Increase Of Inlet Pressure Research Articles

Effect of resistive load characteristics on the performance of Organic Rankine cycle (ORC)

The effects of various organic Rankine cycle (ORC) components, such as evaporator, expander and condenser on the performance of the system have been extensively studied. However, only a handful of studies have focused on studying the influence of external load characteristics. A small-scale ORC test rig of 3 kWe was constructed to experimentally investigate the effect of resistive load on the performance of the system. In order to achieve this, the study combined the thermodynamic method with electrical analysis. The results showed that the increase in output power caused a simultaneous increase in rotational speed, torque and inlet pressure of the expander under constant load resistance conditions. However, the fluid mass flow rate only affected the expander's inlet pressure. The decrease in load resistance increased the expander's inlet pressure and torque, and reduced the superheating and rotational speed. The influences of load resistance on the isentropic efficiency and net efficiency were mainly thorough the expander's inlet pressure and superheating. The net efficiency also benefited from the ideal cycle efficiency due to that decreasing load resistance enlarged the enthalpy drop of expander. The effects of load resistance on performance parameters were restricted by the mass flow rate of the fluid.

An Engine Exhaust Utilization System by Combining CO2 Brayton Cycle and Transcritical Organic Rankine Cycle

For engine exhaust gas heat recovery, the organic Rankine cycle (ORC) cannot be directly used due to the thermal stability and safety of organic fluids. Thus, a creative power system is given by integrating the supercritical CO2 Brayton cycle and transcritical ORC. This system can directly utilize the thermal energy of a high-temperature exhaust gas. The inefficiencies in the heat exchangers are highly reduced by using supercritical working fluid. The mathematical model of the system, covering both the thermodynamic and economic aspects, is built in detail. It is found that the highest irreversible loss takes place in the gas heater, taking 21.14% of the total exergy destruction. The ORC turbine and CO2 turbine have the priority for improvement, compared to the compressor and pump. The increase in CO2 turbine inlet pressure improves the system exergy efficiency and levelized cost of energy. Both the larger CO2 and ORC turbine inlet temperatures contribute to a decrease in levelized cost of energy and a rise in system exergy efficiency. There is a maximum value of system exergy efficiency and minimum value of levelized cost of energy by varying the ORC turbine inlet pressure. The determined exergy efficiency and levelized cost of energy in the proposed system are 54.63% and 36.95 USD/MWh after multi-objective optimization.

Experimental Study of Gas–Liquid Pressurization Performance and Critical Gas Volume Fractions of a Multiphase Pump

Abstract Gas entrainment may cause pressurization deterioration and even failure of pumps under conditions of high inlet gas volume fraction (GVF). When the inlet GVF increases to a critical value, an obvious deterioration performance of pump occurs. Air–water pressurization performance and inlet critical GVFs of a centrifugal multiphase pump are investigated experimentally under different inlet pressures and gas–liquid flow rates. To determine the first and second critical GVFs, a new method is proposed by computing the local extreme points of the second derivative of performance curves. New prediction correlations for two critical GVFs are established with relative errors lower than ±10% and ±8%. Boundaries of three different flow patterns and the transition flow rates are determined and presented by critical GVFs on the flow pattern diagram. Moreover, boundaries of maximum pressurization are determined by performance curve clusters and a power function correlation of gas–liquid flow rates when reaching the maximum pressurization is established. With the increase of inlet pressure from 1 MPa to 5 MPa, two-phase pressurization performance is significantly increased; occurrences of pressurization deterioration are obviously delayed with the first and second critical GVFs increasing by maximums of 8.2% and 7.1%.

Numerical simulation of filling process of cryogenic propellants with inert gas purge

The cryogenic filling process is a complex phenomenon with a combination of thermal and flow transients, especially in the case of inert gas purge during the start-up of liquid rocket engines. A 7-Equation two-fluid model is proposed in this work by adding an extra mass conservation equation for the purging gas compared with the conventional 6-Equation model. And the conservation equations for mass and energy are in the differential form, while the momentum equations are given in quasi-steady state. The model is programmed in Modelica language based on the idea of modular modeling. A two-step rising pressure in the supply system of a real engine shown by the experimental data is also predicted by the model. Then the reason for the pressure surge is analyzed by the numerical results. Finally, the numerical study is carried out to examine the effect of inlet pressure and purging pressure on filling characteristics in the supply system. The results show that within the range of parameter considered, the magnitude of pressure surge in the oxygen dome increases with increase in inlet pressure and purging pressure. The filling rate of liquid oxygen in the dome changes in a positive way with inlet pressure while in a negative way with purging pressure.

