Increase In Discharge Pressure Research Articles

Study of Condensation during Direct Contact between Steam and Water in Pressure-Relief Tank

Direct contact condensation (DCC) is a phenomenon observed when steam interacts with subcooled water, exhibiting higher heat and mass transfer rates compared to wall condensation. It has garnered significant interest across industries such as nuclear, chemical, and power due to its advantageous characteristics. In the context of pressure-relief tanks, understanding and optimizing the DCC process are critical for safety and efficiency. The efficiency of pressure-relief tanks depends on the amount of steam condensed per unit of time, which directly affects their operational parameters and design. This study focuses on investigating the direct gas–liquid contact condensation process in pressure-relief tanks using computational fluid dynamics (CFD). Through experimental validation and a sensitivity analysis, the study provides insights into the influence of inlet steam parameters and basin temperature on the steam plume characteristics. Furthermore, steady-state and transient calculation models are developed to simulate the behaviour of the pressure-relief tank, providing valuable data for safety analysis and design optimization. There is a relatively high-pressure area in the upper part of the bubble hole of the pressure-relief tube, and the value increases as it is closer to the holes. The steam velocity in the bubbling hole near the 90° elbow position is higher. This study contributes to the understanding of steam condensation dynamics in pressure-relief tanks. When the steam emission and pressure are fixed, the equilibrium temperature increases linearly as the initial temperature increases (where a = 1, b = 20 in y = a x+ b correlation), the equilibrium pressure increases nearly exponentially, and the equilibrium gas volume decreases. When the steam emission and initial temperature are fixed, the equilibrium temperature does not change as the steam discharge pressure increases. The correlations between the predicted equilibrium parameters and the inlet steam parameters and tank temperature provide valuable insights for optimizing a pressure-relief tank design and improving the operational safety in diverse industrial contexts.

Experimental study on performance and compressor characteristics of transcritical CO2 heat pump system

The accelerated advancement of the economy has led to a heightened focus on the issue of energy conservation and reduced consumption within heat pump systems. An experimental investigation was conducted to analyze the impact of discharge pressure and outlet water temperature on the performance of the transcritical CO2 single-stage heat pump system and vapor injection heat pump system. The experimental results show that the heating capacity first increases and then tends to be constant or even slightly decreases with the increase of discharge pressure in single-stage heat pump system. When subjected to the same operating conditions, the coefficient of performance of vapor injection heat pump system exceeds that of single-stage heat pump system. Compared with single-stage heat pump system, the performance coefficient of vapor injection heat pump system has increased by an average of 6.21% and the heating capacity has increased by an average of 9.54%. Additionally, the volumetric efficiency of the compressor substantially decreases when producing high-temperature hot water. Semi-empirical models for evaluating the compressor performance in both single-stage heat pump system and vapor injection pump system are established through the parameterization of the volumetric efficiency with respect to the pressure ratio and compressor speed. These models effectively forecast compressor performance.

Mathematical Model of the Working Processes of the Gas Cap of a Piston Pump Installed in the Discharge Line

A mathematical model of the working processes occurring in the gas cap has been developed on the basic fundamental laws of conservation of energy, mass and motion, and the equation of state, both taking into account the change in the mass of the gas due to phase transitions and the solubility of the gas in the liquid, and without taking them into account with a dividing element. In addition, there was developed a mathematical model of the liquid flow from the gas cap through a pipeline of constant cross section. It was found from the results of a numerical experiment that to reduce the feed irregularity, it is necessary to increase the length of the pipeline and the crankshaft revolutions, in addition to the known ratio of the volume of gas in the cap to the working volume of the pump; an increase in discharge pressure and an increase in the diameter of the connecting pipeline increases the feed irregularity.

