Constant Pressure Difference Research Articles

O2/N2 separation via delocalization of the magnetic moment in the TM-CNT nano-magnets array under external magnetic field gradient: A molecular dynamic simulation study

This work presents the design of a new membrane including an array of nano-magnets (magnetic CNTs) as an alternative candidate for efficient O2/N2 separation by using the molecular dynamics (MD) technique. The behavior of the magnetic CNTs is based on the delocalized magnetic moments of transition metal elements which embedded within the CNTs. Hence, the magnetic membrane technology is employed together with the magnetic separation technology for O2/N2 separation; Different responses of paramagnetic oxygen and diamagnetic nitrogen molecules under an applied magnetic field gradient are the basis of the performance of this system. Permeability and selectivity of the membrane are investigated through the involvement of magnetic dipole–dipole and pare-particle Lennard-Jones (L-J) interactions in a constant gas pressure difference on the sides of the membrane. The effects of the multilayering and other design parameters (interlayer distance d, interablock spacing ℓ, slit size s) on the separation performance of MCNTM are investigated. It was found that the separation performance is sensitive to variations in d, ℓ, and s. Furthermore, the influence of the strong or weak magnetic gradient rate and also the temperature are evaluated numerically. Finally, this work provides computational evidence that the magnetic multilayer MCNTM can be used as a high-performance O2/N2 separator, as well as, an oxygen buffer or a temporary storage system at room temperature and 77 K.

Techniques to mitigate membrane displacement for vacuum-membrane solar-dish facets

The prospects of a multifaceted vacuum-membrane solar dish concentrator are considered in this work. The membrane depths of these facets can shift slightly due to varying ambient conditions throughout an operational day, leading to major focal point shifts and a reduced overall efficiency. The purpose of this work was to experimentally investigate different methods of membrane displacement mitigation. A controlled-environment (indoor) enclosure was employed to examine the effects of static ambient conditions, allowing for the independent manipulation of the surrounding pressure and temperature. Various manufacturing techniques were also investigated within the controlled-environment enclosure, which included alterations in pretension, changes in membrane thickness and adjustments to overall facet sizes. Furthermore, outdoor tests were conducted to determine how solar radiation and convection affected membrane displacement as well as to investigate the performance of various membrane depth control strategies using an Arduino Uno microcontroller. The indoor results showed that opting for a small facet would minimize membrane displacement. The results were supported by material tests and a finite element analysis. The outdoor test results indicated that solar radiation and wind affected the internal temperature and consequently also affected the membrane depth. Furthermore, a focus control system maintaining a constant differential pressure across the membrane achieved the required accuracy of ±2 mm membrane displacement limitation. However, another focus control system consisting of a Hall effect module actively monitoring membrane depth emerged as the most effective, with an increase of about 0.09 mm and a decrease of approximately 0.02 mm from an initial depth of 10 mm. This level of stability with a focus control system will ensure that the facet maintains a consistent optical performance, ultimately advancing the reliability and efficiency of low-cost vacuum-membrane technology.

Maximal heat transfer density from cross‐flow heat exchanger with tapered fins using constructal design method

AbstractTapered fins are widely used in heat sinks cooled by forced convection. In this study, maximal forced convective heat transfer from a set of tapered fins in cross‐flow is investigated based on the constructal design method. The tapering of the fins is done for a three‐fin base‐to‐tip ratio (taper ratio). The first taper ratio is TR = 0.5 (fin base < fin tip), the second taper ratio is TR = 1 (fin base = fin tip, straight fin), and the third taper ratio is TR = 2 (fin base > fin tip). In all these cases, the fin length is constant. The fins are heated at constant surface temperature and they are cooled by cross‐flow. A constant pressure difference pushes the cross‐flow toward the fins. The Bejan number ranges from 105 to 107. The forced convective heat transfer density is maximized from the fins for the three taper ratios, and a comparison between them is carried out. The maximization is conducted by numerical and scale analysis. In the numerical analysis, the pressure‐driven flow equations (continuity, momentum, and energy) are solved by means of the finite volume method. In the scale analysis, two extremes are considered. The first extreme is for TR < 1, and the second extreme is for TR > 1. These two extremes are intersected to find the maximal forced convective heat transfer density. The results obtained from numerical and scale analysis confirmed that the maximal forced convective heat transfer density occurs for straight fins (TR = 1) in the whole range of the Bejan number. The heat transfer density from straight fins (TR = 1) is higher than that of tapered fins (TR = 2) by 45.2%, and it is higher than that of tapered fins (TR = 0.5) by 52.7% at Be = 107.

