decrease in porosity and an increase in the accumulated deformation of the solid phase. During radial compaction of thin-walled bushings, deformation of the material occurs locally. Porosity in the product section increases with increasing radius. Increasing the number of technological transitions with a gradual increase in the forming tool diameter reduces the uneven distribution of residual porosity and its value. However, the unevenness of the porosity distribution over the radius remains. In the process of radial compaction, a burr is formed on the ends of the product. The burr can be reduced by changing the initial shape of the blank. The process of direct extrusion allows obtaining more uniform distribution of residual porosity and accumulated plastic deformation of product material. However, this technological process requires the higher loads application, which leads to less stability of the tool. The radial compaction method (which characterized by local deformation) requires not high loads and allows not powerful equipment using. However, the distribution of residual porosity over the radius of the bushing is uneven. Keywords: plasticity theory, powder materials, computer modeling, finite element method, stress-strain state, porosity distribution.

Changes in respiratory mechanics in response to crystalloid infusions in extremely premature infants.

Extremely premature infants are at a higher risk of developing respiratory distress syndrome and circulatory impairments in the first few weeks of life. Administration of normal saline boluses to manage hypotension is a common practice in preterm infants. As a crystalloid, a substantial proportion might leak into the interstitium; most consequently the lungs in the preterm cohorts, putatively affecting ventilation. We downloaded and analyzed ventilator mechanics data in infants managed by conventional mechanical ventilation and administered normal saline bolus for clinical reasons. Data were downloaded for 30 min prebolus, 60 min during the bolus followed by 30 min postbolus. Sixteen infants (mean gestational age 25.2 ± 1 wk and birth weight 620 ± 60 g) were administered 10 mL/kg normal saline over 60 min. The most common clinical indication for saline was hypotension. No significant increase was noted in mean blood pressure after the saline bolus. A significant reduction in pulmonary compliance (mL/cmH2O/kg) was noted (0.43 ± 0.07 vs. 0.38 ± 0.07 vs. 0.33 ± 0.07, P = 0.003, ANOVA). This was accompanied by an elevation in the required peak inspiratory pressure to deliver set volume-guarantee (19 ± 2 vs. 22 ± 2 vs. 22 ± 3 mmHg, P < 0.0001, ANOVA), resulting in a higher respiratory severity score. Normal saline infusion therapy was associated with adverse pulmonary mechanics. Relevant pathophysiologic mechanisms might include translocation of fluid across pulmonary capillaries affected by low vascular tone and heightened permeability in extremes of prematurity, back-pressure effects from raised left atrial volume due to immature left-ventricular myocardium; complemented by the effect of cytokine release from positive pressure ventilation.NEW & NOTEWORTHY Administration of saline boluses is common in premature infants although hypovolemia is an uncommon underlying cause of hypotension. This crystalloid can redistribute into pulmonary interstitial space. In the presence of an immature myocardium and diastolic dysfunction, excess fluid can also be "edemagenic." This study on extremely premature infants (25 wk gestation) noted adverse influence on respiratory physiology after saline infusion. Clinicians need to choose judiciously and reconsider routine use of saline boluses in premature infants.

Novel severe plastic deformation method for extrusion compression composite processing

The capability of a novel severe plastic deformation method for extrusion compression composite processing was investigated. Deform-3D software was used to study the effect of back pressure on the strain distribution of a workpiece by simulating the forming process with and without back pressure. The Mg-12.5Gd-4Y-2Zn-0.5Zr alloy was used to analyze the effect of strain on microstructure and mechanical properties. Results showed that back pressure led to the uniform strain distribution of the deformed workpiece and the decrease in the effective strain standard deviation from 0.73 to 0.68. With increasing strain, the grain size tended to decrease and then increase, contrary to the recrystallization rate trend. The tensile strength gradually increased with increasing strain, but the elongation change trend was changed due to the influence of the bimodal structure.

