Outlet Pressure Difference Research Articles

Experimental study of a high-power generation platform for ocean thermal energy conversion

Ocean Thermal Energy Conversion (OTEC) is a form of power generation that utilizes the temperature difference between the upper and lower layers of the ocean. This paper presents the design and construction of a land-based experimental platform for OTEC using R134a as the working fluid. Through experimental research, we investigated the performance of the thermal energy cycle system under varying external environmental conditions, such as temperature and flow rate. The results show that the net output power of the system increases with the temperature and flow rate of the warm seawater. Similarly, an increase in the cold seawater temperature and flow rate leads to an increase in net output, though the increase is less significant at higher power levels when compared to changes in warm seawater conditions. Adjusting the evaporation pressure to increase the turbine inlet and outlet pressure difference initially increases the output power but then remains constant. The highest recorded output power during testing was 48kW, with the turbine achieving an isentropic efficiency of 80%, and the maximum system efficiency reached 2%. This study provides theoretical basis and empirical data for system design, which can promote the application in the field of OTEC and contribute to the development of renewable energy.

Asymmetric droplet splitting in a T-junction under a pressure difference

In this paper, the phase-field multiphase lattice Boltzmann method is employed to simulate droplet breakup in a T-junction under different outlet pressures. Three behaviors of droplet breakup: non-breakup (flow pattern I), breakup with tunnels (flow pattern II), and breakup with permanent obstruction (flow pattern Ⅲ) are identified. The evolution of morphological characteristics of droplet breakup is quantitatively characterized, based on which the asymmetric splitting mechanisms and the influencing factors are clarified. Additionally, the factors influencing the droplet splitting volume ratio (VII/VI) are elucidated. The results indicate that there is a non-linear relationship between the VII/VI and the flow rate ratio. Moreover, the curve depicting the final VII/VI versus the initial droplet length exhibits a V-shape and has a minimum value. A conclusion is drawn that the Capillary number mainly influences flow pattern II, with the final VII/VI decreasing as the Capillary number increases. Additionally, for flow pattern III, the final VII/VI increases linearly with rising droplet size at low viscosity ratios, whereas it decreases linearly at high viscosity ratios. The growing outlet pressure difference enlarges the flow difference between the two branches, leading to an increase in the final VII/VI.

Non-Isothermal Simulation and Safety Analysis of Twin-Screw Extrusion Process for Synthetizing Glycidyl Azide Polymer-Based Energetic Thermoplastic Elastomer.

In order to study the temperature variation and flow characteristics in the twin-screw reactive extrusion process of synthetizing glycidyl azide polymer-based energetic thermoplastic elastomer (GAP-ETPE), a non-isothermal simulation and a safety analysis were carried out. Firstly, based on the synthesis principle of GAP-ETPE, a mechanical sensitivity test, viscosity test and differential scanning calorimetry (DSC) of GAP-ETPE were carried out. Secondly, a three-dimensional physical model of the intermeshing co-rotating conveying element was established by Gambit. A three-dimensional non-isothermal numerical simulation of the conveying and kneading elements was carried out using FLUENT 19.0 software. The temperature, pressure and shear stress field of conveying and kneading elements with different staggered angles were analyzed and compared. The results show that the maximum temperature of the kneading element is always slightly higher than that of the conveying element at the same rotational speed, but the average temperature in the flow channel is always slightly higher than that of the kneading element. The inlet and outlet pressure difference of the kneading elements with a 90° offset angle is the smallest and the safety is the highest. The shear stress in the flow channel of the conveying element is higher than that of the kneading element as a whole, but the shear stress near the outlet of the 90° kneading element is higher than that in the flow channel of the conveying element. Among the kneading elements, the 90° kneading element has the strongest dispersing and mixing ability, followed by the 60° and 45° kneading elements. According to the thermal and physical parameters of the material, the ignition response time is approximately 6 s, which provides a theoretical guide for the safety design of the GAP-ETPE twin-screw extruder.

