Effect Of Back Pressure Research Articles

Compatibility optimization of a polyhedral-shape thermoelectric generator for automobile exhaust recovery considering backpressure effects

The output performance of thermoelectric generator using thermoelectric modules can be improved by optimizing the heat exchanger structure, but this may cause compatibility issues in the exhaust heat recovery process, such as high backpressure and poor performance for the internal combustion engine. In this study, a polyhedral-shape heat exchanger-based thermoelectric generator system for vehicle exhaust recovery was constructed for the uniform temperature and easy thermoelectric module layout, and the influencing factors of heat transfer and backpressure was evaluated using a realizable k-ϵ turbulence model, and the influence order was analyzed based on the analysis of variance method. Finally, a multi-objective grey wolf optimizer was used to improve the thermoelectric generator system based on the proposed compatibility performance index and optimization objective function. The findings show that the heat transfer performance and backpressure of heat exchanger is obviously affected by different fin length, fin width, fin intersection angle and fin spacing distance. Compared with the empty cavity structure based one and those without optimization, the optimized fin parameters not only obtain high power and satisfactory thermoelectric conversion efficiency, but also ensure low pressure drop and ideal temperature uniformity, which well meets the compatibility requirements for automobile exhaust recovery application.

Inconsistency evaluation of vehicle-oriented fuel cell stacks based on electrochemical impedance under dynamic operating conditions

The dynamic inconsistency performance of the proton exchange membrane fuel cell stack is a crucial indicator for vehicular applications. This paper comprehensively studies for the first time the local dynamic inconsistency of a high-power fuel cell stack with 30 kW rated power based on impedance. The stack is divided into ten groups equally. First, each polarization process and frequency impedance under different working conditions is quantitatively analyzed by the equivalent circuit model combined with the relaxation time distribution. It is determined that 1 Hz, 50 Hz, and 2500 Hz impedance can describe the oxygen transport, charge transfer, and ohmic variation trends, respectively. Then, the effects of loads, air stoichiometry, backpressure, operating temperature, and cathode humidity on in-stack dynamic inconsistency response are evaluated from an internal dynamics perspective. The results show that the local dynamic inconsistent responses in the fuel cell stack depend mainly on the oxygen transfer capacity. Oxygen transport affects the difference in local voltage transient drop after a current step and the inconsistency voltage recovery. These works provide an in-depth understanding of the differences in the dynamic response of high-power fuel cell stacks, which has an important implication for system control and structural design optimization.

A New Model Algorithm for Estimating the Inhalation Exposure Resulting from the Spraying of (Semi)-Volatile Binary Liquid Mixtures (SprayEva).

The spraying of liquid multicomponent mixtures is common in many professional and industrial settings. Typical examples are cleaning agents, additives, coatings, and biocidal products. In all of these examples, hazardous substances can be released in the form of aerosols or vapours. For occupational and consumer risk assessment in regulatory contexts, it is therefore important to know the exposure which results from the amount of chemicals in the surrounding air. In this research, a mechanistic mass balance model has been developed that covers the spraying of (semi)-volatile substances, taking into account combined exposure to spray mist, evaporation from droplets, and evaporation from surfaces as well as the nonideal behaviour of components in liquids and backpressure effects. For wall-spraying scenarios, an impaction module has been developed that quantifies the amount of overspray and the amount of material that lands on the wall. Mechanistically, the model is based on the assumption that continuous spraying can be approximated by a number of sequentially released spray pulses, each characterized by a certain droplet size, where the total aerosol exposure is obtained by summation over all release pulses. The corresponding system of differential equations is solved numerically using an extended Euler algorithm that is based on a discretisation of time and space. Since workers typically apply the product continuously, the treated area and the corresponding evaporating surface area grows over time. Time-dependent concentration gradients within the sprayed liquid films that may result from different volatilities of the components are therefore addressed by the proposed model. A worked example is presented to illustrate the calculated exposure for a scenario where aqueous solutions of H2O2 are sprayed onto surfaces as a biocidal product. The results reveal that exposure to H2O2 aerosol reaches relevant concentrations only during the spraying phase. Evaporation from sprayed surfaces takes place over much longer time periods, where backpressure effects caused by large emission sources can influence the shape of the concentration time curves significantly. The influence of the activity coefficients is not so pronounced. To test the plausibility of the developed model algorithm, a comparison of model estimates of SprayExpo, SprayEva, and ConsExpo with measured data is performed. Although the comparison is based on a limited number (N = 19) of measurement data, the results are nevertheless regarded as supportive and acceptable for the plausibility and predictive power of SprayEva.

