Dead Volume Research Articles

A Computational Fluid Dynamics and Support Vector Regression Combined Method for Predicting the Flow Performance of the Five‐Strand Tundish

To optimize the flow field of a multistrand tundish and improve the steel quality, a prediction model integrating the techniques of computational fluid dynamics (CFD) and support vector regression (SVR) is proposed. A total of 125 cases with different structure parameters, i.e., the diameter and inclination angle of the orifices, are designed. The flow field of liquid steel in the tundish is calculated by CFD, and a sample dataset is established. Then, the SVR, combining the genetic algorithm with K‐fold, is employed to train and predict the sample dataset. In the results, it is shown that the SVR model demonstrates good learning performance on the training dataset. The average absolute errors of predictions for dead volume fraction and consistency are 0.50% and 0.71%. In addition, the SVR model takes much less computational cost than the CFD method to predict the flow performance of tundish in a given baffle structure.

Dead space volumes in cats and dogs with small body mass ventilated with a fixed tidal volume

ObjectiveTo compare the portion of tidal volume (VT) ventilating dead space volumes in nonbrachycephalic cats and dogs with small body mass receiving volume-controlled ventilation (VCV) with a fixed VT. Study designProspective, experimental study. AnimalsA group of eight healthy adult cats and dogs [ideal body weight (IBW): 3.0 ± 0.5 and 3.8 ± 1.1 kg, respectively]. MethodsAnesthetized cats and dogs received VCV with a 12 mL kg–1 VT (inspiratory pause ≥ 0.5 seconds). Respiratory rate (fR) was adjusted to maintain normocapnia. Airway dead space (VDaw) and alveolar tidal volume (VTalv) were measured by volumetric capnography. Physiological dead space (VDphys) and VDphys/VT ratio were calculated using the Bohr–Enghoff method. Data recorded before surgery were compared by an unpaired t-test or Mann–Whitney U test (p < 0.05 considered significant). ResultsThe IBW (p = 0.07), PaCO2 (p = 0.40) and expired VT [VT(exp)] (p = 0.77) did not differ significantly between species. The VDaw (mL kg–1) was lower in cats (3.7 ± 0.4) than in dogs (7.7 ± 0.9) (p < 0.0001). The VTalv (mL kg–1) was larger in cats (8.3 ± 0.7) than in dogs (4.3 ± 0.7) (p < 0.0001). Cats presented a smaller VDphys/VT ratio (0.33 ± 0.03) and VDphys (4.0 ± 0.3 mL kg–1) than dogs (VDphys/VT: 0.60 ± 0.09; VDphys: 7.2 ± 1.4 mL kg–1) (p < 0.0001). The fR and minute ventilation (VT(exp) × fR) were lower in cats than in dogs (p = 0.048 and p = 0.038, respectively). Conclusions and clinical relevanceA fixed VT results in more effective ventilation in cats than in dogs with small body mass because of species-specific differences in and VDaw and VDphys. Because of the smaller VDaw and VDphys in cats than in dogs, a lower fR is required to maintain normocapnia in cats.

Physical and Numerical Study on Right Side and Front Side Gas Blowing at Walls in a Single‐Strand Tundish

The compromise between inclusions removal by small bubbles and proper agitation of fluid flow in tundish by gas blown is challenging. The single‐strand tundish without flow control devices (bare tundish) is used to study the effects of side‐wall gas blowing on the flow field. The water model, particle image velocity measurement and computational fluid dynamics simulation are used to study bubble behavior, fluid flow field, and tracer transport. A large horse shoe vortex and a short circuit flow at the bottom are formed in the bare tundish. Gas blowing at the outlet‐side wall of the tundish creates multiple vortices in the right‐side region, with blowing rate and position greatly influencing the surface flow within the tundish. Gas blowing at the front‐side wall creates a large spiral vortex, agitating the fluid in the tundish and improving the flow field. Increasing the blowing rate strengthens the vortex in the right region, but raising the blowing position affects surface flow and creates a counterclockwise flow toward the shroud. In all schemes, gas blowing at a low position on the front‐side wall with a small gas flowrate is the optimized scheme which shows the smallest dead volume and enhances surface flow.

