Tab Location Research Articles

Air tab location effect on supersonic jet mixing

Abstract Mixing of Mach 2.1 circular, jet issuing from a straight convergent-divergent circular nozzle, in the presence of sonic air tabs at exit and shifted locations along the jet axis was investigated experimentally at nozzle pressure ratios (NPR) 3–6, insteps of 1. Two constant area tubes of 1 mm diameter positioned diametrically opposite, at 0 D, 0.25 D, 0.5 D and 0.75 D (where D is the nozzle exit diameter), were used for fluidic injection. The injection pressure ratio (IPR) of air tabs was maintained at 6. The Mach 2.1 jet operated at nozzle pressure ratio (NPR) in the range of overexpanded states corresponding to NPR 3–6 was controlled with the sonic air tabs operating at the underexpanded state corresponding to IPR 6. The impact of air tabs on jet mixing was studied from the measured Pitot pressure along the jet centerline. The centerline pressure decay of the jet confirms that the air tab promotes jet mixing with the entrained air mass, and the mixing promotion caused by the air tab is dependent on tab location as well as the NPR. In the presence of air tabs, the jet possesses shorter core and experiences faster decay than the uncontrolled jet. Also, the air tabs were effective in reducing the number of shock cells and rendering the waves weaker in the jet core. Among the tab locations, the mixing promoting effectiveness of air tabs at 0 D is better than the tabs at shifted locations. The jet core length reduction caused by the air tab at 0 D increases from 25.4 % to 77.2 %, with increasing NPR from 3 to 6. The same trend was noticed for tab location 0.75 D, but not for 0.25 D and 0.5 D locations. The core length reduction for 0.75 D tab location is about 61.4 %, at NPR 6, and 62.1 % and 55.8 %, for NPR 5 and 4 for tab locations 0.25 D and 0.5 D, respectively. Shadowgraph images of the waves present in the jet core confirms the findings of centerline pressure decay results.

(Digital Presentation) Parameterization of a Commercial 18650 High-Power Lithium-Ion Cell for a Physico-Chemical Model

Li-ion battery is an integral part for the electric or hybrid electric vehicles, as they provide high energy density and power density with extended cycle-life compared to their closest rivals, Ni-MH batteries [1]. Electric vehicles (EVs) require an advanced real-time based battery management system (BMS) that ensure a safe and efficient energy utilization, estimate state-of-charge (SOC) and state-of-health (SOH), and cell balancing [1]. A high performing BMS needs an accurate cell model that can precisely capture the cell dynamics in EVs. Due to the inherent complexity of the physics-based model, BMS are often based on equivalent circuit models [2-4] that are relatively easy to implement but lack the important underlying physico-chemical processes. In order to predicts an accurate cell response, a physico-chemical model based on fundamental governing equations of migration and diffusion processes as well as the kinetics of intercalation require precisely evaluated model parameters for the material under consideration [5].In this work, a commercial 18650 cell is analyzed in order to parameterize a physico-chemical model. The parameters are estimated by the results of experiments performed on the cell material under investigation. For this, the fully discharged cell was opened in a glove box under inert environment with both moisture and oxygen level below 0.5 ppm. The material samples were collected in an air tight desiccator and analyzed using different methodology.The results obtained based on the proposed methodology are presented as: electrodes, electrolyte, and separator composition; kinetic, transport, and thermodynamics parameters; electrodes and separator physical properties, e.g., porosity, microstructure, particle size distribution etc.; cell internal configuration, e.g., jelly roll dimension, electrode tab location and their dimension etc.; and full-cell electrode balancing determination. A range of electrochemical techniques were used to determine the kinetic and thermodynamic properties of the electrode materials, e.g., galvanostatic intermittent titration technique (GITT) was used to estimate the diffusion coefficient of Li-ion in anode and cathode at different state of charge (SOC) also, to ascertain the open circuit voltage (OCV) of the respective electrodes. In order to estimate the exchange current density, electrochemical impedance spectroscopy (EIS) was employed. The SEM images to illustrate the microstructures of cathode, anode and separator and the particle size distribution of cathode and anode are shown in Figure.