Experimental Investigation on Combustion and Performance of Diesel Engine under High Exhaust Back Pressure

The use of exhaust gas recirculation, complex after-treatment systems, advanced technology of high-strength engines, and underwater exhaust will lead to increased diesel exhaust back pressure (EBP). This will increase the residual exhaust gas and the exchange temperature in the cylinder and reduce the fresh air charged in the next cycle. In this work, the effects of two high EBP conditions (10 kPa and 25 kPa) on the performance of medium-speed ship engines under different loads are explored through experiments. The results show that the increase in EBP from 10 kPa to 25 kPa has little effect on the heat release rate, engine power, and engine start-up time. However, it will lead to ignition advance and the maximum pressure rise rate, peak pressure, and exhaust temperature increase. The increase in EBP has a more significant impact on the small valve overlap angle. Because the reduction in the valve overlap angle has led to an increase in the residual exhaust gas, further increases in EBP causes residual exhaust gas effects to be more pronounced. The effect of increasing EBP on fuel consumption depends primarily on which effect of exhaust back pressure on temperature and fresh air intake dominates.

Mechanism and characteristics of thrust generated by a submerged detonation tube for underwater propulsion

The detonation engine, which can produce high specific impulse during the underwater detonation process (UDP), has become the forefront of underwater propulsion. In this paper, the thrust mechanism conducted in UDP and the propagation characteristics of the complex pressure waves are numerically studied, and the correlation between those two features is analyzed. The thrust from UDP is generated in a submerged detonation tube (SDT) and driven by the stoichiometric methane-oxygen mixture. The results show that detonation of the pre-filled combustible gas mixture gives rise to complex pressure waves and delivers several force impulses to the SDT. The impulses present different effects on the thrust performance, which is divided into two stages. In the first stage, before the detonation wave collides with the exterior water, the thrust is provided by the persistent back pressure effect of the detonation product. When the detonation wave propagates through the SDT exit and strikes the gas–water interface, a transmitted shock wave and a reflected shock wave are formed, which produce the impulses dominating the second stage. The reflected shock wave eventually impinges on the inner wall, imposing a force impulse on it. The pressure disturbance on the annular wall caused by the transmitted shock wave and subsequent detonation gas jet leads to another two thrust impulses. Finally, a comparison between the thrust of the SDT and its counterpart in the air is conducted to characterize the influence of UDP, and the effects of dimensional parameters of the SDT are also investigated.

Effect of back pressure on the separation performance of a hydrocyclone

In industrial process applications, to shorten the process flow and use the residual energy of hydrocyclone overflow, the overflow outlet is often directly connected to the subsequent equipment, and the back pressure of the subsequent equipment inevitably affects the normal operation of the front-end hydrocyclone. Therefore, this paper uses numerical simulation to study the effect of overflow back pressure on the internal flow field and separation performance of hydrocyclones. The results show that increasing the overflow back pressure increases the total pressure drop of the hydrocyclone, has no significant effect on the internal radial pressure gradient, and only increases the energy consumption of the hydrocyclone. With the increase in the overflow back pressure, the solid phase yield of the underflow increases, the content of fine particles gradually increases, the content of coarse particles decreases, and the separation accuracy of the hydrocyclone decreases. • The effects of back pressure on the flow field were investigated. • The influences of back pressure on the separation performance were studied. • The particle size distribution of the products were analysed.

Shedding Light on Water Management during Operation of AEMFC with Humidity Sensors

