Flux Control System Research Articles

HEAT TRANSFER ANALYSIS AND TURBULENCE MODELS INVESTIGATION OF NUCLEATE BOILING FLOW IN NUCLEAR REACTOR APPLICATION

Boiling water exhibits an exceptionally high heat transfer coefficient, making it a valuable tool across numerous applications. However, once the heat flux surpasses a certain elevated threshold, the heated surface can no longer sustain continuous liquid contact. This is associated with a significant decline in heat transfer efficiency. The result may be a sudden spike in surface temperature within a heat flux-controlled system, or a dramatic decrease in power transferred in a temperature-controlled system. In the present study, the heat flux has been investigated in a circular channel heated by two roads. Parameters with emphasis on water flow velocity correlated with different heat transfer values from the roads. The methodology contains both laboratory experiments and a simulation model. The obtained results indicate that different heating surfaces play an important role in boiling heat transfer. Also, there is a clear relationship between the water flow and surface temperature. The amount of absorbed temperature increases by about 13% in a flow of 0.45 m/s. while in the water flow velocity 0.89 m/s and 1.34 m/s vary to 16.3% and17% respectively. The other impressive result is the phenomenon of alternate water temperature values due to certain regional temperatures. It's observed that there is a difference in heat absorption based on the amount of heat flux from the surface. The general rate of heat flux in the system was 6736.557 W/1°C for each square meter of heat generation. The obtained information is useful in controlling the boiling water reactor from sudden shutdown and also in controlling the boundaries in the design phase.<p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/soc/0789/a.php" alt="Hit counter" /></p>

Analytical solutions for freshwater lenses in stratified riparian aquifers

Analytical solutions for defining stable freshwater lenses within saline riparian aquifers (“riparian lenses”) are largely limited to homogenous aquifers. However, real-world riparian aquifers typically consist of a surficial layer of low-permeability soils or deposits, the impact of which on the occurrence of riparian lenses has not been investigated. This study develops steady-state, sharp-interface analytical solutions for riparian lens shape and saltwater discharge in a two-layered riparian aquifer. The developed analytical solutions are verified by sand tank experiments and numerical simulations, showing good agreement. The sensitivity analysis based on the proposed analytical solutions suggests that aquifer stratification (i.e., considering a low-permeability layer overlying a high-permeability layer) leads to larger lenses in head-controlled systems (i.e., with the inland constant-head boundary) but smaller lenses in flux-controlled systems (i.e., with the inland constant-flux boundary), compared to the scenario of a homogenous aquifer. The surficial layer with hydraulic conductivity only an order of magnitude lower than the underlying high-permeability layer would have a pronounced effect on lens extent and volume. Importantly, the results suggest that the presence of the surficial low-permeability layer may lead to the outcropping of the groundwater table, favoring the occurrence of saline groundwater seepage near the edge of the river valley (i.e., a phenomenon reported by the field survey of the Murray River floodplains in South Australia). The analytical solution presented in this study can be used to provide a preliminary assessment of riparian lenses in saline stratified aquifers, expanding the applicability of analytical methods to more realistic riparian settings.

Control of the Probe-Sample Interaction Force at the Piconewton Scale by a Magnetic Microprobe in Aqueous Solutions

This article describes the design and implementation of a control system that controls the probe-sample interaction force at the piconewton scale by manipulating a magnetic microprobe in aqueous solutions under a microscope. The control system has two functions, namely accurate force generation by magnetic flux control and precise control of the probe-sample interaction force. Magnetic flux control uses an improved six-input-six-output digital control law along with a disturbance estimator to achieve two control objectives. First, the magnetic flux at each pole tip of a previously developed hexapole electromagnetic actuator can be individually and precisely controlled at frequencies over 4 kHz, and the experimental results precisely followed the theoretical predictions based on the design. Second, together with the optimized flux allocation, the flux control system generates precise magnetic forces, making the six-input hexapole actuator behave like a decoupled three-axis force generator with a bandwidth of more than 4 kHz. Interaction force control compares the measured deformation of the sample with the expected deformation, updated in real time by a deformation predictor, to generate the magnetic force to control the interaction between the probe and the sample. Digital control laws, the estimator, and the predictor are all implemented using a high-speed Field Programmable Gate Array (FPGA) system. Experiments confirm that through mathematical modeling, digital control technology, high-speed electronics, and real-time computation, accurate three-dimensional force generation at the piconewton scale with high bandwidth and precise interaction force control with zero-mean random error, attributed to random thermal force and measurement noise, are achieved.