Optimal control for district heating systems based on imbalance analysis of pipe networks

In district heating (DH) systems, the transmission and distribution process occupy large amount of energy consumption. Hydraulic and thermal imbalance in pipe networks often lead to uneven heating, affecting user comfort and resulting in energy losses. To solve this problem, this study investigates the root causes of hydraulic and thermal imbalances in DH systems. Key factors have been identified such as initial flow rates, initial loads, and positions in the network of end-users. And the relationship between hydraulic and thermal imbalances have been analyzed. Building on this analysis, we further propose a novel strategy for differential pressure set-point adjustment. This strategy is developed based on a quantitative understanding of the flow rate changes and positions of end-users. It aims to rectify imbalances efficiently, thus enhancing the overall performance of the network. The effectiveness of the proposed strategy is validated through comparative analysis with the conventional constant differential pressure (CCDP) control strategy and an exist variable differential pressure (VDP) control strategy. Results demonstrate significant improvements in network performance, including enhanced stability and reduced energy losses. The proposed strategy reduces the average pressure difference in the main pipe by up to 10.9 %, improves the supply and return temperature difference by 10.9 %, and maintains valve openings above 70 % during peak periods. Additionally, it achieves 23.5 % energy savings in transmission and distribution, highlighting its potential to enhance system performance and efficiency. In addition, this strategy is more in line with the actual situation of end-user demand change for valve adjustment.

Research of closed loop characteristics of single and double chamber structure for fuel metering mechanism

There are two forms of engine fuel metering devices which are single and double chamber structures using electro-hydraulic servo valves as electro-hydraulic conversion devices to realize accurate fuel flow measurements and constant pressure differential valve is used to maintain the constant pressure difference of the metering valve. The main purpose of this article is to analyze the time domain and frequency domain characteristics of constant pressure differential valve assembly and compare the closed-loop characteristics of two metering mechanisms. Firstly, the mathematical model of constant pressure differential valve assembly (including the fuel pump and constant pressure differential valve) is established and its time and frequency domain characteristics are analyzed. The conclusion that the constant pressure differential of the metering valve can meet the practical requirements is obtained. Secondly, the mathematical models of single and double-chamber fuel metering mechanisms are established considering the specific working conditions. Finally, the characteristics of two kinds of metering mechanisms are compared and analyzed under the same control method in the time and frequency domain. The extension overshoot with a maximum value of 3.564% of the single chamber control metering valve mechanism is smaller than that of the double chamber control metering valve mechanism with a maximum extension overshoot of 6.04%. The negative overshoot with a maximum value of 1.391% of the single chamber control metering valve mechanism is bigger than the double chamber control metering valve mechanism with a maximum negative overshoot value of 1.17%. In terms of steady-state error, the steady-state error of a single chamber control metering valve mechanism with a maximum value of 0.194 mm and minimum value of 1.25e-6 mm is smaller than that maximum value of 0.302 mm and minimum value of 1.95e-6 mm of double chamber control metering valve mechanism under the same controller parameters. The bandwidth of the extension motion of the single and double chamber control metering valve is greater than that of the retraction motion. Under the same proportional control parameter, the bandwidth of the double chamber control metering valve extension motion system is greater than that of the single chamber extension motion system.

