Varying Flow Rates Research Articles

Impact of operation strategies on performance of integrated kang-floor heating system in severe cold areas

Efficiently and cost-effectively meeting the heating requirements of residents in severely cold regions by utilizing solar energy is currently a pressing need. Therefore, a solar heating system that integrated Kang-floor heating was established and tested for a passive solar house in Gan-nan Tibetan. This study reveals the effects of adjusting the flow/intermittent time periods and implementing variable flow rate operations on performance of system, to improve energy efficiency and optimize sleeping comfort. Findings indicated decreasing flow/intermittent time to 15/15 min had strengthened the average heat transfer from the water side, and mitigated the influence of returning water on internal water temperature of the tank, ultimately enhancing heat supply. The heating period was divided into three stage (18–24, 0–4, 4–8 o'clock), with a specific flow rate assigned to each stage. Under five flow rate configurations(A-E) with identical initial conditions: during constant flow rate, the greater the initial supply water temperature of the system, the more heat was transferred to room, and the higher heating efficiency was achieved, however, under variable flow rate, the effect of the water temperature on heating efficiency was significantly less evident. Mode B (low-to-high flow rate) had the highest heating efficiency and heat supply. The heating rate and cooling rate of Kang surface, temperature variations were notably less compared to the other four modes. Shortening the flow/intermittent periods and implementing variable flow method could improve the system's heat supply and sleep comfort with limited capital and resource investment.

Study on the Operation Optimization of Medium-Depth U-Type Ground Source Heat Pump Systems

Deep geothermal energy is a sustainable and renewable spacing heating source. Although many studies have discussed the design optimization of deep borehole systems, few have accomplished optimization and in-depth analysis of system operation control. In this study, an analytical model of the U-type deep borehole heat exchanger is proposed, and the average relative error between the simulated outlet temperatures and experimental data is −3.2%. Then, this paper presents an integrated model for the operation optimization study of the U-type deep-borehole ground source heat pump system. The optimal control of flow rate is adopted to match the variation in heating load. Compared with the constant-flow rate (110 m3/h) operation mode, the variable flow rate method reduces the power consumption of the heat pump and circulating pump by 22.1%, from 288,423 kW·h to 224,592 kW·h, during 2112 h of operation. In addition, the system has a larger RHS and COP when the thermal conductivity of the backfill material increases. When the borehole depth increases by 200 m from 2300 m, the energy consumption of the circulating pump will drop from 85,844 kW·h to 56,548 kW·h. The COP of the heat pump unit will decrease approximately linearly as the heating load increases, and the total power consumption will increase accordingly. This work can provide guidance for the design and optimization of U-shaped GSHP systems.

Quantitative determination of flow rate variations in reservoir Eco-scheduling: A case study of Yangqu dam in the upper yellow river

Accurate quantification of flow dynamics during reservoir ecological scheduling hinders the maintenance of normal reproductive activities in downstream riverine fish. This study proposed a quantitative method for determining the flow rate changes in reservoir ecological scheduling. The approach utilized the daily flow rate and daily flow-rate increment to characterize the flow process. Adopting the perspective of shifting spawning grounds of adhesive egg-laying fish species in response to flow rate variations, we introduced the Spawning Ground Overlap Rate as an indicator and utilized it to determine flow rate changes. Focusing on the downstream area of the Yangqu Hydropower Station in the upper reaches of the Yellow River, we calculated the distribution of spawning grounds and the Spawning Ground Overlap Rate in the region. We set a threshold for the Spawning Ground Overlap Rate to restrict the flow rate changes. The results indicated that during the fish spawning period, the ecological flow range in the downstream area of the Yangqu Dam was 480–1200 m3/s. It was required to maintain a daily flow rate change of less than 49.45 m3/(s·d) and a maximum seven-day flow difference of less than 227.76 m3/s to maintain the optimal level of spawning ground overlap rate. Additionally, it was necessary to keep the daily flow rate change below 123.83 m3/(s·d) and the maximum seven-day flow difference below 368.84 m3/s to maintain the minimum spawning ground overlap rate. The findings provide foundational data for determining flow dynamics during the ecological scheduling of the spawning period for viscous-spawning fish.

