Dimensionless Power Research Articles

Piezoelectric energy harvests by the usage of a laminar pulsating flow circulating in a rectangular channel

Abstract This work develops a theoretical study of a piezoelectric energy harvester, perturbed through a fully developed laminar flow with an oscillating pressure gradient. Considering a fully developed hydrodynamic flow, the electric energy generated in the piezoelectric element is due only to shear stresses yielded at the inner surfaces of the channel. In this manner, a fraction of the viscous forces is converted into unitary deformations at the piezoelectric, and the other fraction is transformed to induced electric piezoelectric energy.
Using dimensionless analysis, the formulation of resulting dimensionless governing equations for the fluid and the corresponding deformation and electric potential fields for the piezoelectric material constitute a conjugate problem, solved by considering harmonic solutions. Although the dimensionless power output is a multi-parametric function, due to the large number of dimensionless parameters involved, we find that
the main behavior of the electrical power depends very sensitively on two fundamental dimensionless parameters: the Womersley number, α, associated with the oscillating flow and a parameter that measures the physical importance of the electrical energy produced by the action of the velocity field. For the first case, it is seen that the power increases if the Womersley number is decreased while for the second case, the inverse behavior is predicted. Therefore, there is a clear operation of the physical system for which better conditions can be reached by selecting and varying appropriately the assumed values of different dimensionless parameters.

Response of submarine braided channels to varying inflow hydrographs: Geomorphic experiments and stratigraphic implications

AbstractSubmarine channels on the seafloor experience a range of turbidity current‐flood hydrographs. The characteristics of the flood hydrograph influence channel dimensions, the number of channel threads (i.e. braiding intensity) and the depositional properties of sandbars within the channels. However, the morphodynamic response of submarine braided channels to different hydrograph patterns is poorly understood. In this study, six geomorphic experiments are used to test how varied flood hydrographs affect the braiding intensity and sandbar geometry within submarine channels. Three experiments represent the control group with constant density‐current inflow, and three experiments use different time‐varying hydrograph patterns. The experiments show that, as the inflow‐to‐sediment discharge ratio increases, multiple small channels coalesce into a few main channels, causing a decrease in active braiding intensity defined by the channel threads with flow. When the flow returns to the initial low flow rate, active braiding intensity increases again. These observations show that the inflow‐to‐sediment discharge ratio determines the value of active braiding intensity. Additionally, active braiding intensity is directly proportional to dimensionless sediment‐stream power and dimensionless stream power, in agreement with previously established trends for both submarine and fluvial braided channels. In contrast to active braiding intensity changes, the measured sandbar aspect ratio and compactness ratio (i.e. ratio of planform area to perimeter) of submarine braided channels is insensitive to changes in the hydrograph. However, when inflows reach peak discharge, the higher transport capacity erodes pre‐existing deposits, forming noticeable erosional surfaces, and subsequently depositing thicker sandbars during that stage. These observations imply that sandbar planform morphology is largely insensitive to hydrograph, but hydrograph variability induces a greater variability in the resultant stratigraphic packages. The experimental results predict that field‐scale stratigraphy should be dominated by strata deposited during intervals of high flow, but that these strata will also exhibit reduced lateral continuity compared to formation scenarios with constant discharge.

Automated Feedback on Student Attempts to Produce a Set of Dimensionless Power Products from a Set of Physical Quantities that Describe a Physical Problem

Formative feedback is important in learning. Automating the provision of specific, objective, constructive feedback to large cohorts requires complex algorithms that most teachers do not have time to develop, suggesting that a community effort is needed to create a library of specialised algorithms. We present an exemplar algorithm for a class of tasks in ‘dimensional analysis’ relating to the Buckingham Pi theorem. The challenge arises because there are infinitely many valid and invalid answers, but any valid answer is sufficient to complete a task. We present an algorithm that, given one valid reference answer, can evaluate any response to a task. The algorithm uses a vector-space formulation of the Pi theorem. Deployment across seven tasks for 380 students provided feedback 3,090 times, including stating why a response is invalid. The most common reason was that a student-proposed set was not dimensionless, but other educationally relevant reasons were also identified.