Feasibility study of pore-pressure prediction in carbonate rocks

In the recent past, the applicability and uncertainty of pore-pressure prediction methods that work based on seismic signals have been serious challenges in carbonate reservoirs. In this context, enormous research has been conducted on the prediction of pore pressure in these rocks, some of which have ended with failure due to the complexity of carbonates. To address the main cause of such failures, we experimentally simulate the pore fluid in carbonates under reservoir conditions to interpret and classify the factors contributing to the pore pressure. The results are then built into a novel hybrid experimental model for evaluating the feasibility of pore pressure prediction — one that could bridge the gap between laboratory and empirical approaches. For this purpose, 34 core samples are collected from different geologic formations at different wells penetrating reservoir intervals. The mechanical properties of the samples are investigated by conducting experiments in a triaxial cell where pore pressure is applied under different regimes while simultaneously acquiring the ultrasonic response of the sample. Sensitivity analyses of pore pressure are carried out under drained and undrained conditions and the results are used to evaluate our methodology. Pore pressure coefficients of P- and S-wave velocities are introduced in two different conditions, namely constant differential stress and constant pore pressure, with the same dimension as compressibility. Results are interpreted statistically and effective parameters are identified from a pool of many variables; these include the static bulk modulus, Young’s modulus, Biot’s coefficients, porosity, permeability, and sedimentary textures (e.g., micritization, neomorphism, cementation, fracture, blocky calcite, and dissolution). A feasibility study template is further introduced for investigating pore pressure detectability based on commonly available data in carbonate reservoirs by incorporating the main controlling factors. Our template and findings of this research are important for pore pressure prediction before performing further research and implementing operation programs. They also can decrease the risk of underestimating the pore pressure, thereby improving the well planning performance and mitigating the drilling hazards.

Throttling Loss Energy-Regeneration System Based on Pressure Difference Pump Control for Electric Forklifts

At present, the hydraulic systems of electric forklifts and traditional internal combustion forklifts are mostly valve-controlled speed-regulation systems, which have large throttling losses and potential energy waste. To further improve the energy-saving ability of electric forklifts, the forklift’s common working conditions are analyzed in this paper. A throttling loss energy-regeneration system based on pressure difference pump control is designed, and the system’s working principle is described. Aiming to deal with the problem that the pump−valve compound speed regulation with constant pressure difference could not realize high controllability and energy saving at the same time, a control strategy for variable pressure difference pump−valve compound speed regulation based on pressure balance control is proposed. The handle signal is positively related to the target speed of the oil cylinder. In the low-speed stage, the closed-loop control of the actual output torque of the motor/generator keeps the pressure difference across the proportional throttle valve unchanged, and the speed adjustment is realized by changing the opening of the proportional throttle valve. In the high-speed stage, the valve opening area is kept unchanged and the target pressure difference is changed to achieve the target speed. Finally, the feasibility of the control strategy is verified through an AMESim simulation, and the minimum pressure difference switching point is determined through experiments. The experiments show that the system’s energy-saving efficiency can reach 21.5% under a 1 t load. With the increase in the load, the system’s energy-saving efficiency can be further improved.

Stabilizing Effect of High Pore Fluid Pressure on Fault Growth During Drained Deformation

AbstractDilatant hardening is an accepted model for the stabilizing effect of high pore fluid pressure on fault slip and operates when deformation is undrained. To test whether high pore fluid pressure impedes fault propagation under drained conditions, we deformed highly permeable Darley Dale sandstone using strain rates of 10−4 s−1, 10−5 s−1, and 10−6 s−1, respectively. For each strain rate, we compared the inelastic behaviors and faulting styles among rocks deformed under different pore fluid pressures (Pf) (2–180 MPa). The confining pressure (Pc) was attuned to the pore fluid pressure throughout deformation to maintain a constant differential pressure (Pc − Pf) of 10 MPa. In samples deformed at 10−4 s−1 and 10−5 s−1, faulting behaviors were similar regardless of the magnitude of pore fluid pressure. However, when the strain rate was lowered to 10−6 s−1, we observed prolonged stress drops and slower slip velocities in samples deformed under high pore fluid pressures. In samples deformed at 10−6 s−1, we demonstrate that chemically assisted subcritical crack growth played an important role during faulting. A quantitative microstructural analysis revealed that slow faulting at slow strain rates was accompanied by pervasive microcracking and diffuse shear bands, which suggests pervasive subcritical cracking enabled slow faulting under drained conditions at the sample length scale. High pore fluid pressure may have facilitated slow faulting chemically by increasing the rate of subcritical cracking, mechanically via localized dilatant hardening, or both. Our results provide insight into the mechanics of faulting in natural settings where subcritical cracking is prevalent.