Experimental investigation of the matching boundary and optimization strategy of a variable geometry turbocharged direct-injected hydrogen engine

With the higher demand for torque, power, brake thermal efficiency (BTE), and low NOx emissions of hydrogen engines, direct injection and turbocharging are the most effective methods to improve performance. However, due to the large air flow rate variation range with lean combustion and low exhaust gas energy, the turbine needs to be adjusted significantly, and the performance of the conventional waste gate turbochargers is limited. In this study, a 2.0 L direct-injected turbocharged hydrogen engine was studied experimentally and matched with a variable geometry turbocharger (VGT). The working boundary of the VGT determined by abnormal combustion and exhaust back pressure is proposed at all working conditions as it changes from 10-50 % @1500 rpm to 40–75 % @4500 rpm. Control of the VGT to balance combustion and gas exchange was achieved to reach the highest BTE of 42.57 %. Further, high torque of 326 Nm and high power of 125 kW are explored and different VGT opening strategies are compared. An optimized VGT opening control strategy is proposed, which is divided into five regions at different loads to ensure best performance. The VGT opening control strategy based on λ control and the trade-off between combustion and gas exchange efficiency at all working conditions can be valuable in the development of high-performance hydrogen engines.

In situ and post-synthesis polymer stabilization of ferromagnetic nanoparticles synthesized by a membrane or conventional reactor

Membrane reactors have been proven to be effective in producing nanoparticles with reduced polydispersity indices. Recently, our group has incorporated this technology into the synthesis of ferromagnetic nanoparticles. In the initial phase, we conducted post-synthesis stabilization experiments to assess the performance of various polymeric agents. Polyacrylic acid (PAA) was chosen because of its notable affinity for the functional groups on the nanoparticle surface. Subsequently, in situ stabilization experiments were conducted using a membrane reactor, with variations in PAA addition flow rates ranging from 0.33 to 1.5 mL/min and maturation times in an ultrasonic bath ranging from 0.5 to 2 h. The samples were characterized in terms of their hydrodynamic diameter, polydispersity, and Z-potential. Notably, the smallest particle size was achieved at the intermediate point with a PAA flow rate of 0.66 mL/min. However, the influence of maturation time did not follow a predictable pattern; the most favorable characteristics, based on the analyzed variables, were observed at 1.5 and 2 h.

Catalytic biodiesel production from Jatropha curcas oil: A comparative analysis of microchannel, fixed bed, and microwave reactor systems with recycled ZSM-5 catalyst

In this study, we studied the conversion of Jatropha curcas oil to biodiesel by using three distinct reactor systems: microchannel, fixed bed, and microwave reactors. ZSM-5 was used as the catalyst for this conversion and was thoroughly characterized. X-ray diffraction was used to identify the crystalline structure, Brunauer–Emmett–Teller analysis to determine surface area, and temperature-programmed desorption to evaluate thermal stability and acidic properties. These characterizations provided crucial insights into the catalyst's structural integrity and performance under reaction conditions. The microchannel reactor exhibited superior biodiesel yield compared to the fixed bed and microwave reactors, and achieved peak efficiency at 60 °C, delivering high FAEE yield (99.7%) and conversion rates (99.92%). Ethanol catalyst volume at 1% was optimal, while varying flow rates exhibited trade-offs, emphasizing the need for nuanced control. Comparative studies against microwave and fixed-bed reactors consistently favored the microchannel reactor, emphasizing its remarkable FAME percentages, high conversion rates, and adaptability to diverse operating conditions. The zig-zag configuration enhances its efficiency, making it the optimal choice for biodiesel production and showcasing promising prospects for advancing sustainable biofuel synthesis technologies.

