Range Of Efficient Operation Research Articles

Methodological provisions to the formation and the ensuring of efficiency and reliability of district-distributed heating systems

This study proposes a methodology for solving two problems of optimal development of district heating systems: analysis of efficiency areas and reliability of heat supply. In solving both problems, we adopt a nodal approach, which allows us to get detailed results that are most suitable to the real-world conditions. Based on the proposed methods and models, we develop an algorithm for transforming existing district heating systems into district-distributed heating systems with prosumers implemented into the network to serve the loads that fall outside the range of efficient operation of a district heating system. Wherein, the distributed sector is formed based on a prosumer that has its own generation, covering part of its own heat load and providing an additional functional and time redundancy for the system. As a result, conclusions and directions for further research are formulated.

Full-operating-condition performance improvement strategy and optimal design of a two-stage ejector with auxiliary secondary flow for MED-TVC systems

Periodic fluctuation of steam-source pressure occurs in the thermal vapor compression multi-effect distillation (MED-TVC) systems. Because ejectors are sensitive to the boundary conditions, as a key component for recovering excess steam in systems, ejectors experience a rapid decline in performance when the steam-source pressure fluctuates and does not satisfy the design condition. This decline negatively impacts the overall system performance and reduces the energy utilization efficiency. Therefore, a two-stage ejector with auxiliary secondary flow (ASF-TSE) and a full-operating-condition performance improvement strategy were developed in this study to enhance the ejector performance under full working conditions and broaden the efficient operation range of ejectors. The flow field characteristics and performance of the ASF-TSE, single ejector (SE), and two-stage ejector (TSE) in the low and design-pressure ranges were compared and investigated. The results showed that within the design-pressure range, the maximum and average increase ratios of the ASF-TSE for entrainment performance compared with the TSE are 17.53 % and 13.43 %. Moreover, the entrainment capacities of the three ejectors were compared and analyzed in the full operating range. Simulation results show that compared with the SE and TSE, the entrainment performance of the ASF-TSE is improved by 87.5 % and 8.0 %, respectively.

Energy performance improvement for a mixed flow pump based on advanced inlet guide vanes

The sharp decrease in the efficiency of a mixed flow pump within over-load flow rates presents a challenge for coastal drainage pumping stations. To address this issue, two different structures of advanced inlet guide vanes (AIGV), full-adjustable (FA) and half-adjustable (HA) structures, are designed to approach a better energy performance improvement strategy. Entropy production theory is applied into transient flow field to reveal their influence mechanism on the spatial distribution of energy dissipation. The primary findings are as follows: (1) AIGVs effectively solve the sharp decrease in the energy performance of mixed-flow pumps within the over-load flow rate range, broadening its efficient operation range. (2) The decrease in the axial velocity under the effect of AIGV explains the primary fluid physics of the increased efficiency. (3) The improvement in the match between the impeller inflow angle distribution and the impeller blades structure suppresses the generation and transmission of the flow separation on the pressure side, and reduce the near-wall energy dissipation. The novel HA-AIGV obtains a better flow control effect.

Numerical assessment of transient flow and energy dissipation in a Pelton turbine during startup

The Pelton turbine, known for its high application water head, wide efficient operating range, and rapid start-stop capability, is ideal for addressing intermittent and stochastic load issues. This study numerically analyzes the transient two-phase flow and energy dissipation during the startup of a Pelton turbine. Dynamic mesh technology controlled nozzle opening changes, and momentum balance equations managed runner rotation. Findings showed that the runner speed initially increased rapidly and then more slowly, and flow rate matched the nozzle opening variations. Runner torque first rose linearly, then decreased, with the fastest decline during nozzle closing. Hydraulic efficiency peaked early in nozzle reduction but then dropped sharply. Strong vortices formed due to upstream inflow and downstream backflow impact in the distributor pipe. The jet needle and guide vane improved flow in the converging section of nozzle, but flow began to diffuse with increased stroke. Initially, the jet spread fully on the bucket surface, but later only affected the bucket tips. Pressure fluctuations in the water supply mechanism were primarily due to jet needle motion, with higher amplitude during movement and lower when stationary. These fluctuations propagated upstream, weakening over distance. Reynolds stress work and turbulent kinetic energy generation, respectively, dominated energy transmission and energy dissipation, with their maximum contribution exceeding 96% and 70%. High-energy clusters corresponded to jet impact positions, highlighting jet-bucket interference as crucial for energy transport. This study established a performance evaluation method for Pelton turbine startups, supporting further investigation into characteristic parameters, flow evolution, and energy dissipation patterns.