Design and Implementation of a Hardware-in-the-Loop Air Load Simulation System for Testing Aerospace Actuators

This paper presents the design and implementation of the hardware and control strategies of an electrohydraulic air load simulation system for testing aerospace actuators. The system is part of an Iron Bird, which is an energy management research platform developed in collaboration between Saab AB and Linköping University. The purpose of the air load system is to provide realistic forces on the test object through the integration of a flight simulator for full mission evaluation. The challenge with electrohydraulic force control is tackled by increasing the hydraulic capacitance from increased load cylinder dead volumes, together with a feed-forward link based on accurate modelling of the test object and load system by adopting an optimisation routine to find model parameters. The system is implemented for both an electromechanical and servohydraulic actuator as test objects with different performance requirements. The control design is based on nonlinear and linear modelling of the system, and experimental test data are used to tune the models. Finally, test results of the air load system prove its force-tracking performance.

Universal and Versatile Magnetic Connectors for Microfluidic Devices

World-to-chip interfacing remains a critical issue for microfluidic devices. Current solutions to connect tubing to rigid microfluidic chips remain expensive, laborious, or require specialized skills and precision machining. Here, we report reusable, inexpensive, and easy-to-use connectors that enable monitoring of the connection ports. Our magnetic connectors benefit from a simple one-step fabrication process and low dead volume. They sustain pressures within the high range of microfluidic applications. They represent an essential tool for rapid thermoplastic (PMMA, PC, COC) prototyping and can also be used with glass, pressure-sensitive adhesive, or thin PDMS devices.

Studying ion transport dynamics in electrochemical measurements of lateral flow assays

Lateral Flow Assays (LFAs) are among the most widely used biosensors. Conventional colorimetric LFAs yield binary, non-quantifiable results. Electrochemical LFAs (eLFAs) aim to overcome this limitation. However, the reported disadvantage of extreme sensitivity to experimental conditions poses a significant challenge in the development of new eLFAs. In this work, impedimetric measurements were performed to probe the impact of experimental factors such as electrolyte conductivity/ionic strength on the eLFA outcomes. The time-dependent evolution of non-Faradaic impedance measurements coupled with flow velocity computations were employed to investigate ion transport across different LFA configurations and buffer compositions. The analysis of the Péclet number, a characteristic dimensionless parameter of flow dynamics within the LFA, revealed the coexistence of diffusive and convective ionic transport regimes over the LFA operational time. In addition, our findings underscore the critical role of absorbent pad dead volume adjustments in governing the capacity to maintain sample flow within the membrane over extended durations. These electro-fluidics phenomena are essential considerations for conducting electrochemical measurements within LFAs. Overall, this study offers insights into key design parameters for the integration of electrochemistry into LFAs.

Perfluoropolyether-Based Gut-Liver-on-a-Chip for the Evaluation of First-Pass Metabolism and Oral Bioavailability of Drugs.

In the evolving field of drug discovery and development, multiorgans-on-a-chip and microphysiological systems are gaining popularity owing to their ability to emulate in vivo biological environments. Among the various gut-liver-on-a-chip systems for studying oral drug absorption, the chip developed in this study stands out with two distinct features: incorporation of perfluoropolyether (PFPE) to effectively mitigate drug sorption and a unique enterohepatic single-passage system, which simplifies the analysis of first-pass metabolism and oral bioavailability. By introducing a bolus drug injection into the liver compartment, hepatic extraction alone could be evaluated, further enhancing our estimation of intestinal availability. In a study on midazolam (MDZ), PFPE-based chips showed more than 20-times the appearance of intact MDZ in the liver compartment effluent compared to PDMS-based counterparts. Notably, saturation of hepatic metabolism at higher concentrations was confirmed by observations when the dose was reduced from 200 μM to 10 μM. This result was further emphasized when the metabolism was significantly inhibited by the coadministration of ketoconazole. Our chip, which is designed to minimize the dead volume between the gut and liver compartments, is adept at sensitively observing the saturation of metabolism and the effect of inhibitors. Using genome-edited CYP3A4/UGT1A1-expressing Caco-2 cells, the estimates for intestinal and hepatic availabilities were 0.96 and 0.82, respectively; these values are higher than the known human in vivo values. Although the metabolic activity in each compartment can be further improved, this gut-liver-on-a-chip can not only be used to evaluate oral bioavailability but also to carry out individual assessment of both intestinal and hepatic availability.