Indicator of abnormal cathode electron emission state with gas flow in Hall thrusters

The accurate diagnosis of abnormal electron emission state in hollow cathodes is crucial for the stable operation of Hall electric propulsion systems. In this study, a method of reducing the cathode working gas flow rate was used to simulate abnormal working conditions in which the cathode electron emission state (CEES) was deteriorating. By analyzing and comparing the oscillation signals under abnormal and steady-state working conditions, it was found that as the CEES deteriorated, the power content of the breathing oscillation decreased in the 1–40 kHz frequency band, and the main frequency decreased; in contrast, the power content of the transit-time oscillation increased in the 100–500 kHz range, and the main frequency was on the rise. Combined with the current growth rate analysis of breathing and transit-time oscillations, when the cathode gas flow rate decreases, the CEES deteriorates, the coupling voltage drop increases, and the potential drop in the channel decreases. The electron temperature and nonlinear power absorption of the electrons decrease, leading to a decrease in the growth rate of breathing oscillations and the breathing oscillation weakens; however, the time-averaged ion velocity and ion sound velocity in the channel decrease simultaneously, but the ion velocity decreases significantly faster than the ion sound velocity, leading to an increase in the growth rate of the transit-time oscillation, and the transit-time oscillation strengthen. Through comparison of the oscillation signals under different working conditions, such as varied anode flow rate, anode voltage, magnetic induction, it was proven to be a unique feature of CEES deteriorates, and can be used as an indicator of CEES deteriorates during the on-orbit operation of the Hall-effect thrusters.

Influence of Al2O3 nanoparticle mass concentration and aerosol formation parameters on tool vibration during turning of Ti6Al4V titanium alloy

Machining difficult-to-cut materials involves challenging machining conditions, including higher temperatures in the cutting zone, cutting forces and friction. Another important phenomenon is vibration, which is undesirable when manufacturing high quality workpieces. One way to reduce vibration in the cutting zone is to use cooling methods. Due to its environmentally friendly nature, the minimum quantity lubrication (MQL) method has already been widely used in metalworking. However, when combined with nanofluids, it improves the ability of the aerosol to dissipate more heat and increase lubrication in the cutting zone. This paper presents the effect of a polyol ester-based Al2O3 nanofluid due to the varying mass concentration of nanoparticles on the vibration during turning of Ti6Al4V alloy and compares the results with dry cutting and the MQL method without nanoparticles. Four concentrations (0.25−1 wt%), variable nanofluid flow rate E = 0.388−1.182 g/min and air flow rate P = 10−40 l/min were considered. According to the statistical analysis, the most important factor influencing tool vibration was the mass concentration of nanoparticles in the cutting fluid. By combining the MQL method with 0.5 wt% Al2O3, the vibration acceleration RMS values were found to be the lowest. When compared to the MQL method without nanoparticles, the RMS values for dry cutting ranged from 17.8% to 24.9%, and for wet cutting they were reduced by about 10.9-18.5%.

A Moving Horizon Estimation for a Class of Soft Continuum Manipulators

Abstract This work proposes a formulation for the moving horizon estimation technique considering both states and parameters obtained simultaneously with reduced estimation issues. The parameters can be either constant or time-varying, while states are related to complex output trajectories related to underactuated systems. Particularly, the proposed formulation considers additional equality constraints as a counterpart of the dynamics tube-model predictive control. Thus, it becomes less dependent on probabilistic information, such as probability density function and covariance of the process noise. In addition, the calibration of the method parameters has less sensitivity and driven by the tube constraints. The proposed approach can be applied in different systems; however, here it is detailed for a class of soft continuum manipulators with fluidic actuation through a variable flowrate and demonstrated with numerical simulations in planar motion. Results indicate robustness of the algorithm estimation in a challenging scenario arising from underactuation as well as in the presence of uncertainty and external disturbance, while simultaneously states and a vector of structural parameters are coherently estimated.

