Discharge Mass Flow Rate Research Articles

Investigation on saturated vapor and two-phase refrigerant injection in the rotary compressor for the extreme hot and cold conditions

Vapor injection has been widely applied in the rotary compressor to improve the heating capacity and reduce the discharge temperature in the cold condition. However, under the evaporation temperature below −20 °C or the condensation temperature above 60 °C, the discharge temperature is still relatively high, which limits compressor performance and its continuous operation time. To keep the optimal performance and further reduce discharge temperature, this paper focuses on the two-phase refrigerant injection and proposes a mathematical method to investigate the effect of injection vapor quality on the compressor performance. Based on the proposed method, some performance parameters including cooling capacity, heating capacity, EER(COP), power, discharge mass flow rate and discharge temperature have been calculated and an experiment is conducted to test these performance parameters. The calculation errors between calculated and tested results are within 4% and it indicates that the proposed method is accurate to investigate saturated vapor and two-phase refrigerant injection characteristics. The simulated results show that the use of two-phase refrigerant injection results in the trade of a slight drop in cooling capacity, heating capacity and EER(COP) for a large drop in discharge temperature, which is valuable and meaningful for engineering application under the extreme hot and cold conditions.

Study of the thrust response characteristics of Hall Micro Thruster

An advanced Watt class Hall Micro Thruster (HMT) is offered for Space Gravitational Wave Detection (SGWD), and an investigation has been conducted on its start-up, shutdown, rise, and fall response times. The research involved creating a circuit for thruster discharge and signal acquisition, using a Faraday probe to measure the plasma plume signal generated by the thruster, and characterizing the thrust directly. Ultimately the response time of the thruster is extracted from the discharge current and Faraday current signals. The experimental results demonstrate that the HMT has a response time ranging from 1.08 ms to 16.76 ms at mass flow rates of 0.02 mg/s and 0.04 mg/s, meeting the SGWD requirements for micro thruster response time. This research provides a physical foundation and explanation for the variation of HMT response time with discharge voltage versus mass flow rate with several key parameters that affect HMT plasma discharge, such as neutral gas number density (nn) and ionization mean free path (λi). Furthermore, we have examined several anomalies in the signal. Overall, this research provides a brand-new method for measuring the thrust response time of electric thrusters.

Particle motion analysis and performance investigation of a fertilizer discharge device with helical staggered groove wheel

Enhancing the uniformity of fertilizer particles flow is crucial in fertilizer discharge device research, and the analysis of particle motion process contributes to improving fertilization performance. In this study, the discrete element method was employed to conduct a phenomenological analysis and numerical investigation of the particle motion characteristics influenced by structural feature parameters of the groove wheel-type fertilizer discharge device. A performance evaluation model based on the uniformity of fertilizer discharge and supplemented by the flow characteristics and mechanical properties of particles was established. The results demonstrated that the particles flow within the fertilizer bin exhibits a recirculating surge induced by the rotation of the groove wheel. The geometric morphology of the outer edge grooves and their spatial distribution along the groove wheel circumference affect the uniformity of fertilizer filling and discharge mass flow rate. The force exerted on the fertilizer particles and their potential breakage are primarily concentrated during the fertilizer compaction stage, while the particles flow forms a convergence due to the sliding of the fertilizer along the discharge slope. After optimization, the discharge CV is reduced from 91.54 % to 31.48 %, and the uniformity is improved by 60.06 %. This study proposes a helical staggered groove wheel fertilizer discharge device structural model, providing new insights for the optimization of agricultural fertilization machinery equipment.