Research on Cavitation Characteristics of Two-Throat Nozzle Submerged Jet

Ship fouling not only increases ship resistance and fuel consumption but is equally a type of biological invasion, which causes severe ecological damage. Submerged cavitation jet cleaning is an environmentally friendly, high-efficiency, and energy-saving cleaning method. The nozzle structure has an essential influence on the cleaning effect. Thus, a two-throat nozzle was designed for application in submerged cavitation jet cleaning. To investigate the cavitation characteristics of the two-throat nozzle, a high-speed photographic visualization experiment and an erosion experiment concerning the submerged cavitation jet were carried out in this study. The frame-difference method (FDM) was used to analyze the dynamic changes in the cavitation cloud in a single period. The dynamic changes in the cavitation cloud and the characteristics of the submerged cavitation jet were investigated under different inlet pressures. The sample mass loss and the macroscopic and microscopic changes in surface morphology were used to evaluate the cavitation intensity of the two-throat nozzle submerged jet. The experimental results demonstrate that the two-throat nozzle has a good cavitation effect, and the cavitation cloud of the submerged jet has obvious periodicity. With the increase in inlet pressure, the length, width, and area of the cavitation cloud continue to increase, and the shedding frequency of the cavitation cloud continues to decrease. The intensity of cavitation erosion is related to target distance and impact time. There is an appropriate target distance by which to achieve the optimal cavitation effect. The collapse of cavitation bubbles near the sample surface is related to the erosion distribution on the sample surface. Moreover, the magnitude of the absolute values of the root-mean-square surface roughness and surface skewness increase with cavitation intensity. The results in this paper are helpful for a better understanding of the cavitation characteristics of the two-throat nozzle submerged jet.

Exergetic Performance Coefficient Analysis and Optimization of a High-Temperature Proton Exchange Membrane Fuel Cell.

Performance of a high-temperature proton exchange membrane fuel cell (HT-PEMFC) and the influence of different parameters on HT-PEMFC is analyzed in this study. Firstly, mathematical expression for energy efficiency, power density, exergy destruction and exergetic performance coefficient (EPC) are derived. Then, the relationship between the dimensionless power density, exergy destruction rate, exergetic performance coefficient (EPC) and energy efficiency is compared. Furthermore, the effect of flow rate, doping level, inlet pressure and film thickness are considered to evaluate the performance of HT-PEMFC. Results show that EPC not only considers exergetic loss rate to minimize exergetic loss, but also considers the power density of HT-PEMFC to maximize its power density and improve its efficiency, so EPC represents a better performance criterion. In addition, increasing inlet pressure and doping level can improve EPC and energy efficiency, respectively.

Investigation on Unsteady Cavitation Flow and Excited Pressure Fluctuations in Regulating Valve

A multi-field synchronous measurement system for the cavitation flow in a regulating valve was established. The system combines a high-speed full-flow field display system with a pressure measurement system to realize the simultaneous acquisition of cavitation shapes and pressure pulsations. Cavitation flow occurs near the throttle orifice, which is obviously a quasi-periodic behavior. The unsteady cavitation flow mainly includes three stages: the growth of the attached cavity, the fracture and shedding of the attached cavity and the growth and collapse of the free cavity. The time evolution of the cavitation behaviors is highly related with excited pressure fluctuations. With the increasing attached cavity area, the corresponding pressure in the flow field decreases slowly. When the attached cavity falls off and develops downstream, the cavity area decreases gradually, and the pressure increases gradually. When the free cavity shrinks and collapses, the pressure in the flow field reaches the peak value. The pressure pulsation and the change of cavity area have the same dominant frequency, around 2000 Hz, at the monitoring point in the upstream, throat and expansion monitoring points. Furthermore, with increasing inlet pressure, the mean and variance values of cavitation area become larger, and the excited pressure fluctuation at each measuring point becomes more intense. The mean value of pulsating pressure at the throat gradually increases, while the pressure in the expansion section presents a downward trend. The variance of pressure pulsation and the maximum pressure also increase gradually with the increase in inlet pressure. The change of cavitation area and the pressure pulsation in the regulating valve complement each other. The results in this paper could provide experimental guidance on optimizing the structure of the valve, inhibiting cavitation occurrence and prolonging the service life of the valve.