Insight into the inhomogeneous capacity distribution characteristic of LiFePO4 cathode in large-format lithium ion cell

The inhomogeneous capacity degradation distribution of large-format LiFePO4-based lithium ion cell after 2500 charge-discharge cycles is analyzed via the selected regions of the cathodes using half-cell charge-discharge test, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy analysis. The results showed that the initial specific charge capacities demonstrate an obvious position-dependent characteristic, indicating inhomogeneous reactions occurring on the electrode. The low initial charge capacities near the tab location can be recovered after discharging, indicating the capacity degradation is from the active lithium loss, rather than the crystal structure destruction. The X-ray photoelectron spectroscopy and high resolution transmission electron microscopy results further verified these deduction and the X-ray absorption spectroscopy analysis results indicate that the difference on the structure change of LiFePO4 is mainly at the surface, rather than in the bulk.

Thermal behaviors analysis of 55 Ah large-format lithium-ion pouch cells with different cell aspect ratios, tab locations, and C-rates

Recently, large-format LIBs have a problem with product life due to temperature deviation. In this study, a three-dimensional electrochemical-thermal coupled model of 55 Ah large-format LIBs is used to analyze the effect of cell aspect ratios, tab locations, and C-Rates on thermal behavior during discharge. Results show that when the cell aspect ratio becomes far from 2.15, heat generation becomes non-uniform and the temperature deviation increases. The closer the tabs are located, the more temperature deviation increases. The effect of cell aspect ratio and tab location on temperature deviation is increased as higher C-Rate. Also, the effect of cell aspect ratio on the temperature deviation of LIB is larger than tab location. The main cause of temperature deviation comes from different heat generation of each component of the LIB, which is reversible heat and irreversible heat (Joule heat). The influence of irreversible heat is dominant at higher C-rate. Therefore, at higher C-rate, the temperature deviation is effectively reduced by adjusting the cell aspect ratio and tab location that affect current density distribution. In this study, the minimum temperature standard deviation is shown when the cell aspect ratio is 2.15 and negative-positive tabs are located on the opposite side of the cell.

Shear tab connection with composite beam subjected to transient-state fire temperatures

Purpose This study aims to develop a rational model to predict the thermal axial forces developed in shear tab connections with composite beams when subjected to transient-state fire temperatures. Design/methodology/approach Finite element (FE) models are first developed in ABAQUS and validated against experimental data available in the literature. Second, a parametric study is conducted to identify the major parameters that affect the behavior of shear tab connections with composite beams in the fire. This includes beam length, shear tab thickness, shear tab location, concrete slab thickness, setback distance and partial composite action. A design-oriented model is developed to predict the thermal induced axial forces during the heating and cooling phases of a fire event. The model consists of multi-linear springs that can predict the stiffness and strength of each component of the connection with the composite beam. Findings The FE results show that significant thermal axial forces are generated in the composite beam in the fire. This is prominent when the beam bottom flange comes in contact with the column. Fracture at the toe of the welds governs the behavior during the cooling phase in most FE simulations. Also, the rational model is validated against the FE results and is capable of predicting the thermal axial forces developed in shear tab connections with composite beams under different geometrical properties. Originality/value The proposed model can predict the thermal axial force demand and can be used in performance-based approaches in future structural fire engineering applications.

The influence of tabs on fluid dynamic measurements downstream of a backward-facing step

PIV-method was used to study the flow behind a backward-facing step in the presence of tabs for the Reynolds number Re=4000. The studied tabs had rectangular shape and a height of 6 mm, and were installed with a step of 25 and 50 mm. The tabs, depending on the step, had a different effect on velocity profile. At the tab location, the profiles of the average longitudinal and transverse velocity were strongly deformed and became similar to the behaviour behind the solid rib. In the area between the tabs due to the adjacent pair of tab-induced vortices, the attachment of the mixing layer occurred earlier than at streamlining of a smooth step. The recirculation area was noticeably reduced for tabs with spacing of 50 mm, and at the same time, with a reduction in the distance between them to 25 mm, the size of this zone increased.