Study on the synthesis of nanoparticles and their power characteristics in a bubble liquid membrane reactor

Abstract A bubble liquid film reactor is a new type of reactor used for preparing nanoparticles, which has strong inflation ability and dispersion, homogenization, and emulsification effects, especially suitable for preparing loose nanoparticles. In the actual production of enterprises, there is an urgent need to expand production capacity and scale up the reactor. Due to the lack of power characteristic data during the reaction process, it is difficult to select the motor, resulting in unnecessary energy and cost waste. Therefore, the power characteristic data of bubble liquid film reactors urgently needs to be studied. This article investigates the influence of operating conditions such as bubble cap diameter and immersion depth on stirring power and obtains the power characteristics during the operation of a bubble liquid film reactor. The results indicate that the larger the diameter of the bubble cap disk, the stronger the power consumption, but the smaller the power input capacity. The deeper the immersion depth, the higher the power consumption and the stronger the power input capability. Finally, fitting the dimensionless power standard formula provides a mathematical model for reactor amplification, providing theoretical guidance for enterprises to expand production lines and increase production capacity, and providing data support for motor selection.

New Dimensionless Power Number Equation for Horizontal Agitated Drum

New Dimensionless Power Number Equation for Horizontal Agitated Drum

Scale analysis of undercut and bulge driven by thermocapillary convection due to surface-active solute on a solidified surface

This study scales the shape of the undercut, a depression region near the triple-phase line parallel to the scanning direction, and the bulge in the central region within the fusion zone, considering thermocapillary convection affected by a surface-active solute in the molten pool for the first time. Undercuts, commonly encountered in welding, additive manufacturing, and re-solidification processes, reduce fatigue and fracture strength while enhancing stress concentration. Utilizing the interfacial Young–Laplace equation and Bernoulli equations in the shear layer driven by thermocapillary force influenced by the surface-active solute-affected critical temperature, and introducing the concept of mass conservation, the scale analysis finds that the undercut depth and bulge height increase as Marangoni and Prandtl numbers increase, and the loss coefficient decreases. Furthermore, the widths of the undercut and bulge exhibit increases with dimensionless beam power, fusion zone width, and the ratio of solid-to-liquid thermal conductivity. The COMSOL Multiphase code is also used for simulation and successful comparison, aligning with experimental data from laser polishing. This analysis aids in understanding and controlling microstructures in various processes beyond laser polishing.

Predictive process diagram for parameters selection in laser powder bed fusion to achieve high-density and low-cracking built parts

The laser powder bed fusion process (LPBF) has been widely used in many industrial sectors, including automotive, aerospace, and biomedical devices. With the fast development of new materials designed for critical applications, the conventional design of experiments for determining an optimal LPBF process window is a time and material-consuming activity. This can impose difficulties on small-to-medium industrial businesses where investing resources are limited. To address these challenges, this study draws inspiration from a reliable diagram used in laser welding to construct a similar diagram for the LPBF process. The objective is to enable the "right-first-time" selection of parameters that achieve a minimum of 99% density, regardless of the metallic materials and machine platforms. The diagram is established based on dimensionless beam power and velocity, derived from multiple LPBF process parameters (e.g., laser power, scan speed, hatch spacing) and the thermophysical properties of materials (e.g., melting point, density, thermal diffusivity). Furthermore, hot cracking susceptibility is considered by a strain-rate approach incorporated with the dimensionless thermal strain factor, which benefits when processing hard-to-weld alloys. The diagram shows high reliability in determining parameters corresponding to lack of fusion, keyhole porosity and 99% dense parts when plotting against literature data of LPBF for several metallic materials. Similar results were observed when applying to a novel material ABD-900AM Ni-based alloy, for which no previously published data were available. Moreover, the diagram proved effective in selecting parameters to process the high-cracking susceptible CM247LC Ni-based alloy, resulting in significant mitigation of hot cracking in the as-fabricated parts.