Investigation on cavitation initiation in jet pump cavitation reactors with special emphasis on two mechanisms of cavitation initiation

Hydrodynamic cavitation is used in various engineering fields, such as water treatment and chemical processing. Cavitation initiation is critical to assessing the cavitation effect in cavitation reactors, so cavitation initiation should be studied to improve cavitation in various fields. This paper investigates the mechanisms and characteristics of cavitation initiation in jet pump cavitation reactors (JPCRs) to intensify the cavitation. A criterion derived for cavitation initiation focuses on the fluctuating pressures caused by the velocity gradients. Experiments show that the criterion predicts low pressure cavitation and strong shear dominant cavitation in a JPCR. Then, the characteristics of these two cavitation mechanisms are investigated for various geometric parameters and operating conditions and a cavitation initiation regime map is developed for JPCR. The results show that cavitation occurs more easily, and the two cavitation mechanisms become increasingly more difficult to distinguish in the JPCR as the inlet pressure increases. The velocity gradient and loss coefficient increase with a decrease in suction pressure, which promotes cavitation. The low pressure cavitation and strong shear dominant cavitation are both more likely when the area ratio is relatively small. The induced pressure spectra further show that the low frequency component dominates during the formation of the low pressure cavitation, while the high frequency component dominates during the formation of the strong shear dominant cavitation. This study clarifies the cavitation mechanisms with special emphasis on the fluctuating pressure and the corresponding characteristics in the JPCR to provide guidance for JPCR applications in industry.

Investigation of influencing factors of wear in a sandblasting machine by CFD-DEM coupling

In order to study the effect of particle characteristics and operating conditions (particle diameter, density, shear modulus, initial stacking height and inlet pressure) on the wear of the sandblasting machine, the gas-solid two-phase flow inside a sandblasting machine under different operating conditions was simulated by coupling the CFD and DEM methods in this work. Combining with the Archard wear model, the erosion was calculated and the erosion distributions were obtained in different sandblasting machine parts, including the top cover, inlet pipe, cylindrical part, conical part and lower pipe. The simulation results demonstrate that severe erosion in the sandblasting machine occurs at the lower pipe near the outlet, the conical part and the joints between different parts. The erosion volume order for different parts from high to low is: the lower pipe, conical part, cylindrical part, inlet pipe and top cover. The erosion volume of the sandblasting machine increases with the increase of particle diameter, density, shear modulus, stacking height and inlet pressure. Comparatively, the initial stacking height and inlet pressure have more influence on the erosion, while the particle density and shear modulus have less influence.

Theoretical and experimental study on the performance of a high-efficiency thermodynamic cycle for ocean thermal energy conversion

A new high-efficiency ocean thermal energy conversion (OTEC) system using non-azeotropic mixed working fluids with two regenerative cycles is proposed. Based on the first law of thermodynamics, a numerical calculation model for the proposed cycle was established to study the effects of the mass fraction of mixed working fluids, turbine inlet pressure and seawater temperature on the performance of the cycle system. An experimental plant of the proposed OTEC system was established to study the effects of seawater temperature and turbine inlet pressure on the cycle thermal efficiency. The results show that the cycle thermal efficiency and net output power of the system both increase with a decrease in cold seawater temperature or an increase in warm seawater temperature. The system cycle thermal efficiency and net output power both initially increase and then decrease with an increase of the working fluid mass fraction. The system cycle thermal efficiency and net output power both initially increase and then decrease with an increase of the turbine inlet pressure under a certain working fluid mass fraction. The experimental results of cycle thermal efficiency with various performance parameters were basically consistent with the theoretical analysis results; however, the experimental values were lower than the theoretical analysis results.