Influence of structural parameters of distributor disk on flow pulsation in axial piston pumps

Firstly, a virtual prototype of axial piston pump AMESim is used to observe the effects of outlet pressure, swashplate inclination, bulk modulus (compressibility), density, dynamic viscosity, air viscosity, air content, dead space volume, leakage of mating clearance of the moving parts, plunger cylinder clearance, eccentricity, contact length of the copper bushing of the high-pressure piston pump, and the over-flow area of the flow distributing disk on the swashplate torque, the pressure in the plunger chamber, the pulsation in the flow rate, and the backing-up. To explore the influence of fluid noise, mechanical noise and air noise. After comparison, the overflow area of the disk, which has the greatest influence on the noise, is selected as the research object, in which the structural parameters of the disk are the most important influencing factors. Finally, it is found that too large or too small overflow area will aggravate the fluid noise and mechanical noise of the piston pump. Therefore, the optimized design of the structure of piston pump flow distribution plate is of great significance to reduce the vibration and noise of the hydraulic system. This study catches the optimization method of axial piston pump flow distribution shock, which can provide a reference for the design and optimization of axial piston pumps.

Development of Static Mixers for Millireactors and Their Production by Vat Photopolymerization.

The addition of static mixers within reactors leads to higher productivity of a process and an additional increase in mass and energy transfer. In this study, we developed millireactors with static mixers using stereolithography, an additive manufacturing technology. Computational fluid dynamics (CFD) simulations were conducted to study the flow, identify potential dead volumes, and optimize the design of the millireactors. We produced five millireactors with various static mixers and one tubular reactor without static mixers, which served as a reference. The Fenton reaction was performed as a model reaction to evaluate the performance of the millireactors. We observed that some of the reactors with static mixers had air plugs that created a significant dead volume but still exhibited higher conversions compared to the reference reactor. Our results demonstrate the potential of stereolithography for producing intricate millireactors with static mixers, which can enhance the productivity of chemical processes.

A full solid-state conceptual magnetocaloric refrigerator based on hybrid regeneration

The environmental friendliness and high efficiency of magnetocaloric refrigeration make it a promising substitute for vapor compression refrigeration. However, the common use of heat transfer fluid in conventional passive magnetic regenerators (PMRs) and active magnetic regenerators (AMRs) makes only partial materials contribute to the regeneration process, which produces large regeneration loss and greatly limits the regeneration efficiency and refrigeration performance at high frequency. Herein, we propose a new conceptual hybrid magnetic regenerator (HMR) composed of multiple solid-state high thermal conductivity materials (HTCMs) and magnetocaloric materials (MCMs), in which both HTCM and MCM elements participate in the regeneration process. This novel working mode could greatly reduce regeneration losses caused by dead volume, pressure losses, and temperature nonuniformity in heat transfer substances to markedly improve regeneration efficiency at high working frequencies. Using the experimentally obtained adiabatic temperature change and magnetic work and with the help of finite element simulation, a maximum temperature of 26 K, a dramatically large cooling power of 8.3kW/kg, and a maximum ideal exergy efficiency of 54.2% are achieved at the working frequency of 10Hz for an ideal prototype device of a rotary HMR magnetocaloric refrigerator, which shows potential for achieving an integrative, advanced performance against current AMR/PMR systems.

Energy and exergo-environmental performance analysis of a Stirling micro-fridge with imperfect regenerator

In search of very small and ecological refrigeration machines, Stirling chillers are studied on a micro-scale. This article analyzes the performance of a Stirling microcooler using a new modeling approach. This micro-cooler consists of a pillar network as regenerator, a compression and expansion chamber suitable for batch manufacturing, Alpha configuration with helium as working fluid. The Schmidt model with imperfect regeneration is used with consideration of work losses due to gas spring hysteresis. The equations solved analytically using the laws of thermodynamics are used to evaluate the energy and exergy performance of the microcooler. The parameters like height and internal width of the regenerator, phase angle, temperature ratio, swept volume ratio, cooling pressure, dead volume ratio are studied. A numerical code is developed in Matlab. Results show that optimal parameters develop a cooling capacity of 18.99 mW at a phase angle of 45°, a coefficient of performance of 1.104 at an internal height of the regenerator of 0.85 mm, an ecological coefficient of performance of 10.9 mW, an exergy yield of 6.13%, a destroyed exergy of 0.66 mW. The comparison between the present work and those in the literature shows that the current micro-cooler explores a COP improvement of 35%.