Variable Differential Pressure Control Strategy for Variable Water Flow Air Conditioning Systems

In large-scale air conditioning water systems, variable water flow (VWF) control strategies are frequently utilized to conserve energy. This paper presents a variable differential pressure (DP) set-point control strategy for VWF air conditioning systems based on the pipeline characteristic curve. This strategy bifurcates the most unfavorable loop into two segments: the equivalent main pipe (EMP) and the most unfavorable terminal branch pipe (MUTBP). Initially, the impedance of the EMP is obtained by curve fitting the measured values of the water supply and return main pipes (WSRMP), as well as the MUTBP. Subsequently, by calculating the disparity between the DP of the actual pipeline and the DP of the EMP, and comparing it with the DP of the MUTBP, the optimal working condition point for pipeline operation can be identified. Finally, a theoretical calculation is conducted on a typical air conditioning water system. This adjustment strategy achieves an energy-saving rate of 15.27%, 12.10%, and 11.50%, respectively, under the three adjustment conditions of closing the nearest terminal, the middle terminal, and the most unfavorable terminal, as compared with the constant DP set-point control strategy of WSRMP. This strategy boasts fewer control devices, a simple control system, and better operability and engineering applicability than other strategies.

Frequency Domain Design Method of the Aeroengine Fuel Servo Constant Pressure Difference Control System with High Performance

The constant pressure difference regulating mechanism is widely used in aeroengine fuel servo metering systems, and it almost decides the metering precision. However, the design theory and design method of the available constant pressure difference regulating mechanism are unclear, and it is difficult to follow the high stability, high accuracy, and high robustness requirements of the modern aeroengine fuel servo metering system. In this paper, the design theory of the constant pressure difference regulating mechanism is revealed, and it indicates that it consists of two basic control units: a state feedback stabilization controller to ensure the asymptotic stability and disturbance rejection performance; and a servo and feed-forward compensator to ensure the asymptotic tracking ability. In addition, based on the frequency domain analysis method, the decisive influences about the control gains of the two control units on the dynamic performance and stability are analyzed. On this basis, a frequency domain design method of the two core control gains is proposed to complete the design task of the closed-loop system. The simulation results show that, under the adverse conditions of 1 MPa strong step disturbance of the inlet pressure and 50 mm2 strong step disturbance of the variable inlet flow area, the steady-state working range of the controlled pressure difference meets 0.92 ± 0.01 MPa, the steady-state error is not more than 1%, the regulation time is not more than 0.01 s, the dynamic overshoot is not more than 10%, and the designed phase margin is more than 70°.

Optimal control of outdoor transmission and distribution pipe networks for district heating and cooling systems

The optimization of the differential pressure setting value mostly uses the valve position signal as the monitoring parameter, but in the district heating and cooling systems (DHCSs), the end valve position signal has hysteresis and cannot be completely collected. Therefore, a variable differential pressure control strategy based on end-load monitoring is proposed in this paper, which can satisfy differential pressure requirements at the most unfavorable thermodynamic end. Then combined with the optimal control of parallel pumps, pay attention to the situation that the rated head of the variable frequency pump is much greater than the differential pressure of the pipe network, and consider operating at the lower frequency limit of the variable frequency range to minimize the total energy consumption of the pump. A district energy station in Chongqing is used as the research object to verify and evaluate the proposed optimization strategies. The test results reveal that the proposed optimal control strategies demonstrate a positive control effect and the performance of the pipe network and pump operation are significantly improved. Compared with the traditional constant differential pressure control strategy, the energy consumption of the pump under heating conditions can be reduced by up to 34.27%.