Sensor-less Speed and Flux Control of Dual Stator Winding Induction Motors Based on Super Twisting Sliding Mode Control

This paper proposes a direct speed and flux control system for Dual Stator Winding Induction Machines (DSWIMs) based on Super Twisting Sliding Mode Control (STSMC). The proposed nonlinear controller which has finite time convergence of error to zero, is designed such that the Lyapunov stability condition is satisfied. Furthermore, a novel torque-sharing algorithm is introduced for DSWIMs. This algorithm enables them to operate in a wide speed region, including zero speed, such that the required electromagnetic torque is supplied by two winding sets based on their power ratings. In addition, a Sliding Mode Control (SMC) based full order observer is proposed for DSWIMs. This observer, which is able to estimate the winding fluxes, flux angles and rotor speed with high-accuracy, guarantees the optimal flux condition. The functionality of the proposed sensor-less DSWIM drive scheme is evaluated through some experimental tests performed on a 3.3 kW DSP-based DSWIM drive system. The experimental results confirm the effectiveness of the proposed control method, torque sharing algorithm and the full order observer in various speed regions.

Self-regulated thermal comfort control for wearable heating device

In this study, a thermal comfort control model based on heat flux regulation was developed to ensure the thermal comfort in human-clothing-environment system. Compared to traditional temperature control methods, the heat flux control method in this study provided a more stable control for both temperature and heat flux, and clearly quantified human thermal sensation under cold stress. First, a heat transfer model was derived to quantitatively describe the heat transfer of an electrically heating device between two fabric layers. By using three temperature sensors, the mathematical description of derived heat exchange equation was validated and applied to a wearable heating device. The scenarios of a person in cold environments and under various activity levels were also simulated by using an environmental chamber. A control strategy based on the mathematical model was developed to optimize the applied voltage of the electric heater. The skin temperature and sensible heat loss can be stably controlled within standard thermal comfort range (Predicted Mean Vote ~ 0). Finally, an example of human wearing an electrically heated jacket in the freezer room was used to demonstrate the reliability and practicality of the heat flux control system.

The Drive towards Optimization of Road Lighting Energy Consumption Based on Mesopic Vision—A Suburban Street Case Study

This paper presents the research of optimization of road lighting energy consumption by utilizing the fact of human twilight and night vision (mesopic vision) dependency on luminance level and lamp’s light spectral composition. The research was conducted for a suburban street illuminated by smart LED road luminaires with a luminous flux control system with which different luminance levels can be achieved on the road. This road is an access road leading to a town located on the outskirts of Warsaw which is the capital of Poland and a large metropolitan area. Therefore, the traffic here is quite heavy on this road in the morning and in the evening and it is very light at other times of the day. In accordance with EN 13201 standard, lighting control can be applied to illuminate this road. This paper compares energy consumption for different lighting scenarios of the road in question. In the first scenario, the road luminance is compliant with M4, M5, and M6 lighting class requirements depending on the time of the day. In the second scenario, for each M lighting class, the values of luminance levels provided by EN 13201 standard have been reduced to the values resulting from their conversion to the corresponding mesopic luminance values. The conducted research has shown that a 15% saving per year in electricity consumption on the road is possible with such a conversion. Therefore, energy efficiency of a lighting installation can be improved by matching the lighting levels provided by the standard to the mesopic vision.

UV laser cutting of beech plywood

This paper presents experimental and theoretical studies on the UV laser cutting of beech plywood. The multi-technological factors in the laser cutting process were determined using Taguchi’s parameter design approach. The study of the wood material after laser cutting, related to its microstructure, surface morphology, and surface energy, is included. Beech plywood components were cut using pulsed UV lasers with varying parameters to determine superior surface quality, based on SEM, gray level, water contact angle, and optical profiling. The results showed that the surface roughness, in Ra, of beech plywood components at different laser powers, with and without a gas flux control system, can be reduced from 17.3 to 11.1 μm. The burn marks of the laser cut samples were also characterized in terms of gray level estimation. The results indicated that the gray level of the samples was increased by about 16% with a gas flux control system, implying a lesser extent of the burn marks in the plywood. The proposed laser cutting approach was proven to be successful in controlling the surface finish quality of beech plywood components.