Numerical Investigation on Two-Phase Water Density Wave Oscillations in a Pipe under Various Heating Conditions

This study utilizes the finite volume method with a two-fluid model to analyze water characteristics in a boiling channel when density wave oscillation occurs. A 2-D numerical model is utilized to characterize both axial and radial mass and energy exchange, as well as the mechanisms involving flow and heat transfer during density wave oscillation under uniform and non-uniform heating conditions. The numerical model was used to predict the heating power threshold values of two-phase water flowing upward in a vertical pipe under type II density wave oscillation at the working pressure and an inlet–outlet pressure difference of 125 kPa, when the average heating power increased from 44.06 kW/m2 at a speed of 0.5 kW/(m2·s). The flow and heat transfer characteristics before and after the type II density wave oscillation were determined and compared to the flow and temperature fields at various moments. Along the pipe axis, the wall heat flux was loaded under uniform, standard-sine, and inverted-sine types, which represent three typical types of wall heat flux arrangements. Flow oscillation appeared the earliest under the inverted-sine-type heat flux with low vapor quality (approximately 0.13) with a void fraction of 0.6 at the outlet.

Degradation and health prediction of filter components of screw compressor

In the oil screw compressor unit, the filtration device of gas and oil will have an impact on the overall operation of the unit. This paper studies the degradation of the filtration components in the long-term experiment. The experimental results show that with the increase of operation time, the fuel injection device, air cooling device, oil cooling device and oil filter device appear obvious degradation. The fuel injection temperature decreases, the inlet and outlet temperature difference of air cooling and oil cooling device increases, and the inlet and outlet pressure difference of oil filter device increases. Through the calculation of Mahalanobis distance, it is found that the degradation of each device corresponds to the degradation of the whole unit, and the degradation of oil filter device occurs first, followed by air cooling and oil cooling device, and affects the main engine from the fuel injection device. Through the calculation and comparison of artificial neural network, the optimal number of hidden layer neurons corresponding to the prediction model is determined.

On a Casson Fluid Motion: Nonuniform Width Symmetric Channel and Peristaltic Flows

Widely used for modeling biological fluids flows—in particular, blood vessel flows—a Casson flow is studied in a symmetric channel for which the aspect ratio enables one to use the lubrication approximation. Two flow driving conditions are prescribed: inlet–outlet pressure difference and peristaltic oscillations of the vessel walls. In both cases, starting from mass and momentum balance and using lubrication approximation, we investigate the conditions to be imposed on the driving mechanisms so that the inner plug does not come in touch with the walls. The study of the peristaltic flow is of great importance in view of its applications in physiology (including microcirculation applications).

Coupled thermal–hydraulic–mechanical model for an enhanced geothermal system and numerical analysis of its heat mining performance

The operation of an enhanced geothermal system (EGS) involves a complex thermal–hydraulic–mechanical (THM) coupling process, which is important for exploiting the geothermal energy contained in hot dry rocks. In this study, the THM coupling mechanism in an EGS reservoir is explained, and a fully coupled THM mathematical model with local thermal nonequilibrium of a dual media is established, considering the dynamic changes in the properties of the rock matrix, fractures, and fluid during EGS operation. The model is verified through an example of the thermoelastic consolidation of a saturated soil. The heat transfer, fluid flow, and mechanical characteristics of a geothermal reservoir over 40 years are studied via a numerical simulation of a 2D geometric model. The effects of fracture occurrence, coupling conditions, and model parameters on the mining performance are analyzed. The results show that the dual-media model can reflect the anisotropy in the temperature, pressure, and stress due to the presence of fractures. An area with a more complex fracture network and smaller spacing is found to be more conducive for heat transfer. The inlet–outlet pressure differences, thermal expansion coefficient of the rock matrix, and initial fracture permeability have significant effects. When the inlet–outlet pressure difference is increased from 4 to 10 MPa, the heat extraction ratio increases from 56% to 89% at 40 years, and the initial output thermal power is increased from 9.2 to 24.9 MW. When the coefficient of thermal expansion is increased from 1 × 10−6 to 7 × 10−6 K−1, the heat extraction ratio is increased from 54% to 84%, and the initial output thermal power is increased from 8.5 to 19.7 MW. When the initial permeability is increased from 1 × 10−11 to 2.5 × 10−11 m2, the heat extraction ratio increases from 74% to 92%. These results provide a reference for optimizing the mining effect of the EGS.