Impact of tab location relative to the nozzle exit on the shock structure of a supersonic jet

This paper presents an experimental study of a Mach 2.0 jet manipulated using rectangular tabs to understand the mixing enhancement at the overexpanded and perfectly expanded state of the jet. This paper also compares the mixing effectiveness of the tabs in comparison with the fluidic injection reported in our previous work [Kumar et al., “Empirical scaling analysis of supersonic jet control using steady fluidic injection,” Phys. Fluids 31(5), 056107 (2018)]. Tabs used in this investigation were rectangular strips of aspect ratio, AR, 2 (AR = length of the tab/width of the tab) and are positioned at 0De, 0.25De, 0.5De, and 0.95De (De is the nozzle exit diameter) downstream of the nozzle exit. Pitot pressure measurements were carried out along the jet centerline and in the radial directions to examine the supersonic core length (Lc*) and jet spread, respectively. The jet stream has been visualized using the shadowgraph technique in the orthogonal planes of the manipulated jet. The mixing capability of the manipulated jet quantified based on the reduction in supersonic core length ΔLc* strongly depends on the control technique and its location along the downstream direction. Three types of flow categories are identified, i.e., the “jet bifurcation,” “complex and strong shock-cell structure,” and “weak shock structure,” which depend on the tab location (xt*) and account for the jet mixing. The present study reveals that the tabs should be positioned downstream of the first shock crossover point which results in shorter core length and, hence, higher jet mixing. A conceptual model of the flow structure under control is proposed.

Tab location effect on supersonic jet mixing

ABSTRACTAerodynamic mixing of a Mach 2 jet controlled with rectangular flat tab with length equal to the nozzle exit diameter, placed at locations 0.25D, 0.5D and 0.75D, downstream of the nozzle exit, has been studied in the presence of different levels of pressure gradients corresponding to nozzle pressure ratio (NPR) range from 3 to 8. The mixing modification associated with shifted tabs is compared with the mixing caused by the same tab at the nozzle exit (0D). The aerodynamic mixing caused by the mass transporting small-scale vortices shed from the edges of the tab placed at the shifted position is found to be appreciably larger than the tab at nozzle exit, for some levels of pressure gradient. For some other levels of nozzle expansion, mixing caused by the shifted tab is comparable to that of tab at nozzle exit. The waves present in the core of the jet controlled with shifted tab were found to be weaker than that of the jet controlled with tab at nozzle exit. At a marginally underexpanded state corresponding to NPR 8, jet core length reduction caused by the tab at 0.75D is about 39.21%, which is closer to the reduction of 40.2%, caused by the tab at 0D. The corresponding core length reduction for tab at 0.25D and 0.5D are 38.16% and 20%, respectively.

A pseudo 3D electrochemical-thermal modeling and analysis of a lithium-ion battery for electric vehicle thermal management applications

This paper presents an improved pseudo 3D coupled electrochemical-thermal model that can be implemented into active or passive battery thermal management systems (BTMS). The model features more accurate estimate of battery temperature distribution under various discharge rates compared with lumped or empirical models. In this work, a simplified electrochemical model is solved in 1D to make the coupled model streamlined enough to be embedded into BTMS. The Ohmic heat generation and heat conduction in the cells are evaluated in 3D to investigate the non-uniform temperature distribution during the battery operation. The validity of electrical and thermal aspects of the modeling procedure is demonstrated experimentally for a 4Ah NCA prismatic cell. The predicted battery surface temperature distribution and voltage profile are in agreement with infrared imaging and the measured voltage variation. The proposed model reduces the required time for battery modeling which enables the designers to simultaneously simulate the active or passive BTMS in an affordable computational time. The effects of design parameters such as electrode format, active material thickness and tab location on the battery thermal behavior can be evaluated under various cooling scenarios.