SCREW DRUM STRUCTURAL PARAMETERS ANALYSIS ON PROPULSION PERFORMANCE IMPACT

Screw propeller can perform engineering operations in complex environments and have a wide range of applications. To improve its operational efficiency, it is necessary to analyze the influence of the parameters of the screw drum on the performance indicators of the operation, in order to confirm the structural parameters under the optimal operational efficiency. By coupling the Discrete Element Method (DEM) with RecurDyn, the simulation of the locomotion process of a screw propulsion mechanism in a sand environment is conducted. Output results such as travel speed, maximum traction force, and maximum torque are measured. Through computation, performance indicators including slip ratio, traction coefficient, and dimensionless power can be obtained. By coupling the Discrete Element Method (DEM) with RecurDyn, the simulation of the locomotion process of a screw propulsion mechanism in a sand environment is conducted. Output results such as actual speed, maximum traction force, and maximum torque are measured. Through computation, performance indicators including slip ratio, traction coefficient, and dimensionless power can be obtained. Analyzing the numerical indicators of the propulsion system, it is determined that the optimal structural parameters for the screw propulsion mechanism to operate in a sand environment are a helix angle of 40°, aspect ratio of 4, blade height ratio of 0.15, and the number of blades of 4.

Globe valve in single phase flow: experimental and CFD analysis

Flow-induced vibration (FIV) poses risks to engineering systems, prompting efforts for safety. Valves, crucial for fluid control, can induce turbulence-related mechanical loads, leading to vibration and potential failures. This paper combines experimental and numerical methods, using computational fluid dynamics (CFD) for flow analysis. A test loop with nine pressure sensors assesses water flow through a globe valve, testing various conditions. Dimensionless power spectral density (PSD) of pressure fluctuations is compared with CFD results. Steady simulations precede computational fluid dynamics – large eddy simulation (CFD-LES) for quantitative data. Industrial-scale valve analysis explores scalability using different protocols, contributing to design strategy improvements.

Gauge preheating with full general relativity

We study gauge preheating following pseudoscalar-driven inflation in full general relativity. We implement the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) scheme to solve the full nonlinear evolution of the metric alongside the dynamics of the pseudoscalar and gauge fields. The dynamics of the background and emission of gravitational waves are broadly consistent with simulations in a Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime. We find large, localized overdensities in the BSSN simulations of order δ = δρ/ρ ∼ 30, and the dimensionless power spectrum of δ peaks above unity. These overdense regions are seeded on length scales only slightly smaller than the horizon, and have a compactness C ∼ 0.1. The scale of peak compactness is shorter than the Jeans length, which implies that pressure of the matter fields plays an important role in the evolution of these objects.

Integrated Prediction Model for Upstream Reservoir Sedimentation in a Weir: A Comprehensive Analysis Using Numerical and Experimental Approaches

In this study, a new empirical equation was established to predict the sedimentation volume resulting from the construction of a multi-purpose weir or low-head dam using experimental approaches. Applying the 1-D numerical model (STAFF), which is based on Exner’s equation, 2545 cases were simulated and laboratory experiments were conducted with various sediment particle sizes, channel slopes, inlet discharge, and outlet water elevation. Short-term predictions were conducted through laboratory experiments with movable bed, and the results indicated that dimensionless unit stream power and the Shields parameter exhibited the most significant correlation with dimensionless deposition volume. In particular, we analyzed the phenomenon in which the backwater effect and reservoir delta. Using a multiple regression approach, the developed empirical equation was validated for predicting sedimentation in the upstream reservoir of the weir.