Analysis and design of auto-adaptive leveling hydraulic suspension for agricultural robot

The application of agricultural robot in hilly and mountain areas faces several problems, such as bad walking performance, easy tilt, and low safety. The auto-adaptive leveling hydraulic suspension for the agricultural robot can help to eliminate some sort of problems. The design of such system is the main aim of the article. The hydraulic system with load-sensing system and its controlling model were established and then the load-sensing system was modeled and simulated in Advanced Modeling Environment for SIMulation. The optimal proportional–integral–derivative parameters were determined by the optimized algorithm. The simulation results illustrated that the inlet and outlet pressure difference of throttle and the flow rate through throttle are 42 bar and 29.65 L/min, respectively, all the time when the load pressure varies from 0 bar to 100 bar. The load-sensing system has good power follow-up and high control accuracy. And then the experimental bench of auto-adaptive leveling hydraulic suspension was researched and developed to verify the leveling performance. The experimental results demonstrate that auto-adaptive leveling hydraulic suspension can keep frame leveling dynamically on upslope, downslope, side slope, and continuous undulating road surface. The maximum errors of the pitch angle and the tilt angle are −0.93° and 0.97°. The feasibility of the designed hydraulic suspension was verified. The research methods in this article can provide theoretical basis for the design of other auto-adaptive leveling systems in hilly and mountain areas.

Numerical simulation and application of micro-nano bubble releaser for irrigation

In oxygenated irrigation, there are problems of large oxygenated bubble particles, low oxygen concentration in water, and mismatch with current irrigation systems. In this paper, numerical simulation of micro-nano bubble releaser was carried out and the development of oxygenated irrigation equipment was studied. The release method of dissolved gas was selected to generate micro-nano bubbles after comparing different micro-nano bubble generation methods. The basic structure of the core-component releaser of generating micro-nano bubbles was initially determined. Effects of different structures of the release device on water aeration performance were studied by CFD analysis method. An optimal structure of the releaser was determined with orthogonal experiments based on a single factor experiment. The structural parameters included a throat of a 3 mm diameter, a 2 mm thick turbulent cavity, a six-degree exit angle, and two outlets. Optimal inlet and outlet pressure difference of the release device was 0.3 MPa. The bubble had an average particle size of 373.1 nm as measured. The release device was fabricated by 3D printing technology and the micro-nano bubble aeration irrigation device was developed. The system function test was carried out. Under the standard state, the performance parameters of the micro-nano bubble aerator included the maximum oxygen concentration of 11.4 mg/L, a total oxygen transfer coefficient of 0.4139 min-1, 0.0114 kg/h oxygenation capacity, and 60.81% oxygen utilization rate. The device had advantages of a high oxygen-increasing efficiency and a small volume, making it quite prospective in the field of oxygenated irrigation.

Effect analysis on heat dissipation performance enhancement of a lithium-ion-battery pack with heat pipe for central and southern regions in China

A heat pipe (HP) heat dissipation model of a lithium-ion-battery pack is established for the climate in the central and southern regions in China, and the heat transfer effects of various fins with different spacing and thickness are investigated. According to the change of heat dissipation, inlet and outlet pressure difference and average heat transfer coefficient with fin spacing and thickness, the relatively optimal heat dissipation fin structure parameters are determined, and the battery temperature distribution and temperature change under different discharge rates of the battery pack in a high temperature environment, and the characteristics of the HP heat dissipation battery thermal management system(BTMS) are analyzed and the effects of HP-based BTMS on battery startup heating in low temperature are evaluated. The results show that the optimal parameters are that the fin spacing is 5 mm, the thickness is 2 mm, the air flow velocity varies from 4 to 16 m/s, and the average heat transfer coefficient is 7.6–11.9 W/(m·K). The battery pack using the HP can reach the proper temperature of 288.15 K in 682s, 615s, and 375 s at 1C, 2C, and 4C discharge rates respectively.