Numerical Analysis for Effects of Cell Formats on Cycle Life of Lithium Ion Batteries with Large Capacities

Large-format LIBs have been preferentially used for EVs and HEVs to achieve high power and high capacity. Although the technologies of LIBs have been successfully developed in commercial markets for small electronic devices, the scale-up processes of LIBs still have challenges because of the size effects. Large LIB cells usually show different responses to small-format LIBs due to the spatial non-uniformity of the electric potential, current density and temperature over the cell volumes. So, battery manufacturers have difficulties to predict responses of large cells when the cell formats are changed. The complex interactions among various physics, such as lithium ion transport, kinetic reactions, heat transport and etc. make it difficult to estimate the effects of the cell formats on performance and life of LIBs. In this study, we investigate the effects of cell formats on cycle life of LIBs using a numerical model, which resolves thermally, electrically, electrochemically coupled physics. To understand behaviors of large LIBs, a three dimensional model resolving multi-physics in various size scales is required. Relatively long electric current paths in metal current collectors of large LIBs, which are determined by the geometry of the cell, could considerably influence Ohmic heat generation as well as voltage drops. It also can lead the spatial non-uniformity of the electric potential, current density and temperature. Moreover, a ratio of cooling surfaces to cell volumes, which also depends on the cell designs, determines thermal responses of the LIB cell. Therefore, a multi-dimensional model considering the cell geometries is needed to understand the complex physics in a large-format LIBs. In this work, we developed a three dimensional multi-physics model including a degradation mechanism based on the multi-scale multi-dimensional(MSMD) model framework, which resolves various physics in designated length scales as shown in Figure 1 [1-2]. To consider the life fade of LIB cells, the present model calculates growth of the SEI layers at the anode particle surfaces as shown in Figure 2, which is a major cause of the capacity fade [3]. Three different cell formats, pouch, cylindrical and prismatic cells are modeled to investigate the effects of the cell design on cycle life as shown in Figure 3(a)-(c). The pouch cell is considered to be stacked unit cell sandwiches (including pair of electrode layers and current collectors), and it has the positive and negative tabs located on the same side as typical pouch cells in the commercial market. The cylindrical and prismatic cells have wound structures of the unit cell sandwiches and localized tabs as shown in Figure 3(d). All three types of cells have the same capacity, the same volume and the same electrode design for the unit cell sandwich such as electrode material, coating thickness, porosity, particle size and etc. We simulated a pouch cell, a cylindrical cell and a prismatic cell with 20Ah and LFP/Graphite operating same cycles. Figure 4 shows contour results of the current density at 10min during 3C discharge. It is shown that the cell format has significant influences on distributions of electrochemical reaction rates. The non-uniformity of current density in the cylindrical cell is observed to be most severe. This study will present the inhomogeneous degradation of each cell format during the repeated charge/discharge cycles. Reference [1] G.-H. Kim, K. Smith, K.-J. Lee, S. Santhanagopalan, A. Pesaran, J. Electrochem. Soc. 158 (8) (2011) A955eA969. [2] K.-J. Lee, K.Smith, A.Pesaran, G.-H. Kim, J.Power Sources 241 (2013) 20-32. [3] G. Ning, B.N. Popov, J. Electrochem. Soc. 151 (2004) A1584. Figure.1 The concept diagram of multi-scale multi-dimentional(MSMD) model framework Figure.2 Aging mechanism for SEI growth at the anode particle surface Figure 3.Geometry of 20Ah (a) pouch, (b)cylindrical and (c)prismatic cells, (d)wound structures and tab location of cylindrical and prismatic cell.Figure 4.Current density distribution after 10min at 3C discharge of 20Ah cell Figure 1

Lithium Ion Cell/Batteries Electromagnetic Field Reduction in Phones for Hearing Aid Compliance

“The Hearing Aid Compatibility Act of 1988 (HAC Act) generally requires that the Federal Communications Commission (FCC) ensure that telephones manufactured or imported for use in the United States after August 1989, and all ‘essential’ telephones, are hearing aid-compatible”. The electromagnetic field (EMF) emission is generated by electrical currents in the phones’ circuit boards and components, including the battery. Here, we have investigated design changes to reduce the EMF from Lithium Ion (Li-ion) batteries. Changes mainly include: (1) Li-ion cell internal positive/negative tab location and length on cathode/anode layers; and (2) Li-ion cell external positive/negative connectors spacing. Results show that the cell’s internal tab locations and spacing between the cell’s external connectors play critical roles in reduction of battery EMF emissions. It is important that cells’ design changes are compatible with the manufacturing processes.