Research on the Influence of High-Low Pressure-Volume Ratio and Discharge Pressure on the Heating Performance of Transcritical CO2 Single- Machine Two-Stage Compression Heat Pump Water Heater

Background: In order to reduce global carbon emissions, a cross-critical CO2 singlemachine two-stage compression system was proposed. Due to the characteristics of cooling on the high-pressure side of the cross-critical cycle and bipolar compression on the single-stage, the discharge pressure and the high-low pressure volume ratio have a great influence on its heating performance. Objective: The purpose of this paper is to explore the influence of high-low pressure-volume ratio and discharge pressure on the heating performance of the system, so as to obtain the optimal operating conditions of the system. Methods: By constructing theoretical calculation formula of discharge pressure, high-low pressurevolume ratio and intermediate pressure, combined with experiments. Results: Under certain working conditions, with the increase of the volume ratio of high-low pressure, the intermediate pressure increases, the heating capacity of the system increases due to the increase of the discharge temperature and the increase of the heat exchange temperature difference on the hot water side, while the heating performance coefficient decreases slowly because the rate of the increase of the power consumption of the compressor is greater than the rate of the increase of heating capacity. With the increase of discharge pressure, the increasing rate of CO2 discharge temperature will gradually decrease at the high-pressure side, so the heating capacity of the system increases rapidly first and then tends to slow down, and the heating performance coefficient increases first and then decreases. There is an optimal value, that is, when the evaporation temperature is -20 °C, the maximum heating capacity can reach 3 kW. The system heat production performance coefficient has an optimal value of 3.29, and the optimal discharge pressure is 8.5 MPa. The optimal discharge pressure will increase with the increase of evaporation temperature. Conclusion: The selection of reasonable high-low pressure volume ratio and the control of discharge pressure can effectively improve the heating performance of cross-critical CO2 single-machine twostage compression heat pump water heater.

The Effect of Different Pressure Conditions on Shock Waves in a Supersonic Steam Ejector

The complex flow phenomena in a three-dimensional supersonic steam ejector were simulated with a non-equilibrium condensation model including real physical properties in different pressure conditions. The different working conditions include discharge pressure, motive pressure, and suction pressure. The influence of different pressures on shock waves in the steam ejector was investigated comprehensively. The intrinsic causes of shock wave variation with pressure conditions were explained in detail. The results show that the width of the primary shock train region expand with an increase in the motive pressure or a decrease in suction pressure. The diamond shock waves move downstream with an increase in motive pressure or a decrease in suction pressure. The shocking position in the diffuser moves upstream until it reaches the diffuser entrance with an increase in discharge pressure or a decrease in motive pressure or suction pressure. The intensity and number of oblique shock waves in the diffuser increase with an increase in motive pressure and suction pressure or a decrease in discharge pressure. The existence of only one shock wave in the diffuser is a necessary and insufficient condition for the ejector to enter a double choking mode.

A comprehensive investigation on the effect of internal heat exchanger based on a novel evaluation method in the transcritical CO2 heat pump system

With the increasing demand for environmental protection, CO2, as a natural refrigerant, has always been environmentally friendly and safe, which makes transcritical CO2 heat pump system attract more attention. The internal heat exchanger is employed to improve the performance of transcritical CO2 heat pump system to match the traditional heat pump circulation system. In this work, two evaluation methods are proposed, one is the actual operation thermal effectiveness of internal heat exchanger, the other is the actual increase rate of COP. Compared with the experimental results, the conclusions can be extracted that the actual increase rate of COP can effectively evaluate the impact of the internal heat exchanger on system performance. In addition, this research deeply analyzes the influence of the internal heat exchanger on exergy efficiency. The results show that the internal heat exchanger greatly reduces the exergy efficiency under the discharge pressure of 7310 kPa and the ambient temperature of 15 °C, and the difference value between the system with and without internal heat exchanger reaches 39%. However, the influence of the internal heat exchanger on exergy efficiency decreases with the increase of discharge pressure and ambient temperature, the minimum difference value is only 0.1% at 11000 kPa and 30 °C.

E-H mode transitions and high-energy electron characteristics of helical antenna coupled plasma

Metastable and high-energy electron characteristics obtained from optical emission spectroscopy are used to analyze the dependence of the H mode on the magnetic field strength and discharge pressure. The results show that the H-mode characteristics gradually appears as the magnetic field strength is increased, the reason being that electrons undergo multiple acceleration-collision cycles at high magnetic field strength, thereby the metastable ionization will be increased. This improves energy utilization and making the H mode appearing. The variation in the density of metastable states and the Langmuir probe data shows that the electron energy distribution function evolves from non-Maxwellian to Maxwellian. The radial constraint of the magnetic field to the electrons and thus reduces the electron heating efficiency. Moreover, the increase in electric field strength with magnetic field leads to an increase in energy obtained by the electrons per unit distance. The competition between the two makes the number of high-energy electrons decrease rapidly first, and then increase slowly with magnetic field strength increasing. The turning point increases with the increase of discharge pressure and radio-frequency (RF) power. And the higher the pressure the lower the high-energy electron. For fields between 105.5 G and 212.7 G. In the H-mode regime, and with increasing RF power, the number of high-energy electrons will be sudden rise after experiencing a steady increase. The sudden rise RF power increase with magnetic field and decrease with discharge pressure increase. However, at high magnetic fields (>265 G) and high power (>450 W), the high-energy electron density decreases with power increasing.