Research on gas wave refrigeration application of full feedback periodic jet oscillator

Static gas wave refrigeration (SGWR) is a mechanic equipment with no moving parts which realize refrigeration by working on gas through pressure energy. This paper introduces full feedback jet oscillator as the jet distributor of the gas wave refrigerator and shows the switching mechanism of the oscillator in detail through dynamics description. The range of influence of wedge distance (distance between wedge tip and the nozzle) on the pressure retention rate and frequency at the oscillator outlet is discussed, and a SGWR experiment platform is set up to make comparison of the pressure waveform as well as cooling efficiency of the impulse jet from two oscillators with different wedge distance in the gas wave tube. The result shows that jet oscillator performance varies along with the wedge distance, thus influencing the cooling efficiency. To expand the efficient operation range, the principle of jet frequency changing and the impact of narrowing the oscillator structure on jet frequency are discussed in detail, the variation rule equation of the jet switching frequency is derived. Matching experiments of jet oscillator and size of gas wave tube have been conducted under conditions of specific frequency and variable frequency. It is concluded that there exists fluctuation value in gas wave tube refrigeration efficiency versus gas injection frequency curve, which can be up to 15% or more. Based on the present results, the jet frequency control method can make the gas wave tube operate at the refrigeration's peak frequency, thus improving SGWR refrigeration efficiency.

Comparative Studies on Nonlinear Structures with Multiple Tuned Mass Damper and Multiple Tuned Impact Damper

This study proposes integrating the particle damping technology into multiple tuned mass damper (MTMD) to form a multiple tuned impact damper (MTID) system for suppressing the vibrations of nonlinear high-rise buildings under earthquakes. A systematic performance comparison comprising vibration damping effects and working strokes between the optimal MTMD and optimally designed MTID with a distinct multi-objective optimization strategy is addressed. The energy-based analysis is also conducted to essentially reveal the difference in damping mechanisms of the two dampers. Furthermore, due to the parameter deviations of engineering structures in practice, the robustness of MTID and MTMD is evaluated involving structural mass, damping and stiffness. The results show that MTID is capable of transferring more energy to the damper and reducing structural energy to a greater extent, thus presenting superiority in controlling structural root mean square (RMS) responses and nonlinear indicators comprising joint curvature and the number of plastic hinges compared with MTMD. Through parametric evaluation, greater robustness is validated in MTID under deviations of various structural parameters with downgraded performance fluctuation in both range and degree, and the efficient operating range of MTID under the deviation of structural parameters is given. Furthermore, a smaller working stroke of the optimal MTID system is required compared with MTMD, permitting the improved applicability of the MTID system and better space utilization in the practical building.

Study on passive suppression method of rotating stall in mixed-flow pump: Using different impeller rim structures