Theoretical and experimental investigation on the rolling piston compressor with enhance vapor injection for heat pump system

The rolling piston compressor with enhanced vapor injection (EVI) is widely used in the household air-source heat pump system. To study the thermodynamic performance and the optimal injection pressure, this paper presents a mathematical method to simulate the whole working process of rolling piston compressor with EVI, which considers suction backflow process, discharge process, vapor injection process and leakage process. According to the calculation, the effects of injection pressure on discharge mass flow rate, p-V diagram and indicated power have been analyzed. In order to verify the accuracy of simulation, an experiment has been carried out to obtain the discharge mass flow rate and the errors between simulated and experimental results are within 4%, which shows that the proposed method is precise enough. Additionally, the experimental results show that EVI can not only improve the heating capacity and COP but also decrease the discharge temperature. However, the optimal injection pressure corresponding to the maximum heating capacity is different from that corresponding to the maximum COP. From the perspective of the heating capacity, the optimal injection pressure is a little higher than the geometric mean of suction pressure and discharge pressure but from the perspective of COP, the optimal injection pressure is a little lower than the geometric mean.

Study of the effect of virtual mass force on two-phase critical flow

Abstract Critical (choked) flow is a highly concerning phenomenon in safety analysis for nuclear energy. The discharge mass flow rate prediction is crucial for engineering design and emergency response in case of nuclear accidents. Unfortunately, the critical flow is difficult to predict especially when the two-phase flow exists. The accuracy is based on a deeper understanding of the complex phenomenon of critical flow. The influence of virtual mass force on the two-phase critical flow was seldom concentrated on owing to the lack of suitable critical flow models for studies in detail. This study is based on a developed 6-equation two-phase critical flow model. It is confirmed that the virtual mass force contributes to the stability and convergence of the critical flow simulation and it will impact not only the critical mass flux but also the thermal hydraulic parameters along the discharge duct. The magnitude depends on the geometry of the discharge duct and the upstream condition. It is larger when the duct is longer and the pressure is lower. Furthermore, the virtual mass force for each flow regime was studied in detail with a sensitivity study. The results show that the most sensible condition for the virtual mass force is annular flow along a long tube under relatively low pressure. The future work is to develop a correlation of virtual mass force for critical flow specifically since the correlations in the literature were developed under general two-phase flow process conditions.

Examination of the Scaling Law of Fire Phenomena in Compartment with Horizontal Natural Opening using Numerical Simulation

The scaling law was examined using numerical simulation for fire phenomena in a compartment with a horizontal natural opening in this study. The results of the large-scale conversion of the scaled model numerical simulation results ([Small-scale] condition) from the earlier studies obtained by applying the scaling law were compared to those of the large-scale numerical simulation performed in this study ([Large-scale] condition). The overall trends for the effects of horizontal natural opening area and fire source location on the discharge mass flow rate through the horizontal natural opening, temperature distribution in the compartment, and flow velocity through the horizontal opening were found to be identical under the [Small-scale] and [Large-scale] conditions. A complex bidirectional flow was observed through the horizontal natural opening under the conditions of this study and the accuracy in predicting the average W-velocity value based on the scaling law was low; however, the accuracy in predicting the range of velocity fluctuation was higher than the average value under certain conditions. Based on the standard deviation of the numerical simulation results, the percentages of the data within ± 30% of the difference between the [Small-scale] and [Large-scale] conditions relative to the total number of data were 100, 75, and 88% for the discharge mass flow rate, temperature, and flow velocity through the horizontal natural opening, respectively. The accuracy of the scaling law was found to be high for the discharge mass flow rate under the conditions considered in this study.

Experimental investigation on helium valved linear compressors with different active offsets

Piston offset in the helium valved linear compressor (VLC) deteriorates the cooling performance and operating life of Joule-Thomson (JT) refrigerators, especially in aerospace applications. To clarify the influence of piston offset on the VLC performance, an experimental investigation was carried out. Based on a laboratory developed VLC, the effects of piston offset on the suction and discharge pressure, pressure ratio, mass flow rate, motor efficiency, volume efficiency and adiabatic efficiency are systematically studied under two piston motion states (fixed piston displacements and full strokes). The results show that when the piston stroke is constant, the offset will increase the discharge pressure and mass flow rate, and decrease suction pressure. When the piston moves at full stroke, the offset will reduce the discharge pressure and mass flow rate, and increase suction pressure. Regardless of the working conditions, the existence of offset will affect the efficiency of the compressor, hence increasing the power consumption.