Characterisation of La0.9Ce0.1Ni5 alloy for the development of single‐stage thermally driven sorption hydrogen compressor

SummaryIn this study, La0.9Ce0.1Ni5 alloy is characterised to investigate the performance of a single‐stage thermally driven sorption hydrogen compressor (TDSHC). The pressure‐concentration isotherm (PCI) properties of La0.9Ce0.1Ni5 alloy are measured through Sievert's Apparatus, and the thermodynamic properties are estimated by constructing van't Hoff plots at different temperature ranges between 20°C and 140°C. The effects of an increase in operating temperature on hydrogen storage capacity as well as on thermodynamic properties and the corresponding effects on TDSHC performance are studied. It is observed that the hydrogen storage capacity decreased, whereas reaction enthalpy increased, with an increase in operating temperature. It is also observed that the equilibrium pressure increased dramatically with an operating temperature; therefore, this alloy is employed, in this study, for the development of TDSHC. The proposed TDSHC operates at the supply temperature and pressure of 20°C and 15 bar, respectively, in which the compressed hydrogen is delivered at 40°C, 60°C, 80°C, 100°C, 120°C and 140°C with a maximum pressure output of 270 bar. The measured PCI and thermodynamic data are employed to investigate the thermodynamic performance of TDSHC which results in the maximum compressor work of 10.13 W and the maximum cycle efficiency of 27.57% with an average heat input of 35 ± 3 W. The increase in discharge temperature on system performance are observed to increase in compressor work and efficiency due to the increase in discharge pressure, whereas the effect on heat input is not significant due to the reduction in hydrogen discharge amount. Also, the behaviour of metal hydride (MH) bed is predicted through the finite volume method in terms of variations in MH bed temperature and hydrogen transmission. The numerical investigation is carried out by solving the required energy equations and are validated with experimental data. The numerical investigation results into minimum cycle time of 2700 seconds for the operation of TDSHC. It is also observed that the increase in discharge temperature increases the reaction kinetics and hydrogen mass fraction.

Development and Experimental Study of the First Stage in a Two-Stage Water-Flooded Single-Screw Compressor Unit for Polyethylene Terephthalate Bottle Blowing System

The oil-free compressor is a key component in fabricating polyethylene terephthalate (PET) bottles for beverages and water. At present, the main compressor type used for blowing PET bottles is the reciprocating compressor. However, compared to screw compressors, reciprocating compressors have shortcomings of high energy consumption and too many consumable parts. Many manufacturers of PET bottles in Asia are seeking to replace reciprocating compressors with screw compressors, as we know. Screw compressors can be classified as single-screw compressors (SSC) and twin-screw compressors. Since the load in a twin-screw compressor is far larger than that in an SSC, SSCs are more suitable for being developed for high-pressure applications such as PET bottle blowing. This paper presents a performance study on an oil-free single-screw compressor as the first stage of the PET compressor unit. A 5.4 m3·min−1 prototype and its test rig were developed. The thermophysical process of the moist air is theoretically analyzed. The pressure loss on the flow path and the influence of the important parameters are experimentally investigated. It is found that water vapor cannot be separated during the adiabatic compression process. The results also show that the pressure loss from the discharging duct to the check valve accounts for the largest percentage of the total pressure loss. The experimental results further show that the discharge capacity and shaft power increase almost linearly with the motor speed. The efficiency declines with increasing injected water temperature. The discharge capacity and shaft power all increase with the injected water flowrate, and an optimum flowrate is found to ensure a highest isentropic efficiency. With the increase in discharge pressure, the discharge capacity decreases, and the shaft power increases. The isentropic efficiency is found to have its maximum value at a certain discharge pressure.