Enhancing and assessing ammonia-air combustion performance by blending with dimethyl ether

As a hydrogen energy carrier and carbon-free fuel, ammonia (NH3) is being growingly considered as an alternative fuel for combustion systems in an effort to reduce carbon emissions. Unlike conventional fossil fuels, its relatively low flame speed hinders its widespread use in practice. Utilizing the 1D freely propagating flame model in Chemkin-Pro 2019, this work numerically evaluates the impact of blending ammonia with dimethyl ether (DME) on the laminar burning velocity of NH3/air flames. For this, the reaction mechanism is first validated by comparing predictions to experimental data available in the literature. The addition of DME is found to significantly enhance the laminar burning velocity (SL) of NH3 flames, which can be comparable to that of hydrocarbon fuels. This enhancement is a result of the combined thermal and chemical effects. Reaction pathway and sensitivity analyses reveal that adding DME enables the major reaction steps and the sensitivities to be altered, thus positively affecting the overall reaction rate. Furthermore, the SL of NH3/air flames is weakly dependent on the inlet thermodynamic pressure, but becomes stronger with more DME blended. The explanation behind this phenomenon is that the relative importance of the termination versus branching reactions is more significant in binary flames. The overall reaction order characterizing the importance of the chain branching and the terminating reactions shows a decreasing trend with increasing inlet pressure. In general, the present work provides a design guideline on the selection of fuel flexibility and sheds light on the fundamental NH3-DME-fueled flame enhancement mechanisms.

Design of a Supercritical CO2 Compressor for Use in a 1 MWe Power Cycle.

Supercritical CO2 power cycles are considered to be a more effective means to replace the steam Rankine cycle in power generation by power coal in the future. However, CO2 compressors for this application have not been well developed. A conceptual design of the compressor for a 1 MWe cycle has been summarized and a calculation method of the axial force of a supercritical CO2 compressor has been introduced. The influences of inlet temperature and pressure near the critical point on compressor performance, the rotor dynamics analysis for this compressor, and the influence of the rotation factor C0 on compressor axial force were also investigated. The results show that the changes in inlet temperature and pressure near the critical point have great influences on compressor performance and the axial force of the compressor is closely related to the selection of the rotation factor C0. The pressure ratio and power decrease with the increase of inlet temperature; when the inlet temperature increases by 2 °C, the pressure ratio decreases by 7–24% and the power decreases by 1–9%. With the increase of inlet temperature, the maximum efficiency of the compressor decreases, and the maximum pressure ratio of the compressor decreases with the increase of inlet pressure. When the rotation factor C0 is equal to 0 and 0.2, the axial force of the compressor decreases with the increase of rotating speed. When the rotation factor C0 is equal to 0.4, the curves of the compressor with the flow rate at different speeds begin to produce intersections. When the rotation factor C0 is equal to 0.6, 0.8, and 1, the axial force of the compressor increases with the increase of rotating speed.

Rotordynamic characteristics prediction for scallop damper seals using computational fluid dynamics

Enhancing damping characteristic is one of the effective methods to solve the instability problem of the rotor system. The three-dimensional numerical analysis model of scallop damper seal was established, and the effects of inlet pressures, preswirl ratios, rotational speeds, interlaced angles and seal cavity depths on the rotordynamic characteristics of scallop damper seal were studied based on dynamic mesh method and multi-frequencies elliptic whirling model. Results show that the direct stiffness of the scallop damper seal increases with decreasing inlet pressure and increasing rotational speed and cavity depth. When the seal cavity is interlaced by a certain angle, which shows positive direct stiffness. The effective damping of the scallop damper seal increases with the increasing inlet pressure, the decreasing preswirl ratio and the rotational speed and cavity depth. There exists an optimal interlaced angle to maximize the effective damping and the system stability. The leakage of the scallop damper seal is significantly reduced with decreasing inlet pressure. The preswirl will reduce the leakage flowrate, and the rotational speed has a slight effect on the leakage performance. The leakage of the scallop damper seal decreases with increasing seal cavity depth.