Tip leakage flow (TLF) is not only an important factor causing hydraulic loss in mixed-flow pump, but also one of the inceptions of rotating stall. At present, limiting the stall of rotating machinery by restraining the TLF has gradually become a research hotspot of rotating machinery. However, in the field of mixed-flow pump, it is still in the initial stage of exploration. With the development of hydraulic machinery towards large-scale and high-speed, it is necessary to study its rotating stall suppression methods and expand its efficient operation range. Therefore, based on the idea of passive suppression of rotating stall, four new impeller rim structures are proposed in this study to optimize the performance of mixed-flow pump and to suppress or delay the occurrence of stall. The research results show that the geometric structure of the rim clearance has a significant impact on the energy performance of the mixed-flow pump, Bulge_Tip structure and Double_Rib_Tip structure make the critical stall and deep stall operating points shift to the low flow rate operating points, which improves the “saddle area” performance of the mixed-flow pump to a certain extent. However, there are two stall segments in the performance curve of Groove_Tip and Single_Rib_Tip structures, which worsens the pump performance in the “saddle area”. From the analysis of flow mechanism, it can be seen that Bulge_Tip structure and Double_Rib_Tip structure can restrain the loss of turbulent kinetic energy in the gap under stall condition to a certain extent, and limit the position and strength of unsteady secondary vortex (SV) structure at the impeller outlet, so as to shorten the stall range of mixed-flow pump without deteriorating the stall flow field in the impeller. Therefore, Bulge_Tip structure and Double_Rib_Tip structure has a light application prospect in stall suppression of hydraulic machinery.

Does the user behavior effect the productivity of hammer drilling? – Analysis of the influences of feed and lateral force

The objective of this study was to investigate the relationship between feed and lateral force with productivity in hammer drilling. Necessary user forces and vibration caused by hammer drilling leads to user fatigue and long-term injuries. Through an increase in productivity, the stress duration and thus injuries caused can be reduced. The user, who influences productivity, applies lateral forces in addition to the feed force during hammer drilling. Their influence and interaction with the feed force on productivity has not yet been investigated. In this study, a total of 1152 boreholes were performed on an automated test bench. Along with the feed and lateral forces, the setup, consisting of hammer drill and drill bit model, was varied in order to investigate interaction effects as well as discuss transferability of the findings. The productivity was evaluated by the rate of penetration (ROP). It was observed that the ROP decreased with increasing lateral forces (p < .001, r = 0.315) and increased with increasing feed force. The detailed courses of these relationships were setup-specific. At low feed forces, the feed and lateral force interacted on the ROP. The investigated relationships indicate an efficient operating range depending on the user forces and setup used, which enables a reduction of the user's stress duration. The findings help engineers develop power tools that provide more efficient and hence less fatiguing work, making them more ergonomic for the user.

Influence Mechanism of Trimming Impeller Diameter in a Centrifugal Pump by Computational Fluid Dynamics Investigation

Abstract Trimming the impeller diameter of a centrifugal pump is the easiest and most economical way to adjust its efficient operating range based on its original performance. Three impellers obtained by trimming the diameter are investigated. Energy performance, internal flow field, and entropy production analysis have been discussed in different cases. The results show that trimming the impeller diameter causes a great change in the energy performance of centrifugal pumps. The turbulent kinetic energy (TKE) distribution and entropy production also change significantly. The best efficiency point (BEP) shifts to low flowrate with trimming impeller diameter. The BEP shift rate was 6.67% and 20% for trimming amounts of 5.15% and 10.29%, respectively. As the impeller diameter decreases, the backflow phenomenon that occurs at the diffuser inlet at low flowrate improves. The ratio of mechanical energy to kinetic energy and pressure energy is not constant for pumps with different impeller diameters. The energy performance changes are mainly caused by flow changes inside the impeller, chamber, and diffuser. The results could be referred to as the design and selection of centrifugal pumps.

Effect of Operating Parameters on Efficiency of Swash-Plate Type Axial Piston Pump

In an effort to improve the energy economics of hydraulic systems, attention should be paid to reducing power losses in two main entities, energy converting components, and energy controlling and conveying components. Achieving the former requires utilizing components’ most energy efficient operating range. The energy converting efficiency of a pump, which is the primary energy converter in a hydraulic system, is determined by several operational factors. Of these, only pressure and rotational speed are normally considered, but also the fluid temperature and derived capacity with variable displacement pumps have a major effect on the efficiency. Omitting these factors may lead to running the pump outside its most efficient operation range and cause high energy losses. Operating the pump in its optimal region calls, however, for detailed knowledge of its performance characteristics, which are not generally made public by the pump manufacturers. This study presents the performance measurement results of a variable displacement axial piston pump in the form of efficiencies as a function of pressure, rotational speed, derived capacity and inlet fluid temperature. The results show that all of these factors have a significant impact on pump’s energy conversion efficiency and should, therefore, be taken into account when operating a hydraulic pump.