Design, economic analysis, and environmental assessment of an innovative municipal solid waste-based multigeneration system integrating LNG cold utilization and seawater desalination

This paper presents a novel integrated solution for harnessing energy from biomass alongside liquefied natural gas cooling. The process is investigated and evaluated in various scenarios. This integrated system yields electricity, hydrogen, cold water, hot water, and fresh water. Thermodynamic analysis of the process is conducted under different scenarios. Moreover, the overall environmental damage effectiveness factor is calculated using exergo-environmental evaluation, revealing that heat exchanger E-103 exhibits the highest effectiveness factor of environmental damage, with an exergy efficiency of 37.3 %. Simulation results indicate an overall energy efficiency and overall exergy efficiency of 58.24 % and 31.97 %, respectively. Energy efficiencies of the process are found to be 32.15 %, 34.85 %, 36.71 %, and 58.24 % in single generation, combined heat and power, combined cooling, heating, and power, and multi-generation scenarios, respectively. The study evaluates the simultaneous effects of pressure and flow rate variations of liquefied natural gas fluid, input flow rate variations of municipal solid waste biomass, and cyclohexane working fluid pressure variations in the organic Rankine cycle on other variables. Finally, an economic evaluation of the new process outlines its annual cost and the levelized energy cost parameter under base design conditions, which amount to 9,383,042 $ and 0.092 $/kWh, respectively.

Feasible Actuator Range Modifier (FARM), a Tool Aiding the Solution of Unit Dispatch Problems for Advanced Energy Systems

Integrated energy systems (IESs) seek to minimize power generating costs in future power grids through the coupling of different energy technologies. To accommodate fluctuations in load demand due to the penetration of renewable energy sources, flexible operation capabilities must be fully exploited, and even power plants that are traditionally considered as base-load units need to be operated according to unconventional paradigms. Thermomechanical loads induced by frequent power adjustments can accelerate the wear and tear. If a unit is flexibly operated without respecting limits on materials, the risk of failures of expensive components will eventually increase, nullifying the additional profits ensured by flexible operation. In addition to the bounds on power variations (explicit constraints),the solution of the unit dispatch problem needs to meet the limits on the variation of key process variables, including temperature, pressure and flow rate (implicit constraints).The FARM (Feasible Actuator Range Modifier) module was developed to enable existing optimization algorithms to identify solutions to the unit dispatch problem that are both economically favorable and technologically sustainable. Thanks to the iterative dispatcher–validator scheme, FARM permits addressing all the imposed constraints without excessively increasing the computational costs. In this work, the algorithms constituting the module are described, and the performance was assessed by solving the unit dispatch problem for an IES composed of three units, i.e., balance of plant, gas turbine, and high-temperature steam electrolysis. Finally, the FARM module provides dedicated tools for visualizing the response of the constrained variables of interest during operational transients and a tool aiding the operator at making decisions. These techniques might represent the first step towards the deployment of an ecological interface design (EID) for IES units.

Design optimisation of a variable flow CO2 pipeline – A statistical approach

Pipeline transport has emerged as the most cost-effective method for transporting CO2 onshore. The CO2 flow rate is a key factor driving transport costs, underscoring the need to understand the impact of flow rate variability in CO2 pipeline networks on their design and economics. This paper presents an optimal pipeline design methodology for CO2 pipelines operating under variable flow that considers the probability distribution of CO2 flow rate and the pipeline length. The results imply that pipelines designed for optimal performance under variable flow rates often demand a higher level of overdesign compared to pipelines intended for steady-state conditions. Decision-makers must balance the trade-offs between pipeline oversizing and installing multiple pressure boosting stations, especially applicable to large transportation distances and projects of extended duration. The examination of different approaches to pipeline design reveals that a variable flow pipeline design based on mean flow rate is not recommended, because it is incapable of handling the maximum flow rate. This drawback is overcome by adopting the variable flow stochastic pipeline design presented in this paper.

Electrical and thermal performance analysis of hybrid photovoltaic/thermal water collector using meta-heuristic optimization