Effect of back pressure on gas-solid distribution characteristics of cyclone distributor applied in powdered coal-fired circulating fluidized bed combustion system

The cyclone distributor is an essential part of the powdered-coal-fired circulating fluidized bed (PC-CFB) combustion system, and its gas-solid distribution characteristics are significantly affected by the back pressure of the lower outlet. A four-way coupling method using a dense discrete phase model (DDPM) was adopted to simulate the cyclone distributor. The results indicate that the effect of the back pressure on the axial gas velocity is more pronounced compared to that on the tangential gas velocity. With the increase in the back pressure, the particle separation efficiency decreases monotonically, while the rate of change gradually increases. Meanwhile, the gas separation efficiency increases as the back pressure becomes higher. Furthermore, increasing back pressure improves the particle concentration at the outlets of the cyclone distributor. To maintain high particle separation efficiency and ensure the safe operation of the boiler, it is recommended to set the back pressure between 1000 Pa and 2000 Pa.

Effect of Back Pressure and Divergence Angle on Location of Normal Shock Wave

Effect of Back Pressure and Divergence Angle on Location of Normal Shock Wave

Gas atomization of A2 tool steel: Effect of process parameters on powders' physical properties

In this study, powders of the A2 tool steel were produced by close-coupled gas atomization using argon gas aiming their use in additive manufacturing (AM) technologies. The effects of melt overheating and gas atomization pressure on their physical properties were analyzed. The powders were separated into different particle size ranges, and a complete morphological characterization was carried out. The effect of back pressure was verified due to a substantial increase in the gas-to-melt mass flow rates ratio (GMR) with increasing gas pressure. Atomization gas pressure showed a slightly more significant influence on particle size distribution; however, the melt overheating effect was also significant. As the GMR increases, the median particle size decreases to a certain threshold. Above this, particle size cannot be considerably reduced with increasing GMR.

Effects of backpressure on unstart and restart characteristics of a supersonic inlet

AbstractThe unstart phenomenon of supersonic inlets caused by backpressure is dangerous for aircraft during flights because it severely reduces the air mass flow rate through the engine. We used unsteady numerical simulations to evaluate the unstart and restart characteristics of a two-dimensional supersonic inlet during rapid backpressure changes. The effects of the depressurisation time and depressurisation value on the inlet flow characteristics and restart features are discussed. The results show that the depressurisation time affects the restart procedure when the back pressure drops from the inlet unstart value to the normal working state value. When the depressurisation time decreases, it becomes easier for the inlet to restart. However, the inlet cannot restart if the depressurisation time is too long. When the depressurisation time and value were large enough, a short buzz period occurred before the inlet restarted. Both the time and value of depressurisation affected the restart characteristics.

Experimental Study on the Dynamic Characteristics of Gas-Centered Swirl Coaxial Injector under Varying Ambient Pressure

To determine the dynamic characteristics of a gas-centered swirl coaxial injector under backpressure, an experimental system of dynamic injection in a backpressure chamber was constructed. Filtered water and nitrogen were used as simulant media for rocket propellants, which are typically used with this kind of injector. An inertial flow pulsator was manufactured to generate the pulsation of the flows that feed to the liquid injector. The electric conductance method was adopted to measure liquid film thickness. After the pulsation of incoming flow in the feedline was tested, and the operating conditions for the injector to start pulsating were validated, the effects of the chamber backpressure and the recess length of the injector on the dynamic characteristics of spray, such as liquid film thickness, breakup length, and amplitude of pulsation, have been investigated in detail. Experimental results demonstrated that the increase in chamber backpressure prompts the liquid sheet to rupture earlier with a shorter breakup length, which results from the increased density of the ambient gas. Chamber backpressure suppresses the pulsation of the outlet flow, especially for a longer recess length. Moreover, a decrease in the recess length results in a reduction in breakup length due to an intense gas–liquid shearing in a narrower recess section. For a lower backpressure, the amplitude of outlet flow generally increases when the recess length increases. However, this phenomenon is not obvious for the conditions of higher backpressure and lower pulsation frequency.