Study on optimal start-up time and water usage volume of blowdown residue discharge of mesh filter

Abstract The water volume used for blowdown of a mesh filter is one of the important indicators to evaluate the economic benefit of a mesh filter. The amount of water used for drainage of the mesh filter can be controlled by setting the start-up time of the blowdown residue discharge of the mesh filter. Through the indoor prototype test, the sediment of the Manas riverbed in Xinjiang, China, was used as the filter medium to test the mesh filter and analyze the water usage volume at each stage. The test focused on the analysis of the trend of the pressure difference between the inlet and outlet of the mesh filter over the filtration time. The results showed that as the filtration time was prolonged, the inlet and outlet pressure difference of the mesh filter showed an S-shaped curve with time. The pressure difference between the inlet and outlet can be divided into four stages, i.e., the start of filtering to the first inflection point of the abrupt change in the pressure difference, the first inflection point of the abrupt pressure difference change to the median point of filtering, the median point of filtering to the second inflection point of the abrupt change in the pressure difference, and the second inflection point of the abrupt pressure difference change to the end of filtering. At the same time, the water usage volume for blowdown was calculated under various working conditions. This paper analyzed the start-up time of blowdown at three different time points, i.e., after the completion of the entire filtration cycle of the traditional mesh filter, at the first inflection point of pressure difference, and at the second inflection point of pressure difference. The tests were performed under the condition that the filtration cycle of the mesh filter was ten days. The results have shown that compared with the traditional screen filter that starts the blowdown at the end of the entire filtration cycle, starting the blowdown at the first inflection point of pressure difference can save 200–300 m3 of water resources for a single mesh filter, and starting the blowdown at the second inflection point of pressure difference can save 30–90 m3 of water resources for a single mesh filter. Meanwhile, the working conditions in the analyses in this paper were consistent with the actual engineering operating conditions. It is recommended that the mesh filter in the micro-irrigation system use the first inflection point of pressure difference to control the start-up time of the blowdown residue discharge, which can not only save water resources, but also ensure that the mesh filter runs at the optimal filtering conditions.

Numerical Simulation on Hydraulic Characteristics of Spray Regulator Valve

The hydraulic properties of the internal fluid of the spray regulator valve are studied by numerical simulation. The velocity field, pressure field, flow coefficient and adjustable ratio of spray regulator valve at different opening are analyzed. The results show that the main factors affecting the flow field distribution and the maximum flow velocity inside the valve body are the valve opening and the inlet and outlet pressure difference. There is a high speed area in the narrow channel area around the valve spool, which will decrease as the valve opening decreases. The pressure in the fluid domain changes rapidly from the inlet pressure to the outlet pressure at the narrow channel around the valve core. The adjustable ratio of the spray regulator valve is 72.9.

Dynamics and Wear Analysis of Hydraulic Turbines in Solid-liquid Two-phase Flow

Abstract To solve unstable operating and serious wearing of a hydraulic turbine in its overflow parts under solid-liquid two-phase flow, a particle model software and an inhomogeneous model in CFX are used to simulate the hydraulic turbine to understand the wearing of overflow parts and the external characteristics under the solid-liquid two-phase flow. Eleven different conditions at different densities and concentration have been calculated. The simulation results show that the volume distribution of solid particles is larger at the turn of the volute and nose end, resulting in the serious wear in this area. Due to uniform flow at the butterfly edge of volute under solid-liquid two-phase flow, the wear at the entrance of guide vane, the inlet of the blade and the outlet in the shroud is more serious than in other sections. Meanwhile, the collision between the solid phase particles and the overflow components is more intense under solid-liquid two-phase flow in the rotor which can lead to cavitation especially in the outlet and shroud of the blade. In addition, with the increase of density and concentration of solid particles the inlet and outlet pressure difference gradually rises, causing the efficiency loss of the hydraulic turbine.