Analysis and regulation of the cardiovascular system of univentricular heart with different configurations of the total cavopulmonary connection

The cardiovascular system (CVS) is a complex mechanism capable of reacting and regulating various changes in external and internal parameters. A particular problem is the study of CVS with univentricular heart. We studied the hemodynamic response of the CVS to the use of various configurations of bypassing the right side of the heart. During our research, we selected three different configurations of the total cavopulmonary connection. All configurations were made from Clear Flex 50 and tested in an experimental workbench. According to the research results, the TCPC-3 configuration is the most optimal. It has symmetrical output values of flows and pressures and there is no significant increase in inlet pressure. The results of this study can be used to optimize the control of the parameters of the ventricular assist device and the total artificial heart.

Characteristics Analysis of Fluid-Structure Coupling Vibration of spray bar for High gap sprayer

With the progressive improvement of the level of mechanization of agricultural production, the high-gap rod sprayer has gradually become an important component of agricultural production equipment. The stability of spray rod has an important influence on the life and operation quality of spray rod. Therefore, considering the stability of the spray rod of high gap sprayer, a fluid-solid coupling vibration simulation model of the spray rod of high gap sprayer is established in this paper. The influence of inlet velocity, inlet pressure, fluid density and fluid viscosity on the flow rate and dynamic pressure in the pipe was analyzed by fluent. The results show that the exit velocity increases with the increase of the inlet velocity, but when the velocity reaches a certain value, backflow occurs. With the increase of inlet pressure, the dynamic pressure increases, and the local energy loss and the energy loss along the path also increase. The velocity and dynamic pressure decrease with increasing density.

Simulation of Particle Motion Behavior in Fluidized Bed Opposed Jet Mill

In order to study the influence of the internal flow field of the fluidized bed opposed jet mill on the motion behavior of particles, Computational Fluid Dynamics (CFD) and Discrete Dlement Method (DEM) are used for coupling calculations. By adjusting the nozzle spacing and inlet pressure, Numerical simulation is carried out on the process of particles collisions with each other after accelerating under the high-speed jet produced by the nozzle. The trajectory of the particles in the flow field of the collision area and the change of the collision state of the particles are analyzed. Finally, the best parameters are selected based on the total collision energy. The results show that the particles will gradually shift and spread during the acceleration process. The reduction of the nozzle spacing is beneficial to increase the probability of particle collisions. However, if the spacing is too small, the particles cannot be fully accelerated; the increase in inlet pressure will increase the kinetic energy of the particles, and number of collisions is almost unaffected. By comparing the total collision energy, the best-simulated preparation conditions are selected as 110mm and 1.1MPa.

Experimental investigation on the acoustic characteristics and cooling performance of the vortex tube

• Frequency domain analysis of the acoustic signal of the vortex tube was conducted. • The sound energy is mainly concentrated in the frequency range of 4000-5000 Hz. • Higher inlet pressure tends to produce higher acoustic intensity. • Energy separation efficiency increases with the growth of the sound pressure level. • The vortex tube with 5 nozzles has the maximum coefficient of performance. The purpose of this paper is to study the acoustic signal characteristics of a Ranque-Hilsch vortex tube and discuss the energy separation phenomenon behind it. Experiments were conducted with air as the working fluid. The acoustic signal and corresponding thermal fluid parameters are measured. The influencing factors such as inlet pressure, nozzle number, and cold mass fraction were investigated. The results show that the acoustic energy of the vortex tube is chiefly within the range from 4000 Hz to 5000 Hz. Two frequency peaks (about 1500 Hz and 4200 Hz) are observed in the frequency domain. As the inlet pressure increases, the sound pressure level( SPL ) increases, and as the cold mass fraction increases, the SPL decreases. There is a positive correlation between the sound intensity and the energy separation performance. Interestingly, the vortex tube with 5 nozzles produces maximum SPL and COP (Coefficient of performance) compared to the 4-nozzle and 6-nozzle vortex tubes.