Numerical Study on the Effect of Nozzle Incident Angle on the Overall Performance of Gas Wave Refrigerator

Gas wave refrigerator (GWR) is a new type of refrigeration machinery that uses pressure waves to transfer energy between gases. In this paper, the flow characteristics and refrigeration mechanism in the wave rotor are numerically simulated. The nozzle angle is introduced to improve the overall refrigeration performance and expand the efficient operating range of the equipment. After verifying the model and method, the potential mechanism of refrigeration loss in the oscillating tube and the effect of loss on refrigeration efficiency are discussed in detail. Then the influence of incident angle on flow loss, refrigeration temperature drop, and power consumption are discussed. The association model of velocity development pattern and the maintenance of pressure performance at the inlet position of the oscillating tube is established during the high-pressure gas incident. The obtained numerical results show that flow loss and shock intensity loss are the main energy loss factors in the wave rotor. The incident angle determines the loss of the refrigeration process. The optimal incident angle of the device at the working point is obtained. The "balance" of velocity distribution in the oscillating tube can effectively reduce vortex loss. Arranging nozzles in the same rotation direction as the wave rotor can reduce work consumption, and the variation law is approximately negative linear correlation. Furthermore, based on the current simulation results, a set of nozzle design methods are obtained. It laid the foundation for the subsequent experimental research and optimization of GWR equipped with adaptive nozzles.

GMAW power supply based on parallel full-bridge LLC resonant converter

ABSTRACT In order to reduce energy loss and improve the electrical energy conversion efficiency during the welding process and decrease electromagnetic interference (EMI) of the welding power supply, this paper introduces a gas metal arc welding (GMAW) power supply with an LLC resonant converter. The parallel full-bridge LLC resonant converter was selected according to the characteristics of GMAW, including high open-circuit voltage, low arc voltage, high welding current, and changeable arc load. Load simulation tests and welding tests were carried out using the proposed power supply. Results of load simulation tests show that the switching frequency has a significant effect on the power supply. When the load changes from a light load to the rated load, the shape of the primary-side resonant current gradually approaches the shape of a standard sine wave. Welding test results reveal that the proposed power supply achieves complete arc ignition. The stable working point of the welding process is within the efficient operating range of the LLC resonant converter. The weld bead produced in the welding test was well formed.

Performance investigation of Wells turbine for wave energy conversion with stall cylinders

The wave energy conversion of oscillation water column (OWC) systems is limited by the narrow range of efficient operation of Wells turbines. Effective control methods are critical to improving performance. In this study, spanwise stall cylinders were mounted near the blade leading edge to delay the stall using dynamic mode decomposition (DMD) analysis. The performance of the Computational Fluid Dynamics simulation with steady inflow conditions is in good agreement with the experimental data. The results indicate that the aerodynamics and turbine performance is significantly influenced by cylinder wakes, which are associated with the location and radius of the stall cylinders. The relatively optimal location of the stall cylinders is determined at a 10% chord of the blade with a radius of 1% of the chord, producing 19.15% and 26.57% increases in the operation range and maximum torque coefficient, respectively. The cylinders act by intensifying the turbulence in the boundary layer and weakening the tip leakage vortex, causing the cylinder wake vortices to interact with vortices near the boundary layer to guide the flow near the suction side. A larger cylinder radius produces stronger wake vortices, but the efficiency decreases due to increased dissipation losses.