Physics of thermionic, orificed hollow cathodes: I. Theory and experimental validation

A model aimed at illuminating the physics of thermionic, orificed hollow cathodes is developed and validated with experimental data. The model is intended to describe the variation of total (neutrals, ions, and electrons) static pressure with controllable parameters. That pressure must be properly evaluated because it influences important plasma parameters in the cathode such as the attachment length and the electron temperature, which directly impact the lifetime of thermionic inserts. The model, which combines a zero-dimensional approach to the conservation of energy and momentum for the combined plasma-neutral fluid and a charge-exchange-limited ambipolar diffusion model, allows for the computation of all plasma quantities, including the total fluid pressure. The model depends on the operating conditions (discharge current and mass flow rate), cathode geometry, and the gas species, along with two non-controllable parameters: the neutral gas temperature and the sheath potential. Total pressure data at up to 307 A of cathode discharge current were obtained experimentally and were used, along with data from the literature, to validate the model. Good agreement is obtained for all quantities. The model is used in a companion paper to clarify the role of magnetic and gasdynamic pressure in the scaling of total pressure, to derive scaling laws applicable to thermionic, orificed hollow cathodes, and to propose novel cathode design rules.

Advection-diffusion-settling of deep-sea mining sediment plumes. Part 1: Midwater plumes

The evolution of midwater sediment plumes associated with deep-sea mining activities is investigated in the passive-transport phase using a simplified advection–diffusion-settling model. Key metrics that characterize the extent of plumes are defined based on a concentration threshold. Namely, we consider the volume flux of fluid that ever exceeds a concentration threshold, the furthest distance from and maximum depth below the intrusion where the plume exceeds the threshold, and the instantaneous volume of fluid in excess of the threshold. Formulas are derived for the metrics that provide insight into the parameters that most strongly affect the extent of the plume. The model is applied to a reference deep-sea mining scenario around which key parameters are varied. The results provide some sense of scale for deep-sea mining midwater plumes, but more significantly demonstrate the importance of the parameters that influence the evolution of midwater plumes. The model shows that the discharge mass flow rate and the concentration threshold play an equal and opposite role on setting the extent of the plume. Ambient ocean turbulence and the settling velocity distribution of particles play a lesser yet significant role on setting the extent, and can influence different metrics in opposing ways.

Performance Simulation of a 5 kW hall Thruster

Hall thruster is a kind of plasma optics device, which is used mainly in space propulsion. To simulate the discharge process of plasma and the performance of a 5 kW hall thruster, a two-dimensional PIC-MCC model in the R-Z plane is built. In the model, the anomalous diffusion of the electrons including Bohm diffusion and near-wall conduction is modeled. The Bohm diffusion is modeled by using a Brownian motion instead of the Bohm collision method and the near-wall conduction is modeled by a secondary electron emission model. In addition to the elastic, excitation, and ionization collisions between electrons and neutral atoms, the Coulomb collisions are included. The plasma discharge process including the transient oscillation and steady state oscillation is well reproduced. First, the influence of the discharge voltage and magnetic field on the steady state oscillation is simulated. The oscillation amplitude increases as the discharge voltage gets larger at first, and then decreases. While the oscillation amplitude decreases as the magnetic field gets stronger at first, and then increases. Later, the influence of the discharge voltage and mass flow rate on the performance of the thruster is simulated. When the mass flow rate is constant, the total efficiency initially increases with the discharge voltage, reaches the maximum at 600 V, and then declined. When the discharge voltage is constant, the total efficiency increases as the mass flow rate rises from 10 to 15 mg/s. Finally, a comparison between simulated and experimental performance reveals that the largest deviation is within 15%, thereby indirectly validating the accuracy of the model.