A SsrA/NIa-based Strategy for Post-Translational Regulation of Protein Levels in Gram-negative Bacteria.

Strategies to control the levels of key enzymes of bacterial metabolism are commonly based on the manipulation of gene of interest within the target pathway. The development of new protocols towards the manipulation of biochemical processes is still a major challenge in the field of metabolic engineering. On this background, the FENIX (functional engineering of SsrA/NIa-based flux control) system allows for the post-translational regulation of protein levels, providing both independent control of the steady-state protein amounts and inducible accumulation of target proteins. This strategy enables an extra layer of control over metabolic fluxes in bacterial cell factories (see Graphical abstract below). The protocol detailed here describes the steps needed to design FENIX-tagged proteins and to adapt the system to virtually any pathway for fine-tuning of metabolic fluxes. Graphical abstract.

Optimal Reference Frame Angle Approach for Air-Gap Flux Minimization in Dual Stator Winding Induction Machines

Dual stator winding induction machines (DSWIMs), which have two sets of three-phase windings with unequal pole pairs in their stator and a standard squirrel cage rotor, have overcame the narrow speed operation region and circulating current problems exists in other types of dual winding machines. These advantages are resulted from the independent operation of their winding sets. The independent operation of winding sets will be guaranteed if the flux saturation is avoided. This letter proposes a novel reference frame angle determination technique that not only guarantees the flux saturation avoidance but also results in flux optimization in DSWIMs. Despite pervious methods, the proposed method does not require position or speed sensor and it is easily applicable in various control schemes and in different reference frames. This method is implemented in a flux and torque vector control system for driving a 3.3 kW DSWIM. The experimental results confirm the effectiveness of the proposed method. Moreover, by implementing the proposed method, the torque sharing between the two winding sets is properly done according to the power rating of each of them.

Stability and stabilization of garnissage on surface in cylindrical channel

The developed mathematical models of parametric oscillations on the phase change boundaries in a cylindrical channel are presented in a continuation of the previously published paper, which made an introduction to the subject. Analysis of the advanced models and processes described by them, together with the computer simulations, revealed a number of important features of the complex systems with dynamical boundaries of the phase change. Influence of the diverse factors and parameters with their interconnections is investigated in detail: the Peclet number, Bio number, modified Bio number (for the heat flux control system), the ratios of physical properties for the liquid and solid phases, a thickness of a solid layer, and the wave numbers of oscillations. Parameters of a garnissage on the internal surface of a cylindrical channel and the regularities of its instability are discussed for the linear and nonlinear cases. A possibility for the system's stabilization against unstable perturbations is examined using the automatic heat flux control. The control parameters are estimated in computer simulation for a wide range of the variable parameters. The results may be useful for the wall's protection against destruction with the artificially controlled garnissage in the metallurgical machines, as well as in some other applications.

Experimental validation of the Newton observer for a nonlinear flux-controlled AMB system operated with zero-bias flux

ABSTRACT The paper presents the results of experimental validation of the Newton observer for estimation of the magnetic flux within the feedback control of a nonlinear active magnetic bearing (AMB) system. In the preliminary work the Newton observer was adapted for the exact discrete-time model of the simplified one-degree-of-freedom AMB system, operated with zero-bias flux and under the voltage switching strategy, and showed good results in case of numerical simulations. The objective of this paper is to confirm these results on the basis of experimentation. The experiments were conducted on the AMB test rig, developed and manufactured at Bialystok University of Technology.

Impacts of inland boundary conditions on modeling seawater intrusion in coastal aquifers due to sea-level rise

Inland boundary conditions have significant impacts on seawater intrusion (SWI) due to sea-level rise (SLR). This study investigated the impacts of three inland boundary conditions (flux-controlled (FC), head-controlled (HC) and general-head boundary (GHB)) on modeling SWI due to SLR in coastal aquifers. First, we used the TOUGH2/EOS7 software program to solve the standard Henry’s problem and compared the results with those from the literatures. Numerical simulations were performed to investigate the impacts of the three inland boundary conditions on SWI induced by SLR in confined coastal aquifers (standard Henry’s problem) and unconfined coastal aquifers (Henry’s problem extended to unconfined domains). The simulation results show that HC systems in both confined and unconfined coastal aquifers are remarkably vulnerable to the effects of SLR owing to the resulting decreased head difference, while FC systems are relatively insensitive to SLR because the equivalent freshwater head at the inland boundary can increase by a similar magnitude to the SLR. The GHB boundary is more realistic than the other two boundary conditions: the recharge decreases because of SLR depending on the aquifer properties and the head difference between the reference head and the equivalent freshwater head at the seaside boundary.