A Theoretical Method for Evaluating the Lubrication Performance of the Meshing Pair Profiles in Water Flooded Single Screw Compressors Based on the Micro Deflecting Motion Trajectory

To improve the life of the meshing pair in single screw compressor (SSC), several meshing pair profiles (MPP) were proposed for raising the lubrication properties. Therefore, it is necessary to evaluate the lubrication performance of the MPPs. In this paper, an evaluation method based on micro deflecting motion trajectory (MDMT) is proposed and the theoretical model to realize MDMT is established. The model mainly contains a geometric model, a thermodynamics model, a hydrodynamic lubrication model and corresponding algorithm. With the presented method, three kinds of MPP including single straight line type (SSLT), single column type (SCT) and multi column type (MCT) have been analyzed. Obtained results show that compared to the SSLT and SCT, the MCT generates the greatest peak value of the water film pressure. The total torque applied on the gate-rotor generated by the water films decreases with the increment of the discharge pressure and increases with the machine size. The water film stiffness firstly decreases and then increases with the micro deflecting angle increasing. The water film stiffness at trailing side is always larger than that at leading side. As the discharge pressure increases, the MDMT curves approach the leading flank, and the lubrication properties get worse. With the machine size increasing, the MDMT curves move towards the trailing side and the lubrication performance is improved. Comparing to the other two MPPs, the MCT can achieve floating mesh without contact in relatively larger machines and comparably lower discharge pressure.

Thermal Hydraulics and Operating Criteria of Ultra-Micro Steam Injector

A Steam Injector (SI) has capability to be applied to heat pump systems and to have downsized them. A SI works as passive jet pump and heat exchanger without external power sources. It has high heat-transfer performance due to direct contact condensation between steam flow and subcooled water jet. The objective of the present study is to clarify thermal hydraulics characteristics and operating criteria for an Ultra-Micro Steam Injector. To this end, SI with throat diameter of 2.0 mm was designed and investigated experimentally. Visualization of internal flow behavior and measurement of pressure and temperature were conducted. As a result, we confirmed that the formation of the water jet, the stop of drainage from the drain port and the increase of discharge pressure. The internal flow patterns were classified into four types and considering the energy balance of water and steam. One of the operating criteria was clarified that water could completely condense the steam. The discharge pressure was increased up to 2 times at maximum. There is possibility the operating criteria can be predicted from the position where the flow behavior changes.

Research on dynamic leakage flow in the labyrinth seal of a labyrinth piston compressor

To study the labyrinth leakage flow characteristics of a labyrinth piston compressor, firstly, a transient flow model was built to simulate the fluid flow through labyrinth seals. The dynamic pressures in the labyrinth chambers and the leakage flow rate were obtained by solving the transient flow model. Then, an experimental rig based on a labyrinth piston air compressor with rotational speed of 400 to 900 rpm, and discharge pressure of 0.2 to 0.5 MPa was built to validate the simulation results. In the experiments, dynamic pressures in the cylinder and in the labyrinth chambers were measured at different discharge pressures and different rotational speeds. The simulation results of pressures showed a good agreement with the experimental ones with the maximum relative error of 20%. Later, the transient flow model was used to study the dynamic pressure distribution and leakage flow rate through the labyrinth chambers. The results show that the pressure drop across each labyrinth chamber increases along the leakage flow path from the compression chamber side to the environment side. The pressure drop of the last third chambers accounts for 50% of the total pressure drop of all the chambers. The leakage flow rate increases quickly with the increase of the discharge pressure at low rotational speed. At the speed of 500 rpm, the leakage mass flow doubles when discharge pressure increases from 0.2 MPa to 0.5 MPa. However the growth rate slows down at a high speed of 800 rpm. The leakage characteristics indicate that the labyrinth piston compressor should work at a high rotational speed and a low discharge pressure.