The photovoltaic/thermal (PV/T) flat-panel technology has numerous advantages over PV modules and separately mounted solar thermal collectors regarding overall effectiveness and space-saving. Hybrid PV/T solar collectors’ thermal and electrical performance is influenced by design parameters like mass flow rate, tube diameter, tube spacing, packing factor, and absorber conductivity. This paper focused on using several meta-heuristic optimization techniques, incorporating the following: multiverse algorithm, dragonfly algorithm, sine–cosine algorithm, moth-flame algorithm, whale algorithm, particle swarm algorithm, ant-lion algorithm, grey wolf algorithm, and particle swarm optimization algorithm in PV/T collector optimal design according to maximum total efficiency obtained. The outcomes of the various algorithms revealed that the maximum electrical efficiency of the PV/T collector ranged from 13.85 to 14.28%, while the maximum thermal efficiencies ranged from 41.41 to 52.08% under standard test conditions (1000 W/m2 and 25 °C). The optimized values for the design parameters of the PV/T collector were as follows: the absorber conductivity was determined to be 356.6 W/m K, the packing factor was optimized to 0.7, the mass flow rate was set at 0.019 kg/s, the tube width was determined to be 0.035 m, and the tube spacing was optimized to 0.0524 m. The results indicated that the grey wolf optimizer (GWO) algorithm proved to be highly effective in optimizing the design parameters of PV/T collectors. Furthermore, the study examined the relationship between the temperature of PV modules and PV/T collectors by considering variations in mass flow rate, packing factor, and tube width at different solar radiation levels. The results confirmed that the PV/T collector temperature exhibited improvements compared to the PV module temperature. As a result, this led to higher electrical efficiency and an overall increase in the total efficiency of the PV/T collector.

Variation of Stocking Density and Water Flow Rate for the Growth and Survival of Siamese Catfish Fry (Pangasius hypophthalmus)

Variation of Stocking Density and Water Flow Rate for the Growth and Survival of Siamese Catfish Fry (Pangasius hypophthalmus)

Numerical simulation of all-vanadium redox flow battery performance optimization based on flow channel cross-sectional shape design

This paper numerically investigates optimizing trapezoidal flow channel cross-sectional shapes to improve all‑vanadium redox flow battery performance. A 3D steady-state multiphysics model coupling fluid dynamics, mass transfer, and electrochemistry was developed in COMSOL. Eight trapezoidal and one rectangular cross-section serpentine flow fields were simulated at varied flow rates. Results showed the TCS-T06 design reduced pressure drop by 12 % and pump power by 12 % versus the RCS. The concentration distribution of VO2+ was also improved, enhancing mass transfer. At 60 mA/cm2, TCS-T06 achieved 0.9 % higher pump power-based voltage efficiency. The optimized trapezoidal cross-section was proven to minimize losses, improve electrolyte distribution, and enhance VRFB performance. This work provides guidance for optimizing trapezoidal flow channel cross-sections to improve VRFB performance via enhanced mass transfer and reduced pressure drop.

GNN-Based Concentration Prediction With Variable Input Flow Rates for Microfluidic Mixers.

Recent years have witnessed significant advances brought by microfluidic biochips in automating biochemical protocols. Accurate preparation of fluid samples is an essential component of these protocols, where concentration prediction and generation are critical. Equipped with the advantages of convenient fabrication and control, microfluidic mixers demonstrate huge potential in sample preparation. Although finite element analysis (FEA) is the most commonly used simulation method for accurate concentration prediction of a given microfluidic mixer, it is time-consuming with poor scalability for large biochip sizes. Recently, machine learning models have been adopted in concentration prediction, with great potential in enhancing the efficiency over traditional FEA methods. However, the state-of-the-art machine learning-based method can only predict the concentration of mixers with fixed input flow rates and fixed sizes. In this paper, we propose a new concentration prediction method based on graph neural networks (GNNs), which can predict output concentrations for microfluidic mixters with variable input flow rates. Moreover, a transfer learning method is proposed to transfer the trained model to mixers of different sizes with reduced training data. Experimental results show that, for microfluidic mixers with fixed input flow rates, the proposed method obtains an average reduction of 88% in terms of prediction errors compared with the state-of-the-art method. For microfluidic mixers with variable input flow rates, the proposed method reduces the prediction error by 85% on average. Besides, the proposed transfer learning method reduces the training data by 84% for extending the pre-trained model for microfluidic mixers of different sizes with acceptable prediction error.