Improving the Steady-State and Transient-State Performances of PMSM Through an Advanced Deadbeat Direct Torque and Flux Control System

In this paper, a new advanced deadbeat direct torque and flux control (A-DB-DTFC) system is proposed that improves the steady-state and transient-state performances of the permanent-magnet synchronous motor by adopting two improved deadbeat methods. Whenever the error between the torque and its reference value is low, an improved deadbeat method is adopted by the A-DB-DTFC system, in which the phase and time duration of the voltage vector applied to the motor are adjusted in a manner that the stator flux and torque reach their reference values after just one control cycle. Whenever the torque error is high, another deadbeat method is adopted by the A-DB-DTFC system, where the voltage vector phase is adjusted such that the fastest torque response is achieved. In order to assess the effectiveness of the proposed A-DB-DTFC system, the steady-state and transient-state performances of the motor are tested in MATLAB software and in practice, where the simulation and experimental results confirm that the proposed control system reduces the torque and stator flux ripples and achieves the fastest dynamic response. The comparative assessment with the recent DB-DTFC method indicates that the proposed A-DB-DTFC system yields lower torque and flux ripples and a faster dynamic response with the advantage of a lower computation complexity.

Precise Se-flux control and its effect on Cu(In,Ga)Se2 absorber layer deposited at low substrate temperature by multi stage co-evaporation

In-situ Se flux control system is applied for the growth of Cu(In,Ga)Se2 (CIGS) absorber layers by a multi stage thermal co-deposition of elements at low substrate temperature below 500°C. It was revealed that the composition depth profile of the [Ga]/([In]+[Ga]) (GGI) ratio is affected by the [Se]/[Metal] flux ratio. It was observed for the solar cell properties that the change in the depth profiles of GGI induced by the change of [Se]/[Metal] resulted in an increase in the JSC and a decrease in the FF, and hence little influence on the efficiency. Under control of [Se]/[Metal] ratio during the deposition process, the effect of CIGS layer thickness on the solar cell properties was investigated. With increase in the thickness up to 2.8μm, the short circuit current density was increased to over 35mA/cm2 w/o AR coating, resulting in conversion efficiency above 18% using low temperature deposition method.

Uncertainty and sensitivity analyses of the simulated seawater-freshwater mixing zones in steady-state coastal aquifers

The uncertainty and sensitivity of predicted positions and thicknesses of seawater-freshwater mixing zones with respect to uncertainties of saturated hydraulic conductivity, porosity, molecular diffusivity, longitudinal and transverse dispersivities were investigated in both head-control and flux-control inland boundary systems. It shows that uncertainties and sensitivities of predicted results vary in different boundary systems. With the same designed matrix of uncertain factors in simulation experiments, the variance of predicted positions and thickness in the flux-control system is much larger than that predicted in the head-control system. In a head-control system, the most sensitive factors for the predicted position of the mixing zone are inland freshwater head and transverse dispersivity. However, the predicted position of the mixing zone is more sensitive to saturated hydraulic conductivity in a flux-control system. In a head-control system, the most sensitive factors for the predicted thickness of the mixing zone include transverse dispersivity, molecular diffusivity, porosity, and longitudinal dispersivity, but the predicted thickness is more sensitive to the saturated hydraulic conductivity in a flux-control system. These findings improve our understandings for the development of seawater-freshwater mixing zone during seawater intrusion processes, and give technical support for groundwater resource management in coastal aquifers.

An assessment of seawater intrusion overshoot using physical and numerical modeling

[1] In recent years, a number of numerical modeling studies of transient sea-level rise (SLR) and seawater intrusion (SWI) in flux-controlled systems have reported an overshoot phenomenon, whereby the freshwater-saltwater interface temporarily extends further inland than the eventual steady state position. In this study, we have carried out physical sand tank modeling of SLR-SWI in a flux-controlled unconfined aquifer setting to test if SWI overshoot is a measurable physical process. Photographs of the physical SLR experiments show, for the first time, that an overshoot occurs under controlled laboratory conditions. A sea-level drop (SLD) experiment was also carried out, and overshoot was again observed, whereby the interface was temporarily closer to the coast than the eventual steady state position. This shows that an overshoot can occur for the case of a retreating interface. Numerical modeling corroborated the physical SLR and SLD experiments. The magnitude of the overshoot for SLR and SLD in the physical experiments was 24% of the change in steady state interface position, albeit the laboratory setting is designed to maximize overshoot extent by adopting high groundwater flow gradients and large and rapid sea-level changes. While the likelihood of overshoot at the field scale appears to be low, this work has shown that it can be observed under controlled laboratory conditions.