Scaling laws and numerical modelling of the laser direct energy deposition

A computational framework that can be easily implemented into a two-phase flow model has been developed for DED (direction energy deposition) process. The information on the in-flight powder stream is treated by an analytical model and regarded as input to the cladding model. The cladding model utilizes Computational Fluid Dynamics (CFD) technique with the volume of fraction (VOF) method, which considers interfacial dynamics and interaction with the powder stream.Furthermore, we have applied Buckingham π theorem to develop scaling laws for the geometry of the final track. In contrast with the dimensional empirical models proposed in the previous studies, the dimensionless laws in this study can largely match the trends of measured data with noticeable variations of working conditions collected from several different studies. The dimensionless cladding width is dominated by the dimensionless laser power with a positive correlation. The increase in dimensionless laser power and powder mass flow rate usually results in a greater value of the dimensionless cladding height, but this trend could become opposite when the values of catchment and energy efficiencies are close to 100%. A threshold that dilution suddenly goes up has also been provided and validated based on the dimensionless parameters. This study provides a reliable numerical model and scaling laws with sufficient generality. The processing window has also been carried out with constraints of dilution and contact angle, bringing design guidelines to the related industries.

Power density performances and multi-objective optimizations for an irreversible Otto cycle with five specific heat models of working fluid

Power density (Pd) performance for an irreversible Otto cycle is analyzed with constant specific heat (SH), linear and nonlinear variable SH, linear and nonlinear variable SH ratio of working fluid. Relationships among dimensionless Pd (P‾d), thermal efficiency (η) and compression ratio (γ) of cycle are obtained taking three loss items account into. Performances are compared when dimensionless power output (P‾) and P‾d are maximized with five SH models. Choosing γ as design parameter, and P‾, η, dimensionless ecological function and P‾d as performance parameters, multi-objective optimizations are carried out for five SH models by using NSGA-Ⅱ. Evaluating deviation indices (D s) under three decision-making methods, the optimal parameter combination with the smallest D is selected as the better one. Results show that SH model has no qualitative influence on relationship curve of P‾d−γ and P‾d−η, but it has quantitative influence. With linearly variable SH and constant SH, γP‾d reaches the maximum and minimum respectively. With linearly variable SH ratio and nonlinearly variable SH, ηP‾d reaches the maximum and minimum respectively. The D of LINMAP method with constant SH model is the smallest, which is 0.1236, and the D of Shannon entropy method with the nonlinear variable SH ratio model is the largest, which is 0.3664.

Three-way maximized net power output from alkaline membrane fuel cell stacks

This work uses an experimentally validated mathematical model to maximize alkaline membrane fuel cell (AMFC) stacks net power output. Temperature distribution, efficiency, polarization, and power output curves are obtained. Fundamental optimization opportunities exist for the internal and external structure, which led to a two-way optimized AMFC stack for maximized net power. After system optimization, a parametric analysis was carried out for electrolyte KOH mass fraction, stoichiometric ratios and total fuel cell stack size (volume). KOH content was shown to lead to a third optimum, i.e., 40 wt %. The three-way optimized AMFC stack (ξs=1.37×10−3, y = 40 wt% KOH)opt was shown to be independent of the stoichiometric ratio and stack size variation, but (ξy/ξx=ξz/ξx)opt was affected by total stack volume (or size). In fact, it was found that the three-way maximized dimensionless AMFC stack net power output rises as the stack volume rises in a path that is well correlated by W˜net,mmm×10−3=36.266V˜T0.74, which is similar to the allometric law of nature that correlates basal metabolic rate (BMR, W) and body mass (mb,kg) for living beings, i.e., BMR∼mb0.74, that could be understood as an indication that inanimate and animate systems follow the same evolution laws.