Fuel economy improvement of a turbocharged gasoline SI engine through combining cooled EGR and high compression ratio

HEV (hybrid electric vehicles, HEV) is considered to be one of the most important automotive technical roadmaps. Fuel efficiency level of the engine used in HEV has significant impact on vehicle fuel consumption. This paper studies the performance and fuel economy potential of applying high GCR (geometrical compression ratio, GCR) and cooled EGR in turbocharged gasoline SI engines dedicated to the use in HEVs. A 1-D simulation model for a turbocharged EGR engine has been established based on a baseline 1.5T engine. Then the effects of cooled EGR and higher GCRs on engine combustion and performance have been studied and optimized. As increasing GCR from 9.7:1 to higher values that are 12.5:1 and 14:1, the full load torque decreases obviously with the maximal relative decrease of 7.6% and 21.9% respectively mainly because EGR is used to suppress the knock reducing the volumetric efficiency. The fuel economy in the most speed and load range is greatly improved mainly because of higher constant volume degree, combustion efficiency and less heat transfer and exhaust losses. In HEVs, engines mainly work in the efficient operating range, the torque reduction can be compensated by drive motor, and an appropriately high GCR is advantageous.

Loss Characterization of a Conventional Variable Inlet Guide Vane

Variable inlet guide vanes (VIGVs) are most commonly used as the major control unit of integrally geared centrifugal compressors (IGCCs). In order to enhance the efficient operating range of the compressor, the loss mechanisms and utilization limits of state-of-the-art VIGVs need to be better understood. Field measurements in the wake of a typical, commercially used configuration were therefore conducted at the VIGV test facility of the Bundeswehr University Munich. The investigations were carried out at application oriented subsonic flow conditions and stagger angles from 50∘ to 90∘ covering the full low-loss operating range, including the limits of efficient operation. For a precise local loss characterization, an inflow correlation was developed and applied to consider total pressure inhomogeneities caused by the radial inflow velocity profile and minor circumferential velocity deviations. Contrary to previous research efforts, not only the profile losses, but also the secondary flow losses induced by the open blade tips and wall-blade interactions were resolved in full detail. For this reason, a more precise and comprehensive loss assessment of realistic VIGV cascades is acquired.

Increasing Efficiency for MicroHPP Hydroturbines Operating under Variable Head Pressure Using an Aperiodic Blade System

Nowadays, developments in the field of combined power units represent an urgent task for energy supply to consumers. One of the promising directions in this field consists in the development of engineering solutions based on low head pressure (ΔZ ≤ 20 m) microhydroelectric power plants with a siphon penstock, using the terrain features, natural reservoirs with height differences, and a ready industrial infrastructure. One of the specific problems of such combined power units consists in the operation of hydraulic turbines at variable head pressure, which leads to inconsistencies in the generation of electrical energy and a significant idle time in the hydraulic unit’s operation. In this paper, possible solutions to this problem are considered that are associated with the use of hydraulic turbines having an aperiodic blade system designed for the entire design domain of feeds Q and heads H determined from the conditions of joint operation of the hydraulic system–hydraulic turbine complex at different ΔZ. To carry out parametric studies, a design model for the hydraulic part of the cogeneration system has been developed, including a fragment of a siphon penstock and a hydraulic turbine. Studies on the grid viscosity and calculation and experimental verification of the model have been performed and optimal settings for the grid generator and the number of cells have been established: nel = 1 300 000 elements. The optimal settings have been obtained based on achieving an averaged value in calculated and experimental hydroturbine power δN accurate within ±5%. The numerical simulation of several variants for hydraulic turbines with different blade systems designed taking into account the experience of developing aperiodic blade systems in the field of pump engineering has been performed. In particular, such factors affecting the turbine efficiency as the pitch of the blade system at the inlet, outlet, and at the center of the skeletal lines of the blades, as well as the order of the blade arrangement in the aperiodic blade system, have been considered. A comparative analysis of hydraulic turbines with classical and aperiodic blade systems has been performed. It has been established that designing a bladed system of a hydraulic turbine in the design domain makes it possible to increase the efficiency of microHPP operation by 5.5% as well as to extend the range of efficient operation in the feed and head by 21.2 and 7.3%, respectively. At the same time, it should be noted that a low sensitivity of the main target parameter (efficiency of microHPP) with respect to the factors revealed in the course of the study is observed. Based on this, further prospects for the development of this study consist in the development of a parametric design model for a hydraulic turbine with the aperiodic blade system and a series of calculations using the theory of experimental design or stochastic methods for multidimensional optimization.