Rapid High-Precision Non-Linear Calibration for Temperature Sensors in Transient Aerodynamic Heating Simulation Systems

In order to accurately simulate the transient aerodynamic heating conditions experienced by aircraft when flying at high speeds, rapid and highly precise non-linear dynamic control of the heating process in aerodynamic simulation experiments must be conducted using a transient heat flux control system. This process involves carrying out ‘thermoelectric potential - temperature (E-T)’ conversion of sensors. Here a fast and high-precision ‘E-T’ sensor conversion method for the transient aerodynamic heating control systems of high-speed aircraft is proposed. The developed method has the advantages of easy calculation, rapid conversion speed and high calibration precision, and can thus be employed for fast non-linear dynamic control of rapidly-changing temperature fields in the aerodynamic heating process of high-speed aircraft.

CHF enhancement in flow boiling system with TSP and boric acid solutions under atmospheric pressure

In this study, the effects of tri-sodium phosphate (TSP) and boric acid on CHF enhancement were studied. Both TSP and boric acid are used to control pH in nuclear power plants. TSP is a kind of surfactant, and several surfactants, include TSP, have been reported to have an effect on enhancement of heat transfer. Nothing has yet been reported for the case of boric acid. CHF experiments were performed with mass flux ranging from 100-500 kg/m2 s and inlet subcooling temperature of 50 °C under atmospheric pressure. The test section was a vertical circular SS316 tube having an inner diameter of 10.98 mm. Its heated length was 224 mm, and it was heated by a heat flux control system using DC electricity. Fluids in the test loop were plain water, TSP solutions, and boric acid solutions. TSP solutions had three concentrations (0.2, 0.4, 0.6%), and boric acid solutions had four concentrations (0.2, 0.4, 0.6, 0.8%). In the case of TSP, 21.4% enhancement of CHF was observed at the inlet subcooling temperature of 50 °C and extremely low mass flux (100 kg/m2 s). In the case of boric acid, 12.4% enhancement of CHF was observed at inlet subcooling temperature of 50 °C and extremely low mass flux 100 kg/m 2 s.

Impact of Sea‐Level Rise on Sea Water Intrusion in Coastal Aquifers

Despite its purported importance, previous studies of the influence of sea-level rise on coastal aquifers have focused on specific sites, and a generalized systematic analysis of the general case of the sea water intrusion response to sea-level rise has not been reported. In this study, a simple conceptual framework is used to provide a first-order assessment of sea water intrusion changes in coastal unconfined aquifers in response to sea-level rise. Two conceptual models are tested: (1) flux-controlled systems, in which ground water discharge to the sea is persistent despite changes in sea level, and (2) head-controlled systems, whereby ground water abstractions or surface features maintain the head condition in the aquifer despite sea-level changes. The conceptualization assumes steady-state conditions, a sharp interface sea water-fresh water transition zone, homogeneous and isotropic aquifer properties, and constant recharge. In the case of constant flux conditions, the upper limit for sea water intrusion due to sea-level rise (up to 1.5 m is tested) is no greater than 50 m for typical values of recharge, hydraulic conductivity, and aquifer depth. This is in striking contrast to the constant head cases, in which the magnitude of salt water toe migration is on the order of hundreds of meters to several kilometers for the same sea-level rise. This study has highlighted the importance of inland boundary conditions on the sea-level rise impact. It identifies combinations of hydrogeologic parameters that control whether large or small salt water toe migration will occur for any given change in a hydrogeologic variable.

Loudspeaker having adjustable motor strength

A loudspeaker comprises a motor structure which incorporates a magnetic flux control system including a field winding, a controller connected between a voltage source and the field winding and, a polarity reversal switch preferably located across the filed winding. The magnetic flux control system is operative to produce a magnetic flux, which, depending on the level and polarity of electrical current supplied to the field winding, either reinforces or opposes the static magnetic flux produced by the magnet of the motor structure of the loudspeaker, thus altering the motor strenght of the loudspeaker system.