Confinement width and inflow-to-sediment discharge ratio control the morphology and braiding intensity of submarine channels: insights from physical experiments and reduced-complexity models

Abstract. Submarine channels conveying sediment gravity flows are often topographically confined, but the effect of confinement width on channel morphodynamics is incompletely understood. We use physical experiments and a reduced-complexity model to investigate the effects of confinement width (B) and the inflow-to-sediment discharge ratio (Qin/Qs) on the evolution of submarine braided channels. The results show that a larger confinement width results in increased active braiding intensity (BIA) and that BIA takes longer to stabilize (i.e., a longer critical time; tc). At a fixed confinement width, a higher Qin/Qs slightly decreases the BIA. Digital elevation models of difference (DoD) of the experiments allow measurement of the morphological active width (Wa) of the submarine channels and the bulk morphological change (Vbulk) within an experiment, defined as the sum of total erosion and deposition. We find that Wa and Vbulk are proportional to B. We further confirm that BIA is proportional to both dimensionless sediment–stream power (ω**) and dimensionless stream power (ω*). These trends are consistent for submarine braided channels both with and without confinement width effects. Furthermore, we built a reduced-complexity model (RCM) that can simulate flow bifurcation and confluence of submarine braided channels. The simulated flow distribution provides reliable predictions of flow depth and sediment transport rate in the experiments. Using kernel density estimation (KDE) to forecast the probability and trends of cross-sectional flow distribution and corresponding BIA under extreme events, we find that skewness of the flow distribution decreases as discharge increases. The development of braided submarine channels, shown here to extend to conditions of topographic confinement, suggests that factors not modeled here (e.g., fine sediment) may be necessary to explain the abundance of single-thread submarine channels in nature.

Mixing Power Requirement Determination in Agitated Drum Using Dimensional Analysis

The mixing of granular materials in an agitated drum can be characterized by the dimensionless power equation. The equation was created by dimensional analysis, for which the parameters affecting the mixing power requirement were collected based on the literature. The most important of these are the rotational speed, the drum loading factor, the geometric and physical properties of the mixing drum and the granular materials. The dimensionless power equation is used to estimate with reasonable accuracy the Power number within the given range of applicability , which has been validated by measurements. From the Power number, the mixing power requirement of the mixed granular material can be calculated, which can be used as operational data for selecting the mixing motor.

Fundamental optimization of steam Rankine cycle power plants

This paper introduces a mathematical model for the design and fundamental optimization of steam Rankine cycle (SRC) power plants. The model assumes that the plant irreversibilities are predominant in the heat exchangers, thus exergy destruction in the turbine, pump, fittings, tubes and other internal components are neglected. The NTU-effectiveness method was utilized to model the heat exchangers, and water was considered as the working fluid, which changes phase in both heat exchangers. Acknowledging that entropy is generated in any physical system, the fundamental optimization problem selected the dimensionless net power output, and second law efficiency as the objective functions to be maximized, after the identification of plant geometric and operating parameters to be optimized based on the intersection of asymptotes method, subject to a fixed total heat exchangers area realistic physical constraint, i.e., for a finite size plant. As a result, two levels of optimization were identified: i) the working fluid to hot stream mass flow rate ratio, M, and ii) the steam generator, xH, and condenser, xL, area fractions of the plant fixed total heat exchangers area. The model was experimentally validated for a heat recovery driven power plant. Sharp maxima were obtained in both levels, which is illustrated with a base case by ∼ 60 % second law efficiency variation in comparison to the obtained maximum for 0.05 < M < 0.25 in the first optimization level, and ∼ 30 % for 0.2 < xH < 0.7 in the second optimization level, so that (xf,H,xfg,H,xg,H)2wo=(0.14,0.13, 0.23), with (M,xH)2wo=(0.16,0.5), in the base case considered in this study. The two-way optima results sensitivity to several plant geometric and operating parameters were thoroughly investigated. The optimized parameters are shown to be robust with respect to several system’s design and operating conditions. Therefore, the herein reported fundamental optimization results are important for whatever actual SRC power plant.