The performance of anion exchange membrane fuel cells (AEMFC) has dramatically progressed in the past few years, with initial power performance matching, if not exceeding, those of proton exchange membrane fuel cells (PEMFC). The remaining challenges are i) the replacement of platinum-group-metal catalysts by catalysts based on Earth-abundant elements, ii) improved durability, and iii) the carbonatation issue when the cathode is fed with natural air. Compared to PEMFCs, the water management of AEMFC is more challenging, due to higher flux of water transported from one electrode to the other for a given current density, but also due to the high swelling of anion exchange ionomer (AEI) [1]. An optimized water management was shown to be not only critical for AEMFC power performance [2], but also for the cell stability. The chemical stability of AEM and AEI was recently shown to decrease dramatically with decreasing relative humidity [3]. During AEMFC operation, low humidity is expected on the cathode due to water consumption by the oxygen reduction reaction and due to electroosmotic drag from cathode to anode. While the water management of AEMFC is a recognized challenge, only few works have hitherto investigated it with operando techniques [4-5].In this presentation, we will discuss the application of humidity sensors to measure on-line the relative humidity of the gas outlets of a single-cell AEMFC, allowing us to derive the water balance at each electrode (Figure 1a). The setup was applied to study the water balance and understand how it affects the AEMC power performance, focusing on one type of membrane-electrode assembly, comprising of a state-of-art anode (PtRu/C), cathode (Fe-N-C) and AEM/AEI (low density polyethylene/ethylenetetrafluoroethylene). The effect of dew point, backpressure and flow rates on cell performance and water transport were investigated. As an example of the type of results that can be obtained, Figure 1b shows the water balance at the anode and cathode as a function of time (blue and red curves, respectively), for different galvanostatic holds of 5 min each, from 0.2 to 1.2 A cm-2, at otherwise fixed conditions. As expected, the water balance is positive at the anode, and increases fairly linearly with the current density. Importantly, the water balance at the anode is always lower than the anode water balance expected if all the produced water (through the hydrogen oxidation reaction) would stay in the anode. This implies that the electroosmotic drag effect of water transport from cathode to anode is minor, and that the transport of water from anode to cathode (via back-diffusion, or other mechanism) is significant. As a result, the water balance is also positive at the cathode. Figure 1b shows also the total water balance (green curve), and that it matches with the theoretical total simply derived from the cell current density (black curve). In fact, for all operating conditions tested, the water balance was positive at the cathode, implying that the so-called cathode dry-out seldom occurs in AEMFC. The results also generally show that anode flooding is strongly connected with the maximum current density at which an AEMFC can stably operate. In conclusion, the use of humidity sensors can provide quantified insights on water dynamics in operating AEMFC, providing a tool for understanding optimized operating conditions, or for optimizing materials and components when they are designed to improve water management.

Backpressure effects on emitters flow rate in subsurface drip irrigation

Subsurface drip irrigation success depends on surpassing the backpressure obstacle, a phenomenon which occurs when the water application intensity exceeds the infiltration rate of soil, which reduces the emitter flow rate. Thus, this study aimed to determine the flow rate variation, in relation to surface flow, of four drip emitters when buried at two depths in a loam soil (Yolo Loam soil), and the backpressure generated by the soil on subsurface condition. The cavity radius developed around the emitters outlet was also obtained. The experiment was conducted in a completely randomized design, in a strip-plot scheme, with three treatments: installation depth of driplines (two levels: 0.10 and 0.20 m); dripline type (four levels: D5000, JardiLine, TalDrip and and Hydro PCND) and irrigation time (three levels: 0.5, 1.0 and 3.0 h). The results showed that the flow rate variation between the surface and subsurface application on Yolo Loam soil, with inlet pressure of 145 kPa, was greater the higher was the emitter flow rate. For pressure-compensating emitters, even under backpressure influence, this was not enough to cancel the pressure-compensating device operation, of the emitters. The emitters installation depth, as well the irrigation time, did not affect the backpressure and, consequently, the flow rate variation.

Modeling and Parameter Estimation of a Steam Power Plant Including Condenser Back-Pressure Uncertainty Using Operational Data

This article copes with a challenging issue about modeling and parameter estimation of the steam power plants. To this end, a thorough model for steam units is obtained, where the turbine-boiler control strategy is also considered in the modeling procedure. The number of integrated model inputs is optimal, making it appropriate for automatic generation control purposes. This model can work accurately in nominal conditions without abnormal events. Thus, the gathered data from an identification test in a 325 MW steam unit in nominal situations is employed to estimate the proposed model's unkn0own parameters using a genetic algorithm. Additionally, the condenser back-pressure (CBP) effect in the steam unit generation is elaborated. Regarding the CBP dependency on environmental conditions, like the wind speed, this effect is treated as an uncertainty in the article. Consequently, a novel turbine model considering the CBP effect is introduced. Determining the CBP uncertainty bounds is another problem addressed in the article using an efficacious information gap decision theory method on the recorded data in abnormal conditions. Finally, the derived model and parameters in both nominal and abnormal conditions are validated using the operational data, and the results are discussed.

Investigation on behavior of the backpressure based piezoelectric energy harvester driven by compressed air.

A piezoelectric energy harvester with backpressure pre-loaded is designed to investigate the performance that can be driven by the compressed air load in the pneumatic system. The power generation principle and microelement mechanics model are established, which can explain the principle that backpressure changes the internal energy of materials. The backpressure affects the internal stress of materials. The electromechanical coupling coefficient can be adjusted by the backpressure. The power generation obviously changes as the electromechanical coupling coefficient is adjusted. An experimental testing system is established, and the experimental results are analyzed to prove the effect of backpressure on the output power. There is a linear relationship between the peak voltage and backpressure. When the backpressure increases every 1 kPa, the voltage increases by 0.667 V. The voltage increment under backpressure is 5.13 times that without backpressure. The optimal output power is 12.3 mW in 30 kPa backpressure pre-load. The output power increases to the original 237% under the backpressure. The prototype can directly supply energy to the temperature sensor, and it can supply power to a magnetic switch with capacitor energy storage.