Impact of Tab Location on Large Format Lithium-Ion Pouch Cell Based on Fully Coupled Tree-Dimensional Electrochemical-Thermal Modeling

This paper presents extensive three-dimensional (3D) simulations of large LiFPO4 pouch cells. 3D simulations of the Li-ion battery behavior are highly nonlinear and computationally demanding. Coupling electrochemical modeling to thermal models represents an important step towards accurate simulation of the Li-ion battery. Non-uniform temperature, potential and current density through the battery induce non-uniform use of the active material and can have a negative impact on cell performance and lifetime. Different pouch cell designs, with different tab locations, have been investigated in term of performance, current density, potential and heat distributions. The model is first validated with experimental data at different current discharge rates. Afterwards, the electrochemical, thermal and electrical behaviors over each cell design under high discharge rate (4 It) are compared between configurations. It has been shown that the designs with symmetrical configurations show uniform potential and current density gradient, which minimize the ohmic heat and lead to more uniform active material utilization and temperature distributions across the cell surface.Introduction

Validation of a Thermal-Electric Li-Ion Battery Model

Abstract : Commercial vehicle manufacturers are investing substantial resources into the development and testing of advanced battery systems for the next generation of hybrid and electric vehicles. Likewise the US army is investing in lithium ion battery research for power and energy applications including SLI (starter, lights, and ignition), silent watch, unmanned vehicles, and directed energy weapons. A major design constraint is the management of the heat generated by Li-Ion battery systems. Extreme battery temperatures impact both the performance and reliability of the battery system as well as the overall operation of the vehicle. Analysis tools that can address vehicle and battery thermal management issues are needed to accelerate this development. To meet that need, a coupled thermal-electric model for battery cells and packs has been developed and implemented into the existing thermal modeling software RadTherm. This paper documents the comparison of physical test results with a computer model of the thermal response for an actual vehicle Li-Ion battery cell. The thermo-electrical battery model described in this paper predicts an effective driving potential and internal conductance for a cell based on the cell environmental temperature and measure of state of charge. From these parameters a local current density is computed and applied to an electrical model of the voltage distribution on the electrodes. Heat generation is derived from the local voltage difference across the electrodes and the current density between electrodes and then applied to a thermal model to predict local temperature rise over the cell. When applied to a cell, the battery model is useful for predicting the effects of cell size, tab location, and current collector thickness on voltage distribution and local heat generation.

Effect of Tabs on Rectangular Jet Plume Development

The near-field mixing performance of a rectangular jet with and without solid tabs introduced at the nozzle lip was studied under supersonic (underexpanded) operating conditions. The effects of tab shape, tab location, and tab number were investigated. Flow visualization of the jet plume was accomplished via Schlieren imaging, and the velocity and turbulence fields quantified via laser Doppler anemometry measurements. Laser Doppler anemometry data were gathered along the jet centerline and on cruciform transverse and spanwise traverse lines downstream of the nozzle exit. Tab shape has only a minor effect, however tab location and number are sensitive parameters for jet plume development. Tabs located on the nozzle wide edge can lead to jet bifurcation, whereas tabs located on the narrow edge cause increased mixing primarily in the major axis direction. A nozzle with four tabs located on its wide edges was the most effective for overall enhancement of jet mixing.

Impact of tab location relative to the nozzle exit on jet distortion

Cursory observations during the course of the present study revealed that the flowfield distorsion produced by the tab changes drastically if the location of a tab is slightly varied relative to the nozzle exit.