Effects of upslope inflow rate, tillage depth, and slope gradients on hillslope erosion processes and hydrodynamic mechanisms

Inflow rate, tillage depth and slope gradient play vital roles in hillslope soil erosion processes. However, the effects of these factors and their interactions on hillslope soil erosion processes, particularly on long slopes in the Chinese Mollisol region, are still lacking to date. Thus, a set of laboratory experiments, including six upslope inflow rates (0, 50, 100, 150, 200 and 300 L min−1), two tillage depths (5 and 20 cm) and two slope gradients (5° and 10°), were conducted to quantify the impacts of these factors and their interactions on hillslope soil erosion processes. The results showed that soil erosion rates increased as a power function with increase of inflow rate and slope gradient, while they decreased as a power function with an increase in tillage depth. The slope gradient had a greater impact on soil erosion rates than inflow rate and tillage depth. Moreover, inflow rate, slope gradient, and their pairwise interaction mainly governed hillslope soil erosion. Compared with hillslope soil erosion, hillslope runoff rate was dominantly affected by inflow rate. The inflow rate and slope gradient affected the hydrodynamic characteristics and erosion rates by shifting erosion patterns; while tillage depth mainly influenced them by converting surface flow to seepage flow. In addition, the dimensionless effective stream power was the optimal index (R2 = 0.884, NSE = 0.861) affecting soil erosion rates, followed by the dimensionless stream power (R2 = 0.879, NSE = 0.848). The dimensionless soil erosion rates were correlated with the dimensionless hydrodynamic parameter following a power function. Therefore, soil erosion in the Chinese Mollisol region could be effectively prevented by dispersing runoff, increasing deep tillage and reducing the impact of slope gradient through soil conservation measures.

Thermodynamic investigation of a centrifugal reverse Brayton cycle for refrigeration in air conditioning filed

The reverse Brayton cycle (RBC) is known to exhibit a lower coefficient of performance (COP) when compared to conventional vapor-compression refrigeration systems. To tackle this issue, this study proposes a centrifugal reverse Brayton cycle (CRBC) that features a rotating heat exchanger, which utilizes the conversion mechanism between equal potential energy and pressure energy to enhance system performance. The findings indicate that the COP of the CRBC is roughly inversely proportional to the working fluid density, making CO2 a more suitable option for CRBC systems than conventional working fluids. We propose three different cycles for the CRBC system: the diamond cycle, trapezoid cycle, and rectangle cycle. From both technical and operational perspectives, the trapezoid cycle appears to be the preferred choice for CRBC. When the isentropic efficiency of the CRBC system exceeds 95%, its coefficient of performance (COP) ranges from 5.31 to 5.7, whereas the COP of transcritical carbon dioxide refrigeration cycle (tCO2), air RBC, and CO2 RBC are around 4.3, 1.9, and 0.79, respectively. This suggests that the performance of the CRBC system surpasses that of RBC by a significant margin, while achieving comparable performance to conventional vapor compression refrigeration systems. Moreover, the dimensionless power reflecting the installation capacity requirements for CRBC, tCO2, air RBC and CO2 RBC are around 0.2, 0.35, 5.3 and 1.9, respectively. This indicates that the compressor/expander capacity demand for system CRBC approaches the thermodynamic minimum.

Mixing Efficiency of Viscous Fluid in a Multiple‐Impeller Agitated Tank

AbstractThe development of a multi‐impeller reactor for the mixing of non‐Newtonian fluids under full flow regime conditions depends on mixing time, power consumption, and mixing energy. These parameters must be well‐defined with 3‐blade propellers, 4‐pitched turbines, and 6‐flat‐blade turbines. An innovative expression of mixing time for the thermal pulse disturbance method is introduced. The Buckingham's π‐theorem was utilized to denominate and transfer dimensionless power and homogenization number. To achieve consistent mixing, the results indicated that axial flow of the 4‐pitched‐blade turbine is the most effective approach. The examined correlation is a functional tool to determine the mixing energy based on the measured specific power consumption and mixing time.