An indirect flow measurement based high-precision slide valve grinding mechanism for hydraulic servo valve

As a crucial power amplifying component for electro-hydraulic servo valves, the servo-valve spool valve largely determines the overall performance of an electro-hydraulic servo system. Due to the machining errors during the servo-valve manufacturing process, however, it is extremely difficult to characterize such response characteristics in engineering practice, and thus, there may exist certain nonlinearity between the flow rate and valve spool displacement caused by the spool and valve sleeve overlap. To accurately characterize the relationship between the flow rate and spool displacement to facilitate servo-valve production, an indirect flow measurement-based servo-valve spool valve grinding (FM-SVG) scheme is proposed in this study. Specifically, a valve spool overlap measurement mechanism is presented first based on the valve spool grinding principle, and then a data processing method is devised to eliminate the errors introduced by the fluctuations of differential pressure at the valve ports. Meanwhile, a closed-loop control system is also devised to maintain a constant differential pressure at the servo-valve ports. Finally, the FM-SVG scheme is embedded onto a lab-customized electro-hydraulic servo valve platform, and experiments are conducted to verify the feasibility and effectiveness of the FM-SVG scheme. Results show that, by utilizing the devised control scheme to maintain a differential pressure around 2.00 MP, the proposed grinding scheme helps achieve a grinding accuracy of 2.0 μm. With only grinding process needed, such a grinding scheme helps improve both grinding accuracy and production efficiency in practice.

Understanding carbonates from Saudi Arabia: Laboratory measurements of elastic properties. Part I

Laboratory measurements of elastic properties are presented for carbonate samples from the Saudi Arabian Arab formation. Compressional and shear wave velocities (at 1 MHz) and the quasi-static strains of 37 carbonate rock samples were measured as functions of the saturating fluid and the confining pressure. Furthermore, P- and S-wave velocities of the saturated samples were measured at constant differential pressure of 15 MPa. The lithology, mineralogy, porosity, pore type and pore size distribution of each sample were obtained using a combination of thin section and scanning electron microscopy, helium porosimetry and mercury intrusion porosimetry. The samples showed a high sensitivity to the applied differential pressure especially for the high porosity samples. Due to the lack of closing microcracks and compliant pores in low porosity samples, the travel times show slight changes with the confining pressure whereas the high porosity samples showed a remarkable reduction of the travel time with an increase in confining pressure for both P- and S-waves. We found that the sample physically deformed at pressure above 25 MPa. Evidence of inelastic deformation were observed in a few samples even at a differential pressure of 25 MPa. Both P- and S-wave velocities show a visible deviation with respect to the conventional velocity-porosity inverse relationships, with large variabilities in the velocities at a given porosity. The tight samples only measured a 3% average increase in velocity over the pressure range, whereas the porous samples measured a 20% average increase in velocity over the same pressure range. Despite the nature of porosity, the measured velocities showed a general increase with pressure. Also, all measured samples showed an increase in the bulk modulus of the rock after water saturation with 60% and less than 1% increases. There was no trivial correlation between porosity and the magnitude of the bulk modulus increase. Indeed, the shear modulus of the rock should be insensitive to any changes in water saturation, however, we observed some changes. The presence of anhydrite reduced both P- and S-wave velocities and had a significant influence on the velocities of carbonate rocks at any given porosity. A second paper will build on the results and will consist of predicting and validating suitable rock physics models using the measured carbonate data. The data that support findings of this study are openly available in ERA: Education and Research Archive University of Alberta at https://doi.org/10.7939/R3091B

Development of a novel two-dimensional(2D) three-way(3W) fuel flow control servo valve with constant pressure difference

To solve the problems of large volume, and low integration of traditional electro-hydraulic servo valve with constant pressure differential fuel metering device, a new two-dimensional three-way constant pressure differential fuel flow control servo valve (2D3WFFCSV) is developed. It innovatively adopts the advantages of lightweight of “two-dimensional hydraulic technology”, The constant differential pressure function and flow regulation function are integrated into a two-dimensional (2D) main spool with two degrees of freedom (rotational and axial degrees of freedom). The flow control process of 2D3WFFCSV is as follows: firstly, the armature of the torque motor and the two-dimensional piston are coaxially installed at the end of the two-dimensional piston, so the torque motor can directly drive the two-dimensional piston to rotate; secondly the “hydraulic servo screw mechanism”, which can amplify the power, is used to drive the two-dimensional piston to move in line; Finally, a pair of conversion mechanisms (roller group and spiral track conversion mechanism) are converted into the angular displacement of 2D main spool to control the area of flow valve port. The axial degree of freedom of 2D main spool realizes the function of constant differential pressure. To improve the flow control accuracy of the servo valve, the axial position of the 2D piston is detected by the linear displacement sensor (LVDT), and the signal is transmitted to the controller to realize the closed-loop control. To explore its open-loop characteristics, the mathematical models of torque motor, two-dimensional piston and main spool are established to obtain its open-loop transfer function. Then the AMESIM simulation model is built. To optimize the design of the system, through the dynamic simulation of the system, the influence of key parameters on the dynamic response of the system can be studied. An experimental study is carried out to verify the design feasibility of the servo valve. The experimental results show that under the condition of no-load and full-scale input, the closed-loop delay of the servo valve is 1.84%, the linearity is 2.14%, the step response time is 43 ms, and the dynamic frequency response is 38 Hz. The newly developed 2D3WFFCSV has the advantages of high integration, small size, light weight (801.5 g) and high response and control accuracy. It can replace the constant differential pressure, metering valve and hydraulic servo valve in the aeroengine fuel regulator.