Analysis of stream flow and its impact on thermal performance in shell-side of heat exchangers based on flow dead zone

The performance of shell-and-tube heat exchanger (STHE) is primarily determined by different flow paths on the shell-side. The flow path and its impact on the shell-side flow in segmental baffle shell-and-tube heat exchanger with clearance (SC-STHE) is investigated qualitatively and quantitatively, by adopting stream classification and dead zone analysis method. By utilizing Residence Time Distribution (RTD) curves, the influence of different streams on fluid flow and heat transfer is discussed to reveal the intricate interconnections within the shell-side of SC-STHE. Then the cases with baffle-tube clearance (0.2–1.0 mm) and baffle-shell clearance (1.0–5.0 mm) ranges are studied. The study identifies that optimal comprehensive performance is achieved with a baffle-tube clearance of 0.6 mm, resulting in a 3.5 % improvement compared to a clearance of 0.2 mm. An increase of baffle-shell clearance results in a reduction in comprehensive performance by 8.23–19.54 %. The interactions among stream flows and potential mechanisms are discussed by analyzing the influence of each flow path on the flow dead zone volume. It is revealed that the presence of baffle-tube and baffle-shell clearances reduces the volume fraction of flow dead zones compared to structures without clearances. A-stream and E-stream are identified as pivotal, mutually influencing B-stream and C-stream while maintaining relative independence. The result indicates that an increase in baffle-tube clearance results in a 7.60 % expansion of the volume of the dead zone within the B-stream, while in the C-stream, it decreases by 2.58 %. Conversely, an increase in baffle-shell clearance reduces the volume of the dead zone in the B-stream by 5.04 % but increases it in the C-stream by 31.95 %. The flow dead zones are mainly distributed in the B-stream and C-stream regions, and the diversion effect of leakage flows improves the fluid stagnation but also leads to a decrease in turbulence intensity and flow velocity. This study reveals the complex interaction mechanisms among the stream flows, facilitating further analysis and optimization in STHE design.

Impact of reservoir construction on the sediment budget of a downstream-linked freshwater lake

ABSTRACT We investigated the magnitude of reservoir sedimentation upstream and its sediment-shadow effect on a large downstream-linked lake, Lake Tana (Ethiopia). To better understand the reservoir-induced reductions of fluvial sediment downstream, sediment budgets for two scenarios were developed. The results indicated that reservoir sedimentation is extremely high, with annual storage capacity losses (1–4.2%) exceeding the global average. Consequently, unless mitigation measures are implemented, the reservoirs’ dead storage volume will be filled with sediment in less than 42% of their designed life expectancy. The sediment-trapping conditions created by the reservoirs will also reduce sediment inflow from tributaries into the lake by 15–52%, overbank sedimentation on floodplains by 33–48%, and sediment deposition in Lake Tana by 16–54% annually. Overall, under the current environmental set-up, the ongoing and planned reservoir constructions could extend the expected useful lifetime of Lake Tana from 918 to 2022 years.

Management of refined and personalized newborn blood specimen collection

BackgroundIatrogenic blood loss is an important cause of neonatal anemia. In this study, a spreadsheet tool was developed to reduce blood collection, providing a new idea for the prevention of iatrogenic blood loss in newborns. MethodsBased on hematocrit, minimum test volume and dead volume, a new tool was to calculate the minimum blood collection volume and the number of containers required for the test portfolio. We collected data from October 2022 to October 2023 from Xiamen Maternal and Child Health Hospital for analysis and validation. ResultsDuring this year, there were 16,434 patients and 13,696 plasma/serological samples in the neonatology department. Among them, there were 8 test combinations of greater than 1%, and 9490 samples in total. According to the hospital manual, the recommended amount of blood collection is 27,534 ml and 9490 containers. Through the analysis of this tool, total blood collection was 8864.77 ml, marked qnantity of upward containers (closest level to the calculated blood collection volume) was 10301 ml, and the amount of containers was 8835, which decreased by 67.8%, 62.58% and 6.9% respectively. Besides, if the hematocrit information cannot be obtained in advance and the high hematocrit is calculated as 0.8, the recommended amount of blood collection is 14334.3 ml, and the marked amount of the upward container markering is 17340 ml, decreasing by 47.9% and 37.02% respectively. ConclusionWe have developed an auxiliary tool that can manage neonatal blood specimen collection in a fine and personalized way and can be applied among different laboratory instruments by parameters modification.