Hydrodynamic Characterization of Phase Separation in Devices with Microfabricated Capillaries.

Capillary microseparators have been gaining interest in downstream unit operations, especially for pharmaceutical, space, and nuclear applications, offering efficient separation of two-phase flows. In this work, a detailed analysis of the dynamics of gas–liquid separation at the single meniscus level helped to formulate a model to map the operability region of microseparation devices. A water–nitrogen segmented flow was separated in a microfabricated silicon-glass device, with a main channel (width, W = 600 μm; height, H = 120 μm) leading into an array of 276 capillaries (100 μm long; width = 5 μm facing the main channel and 25 μm facing the liquid outlet), on both sides of the channel. At optimal pressure differences, the wetting phase (water) flowed through the capillaries into the liquid outlet, whereas the nonwetting phase (nitrogen) flowed past the capillaries into the gas outlet. A high-speed imaging methodology aided by computational analysis was used to quantify the length of the liquid slugs and their positions in the separation zone. It was observed that during stable separation, the position of the leading edge of the liquid slugs (advancing meniscus), which became stationary in the separation zone, was dependent only on the outlet pressure difference. The trailing edge of the liquid slugs (receding meniscus) approached the advancing meniscus at a constant speed, thus leading to a linear decrease of the liquid slug length. Close to the liquid-to-gas breakthrough point, that is, when water exited through the gas outlet, the advancing meniscus was no longer stationary, and the slug lengths decreased exponentially. The rates of decrease of the liquid slug length during separation were accurately estimated by the model, and the calculated liquid-to-gas breakthrough pressures agreed with experimental measurements.

Design and Simulation of the Key Parameters of Speed Control Valve Based on MATLAB

MATLAB was used to realize the characteristic curve of inlet and outlet pressure difference and flow rate, the characteristic curve of hydraulic force and spring force in speed control valve, and obtain key parameter values. SIMULINK was used to model speed control valve, and the parameter values were substituted into the modeling for simulation verification.

Analysis of Internal Flow in Boiler Water Circulating Pump

As one of the core components of supercritical power station, boiler water circulating pump is a kind of glandless pump in which motor and pump are integrated. The circulating medium in the pump is high temperature and high pressure water. Understanding the internal flow characteristics is helpful to improve the hydraulic design of the pump. The numerical simulation of pressure distribution and streamline in the pump body of boiler water circulating pump were carried out with software ANSYS-CFX under three working conditions (0.6 Q, 1.0 Q and 1.4 Q). The results show that: The pressure near the outer wall of pump body is larger, and gradually decreases to the interior. With the decreases of cross section radius, the number of vortices increases. The vortices gradually decrease with the increase of flow rate, and the flow becomes more and more uniform. The pressure increases from the inlet pipe to the outlet pipe under different flow rates. The inlet and outlet pressure difference is inversely proportional to the flow rate. Under the condition of small flow rate and large flow rate, there are many low pressure zones in the inlet side of the blade.

Experimental study on heat sink with porous copper as conductive material for CPU cooling

With the fast development of information science and technology, the increasing demand for computer data processing caused a rapid growth in central processing unit (CPU) of high power capacity. CPU Cooling plays an important role in guaranteeing reliable working conditions with proper temperature for IT equipment, rack servers and related devices. In this paper, a novel kind of heat sink filled with porous copper is proposed and experiment is conducted to investigate its cooling effect for CPU. The results show that cooling capacity of porous copper increases with increasing inlet and outlet pressure difference, while it almost remains the same with heat flux variations. Moreover, the CPU surface temperatures of two different heat sinks are compared. It indicates that the heat sink coefficient of porous copper increases by 28.5 % and the surface temperature decreases by more than 10 oC, compared to traditional CPU heat sink with micro channels. This work is important for CPU cooling system design and optimization in practical applications.