Theoretical and Experimental Studies on Oil Injected Twin Screw Air Compressor under Unload Conditions

The working process of twin screw air compressor under unload conditions was analyzed. Mathematical model describing the working process of oil injected twin screw compressor under unload conditions was established based on the laws of perfect gas and standard thermodynamic relations, considering the effects of oil injection, gas-oil heat transfer, internal leakage etc. A simulation model of screw air compressor system based on MATLAB was built up, and the effects of rotational speed and discharge pressure etc. on the performance under unload conditions were analyzed. The experiment was carried out to validate the model by a comparison between the results of the simulation model and testing. The simulation and testing results both showed that volumetric efficiency increased with the increase of rotational speed, when the discharge pressure was reduced. The shaft power increased with the increase of discharge pressure and rotational speed. The flow rate increased with the reduction of discharge pressure and increase of rotational speed. This model can be used for performance prediction under unload conditions and it provided reference for the high efficiency and energy saving operation of screw compressors.

Studies on a transcritical R744 based summer air-conditioning unit: Impact of refrigerant charge on system performance

The present study is carried out to investigate the performance of a transcritical R744 based system for air conditioning. In this study, a detailed numerical model of the R744 based system is developed. An experimental test-rig of a R744 based air conditioning unit is designed and developed as well to perform experimental studies and to validate the theoretical model. Using the validated model, simulations are carried out to investigate the effects of refrigerant charge, ambient temperature, and gas cooler face velocity on the performance of the system. The optimum charge for which the system delivers maximum COP is predicted. It is observed that variation in COP is marginal for a charge variation of ± 18% from the optimum value. However, COP decreases significantly if the charge varies more than ± 18% from the optimum value. Results show that for each 10 K increase in the ambient temperature, the system COP decreases by about 24%. It is observed that COP drops gradually up to 17% for a 60% reduction in gas cooler face velocity. However, on reducing the face velocity beyond 60%, COP drops significantly with rapid increase in discharge pressure.

Signal Enhancement with Stacked Magnets for High-Resolution Radio Frequency Glow Discharge Mass Spectrometry.

A method for signal enhancement utilizing stacked magnets was introduced into high-resolution radio frequency glow discharge-mass spectrometry (rf-GD-MS) for significantly improved analysis of inorganic materials. Compared to the block magnet, the stacked magnets method was able to achieve 50-59% signal enhancement for typical elements in Y2O3, BSO, and BTN samples. The results indicated that signal was enhanced as the increase of discharge pressure from 1.3 to 8.0 mPa, the increase of rf-power from 10 to 50 W with a frequency of 13.56 MHz, the decrease of sample thickness, and the increase of number of stacked magnets. The possible mechanism for the signal enhancement was further probed using the software "Mechanical APDL (ANSYS) 14.0". It was found that the distinct oscillated magnetic field distribution from the stacked magnets was responsible for signal enhancement, which could extend the movement trajectories of electrons and increase the collisions between the electrons and neutral particles to increase the ionization efficiency. Two NIST samples were used for the validation of the method, and the results suggested that relative errors were within 13% and detection limit for six transverse stacked magnets could reach as low as 0.0082 μg g-1. Additionally, the stability of the method was also studied. RSD within 15% of the elements in three nonconducting samples could be obtained during the sputtering process. Together, the results showed that the signal enhancement method with stacked magnets could offer great promises in providing a sensitive, stable, and facile solution for analyzing the nonconducting materials.

Computational study on dynamic pressure in a swash-plate axial piston pump connected to a hydraulic line with an end resistance

Time-varying pressure produced in a cylinder chamber of an axial hydraulic pump is closely associated with various crucial issues such as system noise emission, swash-plate control, lubrication in sliding parts and etc. In this paper a computational study was performed to investigate the dynamic behavior of the cylinder pressure considering a general system of a piston pump, a hydraulic line, and an end resistance. Combined lumped and distributed parameter model was used, and led to successful fitting with existing experimental data obtained from a pump/line/resistance system which included a pressure relief valve in series. Using the developed tool, the effects of several dimension and operation parameters were investigated assuming that the end resistance was a simple orifice valve. The calculation results, depicted in both time domain and frequency domain, showed that the harmonics of the dynamic pressure and their amplitudes varied with line size capriciously. It was also shown that the harmonic of maximum pulsation amplitude changed in a periodic way as rotating frequency increased. Lastly, the pulsation amplitudes increased with the increase of discharge pressure proportionally with no change of the harmonics.