Effects of the Operating Parameters of Supersonic Separators on the Supersonic Liquefaction Characteristics of Natural Gas

In this study, a mathematical model for the supersonic condensate flow of natural gas to understand its condensation process in a supersonic separator has been proposed. The effects of export back pressure, inlet temperature, and inlet pressure on the condensation parameters were investigated. The results indicate that the condensation position moves forward with the increase in the inlet pressure and the decrease in the inlet temperature. A method for determining the optimal range of operating parameters (export back pressure, inlet temperature, and inlet pressure) for the supersonic separator is proposed. Within the optimal back pressure range, the region of extreme Mach number in the device should be at the inlet of the straight pipe section after the separation gap, and extreme value distribution areas of low temperature, condensation nucleation, and humidity should be between the nozzle expansion section and the inlet of the straight pipe section. It is important to choose a higher temperature among the optimal values as the inlet temperature and also ensure that the optimal inlet pressure is not higher than the pressure corresponding to the humidity inflection point. At the optimal inlet pressure, the maximum humidity distribution area should be behind the supersonic nozzle expansion section and in front of the inlet of the straight pipe section.

Understanding dynamic behavior of proton exchange membrane fuel cell in the view of internal dynamics based on impedance

• Effects of various conditions on transient response of PEM fuel cell are studied. • 2500 Hz impedance and 10 Hz impedance are used to explain voltage response. • Voltage undershoot and overshoot are observed and interpreted. • Charge transfer loss is closely related to oxygen transport and membrane hydration. The transient characteristic of the proton exchange membrane (PEM) fuel cell is an imperative factor for vehicular applications. Currently, a substantial part of previous experimental study regarding the transient response of the PEM fuel cell only focuses on voltage output, while the dynamic internal polarization process is usually ignored. Considering that the electrochemical impedance spectroscopy can represent internal dynamics at different time scales, in this paper, for the first time, in addition to voltage as an indicator of dynamic response performance, the fixed frequency impedance is also applied as an assist signal for voltage response interpretation and internal mechanism analysis. First, a transmission line model is introduced for polarization loss calculation of measured EIS in various conditions. Through quantitative analysis of each polarization loss and each frequency impedance, it is determined that 2500 Hz and 10 Hz impedance can describe the variation trend of proton transfer loss and charge transfer loss, respectively. Based on this, the effects of different step-current, air stoichiometry, backpressure, air humidity, and temperature on the dynamic response of the PEM fuel cell are investigated. Moreover, to fully reveal the internal dynamic mechanism, the transient variation of 2500 Hz and 10 Hz impedance under a broad range of current density is studied. The results indicated that voltage response is strictly related to internal hydration state and oxygen transfer. Especially, poor internal humidification may lead to local starvation. These works offer a more profound understanding of PEM fuel cell transient response, which is significant for system controller design.

Estimating Inhalation Exposure Resulting from Evaporation of Volatile Multicomponent Mixtures Using Different Modelling Approaches.

In many professional and industrial settings, liquid multicomponent mixtures are used as solvents, additives, coatings, biocidal products, etc. Since, in all of these examples, hazardous liquids can evaporate in the form of vapours, for risk assessments it is important to know the amount of chemicals in the surrounding air. Although several models are available in legal contexts, the current implementations seem to be unable to correctly simulate concentration changes that actually occur in volatile mixtures and in particular in thin films. In this research, the estimation of evaporation rates is based on models that take into account non-ideal behaviour of components in liquids and backpressure effects as well. The corresponding system of differential equations is solved numerically using an extended Euler algorithm that is based on a discretisation of time and space. Regarding air dispersion of volatile components, the model builds upon one-box and two-box mass balance models, because there is some evidence that these models, when selected and applied appropriately, can predict occupational exposures with sufficient precision. That way, numerical solutions for a wide variety of exposure scenarios with instantaneous and continuous/intermittent application, even considering “moving worker situations”, can be obtained. A number of example calculations have been carried out on scenarios where binary aqueous solutions of hydrogen peroxide or glutaraldehyde are applied as a biocidal product to surfaces by wiping. The results reveal that backpressure effects caused by large emission sources as well as deviations from liquid-phase ideality can influence the shape of the concentration time curves significantly. The results also provide some evidence that near-/far-field models should be used to avoid underestimation of exposure in large rooms when small/medium areas are applied. However, the near-field/far-field model should not be used to estimate peak exposure assuming instantaneous application, because then the models tend to overestimate peak exposure significantly. Although the example calculations are restricted to aqueous binary mixtures, the proposed approach is general and can be used for arbitrary liquid multicomponent mixtures, as long as backpressure effects and liquid-phase non-idealities are addressed adequately.