Aerodynamic Modelling of the Airfoil Immersed in Two-Dimensional Jet Flow

In order to study the aerodynamic interaction of the airfoil and jet flow, the free streamline model and the panel method are combined to develop a fast calculation method for the airfoil in two-dimensional inviscid jet flow. The vortex strength and position of the jet boundary are determined by using the free streamline model and the constant total pressure difference assumption, the circulation of the airfoil is solved by the vortex panel method, and the whole process is coupled by relaxation iteration. Firstly, the convergence and effectiveness of the present method are verified. Next, the influence of the length ratio of jet height to airfoil chord, the velocity ratio of jet velocity to freestream velocity, and the ground effect on airfoil aerodynamics are studied. The results show that the aerodynamic characteristics of the airfoil in finite width jet flow and in freestream have a large difference, and it is important to consider the jet deflection for jet/airfoil interaction. In jet flow, the velocity ratio can be regarded as an aerodynamic similarity parameter for the airfoil. When the jet flow is deflected, the airfoil will not only generate lift but also drag, and the ground effect can be used to decrease drag. The developed method in this paper can not only capture the jet deflection but also has higher calculation efficiency than Computational Fluid Dynamic (CFD), which is beneficial for the preliminary design of a powered-lift device.

Modelling and Parametric Analysis of a Brine Treatment Unit Using a High-Temperature Heat Pump and a Vacuum Evaporator

The brine produced from desalination systems is a highly concentrated mixture, including cleansing chemicals from the water treatment processes that can possibly degrade ecosystems in discharge areas. Evaporation is a widely used method for the treatment of high salinity mixtures; however, it requires careful monitoring of the temperature and pressure in order to protect the equipment from the highly corrosive environment of the brine discharge. The proposed brine treatment system is based on the principle of vacuum evaporation with the use of a high-temperature heat pump, which is classified as “green technology”. In this study, a thermodynamic analysis of a vacuum evaporation system with a nominal freshwater production capacity of 160 L/h has been carried out, employing a numerical tool to model the flash evaporator and the heat pump. The analysis focuses on the parameters that present the most significant impact on the system’s efficiency and water production, such as the recirculation ratio, the set-point temperature of the heat pump and the pressure difference provided by the vacuum pump. The results show that, for the constant vacuum pressure difference, the water production increases with the increase in the set-point temperature and the recirculation ratio, but leads to the reduced COP of the heat pump and to an elevated specific energy consumption. Moreover, it is shown that an increased vacuum pressure difference leads to increased water production, but reduces the COP. Finally, the minimum specific energy consumption of 150 kWh/m3 of produced freshwater can be achieved for a set-point at 75 °C and vacuum of 0.21 bar, leading to a levelized cost of water about 11 €/m3.