Influences of trailing edge split flap on the aerodynamic performance of vertical axis wind turbine

AbstractTo improve the performance of a 3.5 kW small H‐type vertical axis wind turbine (VAWT) with the airfoil of NACA0015, a design method for installing split flaps at the trailing edge of a blade is proposed. By solving the two‐dimensional URANS equations, the simulation of VAWTs is carried out. The influences of the length (10% c‐30% c), arrangement positions (90% c‐70% c), and deflection angles (10°‐30°) of the split flaps on the performance of VAWT are determined by orthogonal design when Reynolds number is 2 × 105 and 1 &lt; TSR &lt; 3. In accordance with the influence degrees of these parameters and adopting the maximum wind energy utilization ratio CPmax and the maximum efficient operating range Δλmax as research objectives, the optimum flap length is determined as 22% c, the optimum deflection angle is 10°, and the optimum arrangement position is 92% c. Further studies show that the CPmax is increased by 5.8% and its Δλmax is increased by 25.9% after installing split flaps. Meanwhile, split flaps can change the Kutta‐Joukowsky trailing edge boundary condition, which increases the flow circulation around the airfoil. Also, split flaps can increase the positive pressure difference in the upwind area and reduce the negative pressure difference in the downwind area, which significantly improves the aerodynamic performance of VAWTs.

Influence of Prewhirl Angle and Axial Distance on Energy Performance and Pressure Fluctuation for a Centrifugal Pump with Inlet Guide Vanes

The energy performance and pressure fluctuations in a centrifugal pump with inlet guide vanes (IGVs) are investigated experimentally and numerically in a prewhirl angle range of −24° to 24° and in an axial distance range of 280 mm, 380 mm, and 460 mm. The reliability and accuracy of the numerical method are validated by the satisfactory agreement between the experimental data and numerical results. Prewhirl regulation with IGVs can significantly increase the energy performance and broaden the efficient operation range for the centrifugal pump due to the improvement of flow pattern at the impeller inlet. The prewhirl angle has an obvious impact on pump energy performance, and the maximum amplitudes of pressure fluctuations on the blade leading edge of the pressure and suction sides decrease by 69% and 89%, respectively. The axial distance has a slight impact on pump energy performance, but the maximum amplitudes of pressure fluctuations drop by 35.4% on the blade leading edge of pressure side when the axial distance extends from 280 mm to 460 mm.

Effect of azimuthal diversion rail on an ATON-type Hall thruster

A newly designed azimuthal diversion rail (ADR) is studied and used to enhance the ionization process in an ATON-type Hall thruster. The diversion rail efficiently reduces the neutral flow axial velocity, and hence, increases the resistance time of atoms in the discharge channel of the Hall thruster. Thrust performances, in terms of thrust, anode efficiency and ion beam divergence, are found to be improved because of the application of the diversion rail, especially at low mass flow rate conditions. Experiment results reveal that the ADR increases the mass utilization under insufficient mass flow rate operating conditions. The design of the ADR broadens the efficient operating range of Hall thrusters and has significant contribution to multi-mode Hall thruster development.

Parametric Limits of Efficient Use of a Centrifugal Water Atomizer in Contact Waste-Gas Heat-Utilization Units

The relation for the limiting temperature of water heating in a contact gas–droplet-type apparatus with a centrifugal atomizer has been determined experimentally in relation to the conditions of utilization of heat of power plant waste-gases. Investigations were carried out in the range of excess water pressures in front of the atomizer 0.2–0.6 MPa and of the volume fraction of steam in the vapor–gas mixture at the inlet of the apparatus from 0.02 to 0.45. The possibility of using the obtained dependence for calculating the limiting values of the vapor–gas flow parameters that limit the range of efficient operation of the contact apparatus with steam condensation and in the absence of heated liquid droplet evaporation is shown.