Experimental investigation on spray and ignition characteristics of plasma actuated bluff body flameholder

Stable combustion of aero-engines and ramjet combustors is greatly dependent on the quality of atomization. It is quite difficult to achieve wider ignition boundary and good combustion performance under low pressure and low temperature airflow, because the quality of fuel atomization is comparative bad and there is no enough surface area for fuel droplets to mix with surrounding air and evaporate. Internal mechanism of how plasma assisted ignition on spray performance in model aero-engine combustors and ramjet combustors remains not clear. In this study, a novel plasma-actuated bluff-body flameholder is proposed to help improve the quality of fuel atomization and thus enhance the ignition performance and stable combustion of original bluff-body flameholder. Spray and atomization properties of aviation kerosene (RP-3) were investigated under various operating conditions including inlet pressure, inlet temperature and gliding arc plasma actuation. A rotating arc discharge plasma column could be formed during the high-voltage tungsten electrode and the fins of bluff-body flameholder. Macroscopic as well as microscopic spray properties was analysed through simultaneous LIF/MIE technique along with particle/droplet image analysis (PDIA) system. Flame ignition limit at different inlet temperature was conducted under combustor inlet Mach number of 0.2. Results show that mean drop diameters were decreased with increase of inlet temperature and inlet pressure. Gliding arc plasma actuation help fuel injected from bluff-body flameholder breakup into smaller droplets and improve uniformity of fuel spray through heating and transport effect. With actuation of gliding arc plasma, Sauter mean diameter (SMD) was minished by 13%∼20% at inlet pressure of 30 kPa, while droplet uniformity index was increased by around 21.8%. Due to better fuel atomization quality together with more active components generated by gliding arc plasma, flame ignition limit of bluff-body flameholder was obviously extended by about 13%∼30%. The gliding arc plasma was verified to promote fuel droplets atomization and to achieve homogeneous distribution under low temperature and pressure, which is beneficial to wider flame ignition and stabilization boundary.

Characterisation and comparison of unsteady actuators: a fluidic oscillator and a sweeping jet

PurposeThe purpose of this study is to compare two unsteady actuators: an oscillator and a sweeping jet. Both actuators can produce an oscillating jet of different amplitudes and frequencies without any moving parts, making them an attractive actuator concept. The Coanda effect phenomenon can explain the operating principles of these two unsteady actuators.Design/methodology/approachA numerical study was conducted to compare the amplitudes and frequencies of fluidic and sweeping jet (SJ) oscillators to obtain an efficient actuator to control separated flows at high Reynolds numbers. For this goal, two-dimensional unsteady Reynolds-averaged Navier-Stokes simulations were carried out using computational fluid dynamics (CFD) fluent code to evaluate the actuator performances. The discrete fast Fourier transform method determined the oscillation frequencies.FindingsThe oscillation frequencies gradually increase as the inlet pressure increases. The characteristics and dimensions of the vortices produced in the mixing chamber and feedback loops vary overtime when the injected fluid is swept sideways. The frequencies supplied by the SJ are stronger than those obtained by the fluidic oscillator, which may contribute to improving the aerodynamic performance at a lower power supply cost.Originality/valueThe existence of the splitter in the fluidic oscillator led to the production of separate pulses, which would be useful in various industrial applications, including active control of combustion and mixing processes while other applications such as flow separation control require SJs. With the latter actuator higher and interesting frequencies can be obtained, leading to efficient flow control.

Study on the influence of elbow with different curvature radii on pipeline leak location

Experimental and numerical methods are used to locate the pipeline leakage in the present work. The weak compressibility of the fluid is taken into account when simulating the propagation of negative pressure wave (NPW) in the pipeline. The NPW attenuation coefficient is used to describe the influences of curvature radius on location accuracy. The results indicate that when the curvature radius is small, the location accuracy of pipeline leakage is low. When the radius of curvature increases or the inlet pressure increases, the accuracy of pipeline leak location is improved. Besides, with the change of inlet pressure, pressure, and velocity distributions in the elbow with different curvature radii are investigated. When the curvature radius of the elbow is three to four times of pipe diameter, the measurement accuracy of leakage location is the best. When the inlet pressure of the pipeline is 0.7 MPa, the sensitivity of the pipeline detection is the highest. The cavitation corrosion at the elbow is the most obvious. Therefore, the elbow is the area where pipeline leakage occurs most frequently.