Calculation and analysis of aerodynamic characteristics for airfoils immersed in two-dimensional jet flow

In order to study the aerodynamic interaction of the airfoil and jet flow, the free streamline model and the panel method are combined to establish a calculation method for the aerodynamic characteristics of the airfoil in a two-dimensional inviscid jet flow. Using the assumption of constant total pressure difference and free streamline model to determine the vortex strength and position of the jet boundary, the aerodynamic force of the airfoil is solved by the vortex panel method, and the whole process is calculated by relaxation iteration. Firstly, the relevant theory in this paper is introduced, and the convergence and effectiveness of the present method are also tested. Next, the influence of the position and the ratio of jet height to airfoil chord on airfoil aerodynamics in the jet flow are studied. Finally, the momentum theory is used to analyze the aerodynamic characteristics of the airfoil in the jet flow. The results show that the aerodynamic characteristics of the airfoil in the jet flow is quite different from that in the freestream. When the jet flow is deflected, the airfoil will not only generate lift but also drag. The method in this paper can be used to study the aerodynamic characteristics of the airfoil immersed in the jet flow.

Numerical Investigation on the Internal Flow Field of Electronic Expansion Valve as the Throttle Element

<div class="section abstract"><div class="htmlview paragraph">As one of the key components of the heat pump system, the electronic expansion valve mainly plays the role of throttling and reducing pressure in the heat pump system. The refrigerant flowing through the orifice will produce complex phase change. It is of great significance to study the internal flow field by means of CFD calculations. Firstly, a three-dimensional fluid model is established and the mesh is divided. Secondly, the phase change model is selected, the material is defined and the boundary conditions are determined. According to the principle of the fluid passing through thin-walled small holes, the flow characteristics of electronic expansion valve are theoretically analyzed. Then the flow characteristics of expansion valve are numerically calculated, and a bench for testing mass flow rate of the expansion valve is built. Then the theoretical value, CFD value and experimental value are compared to verify the correctness of the established three-dimensional fluid model. The flow rate changes of expansion valve are studied under the condition of changing geometric parameters such as the cone angle of the valve spool and the radius of circular arc at the end of the valve seat. According to the momentum theorem, the steady hydraulic force is theoretically deduced. Then the changes of steady hydraulic force are studied under the conditions of different inlet pressure and outlet pressure. At the same time, there also analyzes the effects of the conditions of different valve spool cone angle and valve seat arc radius on steady hydraulic force on the valve spool. Finally, transient analysis is carried out by using dynamic mesh technology. The speed of spool movement is defined by User Defined Function (UDF). Under constant pressure difference conditions, the influence of the spool movement on the hydraulic force and outlet flow of the valve is studied. And the change of the internal pressure field are shown.</div></div>

Feasibility Assessment of a Dual Intake-Port Scroll Expander Operating in an ORC-Based Power Unit

The main driver of research in the road transportation sector is almost certainly the development of technologies which allow for the reduction of CO2 emissions from internal combustion engines (ICEs). Wasted heat recovery (WHR) from the exhaust gases of ICEs based on organic rankine cycle (ORC) power units is one of the most promising technological solutions. However, several issues are raised when the recovery unit is scaled down to small applications, not to mention the fact that thermal sources are characterized by their intrinsically transient nature, as is the case with ICEs. In fact, this leads the ORC unit having to work frequently in off-design conditions. To successfully overcome this issue, the proper design and selection of the expanders are crucial. They are generally chosen from volumetric-type machines, thanks to their capacity to deal with time-varying thermo-fluid dynamic inlet properties. Among them, scroll machines represent one of the best solutions, despite them not yet being optimized as expanders, with them having been studied more as compressors. Dual-intake-port (DIP) technology is a novel solution used to enhance the performance of scroll machines. The effectiveness of this technology was assessed thanks to a comprehensive, experimentally-validated theoretical model of the scroll. It demonstrated that DIP technology can produce a 25% increase in mechanical power with respect to the baseline machine, without modifying the in–out pressure ratio. Maintaining a constant pressure difference across the expander at 5.6 bar, the power grew from 1131 W to 1410 W with the adoption of DIP technology. This power boost is lower than that achieved with a comparable DIP sliding rotary vane expander (SVRE) already studied by the authors, but the DIP Scroll achieved a higher efficiency (50–60%) when compared to the DIP SVRE case (40%).

Development of a Novel Two-Dimensional(2d) Three-Way(3w) Fuel Flow Control Servo Valve with Constant Pressure Difference

Development of a Novel Two-Dimensional(2d) Three-Way(3w) Fuel Flow Control Servo Valve with Constant Pressure Difference