Numerical Simulation of Imported Sediment in a Stilling Basin

Sediment buildup at the bottom of a stilling basin can result in premature drainage of spillway structures and can even lead to dam failure in severe cases. Such failures pose ecological and human safety hazards to downstream areas. To evaluate the sudden discharge and potential dam failure associated with sediment buildup, we developed a two-dimensional two-phase flow simulation model built on a particle-based force balance equation. We compared the flow patterns and energy dissipation effects in the stilling basin at different inlet flows (2, 3, 4.5, and 6.75 m2/s), and the subsequent bottom deposition was compared across different sand discharge mass flow rates (0.1, 0.2, and 0.3 kg/s). The results show that the turbulent energy increased with the increasing inlet unit width flow rate. When more vortices were generated and the flow velocity was reduced significantly, the energy dissipation was more effective. The sediment deposition at the bottom of the stilling basin gradually increased with the decrease of inlet unit width flow and the decrease of the sediment mass flow rate. Meanwhile, at a fixed inlet shape, the change in inlet unit width flow had little effect on the maximum sedimentation height at the bottom of the basin. In addition, the average deposition rate at the bottom of the stilling basin was positively correlated with the inlet sedimentation concentration, and the correlation coefficient could be as high as 0.97. In this two-phase flow method, the error of the simulated value over the theoretical value was less than 10%. This simulation of sediment deposition at the bottom of the stilling basin provides a practical reference for dam managers.

Guideline for electricity generation from hot springs (natural energy storage systems): A techno-enviro-economic assessment

The scattered hot springs on the globe are natural thermal energy storages that are available for industrial and recreational advantages. A hot spring is a hydrothermal system that can be used for power generation purposes as well as deep-well geothermal plants. Harnessing energy from hot springs is a practical approach for a future with sustainable power supply. Therefore, there is a demand for a comprehensive study for the estimation of power generation capacity of hot springs based on their mass flow rate and temperature. A techno-enviro-economic study is conducted to estimate the power generation capacity of hot springs as a heat source of the organic Rankine cycle. The organic Rankine cycle plant is modeled and simulated for various temperatures and mass flow rates of hot springs in the present study. The impacts of the temperature and mass flow rate of hot springs on the technical and economic aspects of the power generation plants are investigated. For the hot springs with temperature and discharge mass flow rate from 60 to 90 °C and 5 to 50 kg/s, respectively, the power generation capacity alters from 9.3 kW to 303 kW and the levelized energy cost is from 0.02 $/kWh to 0.11 $/kWh. The results indicate that the hot springs with a higher temperature and discharge mass flow rate have a higher thermal efficiency and power generation capacity for the organic Rankine cycle plant while payback period, levelized energy cost, and specific investment cost shrink. The hot springs with higher temperatures and/or larger discharge mass flow rates are financially ideal candidates for initiating the power generation plants.

Study on the characteristics of pellet movement under different roasting temperature in hopper

Roasting temperature plays an important role in the chemical reaction of vanadium‑titanium magnetite. In order to investigate the effect of roasting temperature on pellet motion characteristics, a non-cohesive and multi-element particle model of discrete element method (DEM) was constructed. On this basis, different diameter pellets (dp = 20.38 mm, 25.02 mm, 29.67 mm, 35.52 mm) with different roasting temperature (298 K ≤ T ≤ 1473 K) were selected to explore the effects on pellet velocity distribution, discharge mass flow rate, wall pressure and average voidage. Our results reveal a large change in the movement characteristics of pellets involving chemical reactions during high-temperature production. The mean voidage is negatively correlated with the diameter. The minimum deviations of pellet velocity distribution and discharge mass flow rate at different roasting temperature were 20.16% and 21%, respectively, and the maximum deviations of wall pressure and average voidage were 63.47% and 7.0%, respectively.

Observation of rotating magnetohydrodynamic modes in the plume of a high-current hollow cathode