Optimizing mixing efficiency of anaerobic digesters with high total solids concentrations using validated CFD simulations

In this article, viscosity dependent mixing in anaerobic digestion (AD) towers is analysed using finite volume based computational fluid dynamics (CFD) simulations validated with ultrasound particle image velocimetry (uPIV). The study focuses on improving mixing characteristics for enhanced biogas production resulting from increased organic loading. Mixing of fluids with viscosity ranges found in real-life AD is investigated using the multiple reference frame (MRF) method. The aim is to increase the energetic efficiency of AD by reducing the energy demand required for sufficient mixing such that microorganisms and organic substrates are homogeneously distributed. The distinguishing feature of this work is the implementation of less power-consuming helical ribbon stirring devices (HRSD) for enhanced mixing in different reactor designs. It is demonstrated that HRSD become progressively effective for increasing total solids concentrations (% TS) ranging from 2.5 % TS to 12.1 % TS, particularly in cylindrical reactors. In comparison with conventional propeller-based mixers, innovative HRSD operation reduces dead volume (DV) by up to 22 %. Additionally, HRSD cause less shear forces and require less power due to lower rotational speed. The most energy-efficient mode of operation reduces the power demand by 9.29 % at 12 rpm, while still providing decreased DV of 13.38 % for the most viscous fluid investigated. The outcome is a more efficient and cost-effective mixing approach, which holds strong potential for mixing applications involving highly viscous fluids.

Robust Graphene-based Aerogel for Integrated 3D Asymmetric Supercapacitors with High Energy Density.

Three-dimensional asymmetric supercapacitors (3D ASC) have garnered significant attention due to their high operating window, theoretical energy density, and circularity. However, the practical application of 3D electrode materials is limited by brittleness and excessive dead volume. Therefore, we propose a controlled contraction strategy that regulates the pore structure of 3D electrode materials, eliminates dead volume in the 3D skeleton structure, and enhances mechanical strength. In this study to obtain reduced graphene oxide/manganese dioxide (rGO/MnO2) and reduced graphene oxide/carbon nanotube (rGO/CNT) composite aerogels with a stable and compact structure. MnO2 and CNT as nanogaskets, preventing the self-stacking of graphene nanosheets during the shrinkage process. Additionally, the high specific capacitor nanogaskets significantly enhance the specific energy density of the rGO aerogel electrode. The prepared rGO/MnO2//rGO/CNT 3D ASC exhibits a high mass-specific capacitance of 216.15 F g-1, a high mass energy density of 74 Wh kg-1 at 3.5 A g-1, and maintains a retention rate of capacitance at 99.89 % after undergoing 10,000 cycles of charge and discharge at 5 A g-1. The versatile and integrated assembly of 3D ASC units is achieved through the utilization of the robust mechanical structure of rGO-based aerogel electrodes, employing a mortise and tenon structural design.

Hierarchical porous N-doped carbon fibers enable ultrafast electron and ion transport for Zn-ion storage at high mass loadings

Zinc-ion capacitors (ZICs) are a promising and safe energy storage system for portable electronics but usually limited by relatively low areal capacity and energy density. Although increasing the mass loading has been suggested, thick electrode layers and clogged pores unavoidably lead to sluggish electron transport and ion diffusion as well as “dead volume” of active materials. Herein, a millimeter-scale 3D thick-network electrode, composed of closely intertwined hierarchical porous N-doped and free-standing carbon nanofibers (HPNCFs), was fabricated via carbonization of nanoscale zeolitic imidazolate framework (ZIF-8) particles embedded in electrospun polyacrylonitrile (PAN) nanofibers. With fast electron/ion transport, large ion-accessible surface area and high utilization rate of active materials, the mass loading of the HPNCFs electrode can reach 48.67 mg cm−2 with a thickness of 4.46 mm. Moreover, the HPNCFs-based ZICs can yield a superior areal/gravimetric capacity of 4.13 F cm−2 /280 F g−1, superior rate capability up to 193.7 F g−1 even at 100 A g−1, high energy density of 99.6 Wh kg−1, and long-term stability for 40,000 cycles. The straightforward approach can provide an opportunity to prepare efficient thick electrodes that could be applied in electrocatalysis, energy storage/conversion, and other electrochemical energy-related techniques.