A PWR core power control using optimized PID controller with SQP based on control rod positioning and variable coolant flow rate

To ensure safety and stability, it is optimal for nuclear power plants to operate at their nominal power level. However, to meet the needs of power systems, NPPs must also be able to adjust their output for load-following purposes. This necessitates finding an effective control algorithmto maintain stable/safe operating conditions. The current study investigates the performance of PID controllersoptimized using Sequential Quadratic Programming algorithm and applied using two control techniques: control rod positioning and variable coolant flow rate. Simulation is done using model of four-loop Westinghouse PWR-1200 MW nuclear reactor. The proposed controller’s performance is evaluated in three scenarios:sudden control rod withdrawal, sudden change in coolant inlet temperature, and linear load tracking. The influences of model parametric uncertainty are also investigated. Simulation results revealed that the performance of the control algorithm applied using variable coolant flow rate was superior to the one usingcontrol rod positioning.

Simulation of heat and pressure transfer in concentric heat exchangers for small industrial scale

Abstract A Heat exchanger is a tool in industry which aims to transfer energy from hot fluid to cold fluid. The amount of heat transferred is an important parameter of the design and performance of heat exchangers. Concentric tube is a type of heat exchanger that is widely used in industries such as material processing and food preparation. One way to get the value of heat transfered before manufacturing a heat exchanger is to carry out computational fluid dynamic simulations. This simulation will make it easier for us to understand the heat transfer phenomenon that occurs from hot fluid to cold fluid. The aim of this study is to calculate how much heat transfer and pressure drop there is in a laboratory scale cocentric tube type heat exchanger. We also get a picture of the pressure drop that occurs due to fluid friction with the inner pipe walls. Experiments and simulations carried out in this study will then be validated. Variations in flow rate on the tube and shell sides are applied. the greater the flow rate, the greater the transfer of heat. The same trend is shown by variations in pressure. The greater the pressure, the greater the pressure drop that occurs. In this study, the pressure drop from the heat exchanger inlet to the heat exchanger outlet was 0.015%.

A PEDOT: PSS/GO fiber microelectrode fabricated by microfluidic spinning for dopamine detection in human serum and PC12 cells.

Rapid and accurate in situ determinationof dopamine is of great significance in the study of neurological diseases. In this work, poly (3,4-ethylenedioxythiophene): poly (styrenesulfonic acid) (PEDOT: PSS)/graphene oxide (GO) fibers were fabricated by an effective method based on microfluidic wet spinning technology. The composite microfibers with stratified and dense arrangement were continuously prepared by injecting PEDOT: PSS and GO dispersion solutions into a microfluidic chip. PEDOT: PSS/GO fiber microelectrodes with high electrochemical activity and enhanced electrochemical oxidation activity of dopamine were constructed by controlling the structure composition of the microfibers with varying flow rate. The fabricated fiber microelectrode had a low detection limit (4.56 nM) and wide detection range (0.01-8.0 µM) for dopamine detection with excellent stability, repeatability, and reproducibility. In addition, the PEDOT: PSS/GO fiber microelectrode prepared was successfully used for the detection of dopamine in human serum and PC12 cells. The strategy for the fabrication of multi-component fiber microelectrodes isa new and effective approach for monitoring the intercellular neurotransmitter dopamine and has highpotential as an implantable neural microelectrode.

Impact of Mass Flow Rate on Thermal Behavior of PCM-Based SWH during Charging Operations

Using phase change materials in solar water heaters presents an intriguing prospect due to their notable energy density and potential for substantial thermal energy storage capacity. In the context of active-type solar water heaters, careful consideration must be given to the water flow rate as a crucial parameter. This paper investigates the thermal dynamics of active-type solar water heaters equipped with phase change materials, examining variations in mass flow rate during the charging process. Indoor experiments utilized horizontal tanks, flat plate collectors, pumps, and solar simulators. Cylindrical capsules filled with paraffin wax were employed and arranged horizontally within the tank, while K-type thermocouples were utilized to monitor water and paraffin wax temperatures. Charging procedures were executed over 160 minutes with mass flow rate adjustments. Data analysis was performed to evaluate the system's thermal performance during charging. Results indicate higher mass flow rates correspond to increased instantaneous, cumulative heat storage, and charging efficiency. The mass flow rate notably affects the thermal efficiency of solar water heater systems incorporating phase change materials.