High-current hollow cathodes are widely used in electric propulsion as well as for laboratory plasma generation applications. The plasma region just outside of high-current cathodes is characterized by the presence of many fluctuations, which can develop coherent plasma structures affecting the operation and life of the cathode. The properties of plasma oscillations have been investigated in the exterior region of a high-current hollow cathode operating at 25–150 A of discharge current with an applied axial magnetic field. Electrostatic and magnetic probes were used to measure the electromagnetic fluctuations, and correlation analysis between each of the probes signals provides the spatiotemporal characterization of the generated waves. The results of this investigation reveal the presence of a coherent magnetohydrodynamic (MHD) azimuthal mode with a fundamental frequency of 58 kHz. This mode has features of a helical kink instability with azimuthal wave number m=1 and axial wavenumber kz=50m−1 that is readily observed in high-speed Fast-Cam images. The occurrence of this mode, the frequency, and the wavenumber at onset are found to be predicted well by the ideal MHD theory, considering the boundary condition of a non-line-tying cylindrical anode. Investigation of the MHD mode properties at different discharge currents and mass flow rate shows additional features that could qualitatively agree with resistive MHD modes. In particular, when the plasma has a finite conductivity associated with anomalous resistivity in the cathode plume, a gradual emergence of modes at relatively low discharge currents are observed.

Axial pressure distribution, flow behaviour and breakage within a HPGR investigation using DEM

The pressure distribution between the rolls in a HPGR (High Pressure Grinding Rolls) is usually expected to vary significantly in the axial direction due to the end effects at the end of the rolls. This is based on the idea that particles near the ends of the rolls are less well confined which makes them more mobile with reduced ability to be trapped and crushed. This can reduce the performance efficiency of a HPGR quite significantly. Experimental measurement of this axial pressure distribution and its consequences for the breakage efficiency, particularly at industrial scale, is very difficult. So little is known about its nature or how this may change with choice of confining structures (such as cheek plates). This problem is tractable using DEM to predict the coupled flow and breakage of particles within the HPGR. A replacement strategy is used where particles are broken when the applied force exceeds a size dependent limit. This allows the DEM model to capture the fracture dynamics sufficiently to allow flow and load prediction. The model is calibrated against an experimentally measured product size distribution and predicts very close agreement across the entire resolved range of particle sizes. This model is used to explore the pressure distribution and how this, and the coarseness of the particles, changes along the rolls. Two mechanisms are identified for producing breakage in the HPGR. For a HPGR with cheek plates the discharge mass flow rate is found to be nearly independent of axial position with the product size distribution being axially invariant. The frictional effects of the cheek plates lead to a moderate axial flow towards each end of the rolls that balances the reduced vertical flow to give axially very uniform discharge behaviour. Finally, it is shown that only small changes in the confining cheek plate locations are needed to allow significant axial bypass, strong axial variation of discharge mass flow rate and a coarser product.

Internal flow and discharge coefficient characteristics of oil jet nozzles with different orifice angles under non-cavitating conditions

The orifice angle has great impact on the internal flow and discharge coefficient characteristics of oil jet nozzles. This paper presents numerical research on the internal flow and discharge coefficient behaviors of oil jet nozzles with different orifice angles. For this purpose, oil jet nozzles with different orifice angles in the range from 0∘ to 90∘ were evaluated under real injection pressure difference conditions (0.10∼0.50 MPa). The main results show that the mass flow rate, discharge coefficient and velocity coefficient decrease first and then increase with the increasing orifice angle. The value of each parameter corresponding to the orifice angle of 90∘ is slightly higher than that of 0∘. The minimum value is obtained with the orifice angle of 30∘, and the relative deviation between the highest and the lowest mass flow rate exceeds 11.5%. On this basis, the prediction formula of angle coefficient with extremely high goodness of fit is obtained by using polynomial fitting method for the multiple groups of normalized discharge coefficients, and the corrected empirical correlation of discharge coefficient and mass flow rate are developed in the light of the angle coefficient. Comparing the corrected empirical correlation prediction results with the numerical simulation results, the maximum deviation of the mass flow rate is 1.9%.