Pore-scale modeling of wettability effects on CO2–brine displacement during geological storage

Abstract Wetting properties of reservoir rocks and caprocks can vary significantly, and they strongly influence geological storage of carbon dioxide in deep saline aquifers, during which CO2 is supposed to displace the resident brine and to become permanently trapped. Fundamental understanding of the effect of wettability on CO2–brine displacement is thus important for improving storage efficiency and security. In this study, we investigate the influence of wetting properties on two-phase flow of CO2 and brine at the pore scale. A numerical model based on the phase field method is implemented to simulate the two-phase flow of CO2–brine in a realistic pore geometry. Our focus is to study the pore-scale fluid-fluid displacement mechanisms under different wetting conditions and to quantify the effect of wettability on macroscopic parameters such as residual brine saturation, capillary pressure, relative permeability, and specific interfacial area. Our simulation results confirm that both the trapped wetting phase saturation and the normalized interfacial area increase with decreasing contact angle. However, the wetting condition does not appear to influence the CO2 breakthrough time and saturation. We also show that the macroscopic capillary pressures based on the pressure difference between inlet and outlet can differ significantly from the phase averaging capillary pressures for all contact angles when the capillary number is high (log Ca > −5). This indicates that the inlet–outlet pressure difference may not be a good measure of the continuum-scale capillary pressure. In addition, the results show that the relative permeability of CO2 can be significantly lower in strongly water-wet conditions than in the intermediate-wet conditions.

Analysis on the effect of venturi tube structural parameters on fluid flow

Fluid flow occurring in a venturi tube was numerically simulated with the Fluent software, and several factors to affect the mass flux and an asymmetric flow were analyzed, including the contraction ratio, ratio of the throat section length to diameter, the diffusion angle and the inlet and outlet pressure difference. Results show that the minimum pressure point occurs at the intersection between the contraction and throat sections in the venturi tube. As the contraction ratio increases, vacuum degree ascends, and mass flux rises. While both vacuum degree and mass flux reduces as the diffusion angle increases. In addition, an increment in the contraction ratio shortens a fully developed section of velocity in the diffusion section. At the contraction ratio less than 0.2 or the diffusion angle less than 35°, velocity in the diffusion section shows an asymmetric and skewed flow. However, as the inlet and outlet pressure difference increases, mass flux goes up, and thereby occurring a back-flowing in the throat section. The calculated results were compared with the reference’s data, both error is within 0.5% – -28%.

Investigation of ITER TF Conductor Hydraulic Resistance

Conductors for winding ITER toroidal field magnets are cable-in-conduit type where multi-stage petals are twisted around central cooling spiral inserted into stainless steel jacket. Every conductor unit length and its components pass various tests during manufacturing and the final acceptance test consists of 760 m or 415 m long conductor global leak test and an investigation of conductor hydrodynamic performances. The hydraulic resistance is one of the main TF CICC's parameter to provide sufficient cool down and stable work of the magnet system during operation. Starting from 2011, when the first copper Dummy conductor was completed, 22 conductors in total were tested in a test facility that was designed and manufactured at National Research Centre “Kurchatov Institute.” A scheme of the pressure drop test facility, measurements technique and results of mass flow rate measurements depending on inlet and outlet pressure difference are presented in this work. Measurements were carried out by flowing nitrogen gas through conductor at room temperature. However, in accordance with the theory of turbulent self-similarity it is possible to develop a simple criterion for estimation of hydraulic resistance at any temperature. The model of two parallel independent flows has been used. The simple explanation of mass flow rate non-linearity at small pressure difference has been provided.