Deep-Hole Drilling Negative Pressure Device Injection Process Simulation Analysis Based on Fluent

In the process of DF system machining the small diameter deep hole, the working parameters of negative pressure device has a great influence, including injection coefficient, chip removal of cross-sectional area ratio, discharge pressure, negative pressure number, etc. Injection coefficient has the non-linear proportional relationship with chip removal of cross-sectional area ratio, with the increasing incidence of negative pressure discharge pressure increases, as well as, increasing negative pressure number to improve chip removal have a good effect. Movement patterns of cutting fluid is simulated, energy loss of cutting fluid in the flow is studied, finding curved edge nozzle has better negative effects than straight edge nozzle. The effect of negative pressure pumping crumbs is analyzed, the injection process of negative pressure device is simulated, and the form of the fluid motion in negative pressure nozzle is got based on Fluent, which have a good guide for the actual production and machining.

미세물분무의 소화성능 개선을 위한 증점제(잔탄검)의 영향

Water is an economical extinguishing agent and has a variety of extinguishing effect. Since water does not adhere to the fire surface due to low viscosity, which causes to reduce extinguishing effect, secondary damage to unburned materials and loss of water. In this study, xanthan gum as a viscosity agent added to water and using water mist nozzle xanthan gum solution applied to wood crib fire and heptane fire to improve extinguishing performance. The results show that in case of wood crib fire in 0.2 MPa, flame suppression time and fire extinguishing time of xanthan gum 0.2% solution are 7.9 times, 2.9 times shorter than pure water, respectively. In heptane fire, fire extinguishing time of xanthan gum 0.025% solution is 5.2 times shorter than pure water in 0.2MPa, but extinguishing is failed after concentration of xanthan gum increase. Also, it is identified that water consumption decrease with extinguishing time and extinguishing performance of xanthan gum on wood crib fire and heptane fire improved according to increase of discharge pressure.

Design and Performance Evaluation of a Cooler Refrigerating System Working with Ozone Friendly Refrigerant

In this study, a cooler refrigerating system was designed, constructed and tested with various charge quantities of an ozone friendly hydro-fluorocarbon refrigerant (R134a) as working fluid. The results obtained showed that the design temperature and pull-down time set by International Standard Organisation (ISO) for small refrigerator were early achieved with refrigerant charges of 100 and 120 g than with 60 and 80 g charges. Approximately the same pull-down time and minimum temperature of -14°C were obtained with refrigerant charges of 100 and 120 g. Discharge pressure is about the same for 60, 80 and 100 g refrigerant charges, but significant increase in discharge pressure was observed as the refrigerant charge increased to 120 g. The rate of increase in the refrigerating capacity and the COP with respect to evaporator temperature for refrigerant charge of 60 g to 100 g are higher than that for refrigerant charge of 120 g. Highest refrigerating capacity and COP of 4.404 kW and 3.1, respectively, were obtained in the cooler refrigerator with 100 g charge. Generally, the best performance of the cooler was obtained with refrigerant charge of 100 g and increase in the charge beyond 100 g affected the performance of the cooler negatively.

Analytical modeling of microscale diaphragm compressors

This article presents a set of simple equations for determining the performance of microscale diaphragm compressors. Equations applicable to circular and square/rectangular microscale diaphragm compressors are provided. Using the model it is possible to determine the influence of material, geometric and operating parameters, under the constraint of constant stroke, on the pressure rise vs. flow rate relationship as well as temporal variation of chamber pressure and volume and actuation pressure. Material parameters considered include Young's modulus and Poisson's ratio of the compressor material and the ratio of the specific heats of the gas. Geometric parameters considered are shape, planar dimensions and depth of compression chamber and thickness of the oscillating diaphragm. For a specific stroke of the diaphragm the least clearance ratio possible for cylindrical microscale compressors is determined to be 2 and correspondingly the maximum pressure ratio, for most gases, is determined to be around 1.76 using the model. For square microscale compressors the least clearance ratio is 2.5 and the corresponding pressure ratio is 1.6. For rectangular microscale compressors, reduction in aspect ratio of the diaphragm below unity increases and decreases the clearance ratio and the pressure ratio, respectively. Moreover, the model predicts that the actuation pressure, for a specific operating condition, increases with increase in discharge pressure and flexural rigidity of the diaphragm. Thus it is best to realize microscale diaphragm compressors with materials of low Young's Modulus or thin diaphragms or a combination of both.