Effects of Backpressure on the Performance of Internal Combustion Engine and Automobile Exhaust Thermoelectric Generator

Abstract The maximum generated power of automobile exhaust thermoelectric generator (AETEG) can be enhanced by applying inserted fins to its heat exchanger, because the temperature difference of thermoelectric modules (TEMs) is increased. However, the added heat exchanger will result in undesired backpressure, which may deteriorate the performance of the internal combustion engine (ICE). To evaluate the backpressure on the performance of both the ICE and the AETEG, the model of ICE integrated with AETEG was established with the GT-power software and validated with the AETEG test bench. The heat exchangers with chaos shape and fishbone shape were proposed, their pressure drop with different engine speeds was studied, and their effects on the performance of both the AETEG and the ICE were analyzed. The results show that compared with the fishbone-shaped structure, the pressure drop of chaos-shaped heat exchanger is larger at the same engine speed, which contributes to the increased maximum power and hot side temperature of the AETEG. Moreover, compared with the ICE without heat exchanger, the brake torque, brake power, volumetric efficiency, pumping mean effective pressure, CO emission, and CO2 emission of the ICE assembled with chaos-shaped and fishbone-shaped heat exchanger reduce, and the corresponding brake-specific fuel consumption increase because of the raised backpressure caused by the heat exchanger.

Effect of Exhaust Backpressure on Performance of a Diesel Engine: Neural Network based Sensitivity Analysis

Effect of Exhaust Backpressure on Performance of a Diesel Engine: Neural Network based Sensitivity Analysis

A recent review on waste heat recovery methodologies and applications: Comprehensive review, critical analysis and potential recommendations

Due to global warming and environmental issues in recent times, the world's concern is oriented nowadays toward discovering new renewable energy sources and energy management methods. Particularly, researchers are emphasizing on heat recovery technologies and applications in both residential and industrial sectors. While there are plenty of review papers in the literature on the subject matter, there is always a necessity to update the literature with the new advancements in the field. In this context, the purpose of this paper is to present a recent and complete systematic comprehensive review along with critical analysis and potential recommendations related to waste heat recovery (WHR) methodologies and applications. In methodologies, heat exchangers, Rankine cycle and thermoelectric generators are studied. Moreover, applications of WHR are discussed in automotive, and in both residential and industrial zones. Studies show that the optimization of heat recovery systems lead to significant magnitudes of energy savings. On the other hand, hybrid heat recovery systems prove to be the most trending research subject nowadays. For future work, the negative effect of backpressure should be taken into consideration when recovering energy from exhaust gases of engines and power generators, and more importance should be given to hybrid systems.

Effect of Exhaust Gas Flow and Back Pressure on Urea Dosing Unit and Pipe of SCR in Industrial Diesel Engine

Effect of Exhaust Gas Flow and Back Pressure on Urea Dosing Unit and Pipe of SCR in Industrial Diesel Engine

The effect of soot accumulation and backpressure of an integrated after-treatment system on diesel engine performance

The effect of soot accumulation and backpressure of an integrated after-treatment system on diesel engine performance

Characteristics of thickness-vibration-mode PZT transducer for acoustic micropumps

The characteristics of a thickness-vibration-mode PZT transducer for acoustic micropumps are evaluated with a U-shaped tube structure. The phenomenon in which the height of the water level can be increased in a U-shaped tube due to the acoustic driving force was used to develop measurement methods for the output pressure and flow rate of the acoustic micropump driven by a PZT transducer. The measurement results showed that the output pressure increases from 22.6 to 37.6 Pa and the flow rate increases from 3.6 to 6.4 ml/min when input voltages of 68–105 Vpp are applied to the PZT transducer and the height of water level is 30 cm above the PZT transducer. To discuss the effect of backpressure, the output characteristics of pressure and flow at water height levels of 31 and 32 cm were measured for comparison with those at 30 cm.

Effect of back pressure on the grinding performance of abrasive suspension flow machining

Effect of back pressure on the grinding performance of abrasive suspension flow machining