Influence of rotor speed, discharge pressure, and clearance size on the unsteady flow dynamics and heat interaction of roots blower

The geometry of the 2-lobe rotors of a roots blower is proposed by the combination of three arcs and is parameterized by two independent variables. By considering a standard combination of these variables, attempts are made to grasp the unsteady interior flow phenomena and thermal interaction in the blower as well as to comprehend the effect of main influencing factors on the performance of the blower using a transient finite volume-based dynamic-mesh-rearrangement method. A grid-independent test is conducted, and the adopted methodology is validated. At first, an endeavor is made to realize the transient internal flow field and heat interaction within the roots blower. Then, individual efforts are made to apprehend the effect of rotor speed, discharge pressure, and clearance size (provided in between the rotors or in between the rotors and casing) on the said transient flow dynamics and heat interaction. Time variation of the discharge velocity, mass flowrate, and discharge temperature are found to be fluctuating in nature. Pressure, velocity, and temperature distributions in the blower, as well as the leakages, backflow, vortices in the blower, etc., at different moments, are found to be strongly dependent on the rotor speed, discharge pressure, clearance size between the rotors or between the rotor and housing. The nature and amplitude of the time variation of exhaust velocity, discharge mass flowrate, outlet-temperature, and the blower performance are also found to be very much sensitive to the chosen rotor speed, discharge pressure, and clearance size.

Thermal modeling and triple objective optimization of a new compressed air energy storage system integrated with Rankine cycle, PEM fuel cell, and thermoelectric unit

Intermittent behavior of renewable energy triggered researchers for using energy storage systems to provide continues operation of renewable-based energy systems. In the current study, an integrated energy system including compressed air energy storage, Rankine cycle, Proton Exchange Membrane (PEM) fuel cell (FC), and thermoelectric generator (TEG) modules are investigated to introduce a new system. To show effects of adding TEG units and PEM fuel cell in the new configuration, three arrangements including conventional compressed air energy storage system (CAES), CAES/TEG and CAES/TEG-FC are investigated. It is found that the proposed CAES/TEG-FC system energy efficiency is 31.85%, which is 1.6% higher than conventional CAES. The exergy efficiency of CAES/TEG-FC is 35.13%, which is 1.44% higher than the conventional one. The proposed system generates 35.6 kW hot water and charge/discharge time are 2.91 hr/4.64 hr. A parametric analysis conducted on the discharge mass flow rate, intercooler outlet temperature, compression pressure ratio, and wind velocity with charging time, exergy efficiency, and total useful products as three major outputs. The tri-objective optimization shows by the technique for order of preference by similarity to ideal solution the optimized value of exergy efficiency, total useful output, and charge time are 34%, 1078.46 kW, and 5.28 hr.

Experimental investigation on air bubble dynamics during fine powder discharge in a silo

An unstable discharge rate occurs during dry fine powder discharge from a silo due to significant two–phase solid/gas interactions that occur in powder flows. In addition, the air bubble phenomenon may occur in a silo during fine powder discharge. The bubble dynamics seriously influence the fine powder discharge stability in the silo. Therefore, for some industrial applications with silo discharge of fine material, it is important to understand it. In this study, we experimentally investigate the effect of air bubbles on fine powder discharge behavior, including the discharge mass flow rate and variation in pressure inside the silo. An initial collapse of the powder bed in the silo is observed at the beginning of the discharge process, causing the pressure to change rapidly. Moreover, the dependence of the bubble size, bubble rising velocity, number of bubbles, and frequency of bubble generation on the size of the fine powder are analyzed in detail. The air–loss index for different particle sizes is calculated to investigate the proportion of the air flowing into the silo that disperses into the voids between the powders and does not become part of a bubble. The bubble properties in the experimental cases that use different particle sizes are consistent with the Geldart particle classification of the used powders. The results of this study successfully illustrate the bubble dynamics and the discharge behavior of fine powder.

Performance analysis of a U-Vane compressor

A new rotary compressor, named ‘U-Vane compressor’ (UVC) has been introduced with the motivation of reducing the size of the cylinder and housing in a swing compressor. The compressor can be used for air and refrigerant compression. In this paper, the dynamics, internal leakages and frictional losses aspects of UVC are modelled. A physical prototype has been fabricated and measurements have been conducted with an open air-test-circuit for verification of the mathematical model. Good agreement is obtained between the predicted and measured power inputs with an average discrepancy of 3.8%. However, the discharge mass flow rate tends to be under-predicted at high operating speeds and low discharge pressures situations. Nevertheless, the mathematical model is capable of predicting the performance of UVC with acceptable accuracy.