Numerical and experimental investigation of stratified water storage tanks: An enhanced adaptive-grid model

Stratified water storage tanks are key in thermal energy systems, effectively balancing energy supply with heat demand, thus facilitating operational flexibility. Accurately modeling both energy balance and thermocline evolution with minimal computational effort is essential for models implementation in real-time control applications. One-dimensional, static-grid models are favored for their easy implementation; however, they require dense grids in order to minimize numerical diffusion and to represent mixing effect correctly, resulting in rather expensive computational effort. This study introduces an adaptive-grid model that comprehensively represents the water storage tank’s geometrical features, including inlet and outlet duct heights and dead volume sizes. It also details the spatially discretized heat diffusion and characterizes the inflow region’s mixing using an empirical equation. Implemented in both TRaNsient SYstem Simulation (TRNSYS) and Modelica environments, the model is validated through laboratory experiments with a hot water storage tank operating under various mass flow and temperature conditions, representative of heat pump-driven heating systems. The results indicate improvements in computational efficiency compared to static-grid models, specifically a 55% reduction in simulation duration with the same level of uncertainty.

Anisotropy Reversal of Thermal Conductivity in Silicon Nanowire Networks Driven by Quasi-Ballistic Phonon Transport.

Nanostructured semiconductors promise functional thermal management for microelectronics and thermoelectrics through a rich design capability. However, experimental studies on anisotropic in-plane thermal conduction remain limited, despite the demand for directional heat dissipation. Here, inspired by an oriental wave pattern, a periodic network of bent wires, we investigate anisotropic in-plane thermal conduction in nanoscale silicon phononic crystals with the thermally dead volume. We observed the anisotropy reversal of the material thermal conductivity from 1.2 at 300 K to 0.8 at 4 K, with the reversal temperature of 80 K mediated by the transition from a diffusive to a quasi-ballistic regime. Our Monte Carlo simulations revealed that the backflow of the directional phonons induces the anisotropy reversal, showing that the quasi-ballistic phonon transport introduces preferential thermal conduction channels with anomalous temperature dependence. Accordingly, the anisotropy of the effective thermal conductivity varied from 2.7 to 5.0 in the range of 4-300 K, indicating an anisotropic heat manipulation capability. Our findings demonstrate that the design of nanowire networks enables the directional thermal management of electronic devices.

A Highly Effective Polysulfide-Trapping Approach for the Development of High Energy Density, Scalable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are identified as one of the most promising next-generation battery technologies owing to their high theoretical specific energy, sustainability, and affordability. However, the commercialization of Li-S batteries has been hindered by severe technical challenges, including the lithium polysulfide (PS) dissolution/shuttling effect, a major cause of fast capacity degradation over cycling. We demonstrated that, for the first time, nanolayer polymer coated high surface area porous carbons (NPCs) were coated directly on sulfur electrodes (NPC-S), which led to a high specific capacity of ∼1,600 mAh g−1 approaching the theoretical specific capacity limit in the NPC-S based Li-S batteries. The NPC-S based Li-S batteries maintained their large initial specific capacity gain compared with the Baseline-S based Li-S batteries (control) over extended cycles. A follow-on study indicated that the NPC-S approach is a necessary and critical step to boost the near-theoretical specific capacity while being stabilized over long cycles with a synergistic strategy. Our experimental and computational results suggest that NPC coated on sulfur electrodes provides not only an effective and strong PS-trapping power but also an increased redox reaction kinetics for sulfur ↔ PS’s conversions during battery charge and discharge, rendering the realization of near-theoretical discharge specific capacity in the NPC-S based Li-S batteries. The findings presented in this study may inspire a new, simple, low-cost, and commercially scalable approach, without adding any appreciable dead weight or volume to the batteries, in the effort to tackle the technical challenges facing SOA Li-S batteries.